Symposium EN04—Advanced Membranes for Energy-Efficient Molecular Separation and Ion Conduction

New polymer membranes are needed to advance energy storage and conversion technologies for distributed and grid-scale applications. We have recently demonstrated new ion-conducting polymer membranes that have achieved excellent performance and long-lifetime stability in vanadium redox flow batteries, a leading technology candidate for deployment in renewable power networks and grid-scale energy storage systems with sizes ranging from 10s to 100s of megawatts. By tuning the nanoscopic self-assembly of the ionic domains in the polymers, we are able to increase the cycle life of the device by impeding vanadium ion transport through the membrane while facilitating high conductivity in the electrolyte to maintain the battery current density. For instance, by decreasing the vanadium permeability of the membrane by a factor of two, we have been able to double the lifetime of the device, which provides significant life-cycle cost savings. We have also demonstrated membranes with nearly zero vanadium permeability that show 100 % coulombic efficiency in flow battery charge-discharge cycling tests. Currently, we are working on demonstrating these membranes over 100s of charge-discharge cycles.
Anion exchange membranes have the potential to rid fuel cell technology of expensive precious-metal catalysts. Acidic fuel cells with NAFION^® membranes require platinum, but anionic membranes that operate at high pH open the door for the use of silver and nickel fuel cell catalysts which would greatly decrease the cost of polymer fuel cell technology. We have developed new anion exchange membrane polymer structures that show exceptional stability under fuel cell conditions and have helped to increase the performance and lifetime of anion exchange membrane fuel cells.
This talk will show how polymers with new chemical structures can be applied to many different types of batteries and other electrochemical devices. Common design principles and considerations for fabricating new ion exchange membranes for energy processes will be discussed.

The solid oxide membrane (SOM) process is an environmentally friendly and innovative technology that can produce valuable metals directly from their oxides by high temperature solid oxide electrolysis. For direct metal-reduction high ionic conductors such as doped zirconia could use as the anode to remove oxide ion in the SOM electrolysis system. Particularly, yttria-stabilized zirconia (YSZ) tube is normally employed as the anode; it is immersed the molten salt containing dissolved metal oxides and oxygen anions that move to the tube where they are reduced without any emission. However, the SOM process for metal production via oxide reduction is limited because of several challenging issues, such as high oxide ion conductivity, YSZ phase stability and yttrium dissolution by the reaction at high temperature electrolysis condition in the harsh corrosive molten salt flux.

In this study, we introduce the layered configuration to improve stability and performance; the thin YSZ dense layer coated on porous Ni-YSZ cermet tube to reduce ohmic resistance of long oxide ion conducting path way in thick membrane, the protection layer coated on YSZ to enhance phase stability of the anode tube, and mixed ionic and electronic conduction (MIEC) materials were employed to reduce polarization of oxygen evolution reaction. When the electrical potential applied between the cathode and anode, it is expected that the ohmic resistance is reduced more than the conventional YSZ tube. It will be discussed that the effect of the functional layered SOM tubes for a current efficiency and the amount of metal reduction.

Lithium ion batteries (LIBs) are the state of art power source in mobile devices like cellphones and electric vehicles. However, there are huge safety hazard due to the volatility and flammability of conventional liquid electrolytes. In the pursuing of high performance solid polyelectrolytes (sPE), polycarbonate (PC) has emerged as the most promising category due to its distinct advantages like extended electro-chemical stability window, decreased crystallinity and higher Li⁺ transference number.
Previously, several advanced PC-sPEs have been developed either by adding plasticizer or adopting the “polymer in salt” strategy. Although good conductivity ranging from 0.1 to 0.4 mS/cm was achieved, these method inevitable led to non-free-standing membranes due to weakened mechanical strength. Another problem of PC-sPE remains unsolved is its instability with lithium metal. The hydroxyl terminations of PC chains is readily reactive towards Li metal, leads to “unzipping” degradation.
To address the aforementioned problems of PC-sPE, an ultimate solution is developed to access free standing sPE with simultaneously achieved Li metal stability and high ionic conductivity. Firstly, an acrylate monomer with pendant propylene carbonate (DB-PC) is synthesized. Upon UV irradiation, this monomer is shown to polymerize within several minutes. Unlike the conventional PC-sPE, the UV cured sPE (UVPC-sPE) adopts polyethylene as mainchain and cyclic propylene carbonate as pendant group, thus avoiding thermal triggered main chain random scission and terminal –OH group triggered “unzipping” degradation respectively.
Besides, the abstraction of hydrogen attached to carbonate ring lead to enhanced chain transfer reaction and efficient crosslinking process. As a result, the free standing UVPC-sPE exhibits high room temperature conductivity up to 1 mS/cm, which is a significant upgrade to the conventional PC-sPE. In addition, the assembled Li/UVPC-sPE/LFP full battery shows excellent cycling performance at 0.5 C (25 ^oC) and 1C (65 ^oC), demonstrating its promising potential in Li ion battery applications.

The development of new proton conducting materials would be beneficial for a variety of applications, including hydrogen separation membranes and fuel cell electrolytes. Much of the work on proton-conducting inorganic materials has been limited to a few well-known structure types, and many classes of materials remain relatively unexplored for their ability to conduct protons. We present the results of a high-throughput computational search for new classes of proton-conducting oxides. As the use of density functional theory (DFT) to directly screen for proton mobility would be prohibitively expensive, we have developed a potential energy model for rapidly screening candidate materials to identify classes of materials that are most likely to exhibit high proton mobility. We will present the results of our model on thousands of candidate materials, including both well-known proton-conducting oxides and a new class of stable oxide materials that are predicted by both our model and DFT to have exceptionally low activation energies for proton conduction.

We have been developing alkaline-durable anion conducting electrolyte membranes (AEMs) for liquid fuel (hydrated hydrazine) type fuel cell (FC) vehicles. Even though the AEM-FC system have been significantly attractive because of non-precious metals used as active catalysts, there is no commercially available AEMs due to the severe damage of the membranes in alkaline operating conditions [1]. Thus, we applied the radiation-induced grafting technique to introduce various anion conducting graft-polymers into a thermally and mechanically tough poly(ethylene-co-tetrafluoroethylene) (ETFE) film to develop new AEMs.

Recently, we investigated a series of imidazolium-type AEMs because of the low basicity of imidazolium hydroxide as an Arrhenius base [2]. Most of the imidazolium-type AEMs exhibited lower water uptake and higher thermal stability than those of the corresponding AEMs containing trimethylammonium hydroxide. Furthermore, AEMs containing weak base imidazolium groups suffered less damage of polymer backbones via self-base catalyzed degradation. Even though N-vinylimidazolium graft-type AEMs are subjected to β-elimination and hydrolytic ring opening degradation to reduce the anionic conductivity in an alkaline solution at elevated temperature (1M KOH, 80°C), we introduced the graft-copolymers of vinylimidazolium with styrene because the adjacent vinylimiazolium cations led very fast elimination due to the double β-positioned hydrogen. Furthermore, for suppressing hydrolysis, the protecting group is introduced at 2-posion of imidazolium rings, which are subject to hydroxide attack. The alkaline durability of the AEMs having the abovementioned molecular designs showed drastically improved alkaline durability. Namely, a poly(2-methyl-N-vinylimidazolium hydroxide-co-styrene)-grafted ETFE (MIm/St-AEM, MIm/St ratio of 60/40) retained 26% of the initial conductivity (>14 mS cm⁻¹) after 1300 h in the actual fuel of 5% hydrated hydrazine in 1 M KOH at 80 °C. The membrane-electrode-assembly (MEA) consisting of MIm/St-AEM with the anion conducting ionomer having a similar polymer structure to the grafts, showed a maximum power density of 230 mW cm⁻² in a direct hydrazine hydrate FC [3].

Since the electrolyte properties, durabilities, and fuel cell performance of the graft-type AEMs could not be elucidated only by these chemical structures of the graft-type AEMs, we performed the hierarchical structure analysis of the synthesized AEMs. Contrary to the above mentioned MIm/St-AEM, the AEM with higher styrene ratios (MIm/St = 40/60 and 20/80) showed less durability in the alkaline solution. By a SANS contrast variation method, only the AEMs with MIm/St = 40/60 and 20/80 showed water puddle sphere with a diameter of 3-4 nm. Thus, we concluded that the imidazolium groups around the water puddle are subjected to the hydrolytic attack to lead the degradation of the AEMs [4]. We find out that the elucidation of hierarchical structures of the AEMs takes important role to develop alkaline durable AEMs.

Acknowledgement:
This work was supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) from the Japan Science and Technology Agency (JST).

References:
1) J. R. Varcoe, P. Atanassov, D. R. Dekel, A. M. Herring, M. A. Hickner, P. A. Kohl, A. R. Kucernak, W. E. Mustain, K. Nijmeijer, K. Scott, T. Xu and L. Zhuang, Energy Environ. Sci., 7, 3135 (2014).
2) B-S. Ko, K. Yoshimura, S. Warapon, H. Shishitani, S. Yamaguchi, H. Tanaka and Y. Maekawa, J. Polym. Sci., A, Polym. Chem., 57, 503 (2019).
3) K. Yoshimura, A. Hiroki, H-C. Yu, Y. Zhao, H. Shishitani, S. Yamaguchi, H. Tanaka and Y. Maekawa, J. Membr. Sci., 573, 403 (2019).
4) K. Yoshimura, Y. Zhao, A. Hiroki, Y. Kishiyama, H. Shishitani, S. Yamaguchi, H. Tanaka, S. Koizumi, J. E. Houston, A. Radulescu, M-S. Appavou, D. Richterf and Y. Maekawa, Soft Matter, 1, 9118 (2018).

Among all choices of electrolytes, polymer-based systems have attracted widespread attention due to their utility in cell design and excellent processability. Polymer electrolytes have an intrinsic feature: they lose mechanical properties with increase in ionic conductivity. Thus, in order to make high performance media, they must be mechanically supported (composited). This paper will provide a review on how this problem has been historically addressed including a survey of different composite media including fabrics, microporous media and discrete fibers and fillers and their impact on polymer electrolytes from an industrial point of view, leading to the current state of the art. The paper will discuss other critical features in polymer electrolytes where compositing can make a critical contribution to overall system performance – such as improved processability, cell separation, reduced reactant cross-over, reduced volume of electrolyte use, incorporation of crucial additives within support matrix, improvement of ionic continuity, ionic modification, and improved designs. Each aspect is discussed in detail. Specific polymer electrolyte composite strategies for different applications such as industrial electrolysis (Chlor-alkali), fuel cells, pervaporation and others are reviewed. In-situ measurements and specific features and benefits are discussed.

Large scale grid storage is imperative for an efficient use of renewable energies. While aqueous redox flow batteries (RFBs) such as vanadium-based aqueous RFB are relatively mature technologies for a grid storage, non-aqueous RFBs present an attractive alternative strategy for potentially providing much higher energy density. One of the key enablers for non-aqueous RFBs is mechanically robust and highly ion-conductive membranes. In aqueous RFBs, membranes can achieve high proton or anion conductivity due to water mediating their ion conduction, thus there are various high performance membranes for aqueous RFBs. On the other hand, for membranes in non-aqueous RFBs, achieving high ion conductivity while maintaining mechanical and chemical stability is a major challenge. The design principle for such membranes is poorly understood due to the complexity of the system. Our membranes are developed for a non-aqueous RFB with an alkali alloy anode technology that has the potential to achieve high energy density, high safety, low cost and long cycle life. This presentation will discuss the fundamental design principle in polymer membranes for non-aqueous RFBs and our recent efforts on the development of novel plasticized polymer membranes that simultaneously provide high conductivity and tailored mechanical modulus. In one system, mechanically robust crosslinked poly(ethylene oxide) membranes were synthesized and doped with sodium triflate and tetraglyme. The relationships between ion conductivity (reached up to 10^-4-10^-3 S/cm at r.t.), salt/gel content, glass transition temperature (T_g) and mechanical properties are investigated. The synthesized membranes are mechanically robust with storage modulus maintaining at ~1 MPa from -20 °C to 180 °C even saturated with tetraglyme. In another system, mechanically tailored novel single-ion conducting polymer electrolytes (SICPEs); trifluoromethane sulfonylimide (TFSI) functionalized block and graft copolymers are synthesized and investigated. The SICPEs with covalently attaching TFSI moieties to the polymer backbones only allows specific cations, such as lithium (Li) or sodium (Na) ions, to move freely and provide ionic conductivity (i.e. the transference number is close to 1), which is imperative for RFBs. The Li and Na ion conductivity and the mechanical properties with the presence of a plasticizer (non-aqueous solute in RFB) are investigated. RFB performance such as a cross-over behavior is evaluated.

Ion-conductive membranes are the core components of electrochemical energy conversion devices (including fuel cells, electrolyzers and flow batteries) which offer a tremendous potential to reshape clean and renewable energy technologies for stationary and transport applications. Key to the sustainable performance of these devices is the concerted improvement in membrane transport and stability, which can be related to their functionality as the polymer solid-electrolyte and separator. Nevertheless, material parameters and operational environment that are optimized for membrane functionality and performance (e.g., ion-exchange capacity and hydration) could undermine mechanical stability. Understanding the interrelation of transport and stability, and how it is affected by structure and environment, is challenging for ion-containing polymers due to the complex polymer-ion-water interactions in a chemically-heterogeneous morphology. While such interactions have been studied for proton-exchange membranes (PEMs) for fuel cells, there is need to extend these investigations to membranes exchanged with various cations and anion-exchanged membranes (AEMs) employed in fuel-cells and electrolyzers. In this talk, the role of structure and hydration in mechanical properties of various ion-containing polymers will be explored to investigate environmental and structural factors governing the membrane’s transport-stability relationship. First, impact of environment on structure-mechanics relationship of cation-exchanged and composite perfluorinated sulfonic acid (PFSA) membrane will be presented, with a focus on the interplay between their mechanical response and hydration behavior. The results will be discussed to elucidate how a membrane’s mechanical properties change due to chemical structure and water-ion interactions. Then, these investigations will be extended to selected AEMs to present a broader picture on ion effects. Lastly, various mechanical properties will be compared and discussed to provide insight into mechanical testing techniques that could best characterize membrane stability relevant to the operation environment in energy conversion devices.

Anion exchange membrane (AEM) fuel cells have gained significant attention due to the possible use of non-precious metal electrocatalysts which reduce the cost of fuel cells. However, there has been a lack of AEMs simultaneously satisfying high chemical stability, robust mechanical properties and high anion conductivity, under high pH operating conditions. Herein, we suggest a convenient method for the preparation of AEMs by Brønsted acid catalyzed Friedel-Crafts alkylation of aromatic polymers using bromoalkylated tertiary alcohols, followed by amination with trimethylamine. This simple one-step “bromoalkylation” allowed convenient control of both the degree of functionalization and cation tether length, by changing the molar ratio and the structure of the bromoalkylated tertiary alcohol. A series of elastomeric polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) based AEMs with different ion exchange capacities (IEC) and ion tether lengths were systematically investigated by comparing water uptake and anion conductivity. Since the backbone of the SEBS AEMs are composed of all carbon-carbon bonds, they showed good alkaline stability under 1 M NaOH aq. solution at 80 °C. To enhance the mechanical properties of the AEMs, the hard segment PS units were crosslinked by 1,6-hexanediamine. The crosslinking of SEBS AEMs significantly reduced their water uptake (e.g., 155% vs. 28%) preserving IEC and ionic conductivity. Alkaline membrane fuel cell performance was evaluated with the crosslinked SEBS AEM, and a peak power density of 520 mW/cm² was achieved at 60 ^oC under H₂/O₂ conditions.

As a promising alternative to proton exchange membrane fuel cells (PEMFCs), anion exchange membrane fuel cells (AEMFCs) based on hydroxide conducting polymers have received great attention in recent years. The high pH operating condition of AEMFCs allows use of non-precious metal catalysts and less expensive metal hardware. Recently, a power density over 1.0 W cm^-2 has been achieved for AEMFC approaching close to that of PEMFCs. One of key requirements for high performance of AEMFCs is anion exchange membranes (AEMs) with high ion conductivity, good chemical stability and mechanical durability. New materials development using novel polymer backbones and side chain ionic functional groups have been extensively investigated over the past decade.
In this presentation, we will present the effects of different structures of polymer backbones and the location of ionic side chains on the membrane properties of AEMs and their device performance in fuel cell and electrolysis. Polymers made of soft backbone, such as polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS), and rigid backbones, such as polyarylenes containing biphenyl and terphenyl core groups (namely BPN and TPN series), have been evolved from my group at RPI over the past years. Because the backbone of those polymers are made of all carbon-carbon bonds, they showed excellent chemical stability under alkaline conditions. The high molecular weights (>100,000 g/mol) of those functionalized polymers also afforded good mechanical strength and high strain when made into film. A perspective of quaternary ammonium-functionalized polymers that have been developed from RPI will be presented with emphasis on synthetic strategy and materials performance in AEMFC test condition.

As soft electronic devices increasingly require stretchable, conformable batteries, safety concerns regarding the use of liquid electrolytes in lithium ion batteries (LIBs) arise. Unfortunately, the canonical tradeoff between mechanical strength and ionic conductivity in polymer electrolytes has forced most reported stretchable batteries to incorporate mechanically weak electrolytes containing flammable liquids within strain engineered structures. Herein, we introduce a supramolecular design as a novel strategy to decouple ionic conductivity from mechanical strength in polymer electrolytes. The supramolecular lithium ion conductor (SLIC) is a block copolymer that includes a hydrogen-bonding domain based on 2-ureido-4-pyrimidone (UPy) and an ion conducting domain based on poly(propylene glycol)-poly(ethylene glycol)-poly(propylene glycol) (PPG-PEG-PPG). By systematically tuning the amount of UPy in the polymer backbone of SLIC, we demonstrate that the UPy domains and the PPG-PEG-PPG domains are orthogonally functional, and that varying the amount of UPy in the backbone has little effect on the ionic conductivity of the polymer. The resulting SLIC polymer containing 23 mol.% UPy in the backbone yields a polymer electrolyte with high resilience (4.9 MJ m^-3) and high ionic conductivity (1.2*10^-4 S cm^-1 at 25° C ). Implementation of SLIC as a binder material allows for the creation of stretchable Li-ion battery electrodes with strain capability of over 900% via a conventional slurry process. Impressively, strain capability of 100% is maintained when the loading of polymer in the electrode film is as low as 20 wt.%. The supramolecular structure of SLIC allows for intimate bonding at the electrode-electrolyte interface. Good adhesion between the stretchable battery components enables the fabrication of the first intrinsically stretchable LIB. The SLIC battery has a capacity of 1.1 mAh cm^-2, an operating voltage of 1.8 V, and functions even when stretched to 70% of its original length. The method reported here of decoupling ionic conductivity from mechanical properties opens a new route to create highly resilient ion transport materials for energy storage applications.

Gel polymer electrolytes consisting of a crosslinked polymer electrolyte swelled with a plasticizer overcome the weakness of low ionic conductivity of typical dry polymer electrolytes. With a large amount of plasticizer, however, the mechanical strength of gel polymer electrolytes is weakened. The poor mechanical properties may render gel polymer electrolytes prone to lithium dendrite growth.

In this work, we fabricate gel composite electrolyte membranes by incorporating lithium-ion-conducting ceramic particles into the gel polymer matrix. The purpose of this work is to test the hypothesis that the high modulus of the ceramic particles helps preventing Li dendrite growth. Our results show that the room temperature ionic conductivity of the gel composite electrolyte is 1 × 10^-4 S/cm, the same as the gel polymer electrolyte without ceramic. The handleability of the gel composite membrane is significantly improved. Li symmetrical cell cycling performance is evaluated with different ceramic loadings. We also compare the ionic conductivity and Li symmetrical cell cycling performance of gel composite membranes with a single-ion-conducting gel polymer host.

Acknowledgements: This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE), under contract DE-AC05-00OR22725, was sponsored by the Office of Energy Efficiency and Renewable Energy for the Vehicle Technologies Office’s Advanced Battery Materials Research program.

Diblock copolymer materials exhibit a rich equilibrium phase diagram, qualifying them for applications in fuel cells, filters, and battery materials. Self-assembly of these materials rarely results in the equilibrium structures. Instead, configurations are trapped in long-lived meta-stable states and can be stabilized via cross-linking or cooling below the glass transition temperature of one component. The properties of these structures, such as ion-conductivity and mechanical stability, can deviate from those of the corresponding equilibrium phases.

SOMA, our massively-parallel implementation of the Single-Chain-in-Mean-Field (SCMF) algorithm, enables us to study systems with billions of particles and predict their structure formation, thus unraveling the transport properties of self-assembled diblock-copolymers as a function of volume fraction, f . Our investigations show that non-equilibrium morphologies exhibit a large scale fractal-like domain structure that influences the transport properties. The length scale of
these structures highlight the necessity of the simulation large system sizes with micrometer scale to obtain bulk properties. We quantify the transport via the tortuosity and the diffusion inside the network phase and show that equilibrium phases overestimate the transport capabilities of random networks.

The self-assembly of block polymers (BPs) presents unique opportunities to design materials with attractive chemical and mechanical properties based on the ability of BPs to form periodic structures with nanoscale domain spacings. One area of recent progress in our group focuses on the behavior of tapered BPs in which the segment distribution at the interface between blocks is synthetically varied to tune morphology, domain density profiles, thermal transitions as well as mechanical and transport properties. Two application targets for these materials are lithium-ion conducting membranes for batteries and nanostructured thin films for nanotemplates and barrier membranes. In the first target area, we found that the taper volume fraction and composition allow us to manipulate the self-assembly of salt-doped BPs in a well-defined manner that permits optimization of morphology and ion-content. Additionally, we found that the tapered interfaces influence the glass-transition behavior of the ion-conducting block leading to significant changes in lithium-ion transport (ion conductivity). In the second target area, we found the taper content alters the rate of self-assembly as well as the rate of island/hole formation (and ultimate island/hole size) upon thermal annealing. Additionally, using reflectivity techniques, we probed the domain density profiles as a function of taper composition and linked these profiles to changes in domain spacing and glass transition temperature. Overall, these studies show the versatility of tapering to provide a unique handle for simultaneously optimizing multiple materials properties.

Solid polymer electrolytes (SPEs) have received sustained interest as a potential replacement for liquid electrolytes in lithium ion batteries because they are intrinsically nonflammable, processable, and mechanically robust. In the past decade, polymer networks with dynamic bonds that can undergo associative exchange processes, also known as vitrimers, have been investigated as recyclable and self-healing materials. It is an open question if a dynamic network can provide not only mechanical integrity to suppress dendrites, but also substantial conductivity. Here, we develop a vitrimer for Li ion conduction consisting of triethylene glycol, boric acid, and a lithium salt (LiTFSI). These networks were studied over a range of Li/ethylene oxide ratios and exhibit storage moduli > 1 MPa at room temperature but the ability to flow upon heating. Conductivities up to 10^-4 S/cm were measured in the absence of solvent at 90 °C. The vitrimers also show an interesting phenomena where the network is no longer formed at high LiTFSI concentrations, likely due to anion interactions with boron. We report on conductivity and modulus trends as a function of molecular structure to demonstrate that vitrimer electrolytes are a promising platform for SPEs.

The performance of proton-conducting ionomer membranes is complicated by an intricate interplay between chemistry and morphology that is challenging to characterize and control. Here, we report on a class of perfluoro ionene chain extended (PFICE) ionomers that contain either one (PFICE-2) or two (PFICE-3) bis(sulfonyl)imide groups on the side-chain in addition to a terminal sulfonic acid group. PFICE ionomers are promising new materials, exhibiting greater water uptake and conductivity over a range of relative humidity values compared to prototypical perfluorinated sulfonic acid (PFSA) ionomers. Advanced in situ synchrotron characterization combined with simulations reveals insights into the connections between molecular structure and morphology that dictate performance. Energy-tunable X-rays with sensitivity to sulfur can decipher the unique bonding environment of different protogenic groups on the polymer side-chain. Guided by simulations, X-ray absorption spectroscopy can be sensitive to hydration level and configuration that dictates proton dissociation. In situ resonant X-ray scattering reveals that PFICE ionomers have a phase-separated morphology with enhanced short-range order that persists in both the dry and hydrated state, allowing for improved transport pathways across hydration levels. Furthermore, side-chain chemistry and length can be used as a molecular design parameter to predict phase-separated domain spacing. The enhanced conductivity of PFICE ionomers is attributed to a unique side-chain chemistry and structure promoting hydrogen bonding configurations that facilitate proton dissociation at low water content in combination with a well-ordered morphology that forms transport pathways. Our findings also show how energy-tunable X-rays can reveal additional details on the disordered morphology of well-studied PFSAs. Overall, these results provide guidelines to design new ionomers with improved transport properties and demonstrate the value of in situ characterization methods such as resonant X-ray scattering and spectroscopy for unraveling the structural features in chemically-heterogeneous polymer membranes.

Order-disorder and order-order morphological transitions of block copolymers are important phenomena to consider in mechanical properties and ion transports for various electrochemical devices. Among others, the transitions can often be caused by the addition of ionic liquids (room-temperature “molten” salt), but understanding the role of molecular interactions in the phase stability of the mixture of a block copolymer and an ionic liquid is still limited. To provide a better guiding principle to control phase behaviors, we developed a mean-field theory that accounts for the electrostatic interactions, excluded volume effect, and dielectric response between the species. Our theory compares favorably with observed transitions between the ordered microstructures corresponding to lamellae, hexagonally close-packed cylinders, body-centered cubic lattices, and double-gyroid phases, but it still poses a question about the stability of the gyroid phases. We will also discuss the effect of the dielectric contrast between the species on morphological transitions.

The popularity of two-dimensional (2D) materials such as graphene and molybdenum disulfide (MoS₂) have provided renewed interest in the development of laminar membrane technology. These membranes can be used for a variety of applications including water filtration, desalination, ion exchange, electrodialysis, reverse osmosis, and electrodeionization (EDI). Laminar membranes of two-dimensional materials are excellent candidates for applications in water filtration due to the formation of nanocapillaries that can exhibit a size and charge sieving effect, while allowing high water flux.
Previously we have demonstrated that laminar membranes of MoS₂ show outstanding potential for practical applications in energy conversion/storage, sensing, and as nanofluidic devices by tuning their ion permeability by chemical functionalization.¹ Chemical modification of these MoS₂ membranes has been shown to improve their ionic rejection, however the mechanism behind this improvement is not well understood and further work is needed. To elucidate this mechanism we report the potential dependent ion transport through these functionalized MoS₂ membranes.² The effect of pH, solute concentration, and ionic size/charge on the ionic selectivity of the functionalized MoS₂ membranes is also reported. Similarly graphene membranes are produced by simple liquid phase exfoliation possessing a low oxygen content, unlike the GO/rGO material commonly used, and their effectiveness in potential dependent ion sieving applications demonstrated.³ We observe a strong dependence on flake morphology, with decreasing flake size leading to an increase in the number and tortuosity of the nanochannels, resulting in a significant reduction of ion transport. By controlling the number of edge sites and hence surface functional groups this again demonstrates that the surface chemistry of these 2D materials can be used to carefully tune the ion permeability when used to form laminar membranes.

1. Hirunpinyopas, W.; Prestat, E.; Worrall, S. D.; Haigh, S. J.; Dryfe, R. A. W.; Bissett, M. A., Desalination and Nanofiltration through Functionalized Laminar MoS₂ Membranes. ACS Nano 2017, 11 (11), 11082–11090.
2. Hirunpinyopas, W.; Prestat, E.; Iamprasertkun, P.; Bissett, M. A.; Dryfe, R. A. W. Potential Dependent Ionic Sieving Through Functionalized Laminar MoS₂ Membranes arXiv e-prints [Online], 2019. https://arxiv.org/abs/1906.03096.
3. Hirunpinyopas, W.; Iamprasertkun, P.; Bissett, M. A.; Dryfe, R. A. W., Tunable Charge/Size Selective Ion Sieving with Ultrahigh Water Flux in Laminar Graphene Membranes. Submitted 2019.

As the concentration of greenhouse gases, such as CO₂, in the atmosphere increases, one method being considered to minimize its effects involves developing materials to capture and remove significant quantities of CO₂ from the atmosphere. Chemically modified and heat-treated serpentine (HTS) has the potential to be such a carbon sequestration material. HTS, which contains magnesium silicate (Mg₂SiO₄), can be activated to react with CO₂ producing water (H₂O), silica (SiO₂), and magnesium carbonate (MgCO₃). The studied HTS was subjected to various treatment procedures that lead to an optimized activated product. ²⁹Si magic-angle spinning nuclear magnetic resonance (MAS NMR) is useful to analyze the local silicate structure (the Q-distribution) in order to monitor the activation process. The Q-distribution is specified by the fraction of resolved Qⁿ resonances where “n” is the number of bridging oxygens (from one to four) in a silicate unit. The silicate composition, deduced from these experiments, provides information about the evolution of HTS’ silicate environment under various activation treatments.

Harmful dye compounds found in dyeing industry wastes can have deleterious effects on human health and the environment, especially in developing regions. Also, the accumulation of coconut waste in developing areas poses a need for novel methods for coconut waste utilization. This study transformed waste coconut biomass into a negatively-charged Nitro-Oxidized Carboxycellulose Nanofiber (NOCNF) adsorbent for cationic dye removal in water by using the nitro-oxidation method. Nitro-oxidation has been noted as a simpler and more cost-effective method to extract CNF from raw biomasses compared to conventional methods, such as carboxymethylation and TEMPO Oxidation. In another step, positively-charged NOCNF was synthesized by modification with glycidyltrimethylammonium chloride (GTMAC) for the remediation of anionic dyes. Both the anionic and cationic NOCNF were characterized using FTIR, 13C CPMAS NMR, WXRD, TEM and SEM. Anionic NOCNF was found to possess carboxylate groups in the range of 0.777 mmol/gram. Moreover, the cationic NOCNF demonstrated 6% nitrogen content, indicating that the cationic charge existed in the form of NH₃⁺charge. Adsorption studies were conducted for Basic Red 5 (BR 5) and Malachite green (MG) dyes with anionic NOCNF and cationic NOCNF, respectively. Interestingly, both substrates showed significant removal of their respective dye in the range of 40-75 ppm with a removal efficiency of ~90-75% and ~92-70%. Anionic NOCNF exhibited maximum removal efficiency of BR5 with 100% at pH=4. Moreover, cationic NOCNF presented maximum removal efficiency of Acid Orange (AO) with ~100% at pH=8. The above studies show that coconut waste material is excellent for dye removal after using the simple nitro-oxidation method. Furthermore, this novel approach could be applied to solve the problem of overabundance of coconut waste in developing regions.

Recently, the ceramic and inorganic membrane materials draw attentions in both conventional and emerging molecular separation applications due to their outstanding mechanical, chemical and thermal stability in various liquid, gas and vapor environment. However, there are several hurdles to compete with conventional polymeric membranes in the market such as high production cost, difficult scale-up, low packing density and productivity. In addition, ceramic membranes for ultrafiltration, nanofiltration and gas separation range need repeated coating, sintering or reaction processes to apply thin separation layers on the surface of porous ceramic substrates to maximize their permeability. Still, the preparation of ceramic composite membranes with both high permeability and nano-size pores is limited for large area production. Here, we newly developed a simple and facile pre-coating method to prepare defect-free, ultrathin film composite ceramic hollow fiber membranes. Prepared composite membranes showed outstanding separation performance compared to membranes prepared by the conventional method. The thin separation layers with the thickness under a few hundreds nanometers were successfully coated on highly porous substrates without any defects and pore-clogging. The results clearly showed superior molercular separation properties of prepared membranes and the potential for the applications in separation processes at harsh conditions such as organic solvents, high feed temperature or concentration.

The traditional Mediterranean diet is characterized by the preferential consumption of vegetables, legumes, fruit, nuts, and cereals, and olive oil is the main dietary fat. Extra virgin olive oil (EVOO) is obtained from pressing Olea europea (olive) fruit. The characteristic aroma, taste and color of this oil distinguish it from other edible vegetable oils. The excellent organoleptic and nutritional properties of EVOO and the current tendency of consumers to select minimally processed food, have prompted a re-assessment of its consumption in daily diet. Recently, the consumption of olive oil blended with other refined vegetable oils is increasing for use as frying oil, due to economic reasons and customer desire for taking healthy components. However, as-extracted EVOO is still turbid and opalescent and, contains impurities such as free fatty acid (FFA), chlorophyll and pieces of fruit or stone that can compromise the quality of EVOO since they facilitate hydrolysis, fermentation and can cause the oil to become rancid.
The filtration process is considered to efficiently removes these damaging substances. In particular, nanofiltration (NF) is developed for molecular separation on the basis of size and charge differences. Beyond drinking water production and wastewater treatment, NF technology has also been applied for the separations carried in organic solvents such as in the pharmaceutical, petroleum and food industry. NF membrane can be expected to efficiently separate the damaging substance from EVOO.
Cellulose has emerged as an indispensable membrane material due to its abundant availability, low cost, and environment benignancy. However, this unique molecular architecture also leads to cellulose insolubility in the common organic solvents. Only very few usable solvents are known and those are often highly reactive, toxic or impractical for industrial use. Moreover, cellulose membranes typically have meso- or macro-pores, making them suitable only for ultra- or microfiltration. In previous our research, it was proposed that the morphology of cellulose can be controlled by the cellulose molar mass of the cellulose in an ionic liquid. Compaing to the typical cellulose membranes, cellulose formed from ionic liquid is expected to possess micropores suitable for nanofiltration that can separate from molecular level.
In this study, a simple method is provided to prepare cellulose NF membrane from cellulose hydrolyzed in cellulose, and then it was applied to the selective separation of FFAs and chlorophyll from EVOO. To verify the effects of pore size and surface functionality, a series of cellulose NF memebrane with various pore size was prepared, and then they were functionalized by amine group to improve interaction of FFAs. The fatty acid composition and anti-oxidant content (total phenols and tocopherol) were analyzed to demonstrate the selective separation of the amino-functionalized cellulose NF membrane without a component conversion. To confirm the thermal stability, we observed the smoking point of EVOO filtrated by cellulose NF memebrane and compared the smoking point with that of crude and physically refined EVOO. The surface functionalization and pore size of NF membrane significantly influenced the separation efficiency for FFAs and chlorophyll, respectively. It was found that the amine group on the surface of cellulose was necessary to improve the selectivity and adsorption capacity. It also demonstrated that the chlorophyll separation efficiency was optimized when the pore size was smaller than 7 nm. The resulting absorbent selectively removed 90% and 81% of FFAs and chlorophyll, respectively, without the composition change of fatty acids. This study can provide a facile method for enhancing thermal stability of EVOO and thus aid the development of better treatment process for crude oils using cellulose NF membrane.

Electrochemical deposition has been developed and started attracting a number of research attentions in this decade for membrane production. Due to its ease of operation, low cost, and ability for continuous production, it has been widely accepted as a promising approach for large-scale industrial membrane production. Currently, the research in this area is still in its early stage with most efforts being gravitated towards MOF film fabrication. Recently, our group has developed an aqueously cathodic deposition (ACD) approach for ultra-facile membrane production without any post-synthesis treatment. The obtained defect-free membrane exhibits superior performance in C₃H₆/C₃H₈ separation. ACD can be extended for other types of MOFs and is considered as an attractive approach for scalable membrane fabrication. As a new approach, the mechanism behind of ACD was not well understood.
Here, we conducted a detailed investigation to understand the fundamentals of ACD approach for membrane fabrication. Through this study, we achieved an in-depth understanding of cathodic reactions involved in membrane formation via cyclic voltammetry study. The influence of precursor compositions, current density and counter-electrode were demonstrated. Following these understandings, we are able to ultimately shorten the fabrication time from 60 min to 20 min, tune the thickness of the membrane from 100 nm to 500 nm, and enhance the membrane chemical stability for exceptional performance in gas separations.

Many of half cell reactions for electrochemically driven energy conversion devices consist of movement of ions and electrons simultaneously during anodic and/or cathodic reactions to complete full electrochemical cells. In addition, Ions generated at electrodes move from anode to cathode or vice versa for electron exchanges. Pathway for ions is normally in an aqueous phase. Regardless, the introduction of any aqueous phase in energy conversion devices causes many problems during fabrication, operation, maintenance, and so on. Thus, much efforts have been devoted to develop quasi-solid electrolytes such as gel polymer, ion exchangeable polymers, impregnation of ions in porous matrix and so on. One of major disadvantages to use polymeric electrolytes is significant Ohmic voltage decay due to high areal resistance compared to aqueous phases. An approach to minimize areal resistance of film-type polymeric electrolytes is to make film thickness as thin as possible. Free standing polymeric electrolytes, however, show low mechanical properties. Thus, composite membranes could be used by impregnating polymeric electrolytes into thin porous substrates. In this study, three-layered (electrolyte-skeleton/electrolyte-electrolyte) composite membranes with various thicknesses were prepared. A technique to impregnate polymeric electrolytes into hydrophilic or hydrophobic porous substrates were intensively developed so as to prepare void-free composite membranes. Characterization in terms of ion conductivity, ion exchange capacity, water uptake, dimensional stability, mechanical strength was carried out.

Acknowledgement
This work was supported by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20193010032480).

Microbial fuel cell (MFC) has been nominated as an alternative to nonrenewable sources of energy capable of transforming organic matters directly into electricity by bacterial anaerobic respiration on the anode surface and oxygen reduction reaction on the cathode surface. It is low cost because of exploiting waste matters as fuel. But low electricity generation is a big challenge in this technology [1]. Two pathways are possible for bringing MFC to commercialization: i) increasing electricity generation; ii) using cheaper components like electrode and membrane.
In MFCs, membrane play the role of separator for taking anode and cathode apart each other. Anode’s required condition is anaerobic while cathode needs oxygen. Therefore, the membrane should be impermeable to oxygen. On the other hand, the membrane’s capability in transfering hydronium ions or cations from anode to cathode compartment is in high level of importance. Although using membrane results in increase in internal resistance of MFC, but for long-term operation of MFC it can protects cathode against contaminant and microbial biofilm formation on the electrode surface [2].
In single Chamber MFCs the cathode can be used as membrane-less and or membrane assembly electrode (MEA). An MEA is an integrated electrode system resulting in electron and ion transfer to reach cathode surface in presence of oxygen. There are two main positive points in using MEA i) lower internal resistance of MFC in comparison with double chamber MFC; ii) higher durability of SCMFC’s compared to membrane-less ones. Therefore, making a cheap MEA with high performance for MFC is an interesting and vital field of research.
Bacterial cellulose (BC) produced by some species of bacteria like acetobacter xylinum is a three dimensional network of nano cellulose fibers. The latter can be easily modified by carbon materials and conductive polymers to develop air-breathing cathodes. From this point of view, it has the potential to be used as a cheap substrate for high performance membrane specially compared with Teflon based composite cathodes [3].
Here we report about fabricating a novel cellulose based air-cathode coated with multi-walled carbon nanotubes (CNT) and polyaniline (PANI). Also BC was treated by nano-zycosil (Zyc) to be hydrophobic. The results of the electrochemical test are presented and compared to those obtained with conventional Teflon-based cathodes. Our work aims at demonstrating new routes to develop a cheap, high performance and green MEA for MFC technology.



Acknowledgments
This work was supported by Iran National Science Foundation (INSF), grant number: INSF-95819857 and Babol Noshirvani University of Technology. Also, the research has been carried out under the Italy-South Africa joint Research Programme 2018-2020, Italian Ministers of Foreign Affairs and of the Environment.

References:
[1] C. Santoro, M. Kodali, N. Shamoon, A. Serov, F. Soavi, I. Merino-Jimenez, I. Gajda, J. Greenman, I. Ieropoulos, P. Atanassov, J. Power Sources, 2019, 412, 416-424.
[2] M. Rahimnejad, G. Bakeri, G. Najafpour, M. Ghasemi, S.-E. Oh, Biofuel Research Journal, 2014, 1, 7-15.
[3] M. Mashkour, M. Rahimnejad, M. Mashkour, J. Power Sources, 2016, 325, 322-328.

Current research aims to quantify self-healing capabilities of iron oxide (Fe₃O₄) nanoparticle (NP) infused poly(ethylene oxide) (PEO). Iron oxide NPs of varying surface chemistries (bare, aminopropyl triethoxysilane coated, and polyethylene glycol α–, ω–diphosphate coated) are used to prepare nanocomposites of varying concentrations less than 1% by weight. Each sample, in the form of a cylindrical disc, is indented using a LECO M400 Microindenter at five different locations between the center and edge. The indentation site is examined before and after being placed in an alternate magnetic field (AMF) to induce healing. The micrographs of each indent were collected with an Olympus PMEG microscope at the same imaging parameters. Healing efficiency is quantified using visual and software-based image analysis, identifying the percentage of healing as a function nanoparticle concentration and surface chemistry. Multiple methods of software-based image analysis were developed to perform this analysis. Nanoindentation experiments were also carried out to evaluate impact of surface coating and concentration on mechanical properties and viscoelastic behavior of these nanocomposites.

*This material is based upon work supported by NSF Grant 1825254.

Comb shaped polymer electrolyte membrane was synthesized by grafting highly sulfonated poly(arylene sulfide sulfone) side chain to poly(arylene ether sulfone) backbone, differing the molecular weight and the density of the side chain. Side chain, synthesized from A-B type monomer, was designed with monofunctional terminus to avoid crosslinking in grafting. Furthermore, side chain is highly sulfonated with one sulfonic acid group per one benzene ring, inducing well-developed microphase separation. Structure-property relationship was investigated by varying the architecture of graft polymer, comparing graft polymer structures with dense, short side chains to those with sparse, long side chains at similar ion exchange capacity. Analyses for proton conductivity, water uptake, dimensional change, and membrane electrode assembly performance have been conducted. Fuel cell performance of graft polymer at 0.6 V resulted in 0.7957 A cm^-2 at 100% hydrated condition. Also, graft polymer endured 730 hours before the OCV drop and 17000 wet/dry cycles before reaching 2 mA cm^-2, the Department of Energy (DOE) standard of fuel cross over, showing remarkable chemical and physical durability. The synthesized graft polymer may be a promising candidate as a polymer electrolyte membrane for fuel cell application.

Membrane separations are energy-efficient, simple, and scalable. Yet, their broader use is limited by the separation capabilities of membranes prepared by conventional methods, typically confined to size-based separations. Self-assembly of functional polymeric materials is a powerful method for designing membranes capable of new separations, including the separation of organic compounds of similar size from each other. This can potentially be achieved by membranes that mimic biological pores such as porins, with pores that are only slightly larger than the target solute and functionalized with groups that selectively interact with one compound over another. Our group has developed a method for preparing such membranes by the spontaneous self-assembly of random amphiphilic copolymer in methanol into micelles that are then coated onto a support to form a selective layer of tightly packed micelles. These membranes, produced by a simple manufacturing process, have ∼1-4 nm pores lined with carboxylic acid groups that enable charge-based separation of organic solutes. Additionally, the carboxylic acid groups can be converted to a wide range of possible functional groups through coupling reactions. This can provide selectivity towards solutes by affinity. Because of the distinctive geometry and selectivity of these membranes, it is valuable to assess the versatility of this technology. The goal of this study was to tune the pore size by changing the micelle size, and analyze the robustness of these thin film composite membranes. The pore size was tuned by interactions of dissolved metal ions with micelles while the robustness of the system was altered by different crosslinking procedures.

Water purification is necessary for the well-being of both people and the environment. While membranes are firmly established as the leading water purification technology, they still face a host of challenges that limit their performance. For conventional polyamide nanofiltration membranes, the main challenges are selectivity, fouling, and chlorine sensitivity. In the present work, we created a random terpolymer that can self-assemble into a membrane with a tunable pore environment. We added charge to the pores, which granted the membrane with selectivity comparable to commercial nanofiltration membranes. By virtue of the material, these membranes are also fouling resistant and chlorine tolerant.
Self-assembly is defined as the formation of hierarchical structures from simple molecular building blocks. This process is driven by interactions between said building blocks, and can be used to engineer ordered structures ranging from nanometers to micrometers in size. Zwitterions are defined as molecules that contain an equal number of positive and negative charges. This charge disparity grants zwitterions an enormous dipole moment, which leads to powerful electrostatic forces occurring between neighboring zwitterions. These forces drive self-assembly, even in random copolymers with very short zwitterionic segments. In the present work, we show that random terpolymers comprised of zwitterionic, hydrophobic, and zwitterion-philic repeat units self-assemble to form a bicontinuous nanodomain of zwitterionic/zwitterion-philic and hydrophobic sections, each 1-2 nm in size. When these terpolymers are coated onto a porous support to form the selective layer of a thin film composite membrane, the zwitterionic/zwitterion-philic domain acts as a network of nanochannels for the permeation of water and other solutes. Through pragmatic choice of the zwitterionic-philic repeat unit, it is possible to tune the properties of these nanochannels. Here, we show that the random terpolymer poly(trifluoroethyl methacrylyate-r-sulfobetaine methacrylate-r-methacrylic acid) (PTFEMA-r-SBMA-r-MAA) can be used to fabricate nanofiltration membranes that address the challenges faced by conventional polyamide membranes. The presence of charged groups, through dissociated MAA repeat units segregated into these nanochannels, leads to the selective rejection of salts and charged organic compounds. These membranes are also resistant to fouling and exposure to chlorine. Furthermore, we demonstrate that the properties of the nanochannels and the selectivity of the membrane can be further tuned by the functionalization of carboxylic acid groups on MAA repeat units to access additional separations. These features demonstrate the promise and versatility of this new polymer family for a wide range of membrane applications.

Composites proton conducting material based on cesium dihydrogen phosphate were prepared and doped with zirconium oxide and observed the structural, thermal and transport properties of composites proton electrolytes in terms of X-ray diffraction(XRD) analysis, Fourier Transform Infrared Spectroscopy( FTIR ), Differential Scanning Calorimetry (DSC), Raman spectroscopy and conductivity measurements. We have investigated that the ionic conductivity of un doped CsH₂PO₄ increases up to three order of magnitude within the transition temperature 230^oC to 250^oC, Which is in small limit range and unstable. We doped ZrO₂ with different composition (1-x) CsH₂PO₄/x ZrO₂ (0≤x≤0.4). CsH₂PO₄ transition temperature range is (230^oC -250^oC) after doping of ZrO₂ its transition temperature range increases from 230^oC to 280^oC. The stability, ionic conductivity and fuel cell performance were investigated within the temperature range 230^oC to 280^oC under environments atmospheric humidification. The superprotonic transition of CsH₂PO₄/ZrO₂ Composites was identified with advanced silver electrode by vapor deposition of silver.

3D printing (additive manufacturing) can be applied in various ways because of its infinite versatile approaches in its structure and materials, etc. In addition, the application range can be expanded without restrictions when applied with different material. For this point of view, optimization of printing scheme and printed material property (frame material, structure, pore distribution, shape and particle size etc) with respect to the appropriate purpose could be essential factor for maximizing efficiency of printed output

In addition,various studies have been carried out on the fine dust(PM 2.5), which is one of the global disasters as an urgent field to understand the generation behavior and occurrence of PM these days.
The designed 3d printed structure and defined distribution with the inner flow pattern could be a good tool for understanding the complex action of various factors for removal characteristics with controlled condition

For this purpose, we have applied various methods to fabricate porous structures of various structures through FDM 3D printing and to obtain basic data for evaluating complex reaction characteristics of precursors for PM secondary particle production.

Here we introduce the relationship between the structural parameters of the reaction kit and adsorption characteristics of the prepared filter were confirmed in two aspects. First, a reaction kit was designed, fabricated and the inner flow characteristics were defined. Second, the 3d printed structures for adsoption/desorption behavior of PM precursor (NH3, SOx) were studied for each physicochemical conditions by using various zeolites with different pore variance as adsorbent, and their reaction chacterized through the analysis of adsorption/desorption behavior - breakthrough curve analysis.
We expect that this study on the relationship with the structural parameters of the designed filtration provide important basic knowledge for design efficient membranes for removal of PM

Anion exchange membrane (AEM) fuel cells is a promising alternative to proton exchange membrane (PEM) fuel cells through the ability to operate with a non-precious metal catalysis and faster kinetics of the oxygen reduction reaction; however, AEMs are not widely commercialized due to their inferior hydroxide ion conductivity, inadequate mechanical properties, and lack of chemical stability under alkaline conditions. Recently, biphenyl and terphenyl based polymers were synthesized and exhibited favorable electrochemical properties. In this study, the thermal and mechanical properties of these polymers were analyzed by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) to determine their capability of manipulating membrane electrode assembly for fuel cell applications. A two-day annealing process was also performed and studied to evaluate its effects on mechanical properties. Thermal analysis results indicated that these AEMs remained both chemically and mechanically stable within a fuel cell operating temperature range. The glass transition temperature (Tg) of mTPBr and BPBr are 174°C and 188°C respectively. After quaternizaion, mTPN1 and BPN1 didn’t show a Tg.

In recent years, GO-based filtration membranes have received a lot of attention in the field of filtration technology. In this study feature of the multilayered reduced graphene oxide (rGO) membranes on different polymer substrates (Polyvinylidene difluoride (PVDF), Polytetrafluoroethylene (PTFE) and Anodic Aluminum Oxide (AAO) membranes (Millipore) are given.
GO powders were prepared from graphite powder by the modified Hummers method. For comparison GO of Sigma-Aldrich brand was also used.
rGO membranes prepared by vacuum filtration and drying of the powders GO in water with the subsequent ultrasonic influence within 30 min. Later GO was deposited on a polymeric PVDF membrane.
rGO suspensions and membranes were characterized by Fourier Transformation Infrared Spectroscopy (FTIR) using NicoletiS10 FTIR, Raman spectroscopy, scanning electron, and atomic force microscopy.
Filtration abilities were measured by pH meter (Mettler Toledo S20-KS SevenEasy) and desalination rate was measured by Ion Chromatography (Metrohm 930 Compact IC Flex). Experimental salt solution (pH=8.5) was used for desalination experiments.
The possibility of efficient rGO/PVDF membranes creating by using GO on the surface in standard polymeric PVDF membranes is shown. rGO/PVDF membranes have the best effectiveness of filtration than standard polymeric PVDF membranes. The increasing of water transportation speed across rGO/PVDF membranes with a decreasing of the sizes of membrane nanochannels are observed. It is experimental fact is explained by a decrease of activation energy of shear viscosity of the liquid in nanochannels.

Fluid flow process in an isolated system at nanometer scale has great fundamental importance in nanofluidics. Nanofiltration process through advanced two-dimensional nanomembranes using reverse osmosis method has a particular interest in water desalination and purification.
In this work, computational model was created, in order to simulate a process of water filtration through 2D materials such as graphene, graphene oxide, MoS₂ and BN using molecular dynamics method. All 2D materials had a hexagonal structure, the diameter of pores were between 6 Å and 10 Å. The volume of water containing ions was 28,830 ų, the volume of water was 15360 ų. The piston pressure was 3,5 GPa.
To assess the structural relationship in the liquid solution, the radial distribution function was calculated. Obtained data have a good agreement with the experimental results. Our computer simulation results clearly indicated that nanomembranes based on two-dimensional materials were able to reject salt ions, providing a high flow of water molecules. The highest water flow rate and lowest salt penetration ratio was observed in MoS₂ membranes, due to the low energy barrier and unique pore structure, with alternating hydrophobic and hydrophilic edges.
Thus, the computational model of a nanofiltration system using 2D materials and reverse osmosis method was created. Our computer simulation results showed that 2D nanomaterials can be used as new generation desalination membranes. Such membranes are expected to be more energy-efficient in comparison with other modern membranes used today.

Samaria-doped ceria (SDC) oxide ion conductors and mixed alkali salts (e.g., Li, K) were proposed as electrolytes for intermediate temperature (500 ^oC-700 ^oC) solid oxide fuel cells and as membranes for high temperature CO₂ separation. In this work dual-phase composite membranes were obtained by two techniques: i) producing a porous GDC pellet using alkali halides as sacrificial pore former, followed by molten carbonate vacuum infiltration, and ii) electric field-assisted sintering by applying a low voltage at 420 ^oC to a (75 wt.% GDC+25 wt.% eutectic Li-K carbonate mixture) pressed green pellet. The microstructure of the impregnated porous ceramic and the electrical field assisted sintered pellet were observed by scanning electron microscopy to evaluate the distribution of carbonates. The electrical behavior of the membranes was assessed by electrochemical impedance spectroscopy measurements in the 350 ^oC-550 ^oC range, and these data used to draw Arrhenius-type plots. Membranes obtained by electric field-assisted sintering have electrical conductivity higher than those based on impregnated porous ceramics.

Polymer-containing liquid mixtures can exhibit macroscopic phase separation and microphase separation. For example, diblock copolymer melts show the phase transition from a homogeneous to a lamellar phase when the temperature is decreased. Molecular simulations such as molecular dynamics and Monte Carlo simulations and thermodynamic theories are conventional approaches to understanding the phase behaviors of polymer mixtures. However, more computationally fast simulation methods that are fairly robust against the choice of force fields and applicable to various phase behaviors are greatly needed because we must analyze the abundant and diverse experimental data obtained concurrently. To address this challenge, we develop deep neural networks (DNNs) as a third approach to assist with the existing theories and simulations and experimental analyses. In this talk, we discuss our new hidden layer that is constructed through coarse-grained mean-field theory and the scaling laws in polymer physics. This characteristic hidden layer enables us to perform the learning process efficiently with relatively small numbers of artificial neurons and provides the DNNs with reasonable predictive power. To demonstrate the efficacy of our DNNs, we will discuss the phase diagrams of polymer solutions, and the salt-free and salt-doped diblock copolymer melts. Moreover, we will show the predictive power of the DNNs by considering some experiments for the lithium salt-doped diblock copolymers such as PEO-b-PS. <div class="grammarly-disable-indicator"> </div> <div class="grammarly-disable-indicator"> </div>

In recent years, fuel cell technology has become an integral part in modern and sustainable concepts of energy storage and conversion. Proton-conducting polymer electrolyte membranes (PEMs) play a key role in this respect. Standard materials such as Nafion tend to be expensive and their proton conductivity is often strongly humidity-dependent. Metal-organic frameworks (MOFs) and other coordination polymers (CPs) have recently attracted attention as potential alternatives [1-3]. Still, profound knowledge of the underlying mechanisms of proton conduction in coordination polymers is scarce. Impedance spectroscopy is a powerful and versatile tool for studying proton conduction in coordination polymers [4]. It is usually applied to powders; we have recently reported on impedance measurements on MOF single crystals [5].

We present impedance spectroscopic studies of proton conductivity in a single-crystalline coordination polymer of composition [Ba₂(HSPP)(H₂O)₂] H₂O that consists of Ba²⁺ ions connected by organic phosphonatosulfonate linker molecules (HSPP^4- = [(O₃PCH₂)₂N(H)-CH₂-C₆H₄-SO₃]^4-). From the crystal structure proton conduction by a proton 'hopping' mechanism could be anticipated [6]. However, the crystal structure also contains non-coordinated water molecules that may affect the proton conductivity. The material forms elongated crystals. We have measured impedance data by varying the temperature, relative humidity, and, especially, the orientation of the single crystal with respect to the contact electrodes. Proton conductivity turns out to dependent on said orientation, which implies anisotropic conduction paths in the crystal structure.

[1] M. Yoon, K. Suh, S. Natarajan, K. Kim, Angew. Chem. Int. Ed. 52 (2013) 2688-2700.
[2] S. Tominika, A. K. Cheetham, RSC Advances 4 (2014) 54382-54387.
[3] A.-L. Li, Q. Gao, J. Xu, X.-H. Bu, Coord. Chem. Rev. 344 (2017) 54-82.
[4] S.M. Rezaei Niya, M. Hoorfar, J. Power Sources 240 (2013) 281-293.
[5] H. Bunzen, A. Javed, D. Klawinski, A. Lamp, M. Grzywa, A. Kalytta-Mewes, M. Tiemann, H.-A. Krug von Nidda, T. Wagner, D. Volkmer, ACS Appl. Nano Mater. 2 (2019) 291-298.
[6] O. Beyer, T. Homburg, M. Albat, N. Stock, U. Lüning, New J. Chem. 41 (2017) 8870-8876.

The 73 – 216 µm thick nanostructured membranes based on free two-layer films of nanoporous anodic alumina with pore diameters about 55 nm are discussed to be formed by the two-side anodization in the electrolyte of oxalic acid and further bipolar anodizing. The basic idea of the bipolar anodization is to use a two-chamber electrolytic bath, in which the alumina membrane with Al inclusions was placed as an insulating partition. One of the chamber is filled with the anodization electrolyte (7 % H₂C₂O₄), while the buffer electrolyte (10 % CuSO₄) is used in the second chamber. The cathode electrode (-) is placed in the first chamber and the anode electrode (+) is connected to the second one. When the current is switched on (U ~ 55 V), a positive charge appears on one side of the membrane opposite the Al inclusions. The membrane becomes an anode, and anodic oxidation (anodizing) of Al inclusions takes place. The second side of the membrane is charged negatively and becomes a cathode. The recovery of buffer electrolyte cations (Cu²⁺) on the cathode side opposite the Al inclusions was observed with a guaranteed absence of sparks and burn-through of the oxidized layer in these zones. The volume growth coefficient in the conversion of Al to Al₂O₃ was 1.44 – 1.46. The membranes obtained demonstrated high resistance to cracking and the ability to save the form at high temperature exposures. Highly ordered nanostructured nature of their cellular porous morphology that can be controlled by electrochemical and temperature modes of the electrochemical anodizing process appears to have considerable promise.

The development of advanced hybrid materials based on polymers from biorenewable sources and mineral nanoparticles is currently of high importance. Lignin has a great potential as a sorbent for removal of transmission metals and organic pollutants from wastewater. By combining lignin with inorganic carrier, organic-inorganic hybrid composites with improved sorption properties can be obtained.

Lignin-based composites were synthesized by crosslinking of different amount of lignin on silica. For that, lignin solutions with concentration from 1 to 10 % were adsorbed on mesoporous silica surface. FTIR spectroscopy confirmed the creation of lignin layer on silica surface. Concentration of immobilized lignin was estimated using thermogravimetric analysis. Specific surface area and changes in pore size distribution with increasing of lignin concentration as composites component were estimated.

Synthesized hybrid composites were found to be effective as sorbents for the recovering of cobalt(II) from aqueous solutions.

Acknowledgment: This work has been financially supported by the Olle Engkvists Stiftelse (Grant Nr. 198-0329) and the ÅForsk Foundation (individual grant number 19-676).

In quest of a viable method for low-cost carbon capture and release, the integration of photoswitchable elements into porous materials in order to modulate their CO₂ adsorption and release properties on demand is of great interest. Serving as an attractive stimulus, light is naturally abundant, and it could be harnessed to replace conventional energy-intensive regeneration techniques.
Among the light-responsive elements, azobenzenes interconvert from the thermodynamically stable form of trans to the cis configuration by rotation of the aromatic rings around the -N=N- bond upon UV and visible light irradiation, respectively. Considering amine functional groups as proven CO₂ adsorptive sites, the CO₂ capture and release properties of an adsorbent could be tailored by the interplay between amine sites and photoresponsive azobenzene groups in a porous structure. Simply put, by accommodating amine groups on the far end of azobenzene pendant groups, the exposure of active amine sites to CO₂ molecules are regulated by light-driven isomerization.
Despite the investigation of several photoresponsive systems for CO₂ adsorption, various challenges are yet to be addressed prior to achieving a concrete material design. More precisely, the photoresponsive adsorbents usually suffer from delayed response upon irradiation, largely due to sterically hindered azobenzene isomerization in the relatively small pore structure. Moreover, their cavity is partially occupied by the photoswitchable pendant groups, leading to lower CO₂ uptake capacity.
To tackle these constraints, in this work, we first conduct a structural optimization of the porous material hosting azobenzene groups by means of density functional theory (DFT) methods. In the following steps, the cis-isomer and trans-isomer contents in light-responsive adsorbents are determined by NMR after certain irradiation time to validate the effectiveness of irradiation. The CO₂ uptake amount of the as-synthesized adsorbents are subsequently investigated by applying UV and visible light for a range of time and intensity. Further characterizations including XRD, FTIR, BET surface area and UV-vis spectroscopy are also performed to discuss the effect of photoswitching on CO2 adsorption properties of adsorbents.

Membranes have had a huge impact in molecular separations in aqueous systems, especially desalination. The workhorse membrane for reverse osmosis is the thin film composite (TFC) membrane formed by interfacial polymerisation. This presentation will focus on research into understanding the formation and function of TFC membranes for both desalination and Organic Solvent Nanofiltration (OSN) [1].

Advanced imaging and tomography has been used to understand the morpholopgy of commercial TFC membranes and the flow paths through them [2]. To better reveal the relationship between fabrication and function, ultra-thin polyamide films (sub-10nm) have been formed by interfacial polymerisation and then used to fabricate composite membranes [3]. These ultra-thin polymer films 6-8nm thick are strong, and can be several centimetres in lateral dimension. Interestingly, the morphology of these films can be manipulated from smooth to highly crumpled, by adjusting the reaction conditions. The films can be applied in liquid filtration, and show unprecedented permeances in organic solvents, and high rejection of all solutes. Because the films can be prepared free-floating at a liquid-liquid interface, they can be used to explore how composite membranes function. This reveals that through matching of rough and smooth films with different supports, it is permeance rather than surface roughness, that determines fouling. Further, we find that the support permeance has a strong effect on the composite membrane permeance, for the same film placed on different supports [4], and that that the support rather than the thin film separating layer of a composite membrane leads to physical aging and flux decline. These insights are counter-intuitive to current thinking.

Intrinsic microporosity can be introduced into the ultra-thin polymer films through selection of contorted monomers for interfacial polymerisation. These intrinsically microporous polymer nanofilms provide higher interconnectivity of pores and greater permeance than films obtained from planar monomer systems [5]. Finally, the potential for ultra-high permeance membranes to impact on actual molecular separation processes will be discussed, including the relative merits of selectivity, permeance and stability [6].

References

Marchetti P, Jimenez-Solomon, MF, Szekely, G and Livingston AG, Molecular Separation with Organic Solvent Nanofiltration – A Critical Review, Chemical Reviews, 114, 10735 – 10806 (2014)
Klosowski, MM, McGilvery, CM, Li, Y, Abellan, P, Ramasse, Q, Livingston, AG and Porter, AE, “Micro-to nano-scale characterisation of polyamide structures of the SW30HR RO membrane using advanced electron microscopy and stain tracers”, J.Mem.Sci (2016) 520 pp.465-476
3) Karan S, Jiang Z, Livingston AG, Sub-10 nm polyamide films with ultrafast solvent transport for molecular separation, Science 348 pp 1347-1351 (2015)
4) Z Jiang, S Karan, AG Livingston “Water transport through ultrathin polyamide nanofilms used for reverse osmosis” Advanced Materials (2018) 30 (15), 1705973
5) Jimenez-Solomon, MF, Song, Q, Jelfs, KE, Munoz-Ibanez, M and Livingston, AG, Polymer nanofilms with enhanced microporosity by interfacial polymerization, Nature Materials Vol 15, Issue 7, pp.760-767 (2016)
6) Shi B, Marchetti P, Peshev D, Zhang S and Livingston AG Will ultra-high permeance membranes lead to ultra-efficient processes? Challenges for molecular separations in liquid systems J.Mem.Sci (2017) 520 pp.35-47

Block copolymers (BCPs) readily self-assemble into highly ordered morphologies, such as lamella, cylinders and gyroids and are promising materials for applications in microelectronics, catalysis, and membranes. The cylinder morphology has been extensively studied for isoporous membranes with channels on the nanometer length scale, but this morphology suffers from alignment issues: The channels must be oriented perpendicularly to the surface while also extending through the full thickness of the membrane. Gyroids, on the other hand, form networks of isoporous channels that are connected in all three dimensions, thereby avoiding the orientation challenge of cylinders. Thus, the gyroid morphology is of great interest, but the fabrication of such materials presents a challenge with both synthesis and processing.

The synthesis and characterization of three different gyroid-forming di-block copolymers will be presented. In these materials, one block is made of the easily degradable polylactide (PLA) and the other features a functionalized polystyrene block to offer rigidity. Anionic polymerization in conjunction with organocatalytic ring-opening polymerization was used to provide BCPs with low polydispersity and a high degree of control over the relative volume fraction. These materials can be made reproducibly and on multigram scales.

Thin films of the materials were studied before and after the removal of the PLA block and processes were developed to overcome wetting layers that close the surface of the gyroid film. Atomic layer deposition was explored as a means of changing both the pore dimension and surface energy. These BCPs have been combined with a polyethersulfone (PES) layer to generate composite membranes composed of a thin, selective gyroid layer and a mechanically strong, porous PES layer. These composite membranes were investigated for applications in batteries, gas separation, and water purification.

The design and synthesis of membranes for gas separations has mainly relied on isotropic materials. Physically, isotropic materials control the magnitude of the flux and separations in isotropic systems occur as a result of different flux magnitudes of the species of interest. We have recently introduced a novel approach for the design of membranes based on anisotropic materials in which flux directional control is induced to perform separations. Remarkably, the use of anisotropic materials provide membranes in which selectivities and permeabilities are spatially dependent. In this talk, we discuss the capabilities of these novel anisotropic membranes for gas separations under planar configurations and provide unprecedented selectivities for separations of binary mixtures. We also discuss how anisotropic materials can be used to improve the separation ability of current isotropic membranes, pushing the limits of existing technologies. Furthermore, we discuss the existence of a unique trade-off relation between selectivity, permeability and collected fraction of permeate. Our findings are applied to the separation of binary mixtures of O₂/N₂ and H₂/CH₄.

Polymer membranes utilize the difference in permeability between molecules and ions to achieve molecular separation. For both gas separation and desalination processes, the transport of permeates through polymeric barrier layer films occurs through a solution diffusion process. Typically, the transport is modelled as one-dimensional, i.e. along the thickness direction of the barrier layer. However, recent evidences suggest that these films are often heterogenous in terms of structure and composition. The effect of spatial heterogeneity, both in terms of length scale and spatial arrangement, on the transport behavior (especially permeability) remains unclear. Besides homogenous membranes, recent developments in mixed matrix membranes aim to use more permeable additives (e.g. metal organic framework or MOF particles) to enhance the permselectivity of the matrix membranes.
In this work, we demonstrate a new type of polymeric membrane with tunable, well-defined, spatially heterogeneous permeability. This is achieved by photopatterning over a two-stage thiol-ene polymer network, which leads to spatially varying rubbery and glassy networks with nearly identical chemistry but different permeability. This talk will discuss the materials formulation; photopatterning with regards to both resolution and spatial arrangements; mechanical, and gas transport properties of these films. Further, the effects of both domain size, interfacial profile, and volume fraction of the glassy regions on the overall gas permeability of the membrane will be compared with composite models. Besides their potential applications in molecular/ion separation, the films are promising in areas of encapsulating nanodevices that require spatially varying permeability.

Despite the wide use of ion-rejecting and ion-conducting polymeric membranes in processes such as nanofiltration (NF), reverse osmosis, electrodialysis (ED) separations, membrane electrolysis and fuel cells (FC), understanding ion transport and selectivity still presents a challenge. Mean-field models of charged nanopores (e.g., Donnan or Poisson-Boltzmann) have been the standard for last few decades, yet they fail to reproduce correctly some observed trends, e.g., , multi-ion separations in NF or ion specificity in ED. These difficulties can be traced back to inherent flaws of mean-field models in charged low-dielectric media. On the other hand, simple phenomenological models with adjustable ionic permeabilities work well, but require ad hoc composition-dependent parameters and the physics behind this dependence remains obscure.
Here, we abandon the standard mean-field nanopore picture and introduce a simple solution-diffusion model of a homogeneous NF membrane that treats the strong departures from mean-field by adding ion association effects in a manner of classical Bjerrum theory. The model consistently explains our recent elaborate NF data for NaCl+CaCl₂ mixtures [1] and other published data, e.g., a high portion of nominal ion-exchange capacity in FC membranes inactivated by presumable “condensation” (association) of counter-ions on fixed charges [2]. It also addresses the fact that, in a non-mean-field treatment, ion uptake and mobility are no more decoupled (like in the Donnan model) and must be computed in a consistent manner from the same physical picture.
The results emphasize the importance of non-mean-field effects in general and ion association in particular for correct modeling of ion uptake, permeation and conductance in polymeric membranes. Our analysis also highlights the fact that simple continuum electrostatics is unable to supply an accurate quantitative description of effects such as association and solvation, for which the new model offers a simple and approximate yet physically sound and transparent way to treat the problem and define relevant ion-specific parameters.
[1] N Fridman-Bishop, KA Tankus, V Freger, Permeation mechanism and interplay between ions in nanofiltration, J. Membr. Sci., 2018, 548, 449-458
[2] KM Beers, DT Hallinan Jr, X Wang, JA Pople, NP Balsara, Counterion condensation in Nafion. Macromolecules 2011, 44, 8866-8870.

Proton exchange membrane fuel cells are a potential zero emission power source to reduce and replace dependency on fossil fuels. While research and development efforts to date have concentrated on materials and systems that either function below the boiling point of water (25-100 C) or systems where the conductive medium is a ceramic or glass requiring very high temperatures (> 500 C), materials and systems that operate at intermediate temperatures (150-300 C) have received considerably less attention. Moving to this temperature regime can provide a number of advantages, including the requirement of a lower catalyst loading, reduced potential for catalyst poisoning, and reduced complexity from removing bulky and costly humidification systems, while also allowing for the use of lower cost non-precious catalysts. One of the key challenges to operating fuel cells at intermediate temperatures is the search for new proton conducting electrolyte materials that show conductivities >10⁻³ S/cm and good chemical stability under these conditions. Here we have explored a new family of solid-acid compounds, the borosulfates, as proton conducting electrolytes. These materials show promise, with measured conductivities on the order of 10⁻⁴ S/cm at ambient temperatures/humidity with further increases in conductivity to 10⁻³ S/cm above 100 C. TGA measurements show that these materials are stable to temperatures above 300 C, and we also demonstrate that this material can be consolidated into dense pucks at mild temperatures using a standard hydraulic press.

Understanding the structure and property relationship is critical to designing high-performance membrane materials for gas separation, particularly for materials with balanced permeability and selectivity above or near the upper bound. Herein, a modified free volume is adapted to describe the upper bound for the separation of several gas pairs, such as O2/N2, He/CH4, CO2/CH4, and H2/CO2. The results are compared with conventional activation energy model reported in the literature. More importantly, this model can be used to predict the structure of polymers with targeted separation properties on demand. I will demonstrate that for the separation of specific gas pairs, polymers with specific free volumes can achieve the best performance. Such an understanding may be useful for the design of membrane materials through data mining or machine learning.

Membrane stability is a crucial determinant of the performance and lifetime of energy storage and conversion devices such as batteries, fuel cells, and photoelectrochemical CO2 reduction (CO2R) devices. In direct methanol fuel cells (DMFC) and CO2R devices, membrane stability is compromised by methanol, which solvates many polymeric membrane materials. Stability can be assessed by evaluating membrane permeability over time, with constant permeability suggesting a stable material and allowing for stable device performance. However, permeabilities obtained from experimental data are often average values and may include the effects of swelling, liquid-membrane boundary layers specific to the device architecture, and changing material properties. This talk reports a combined experimental-simulation study of methanol permeation through Nafion to determine intrinsic permeability, building on our prior modeling work examining time-dependent sorption in this system. Experiments provided independent measurements of swelling, sorption, and time-dependent permeation. Computational fluid dynamics simulations were used to generate an independent estimate of boundary layer thickness in the experimental system. A multiscale reaction-diffusion model was constructed using these data, and stochastic simulations were used to predict the intrinsic membrane permeability as well as apparent permeability for comparison to the experimental data. Deviations of experimental data from theoretical predictions using a standard permeation model as the system approaches equilibrium are explained. The approach we used is general, and is valuable for understanding and predicting the kinetics of structure-property-performance changes for polymeric membranes.

Current industrial gas separations, such as CO2 removal from natural gas, rely primarily on energy-intensive and environmentally unfriendly processes. Polymer membranes offer a promising alternative due to their potentially lower energy costs and ease of operation, but they are infrequently deployed because of performance limitations of currently available polymers. In this work, the effect of backbone functionalization and polymer packing structure on transport performance was investigated for a high-performance polymer of intrinsic microporosity, PIM-1. Through post-synthetic modification reactions, the PIM-1 backbone was altered in various ways. First, carboxylic acids (PIM-COOH) and amines (PIM-NH2) were introduced to promote hydrogen bonding and improve the affinity between the polymer and CO2. Second, bulky protecting groups (PIM-PROT), which could subsequently be removed to manipulate packing structure, were also considered. A facile and time-efficient PIM-1 hydrolysis method has been developed, yielding solution-processable PIM-COOH with greater than 90% conversion. Transport measurements reveal that when converted to PIM-COOH, permeability decreases and selectivity increases for CO2-related gas pairs, while, when converted to PIM-NH2, permeability and selectivity for CO2-related gas pairs both decrease. These trends are mechanistically evaluated through a suite of materials characterization tests including surface area measurements and positron annihilation lifetime spectroscopy (PALS). Additionally, a deconvolution of sorption and diffusion up to high pressures (i.e., > 30 bar) is presented to assess how changes in backbone chemistry and packing structure influence transport behavior. Moreover, plasticization behavior is presented. The PIM-COOH sample shows reduced plasticization resistance as compared to PIM-NH2, and these results are likewise assessed from the framework of the solution-diffusion model.

We present an overview of mechanisms controlling molecular and ion transport in polymer membranes. Molecular permeability is controlled by solubility and diffusivity. Elastic forces provide the major resistance to molecular diffusion. The polymer shear modulus G, the size of the molecule R, and available free volume define the energy barrier controlling molecular diffusion through a polymer membrane. This leads to the exponential dependence of diffusion on molecular size [1] and provides the basis for the size-sieving selectivity approach used in most of the glassy membranes for gas separation. We show that Anderson-Stuart model [1] provides reasonable description of molecular diffusion in many polymers. However, when molecular size are comparable (e.g. CO₂, N₂, O₂), selectivity in solubility becomes the most important parameter controlling selectivity of molecular permeability through the polymer membrane. It also provides the main selectivity for transport through rubbery membranes where elastic forces have rather low energy barrier due to much lower G. We show examples of some rubbery polymers where by tuning molecular solubility one can significantly improve selectivity for permeability of CO₂ vs N₂ [2,3].
In the case of ion transport, coulombic interactions provide additional resistance for ion diffusion. The energy barrier in that case varies inversely with the ion size. As the result the energy barrier for ion transport has a non-monotonous dependence on the ion size. Indeed analysis of the energy barrier controlling ion diffusion in polymerized ionic liquids has a minimum, and increases sharply for small ions, such as Li, due to strong coulombic interactions, and then increases with ion size for large ions, such as TFSI, due to elastic forces [4,5]. We demonstrate that Anderson-Stuart model [1] can describe well the energy barrier controlling ion diffusion in polymers. We suggest that this additional coulombic term is the major reason for improved water desalination performance by polymer membranes containing attached ions. We also demonstrate that the ion conductivity in polymers is strongly affected by ion-ion correlations (the so-called Haven ratio) that might reduce the ionic conductivity by more than 10 times [4,5]. At the end we propose polymer structures that might provide significant ionic conductivity at ambient temperature even in the dry state.

1. O.L. Anderson, D.A. Stuart, J. American Ceramic Society 37, 573 (1954).
2. T. Hong, et al., Adv. Sust. Systems 2, 1700113 (2018).
3. H. Feng, et al., Polymer Chemistry 8, 3341 (2017).
4. E. W. Stacy, et al., Macromolecules 51, 8637 (2018).
5. A. Kisliuk, et al., Electrochimica Acta 299, 191 (2019).

Processing sub-quality natural gas remains an economic and environmental challenge, especially as natural gas demand increases. Toxic and/or corrosive sour gas contaminants, such as hydrogen sulfide (H₂S) and carbon dioxide (CO₂), must be removed from methane (CH₄) to meet pipeline specifications. Gas separation membrane technology offers a low cost alternative to traditionally energy intensive adsorption-based separations. This work describes a series of hydrophilic network polymer membranes synthesized for sour gas applications. Oligomeric poly(ethylene glycol) (PEG) of varying molecular weight was reacted with stoichiometric amounts of a triisocyanate crosslinker to create highly crosslinked amorphous gels cast directly on top of membrane supports. Polymer network structure was confirmed by FTIR, DSC, and DMA. Thermal characterization showed dramatic increases in polymer T_g as PEG chain length between crosslinks decreased from 2000 Da to 200 Da, transitioning from rubbery to glassy around 600 Da. Predictably, gas permeabilities decreased over the same range of PEG molecular weights due to the higher crosslink density and corresponding network rigidity. However, pure gas CO₂/CH₄ followed a bell-shaped trend with maximum selectivity achieved by the 600 Da PEG membrane, subverting expected tradeoff relationships. High pressure mixed gas permeation tests performed at 800 psi with simulated sour gas feeds containing up to 20% H₂S by volume demonstrated superior membrane performance and stability of the PEG-based materials compared to commercial controls. The highest performing PEG membrane exhibited 3.0 times higher H₂S permeability and 1.9 times higher H₂S/CH₄ selectivity than cellulose acetate as well as 1.8 times higher CO₂/CH₄ selectivity and 1.2 times higher H₂S/CH₄ selectivity compared to commercially available Pebax. Finally, we explore the amenability of this technology to thin film processing to improve membrane productivity.

We have investigated nearly identical linear and network PILs containing precise linker lengths between ammonium cations. Two different linker chemistries, either an 11 atom hydrocarbon (HC) or 11 atom ethylene oxide (EO) chain, to vary the polarity. Wide-angle X-ray scattering measurements revealed that the ionic aggregation peaks were less intense in the EO systems, consistent with a more polar chemistry providing better ion solvation. Network PILs of both HC and EO linkers had a more pronounced ionic aggregation peak intensity than their linear counterparts, indicating that polymer architecture impacts ion clustering. In addition to a more pronounced aggregation peak, the EO network showed a two order of magnitude increase in conductivity relative to the linear analogue at T_g + 10 °C. Conversely, linear and network PILs with HC linkers show identical Tg normalized conductivities. In the HC networks, we systematically increased the length from 4 to 12 carbons and observed pronounced odd-even effects on Tg and conductivity which shifted as much as 50 K and 2 orders of magnitude, respectively, by adding one carbon between ionic sites. This systematic study provides a new insight on how polymer architecture, polarity, and precision can influence aggregation and transport of ions in PILs.

Precise network polymerized ionic liquid membranes (PILMs) with tethered imidazolium cations, variable anion, and controlled crosslink density were developed to understand how molecular structure impacts solubility and diffusion in the context of toluene/heptane separations. Switching the anion from tetrafluoroborate (BF₄) to bis(trifluoromethane)sulfonimide (TFSI) led to a 25 K drop in the glass transition temperature, concomitant increase in penetrant diffusion coefficients, and increased solubility of toluene relative to heptane. Reducing crosslink density led to an increase in toluene swelling, while heptane uptake remained relatively low and constant. Differences in toluene and heptane diffusion coefficients exhibited a maximum selectivity at intermediate crosslink density. It is hypothesized that a fully crosslinked network has a mesh size small enough to impede transport while lower crosslink densities allow toluene to swell the system to a greater extent in contrast to heptane. The interplay of diffusion and solubility effects lead to a non-monotonic trend in selectivity, which will inform the design of membranes as effective organic liquid separations media.

Development of membranes for highly specific separations is challenging and will depend on specific surface interactions. Here we have investigated the feasibility of using ionic liquids and polyionic liquids containing imidazolium groups trapped within the pores of a membrane (supported ionic liquid membrane) to separate compounds with differing p-electron cloud densities due to their interactions with pi-electron clouds. In this study, these supported ionic liquid membranes are used for the separation of stereoisomers, amino acids as well as similar heterocylclic compounds. A 0.45 micron pore size polypropylene microfiltration membrane is used to trap 1-hexyl-3-vinylimidazolium bromide within the membrane pores. The separation of furan and thiophene in hexane (organic solvent) and cytosine, guanine, and thymine in water (aqueous solvent) has been investigated. The specificity for separation was found to be related to the affinity of the ionic liquid towards the p electron cloud density and extent of conjugation in the solute. Polyionic liquids that are formed from 2-vinyl pyridine or 4-vinyl pyridine are used to separate stereoisomers. The ability of the polyionic liquids to separate stereoisomers at ambient temperature indicates their potential for energy-efficient separations of similarly structured compounds with varying pi-electron clouds. The incorporation of ionic liquids and polyionic liquids into the membrane is verified using infrared spectroscopy and/or imaging with scanning-electron microscopy. The results obtained here indicate that membranes for highly specific separations could be developed based on p electron cloud interactions.

The state-of-the-art membranes for desalination are comprised of thin film composites where the permselective layer is a thin, interfacially polymerized polyamide. Although effective, the rapid polymerization rate and reaction conditions produce films with rough surface structures and chemical heterogeneity, which precludes some exquisite characterization techniques for probing thin and ultrathin films. In 2011, we proposed a paradigm shift in how these types of membranes are fabricated, where the selective layer is created layer-by-layer through a reactive deposition process. Even so, there are still many challenges yet to overcome, from membrane support design to membrane characterization. In this talk, I will describe our efforts to meet these challenges through judicious experimental design and materials selection. Specifically, I will describe efforts to measure the internal structure of these membranes using resonant and non-resonant x-ray scattering, as well as measure the dynamics of water and salt in these membranes using quasi-elastic neutron scattering and electrochemical impedance spectroscopy, respectively. Then, I will discuss how these measurements have challenged our thinking in how these materials selectively pass water while rejecting salt.

Membrane-based separation processes have been considered as one of the most promising technologies for post-combustion carbon capture due to lower energy consumption, smaller environmental footprint, and the potential to be installed in an existing power plant as a true bolt-on technology. However, polymeric membranes, currently considered the most promising candidate for industrial application, are limited by a trade-off upper bound between the productivity and separation efficiency. Metal–organic frameworks (MOFs) are promising candidates to overcome the limitations of polymer membranes, by fabricating mixed matrix membranes (MMMs) due to their high surface area and porosity, diverse functionalities and tunable pore structures.
In this presentation, several MOF-based mixed matrix membranes were developed by incorporating different types of MOF crystals (e.g., surface functionalized UiO-66 and nano-sized zeolitic imidazolate framework-8) into a variety of polymers (e.g., polymers of intrinsic microporosity, poly(ether-block-amide) copolymers, polymer blends composed of PIM-1 and MEEP80 polyphosphazene) for highly energy-efficient carbon capture. The mixed gas permeation results showed that these MOF-based mixed matrix membranes have displayed superior separation performance (the CO₂ permeability of up to 6000 Barrers with a CO₂/N₂ selectivity of higher than 22), surpassing the 2008 Robeson upper bound. Testing these membranes using real flue gas streams at the National Carbon Capture Center (Wilsonville, Alabama) will also be presented. We demonstrated that the excellent CO₂/N₂ separation performance makes MOF-based mixed matrix membrane a very promising platform for practical CO₂ separations.

Natural gas use as a primary energy source has expanded rapidly over the past several decades. A 69% increase in worldwide consumption for natural gas over the 2012 level is anticipated by 2040. However, raw natural gas from some wells can contain significant amounts of other gas components, including H₂S, CO₂, N₂, water, and other hydrocarbons (C₂₊). Among these contaminates, the acid gases (H₂S & CO₂) must be treated to avoid corrosion of transportation pipeline and to meet the standard pipeline specifications of sales gas. Polymeric membrane-based technologies have gained great industrial attention for natural gas upgrading and treatment due to their relatively energy-efficient and environment-friendly footprint. Current commercial rubbery polymer membranes for acid gas removal from natural gas, such as poly(ether-b-amide) copolymer (PEBAX), show a decline separation performance under industrially relevant feed streams and testing conditions. In this talk, we describe a modification of the polymer backbone by blending and crosslinking to develop novel PEBAX membrane materials for simultaneous CO₂ and H₂S removal from natural gas. Modified PEBAX membrane materials comprised of crosslinked polyethylene glycol as a CO₂-pohilic additive were produced via either UV crosslinking of diacrylated-terminated polyethylene glycol or chemical crosslinking of a diisocyanated-terminated polyethylene glycol by controlling crosslinking moieties and crosslinked networks in the membrane matrix. High-pressure pure and mixed sour gas transport properties of these modified PEBAX membranes were investigated as a function of loading, feed pressure, temperature, and gas composition at moderate to high H₂S% concentration. The modified PEBAX membranes demonstrate improvements in gas separation performance (16% and 12% increase in H₂S/C₁ and CO₂/C₁ selectivities) and enhanced membrane stability (64% and 100% increase in mechanical strength and swelling resistance) compared to neat PEBAX membrane under industrially relevant feed streams and testing conditions (e.g. feed pressure of 800 psi and 20% H₂S). Based upon the enhanced membrane performance, this modified PEBAX membrane material can be a potential candidate in combination with amine absorption system for acid gas separations from natural gas.

Enzymatic pathways that perform multi-step biochemical reactions in biological cells constitute a crucial part of life. Biomimetic reconstruction of these metabolic pathways by incorporating multiple enzymes and relevant cofactors in a confined environment holds tremendous promise for sustainable green synthesis of fine chemicals e.g., pharmaceuticals, biofuels, and consumer products, as well as developing efficient biomolecular devices. Controlled localization of enzyme immobilization onto support platforms, however, remains a major challenge. In metabolic pathways, enzymes are spatially coupled to prevent unfavorable side-reactions, eradicate inhibitory products and channel metabolites sequentially from one enzyme to another. Biomolecular assemblies mimicking natural cascades can be reconstructed using monolithic mesoporous anodized aluminum oxide (AAO) membranes that allow sequential mass transport of catalytic products between spatially immobilized enzymes under convective flow. Here, we developed a peptide-guided approach for spatially controlled immobilization of a bi-enzyme model, L-Lactate dehydrogenase and Formate Dehydrogenase, with high precision for cascadic biosynthesis. Each enzyme is fused with a solid-binding peptide to direct self-directed immobilization across the membrane that facilitates sequential production of L-lactate with the concomitant regeneration of nicotinamide adenine dinucleotide (NADH). Catalytic turn-over rates of immobilized enzymes are found to be consistent with homogeneous solution rates. The 85% overall sequential reaction efficiency is achieved at a flow rate that kinetically matches the residence time of the slowest enzyme. Furthermore, 84% of initial catalytic activity is preserved after 10 days of continuous operation. Peptide-guided immobilization described herein is an effective strategy to build robust bioreactors and diagnostic devices involving cascadic systems. The study was supported by NSF-DMREF program through the grant DMR-1629071 and NSF-CBET Program through the grant 1460922.

Cross-linked, ionic lyotropic (i.e., surfactant) liquid crystal (LLC) assemblies have periodic, uniform-size, charged pores in the 0.7–1.0 nm range that allow them to be used as new type of polymer membrane material for molecular size separations in water. Ordered, 3D-nanoporous LLC networks with a type I bicontinuous cubic (Q_I) phase can be prepared from an imidazolium bromide-based gemini LLC monomer blended with glycerol. These Q_I assemblies can be readily processed and polymerized into supported thin-film composite (TFC) membranes that have 0.96-nm-wide annular pores with fixed cationic imidazolium sites in the walls and mobile bromide counteranions in the pore interior. After exchange of water for glycerol in the pores, the resulting TFC Q_I membranes can exclude dissolved molecular solutes and small salt ions from water via a combination of size sieving and charge repulsion effects in the pores. In addition to water purification, these charged, nanoporous membranes may be useful for selective ion conduction applications, such as separator membranes for aqueous flow batteries. However, one of the liabilities of this ionic membrane material is that the mobile counteranions can be easily exchanged with other anions from external salt solutions, thereby resulting in unwanted changes in effective pore size and water/salt transport properties during application. Herein, we show that the cationic pores of this cross-linked Q_I LLC material can be modified by exchange of the original Br^– ions in the pores with polymerizable organosulfonate anions, followed by in-situ polymerization of the reactive counteranions inside the Q_I pores. The resulting ordered ‘snake-in-cage' nanocomposite was found to be highly resistant to ion-exchange: the formed anionic polymer was found to remain inside the nanopores even when the bulk material is exposed to concentrated (i.e., 1 M) aq. salt solutions for long periods of time. After polyanion formation inside the pores, the LLC material loses its overall ion-exchange capacity, presumably due to ionic cross-linking between the cationic pore walls and the anionic groups on the confined polymer chains. However, the pore environment remains ionic, as confirmed by water and salt sorption measurements. Aqueous ion transport tests on TFC membranes made from the modified Q_I material with polyanion chains in the pores show that salts such as MgCl₂ and K₂SO₄ permeate through at significantly different rates than unmodified TFC Q_I membranes with mobile counteranions in the pores. This relatively simple modification procedure provides a new way to modify and stabilize the transport properties of nanoporous ionic LLC networks for use in selective ion transport applications. The relative merits and avenues for control of this approach will be discussed.

Water purification membranes usually suffer from surface fouling, which dramatically decreases water permeance. The fouling is often mitigated by hydrophilizing the membrane surface, such as coating by hydrophilic zwitterions (ZWs) and poly(ethylene glycols) (PEGs). We demonstrate a facile method to graft the ZWs and PEGs onto the membrane surface by co-depositing with dopamine. Dopamine can be easily polymerized to polydopamine (PDA), which can covalently bind ZWs or PEGs containing acrylate or amine functional groups through Michael Addition. Specifically, acrylate-terminated compounds include sulfobetaine methacrylate (SBMA) and PEG-diacrylate (PEGDA), and amine-terminated SB-amine and PEG-diamine were are co-deposited with dopamine onto the silicon wafers and ultrafiltration (UF) membranes. The effect of the composition of coating solutions and coating time on the coating layer thickness, compositions, and hydrophilicity are investigated. The coating can deposit a layer of 10 – 50 nm containing 30 – 72% ZW or PEG. The effect of coating and surface chemistry on the membrane properties (including molecular weight cut-off and water permeance) will be systematically investigated to derive the structure/property relationship.

Membrane fouling by organic compounds is still one of the main challenges faced by membrane separation processes. Advanced fouling-resistant membranes can be obtained by increasing the hydrophilicity of the membrane surface. Hydrogels are materials that can absorb large quantities of water and swell, which makes them inherently fouling resistant. Zwitterions, defined as neutrally charged molecules with equal numbers of cationic and anionic groups, and very high dipole moments, exhibit strong hydration layers and, accordingly, excellent fouling resistance. These properties make hydrogels, especially those incorporating zwitterionic groups, promising membrane materials. However, the applicability of hydrogels as fouling-resistant selective layers of thin film composite membranes has been hindered by the lack of a fabrication process that allowed for the formation of a thin, defect-free hydrogel layer on a porous support. We have recently demonstrated a new method, namely Interfacially Initiated Free Radical Polymerization (IIFRP), to address this challenge. In IIFRP, the monomer and photoinitiator are separated into two immiscible phases. The aqueous phase is impregnated into a porous support. Its surface is then covered with an organic phase containing a photoinitiator and exposed to UV light. The ultrathin hydrogel selective layer, as thin as ~80 nm, is then formed at the interface of the two phases, at the membrane surface. The goal of the present study was to explore the incorporation of zwitterionic (ZI) groups into hydrogel selective layers obtained by IIFRP. We have shown that the incorporation of ZI moieties can further increase membrane fouling resistance and improve membrane properties such as hydrophilicity and permeability. The partial substitution of poly(ethylene glycol) diacrylate (PEGDA) units in the hydrogel layer with the zwitterionic monomer sulfobetaine methacrylate (SBMA) led to an increase in permeance of almost an order of magnitude (from 3.9±0.4 L/h.m².bar to 34.7±0.8 L/h.m².bar). Moreover, although this substitution for SBMA also decreased the crosslinking density of the hydrogel, the rejection properties of these membranes remained essentially constant (99.2±0.6% and 98.7±0.6% myoglobin rejection, respectively). Furthermore, the zwitterionic-hydrogel membranes exhibited higher fouling resistance to oil emulsions compared to both commercial membranes and the zwitterion-free hydrogel membranes. Consequently, zwitterionic-containing ultrathin hydrogel selective layers obtained by IIFRP are very promising materials for fouling-resistant ultrafiltration membranes.

Membrane has been applied to various separation systems, in particular, for the separation of aqueous or organic solvents. membrane separation is considered promising for reducing CO₂ emission in terms of energy efficiency.For a development of more efficient membrane process, better understanding of separation mechanism of solvent including multicomponent species is of fundamental. Molecular modeling becomes a powerful tool for prediction of membrane performance and design of membrane materials for particular separation systems. Our group has reported a novel simulation scheme of molecular dynamics for the permeation of feed solution through nano porous membranes. Molecular dynamics of multi component species in the feed, however, is still difficult to be simulated because a feed concentration of multicomponent such as ions cannot keep at a constant in our simulation techniques as well as other conventional non-equilibrium molecular dynamics scheme. In this paper, to model multicomponent solutions through nanofiltration or reverse osmosis membranes, we will present a novel molecular dynamics technique that can control the feed concentration including multicomponent species at constant. This simulation technique is completely new and first methodology that could model multicomponent solution systems in membrane separation from atomistic level, as long as our knowledge. We will report that this simulation technique works well and can produce the permeation of multicomponent feed solution. The flux and solute moleculars selectivity were calculated and compared to the theoretical values to examine the validity of our proposed scheme.

Providing sustainable supplies of purified water and energy is a critical global challenge for the future, and polymer membranes will play a key role in addressing these clear and pressing global needs for water and energy. Controlling rates of water and/or ion transport in these membranes is critical for efficient separation processes (e.g., water purification or dialysis) and energy technologies (e.g., flow batteries or reverse electrodialysis). Much remains unknown about the influence of polymer structure on intrinsic water and ion transport properties, and these relationships must be developed to design next-generation polymer membrane materials. Here, we report and discuss measurements and modeling related to the influence of chemical functionality on rates of water and ion transport in hydrated polymers. Our results demonstrate how polymer properties (e.g., backbone rigidity, functional group type, and/or polarizability) can be engineered to enhance selective transport via thermodynamic and kinetic contributions to the transport process.

Metallic thin films were deposited onto commercial ultrafiltration (UF) membranes to produce composite structures which show promise both for separations and for catalysis applications. Magnetron sputtering was used to deposit thin films of tantalum and MgPd alloy on top of polysulfone (PSf) membranes. The thin Ta films were found to have significant effects on flux and separation properties of the membranes. The composite membranes with MgPd films were subsequently dealloyed to produce nanoporous Pd, which performs well as a catalyst for wastewater remediation applications. Both types of composites will be presented here.
The addition of just a thin (10 nm) layer of Ta to the surface of the UF membrane was found to dramatically alter its properties as a membrane. Membrane flux dropped from 180 LMH/bar for the base UF PSf to 10 LMH/bar for the Ta composite system. Dye tagged dextran used as a model compound for the determination of molecular weight cutoff (MWCO). The UF PSf was found to have a MWCO above 70 kDa while the Ta composite membrane showed a MWCO below 5 kDa. Modifying the rejection characteristics of a membrane with only a 10 nm added layer is a valuable technique, especially as tantalum is a corrosion resistant metal. This makes this composite membrane applicable to both solvent based separations and separations in corrosive environments.
For the membranes with the MgPd film, a subsequent dealloying step in water was performed to remove the Mg component of the film and create a nanoporous film of Pd. This generates a high surface area, sponge-like structure of interconnected nanowires known as ligaments with characteristic size of <10 nm. The nanoporous palladium film was used as a catalyst with hydrogen gas for the degradation of pollutant compounds in wastewater. Specifically, PCB’s were dechlorinated while permeated in a water solution under pressurization with 5% hydrogen gas (remainder argon). In permeation testing over 60% of PCB-1 was degraded in solution with a single pass through the composite membrane at 40 LMH. Adding a high surface area nanostructure like a nanoporous metal to the surface of a membrane in this way produces a composite structure that can drive reactions as solutions are permeated through the membrane, giving favorable reaction rates. Furthermore, since this nanostructure is produced spontaneously as the MgPd alloy is dealloyed in water, production is straightforward and reproducible.

Every year more than three million people die from water-related diseases. Having access to clean and good quality drinking water is a continuous challenge in our world. Increasing the world’s population together with the declining the water tables and increasing the salinity of water resources, resulting in a crisis that is already a major concern, while the situation getting worse every year.

Among various water desalination membrane technologies, Membrane Distillation (MD) is an emerging thermally-driven, membrane-based desalination technology highly suitable to treat hypersaline solutions. MD is a thermally driven process involving a nano/microporous, hydrophobic membrane through which only water vapor can diffuse. Compare to other membrane technologies, MD is a compact and low energy separation technology (the temperature requirement for MD is ~70°C). Although MD has been investigated by researchers, still it cannot compete with other technologies such as reverse osmosis (RO), mainly due to lower production rate, energy efficiency, consistency performance, energy efficiency, and fouling resistance to be named.

In the present study, modified PVDF electrospun nanofiber membrane composites with various support structures were studied for DCMD application. Hydrophobicity of the nanofiber membranes was investigated and different filler and parameter setting of the electrospinning process has been optimized in order to optimize the performance of the nanofiber membrane in the water desalination process. Surface modification of the nanofibers has been investigated using atomic force microscopy (AFM), in order to correlate the nanostructure of nanofibers, with the performance of the nanofiber membrane in DCMD. In order to enhance the performance of the system, nanofibers decorated with different nanoparticles were used to increase the hydrophobicity of the membrane. surface treatments were considered as another approach to enhance the performance of the desalination system using electrospun nanofiber membrane.

Nanofiltration technology for water desalination and other fluids purification from salts, germs, bacteria and viruses are based on the so called Nanopumping (NP) effect, when a fluid flow through nanomembranes and nanochannels is actuated using surface acoustic waves (SAW) is presented.
The paper considers processes of water nanofiltration through a carbon nanomembrane using SAWs under different RF powers and frequencies. A prototype device was build using LiNbO3 piezoelectric substrate and carbon nanomembranes on the substrate. The process of nanofiltration consisted of filtration of droplet volume of 3, 5 µl and in using SAW transducers with different frequencies from 34 to 58.2 MHz, with power range 0.1-1.23 W. The process of nanofiltration of water includes the processes of droplet moving, atomization and passage through nanopores.
We analyzed optimization of the basic characteristics of a SAW device, selection the optimum operating parameters of the SAW device and fabrication working prototype of the SAW device. This work is devoted to the development of an active model of the SAW device that demonstrates the work on water filtration using nanomembranes, in which liquid motion is driven with the help of sufficiently powered SAW.
The dependences of the travel time of droplet moving and atomization of water on the power, the frequency vs. time, frequency vs. volume of the droplet are established.
It is shown that with increasing of power and frequency of SAW, the filtration process proceeds rapidly and has a power-law character.
We investigated this problem both experimentally and numerically in 3D using COMSOL Multiphysics software.

Room-temperature ionic liquids (ILs) are a novel class of designer organic solvents with unique properties of great interest in energy storage, supercapacitors and ion-based sensors and electronics. Metal-organic Frameworks (MOFs) are a unique class of designer nanoporous functional-material platforms compound of metal ions and organic linkers.

In our investigation of dynamic properties of IL embedded in porous hosts of MOF, specifically [BMIM][NTf2] in HKUST-1, we observe a drastic change in ion mobility from combined analysis of molecular dynamics simulation and experiment.

We found at low loading of ILs in MOF, ions drift in MOF pores along external electric field, forming a homogeneous flow; whereas at increased IL loadings, collective field-induced interactions of cations and anions lead to transient blockage of ion transport, suppressing ion mobility and tremendously decreasing the conductivity. At extreme loading as IL fills MOF pores, cations and anions travelling in opposite directions bunch-up to form a dense, inhomogeneous, and immobilized IL layer.

Novel molecular-level dynamics insights into IL in nanoconfinement provide guide lines in tuning of quantitative structure-property relationships of IL materials.

Our work is published as:
Bunching and Immobilization of Ionic Liquids in Nanoporous Metal–Organic Framework
Anemar Bruno Kanj, Rupal Verma, Modan Liu, Julian Helfferich, Wolfgang Wenzel, and Lars Heinke
Nano Letters 2019 19 (3), 2114-2120
DOI: 10.1021/acs.nanolett.8b04694

Membrane technology is highly attractive for H₂/CO₂ separation for pre-combustion CO₂ capture, which requires membrane materials with both high H₂ permeability and H₂/CO₂ selectivity at 100 – 300 ^oC. Herein, we present carbon molecular sieve (CMS) membranes with superior H₂/CO₂ separation properties via the pyrolysis of polybenzimidazole (PBI, a leading polymer for H₂/CO₂ separation). We thoroughly investigated the effect of the pyrolysis temperature on physical properties (pore size, d-spacing, density, solubility, diffusivity) and H₂/CO₂ separation properties of the CMS films. PBI exhibits H₂ permeability of 27 Barrers and H₂/CO₂ selectivity of 14 at 150 ^oC, while the CMS films pyrolyzed at 600 ^oC, 850 ^oC, and 900 ^oC exhibit H₂ permeability of 370 Barrers, 190 Barrers, and 54 Barrers at 150 ^oC, respectively, and their corresponding H₂/CO₂ selectivity of 8.9, 16, and 80, respectively. The pyrolysis forms micro-cavities leading to high gas permeability and ultra-microporous channels leading to strong size-sieving ability, which is also confirmed by the Positron Annihilation Lifetime Spectroscopy (PALS). As the pyrolysis temperature increases from 600 ^oC to 850 ^oC and then 900 ^oC, the free volume element size increases from 5.08 Å to 5.46 Å first and then decreases to 4.90 Å. When tested with a mixture containing 50% H₂ and 50% CO₂ at 150^oC, CMS pyrolyzed at 900 ^oC show H₂ permeability of 39 Barrers and H₂/CO₂ selectivity of 53, which surpasses the Robeson’s upper bound for H₂/CO₂ separation at 150 ^oC. The film shows stable mixed-gas separation performance for 40 h. When water vapor of 0.31 mol% is introduced, the H₂ permeability slightly decreases to 37 Barrers while the H₂/CO₂ selectivity remains the same. The mixed-gas H₂ permeability increases to 39 after the water vapor is removed. The stability and robust H₂/CO₂ separation properties demonstrate the potential of PBI-derived CMS for practical H₂ purification and CO₂ capture

In this study, we investigate the separation properties of several type zeolite membranes by NEMD for CO₂/CH₄ separation, and suggest the ultra-selective membrane structure for CO₂ by utilizing the effect of grain boundary on ternary separation systems. In the non-equilibrium molecular dynamics (NEMD) simulation, a single crystal membrane model and two types of polycrystalline membrane models were considered. In the polycrystalline membrane models, two patterns were examined, one in which grain boundary is present inside the zeolite crystal and the other in which the grain boundary is exposed on the surface of the zeolite crystal. In the upper part of the membrane models, the gas molecules were made to appear at regular intervals to keep the partial pressure constant, and the gas molecules which permeated through the membrane were deleted at the lower part of the membrane. Our NEMD results indicates that the presence of grain boundary could increase the selectivity, which means that a control of grain boundary is a key factor to enhance the selectivity.
On the other hands, conventional natural gas is multi-component gas including trace components e.g. hydrocarbon, and there is a concern about the effect of the trace components for membrane performance. In addition to that, grain boundaries in inorganic porous membranes are known to degrade membrane performance, however, the detailed information of effect on selectivity for multicomponent gas systems still difficult to predict prior to the permeation test. The NEMD simulation is an atomistic-scale modeling, thus this can easily apply to the prediction of permeability and selectivity in multicomponent gas systems. The effect of trace components for membrane performance can be also investigated using NEMD. Since the structure of the membrane can be arbitrarily modeled in the NEMD simulation, it is possible to investigate the behavior of the multicomponent gas in the zeolite membrane having grain boundaries by using the NEMD method. In the conference, we will suggest an ultra-selective zeolite membrane based on the interesting phenomenon that the selectivity is enhanced by the structure of grain boundaries.

Membrane-based propylene/propane separation can reduce the operation cost in petroleum refining and petrochemical industries; however, developing advanced membranes with promising performance is still challenging due to the close size (~0.15 Å difference) between these two components. We hereby address such a critical scientific question by a novel strategy: first, attention to detailed conformational differences accessible to propylene and propane; next, identification of a suitable MOF pore-aperture to exploit the accessible conformational differences; thirdly, matching polymer properties with the MOF to achieve promising performance.

Specifically, with both C-C single bonds rotated (double eclipsed conformation), the C₃H₈ molecule exhibits its minimum end-on essentially triangular shape but with a rotation energy barrier. Our strategy is to design/screen a “triangular” pore-aperture to allow only the double eclipsed C₃H₈ conformer to pass through, effectively preventing all other C₃H₈ conformers from diffusion jumps. This combination of factors leads to a very low C₃H₈ diffusivity. On the other hand, the more compact C₃H₆ molecule can pass through the pore-aperture with relative ease. According to our theoretical calculations based on transition state theory, a membrane with such desired pore-aperture can offer a C₃H₆/C₃H₈ diffusion selectivity over a thousand. We further identified a MOF, Zr-fum-fcu-MOF, possessing the desired contracted triangular pore-aperture and fabricated mixed-matrix membranes using this MOF as an efficient filler. The fabricated hybrid membranes display very attractive C₃H₆/C₃H₈ separation performance, far beyond the current trade-off limit of polymer membranes. Back-calculations using composite theory suggests the MOF displays a diffusion selectivity, like the ideally targeted, above 1000. This is the highest value reported for the C3 pair to date, and we refer to this phenomenon as “conformation-controlled molecular sieving effect”. Furthermore, we optimized the membrane performance by matching the polymer properties with the MOF to (i) achieve higher C₃H₆/C₃H₈ separation efficiency, and (ii) overcome the plasticization effect. The developed membranes show record performance on C₃H₆/C₃H₈ separation at high pressures (~ 900 kPa), surpassing all mixed matrix membranes reported by far. Our work establishes a novel bottom-to-up strategy to develop membranes for gas separation.

Pd membranes are widely used for hydrogen separation and purification attributed to their excellent combination of H selectivity and permeability. During (de)hydrogenation process, a large number of vacancies forms in the α Pd-H solid-solution phase and β-Pd hydride phase, so-called superabundant vacancies (SAV).¹ The H atoms will be trapped near the vacant sites, which leads to a complexed H diffusion behavior.² Recently, many researchers found the (de)hydrogenation process can also promote the multiplication of dislocations and nanotwins.³ However, the transport properties of H in the defected Pd membranes have yet to be well understood.
In present work, we use Pd vacancy as a typical example to study the correlation effect of a defected zone on the H diffusion in Pd membranes. The results show a strong biased interstitial diffusion around the Pd vacancy. The H is prone to sink into the first nearest neighbor shell of Pd vacancy. The second nearest neighbor shell, which has a very low jump rate, prevents the reverse diffusion of the H atoms. Using Koiwa’s matrix method,⁴ we have derived an analytical formula for the H diffusion around the vacancy. The correlation effect is then estimated for H diffusion as a function of Pd vacancy concentration. Our findings could possibly clarify the uncertainty on the H diffusion coefficient in pure Pd and also shield lights on the interstitial diffusion in other defected systems or alloyed cases.
1 Y. Fukai and N. Akuma, Phys. Rev. Lett., 1994, 73, 1640–1643.
2 O. Y. Vekilova, D. I. Bazhanov, S. I. Simak and I. A. Abrikosov, Phys. Rev. B, 2009, 80, 1–5.
3 M.-S. Colla, B. Amin-Ahmadi, H. Idrissi, L. Malet, S. Godet, J.-P. Raskin, D. Schryvers and T. Pardoen, Nat. Commun., 2015, 6, 5922.
4 S. Ishioka and M. Koiwa, Philos. Mag. A, 1985, 52, 267–277.

Electrochemical deposition has emerged as a novel approach to fabricate MOF films. This approach requires relatively minor or none pre-treatment of the substrate, shorter synthesis time, and milder synthesis condition. It also allows for continuous production which acts as a major advantage compared with other methods for industrial scale-up. As a promising approach, research on electrochemical deposition of MOF is still at its infant stage with most of the efforts being focused on thin film production, only a few works have been published for membrane fabrication. The deposition procedure and set-up are mostly delicately controlled such as careful selection of electrolyte and reference electrode, using double electrolyte cell to eliminate the disturbance of the reactions occurred on the counter electrode, and prolonged post-synthesis treatment, which makes this approach challenging to be used for scale-up production. In addition, little publication has used this approach to achieve satisfactory performance in gas separation with both high permeance and selectivity.
Here, we developed an aqueously cathodic deposition (ACD) approach to fabricate ZIF-8 membrane without addition of any supporting electrolyte or modulator. The fabrication process used 100% water as solvent and a defect free membrane was obtained in only 60 min without any pre- or post-synthesis treatment. The membrane exhibited superior performance in C₃H₆/C₃H₈ separation with 180 GPU C₃H₆ permeance and 142 selectivity, making it sit at the upper bound of permeance vs selectivity graph, outperforming majority of the published data up to 2019. Notably, this approach uses water as the sole solvent, adopts an extremely low current density (0.13mA/cm²), and employs an ultra-facile apparatus set-up, enabling an attractive way for environmentally friendly, energy efficient and easily scalable MOF membrane fabrications. This approach also opens a door for aqueously electrochemical deposition of MOF membrane in the future research.

Membrane distillation (MD) displays superiorities to alleviate the ever-increasing freshwater crisis through seawater desalination and/or wastewater recycling. However, MD faces critical challenges of fabricating high-performance membranes. Our study introduced a novel hierarchical fibrous composite (HFC) hydrophobic membrane with great achievements in elevating the MD performance. This HFC membrane comprises of a thin active dense layer with nanofibers for the maximum mass transfer and a thick support layer with microfibers for the minimum heat transfer. By tailoring the structures of both active and support layers to dissolve the trade-off between mass transfer and heat transfer during the MD process, the optimized HFC membrane could obtain the reported highest water flux of as high as 79.21±4.17 L●m-2 ●h-1 and salt rejection higher than 99.9% using 3.5 wt% NaCl as a feed under the temperature difference of 40°C in the direct contact membrane distillation (DCMD).

Mixed ionic and electronic conducting (MIEC) membranes have been applied to increase the efficiency of oxygen separation, and water and carbon dioxide thermochemical reduction [1, 2]. Both surface reactions and bulk diffusion can impact the oxygen flux depending on the operating conditions. Efforts have been focused on developing new membrane materials, i.e., doped perovskites and dual-phase materials, and catalysts to accelerate the oxygen permeation fluxes.

Herein, we present a novel Janus membrane [3] concept for MIEC oxygen permeable membranes, which have different properties on the two surfaces to favor the respective surface reactions based on thermodynamic considerations. The high oxygen chemical potential side consists of a material with high oxygen vacancy formation energy which favors oxygen incorporation or water reduction, while the material on the low oxygen chemical potential side favors oxygen evolution and reaction with fuel. As a result, this Janus membrane can achieve higher performance compared to membranes of uniform chemical compounds when surface reactions are the rate-limiting step. To demonstrate the concept, this study investigates the co-production of hydrogen (H₂) and syngas (a mixture of H₂ and CO) from H₂O-splitting and methane (CH₄) partial oxidation, respectively, using La_0.8Sr_0.2Cr_0.95Co_0.05O_3-δ (LSCrCo) at the H₂O-splitting side and La_0.8Sr_0.2CoO_3-δ (LSCo) at the CH₄ partial oxidation side.

One major challenge related to the feasibility of the concept is the fabrication of two intact layers with high mechanical and chemical stability. We have explored several ways, such as co-sintering and screen-printing. In the co-sintering approach, the two different materials in the Janus membrane may lead to different shrinkage during sintering due to the factors such as particle sizes and applied pressure. We optimized the parameters such as calcination temperature of the oxide powders, uniaxial applied pressure and heat treatment to avoid the shrinkage mismatch when sintering the Janus membrane. In the second approach, LSCo ink was screen printed on LSCrCo membrane. The viscosity of the ceramic paste was adjusted by adding terpineol based ink vehicle to the ceramic powder. The ink printed layer was heat treated at 1350^oC for 3 hours to ensure adhesion.

Experiments showed that the single-layer LSCrCo membrane has high H₂ production rate equal to 0.45 μmol/cm² s when operating at 1000^oC with 50% steam concentration diluted by nitrogen at the feed side and 20% CH₄ concentration diluted by argon at the sweep side. The performance of this material remained stable for more than 100 hours. With the second layer of LSCo added on the CH₄ side_, the Janus membrane is expected to have enhanced performance due to the faster CH₄ oxidation kinetic on the side.


*Xiao-Yu Wu and Georgios Dimitrakopoulos contributed equally to this work

References:
[1] Wu, X. Y., & Ghoniem, A. F. (2019). Mixed ionic-electronic conducting (MIEC) membranes for thermochemical reduction of CO2: A review. Progress in Energy and Combustion Science, 74, 1-30.
[2] Zhang, C., Sunarso, J., & Liu, S. (2017). Designing CO 2-resistant oxygen-selective mixed ionic-electronic conducting membranes: guidelines, recent advances, and forward directions. Chemical Society Reviews, 46(10), 2941-3005.
[3] Yang, H.-C., Xie, Y., Hou, J., Cheetham, A. K., Chen, V., & Darling, S. B. (2018). Janus Membranes: Creating Asymmetry for Energy Efficiency. Advanced Materials, 30(43), 1801495.

Dual-Phase ceramic membranes are a promising candidate for mixed ionic-electronic ceramic conductors. These composites have inherited good traits of both perovskite and fluorite phases in order to separate oxygen from air under harsh working conditions. While they are capable of working around 1000^oC and under both oxidizing and reducing atmospheres (p(O₂)=0.21 to 10^-22 atm), the long term compatibility between these two phases are still challenging. The current research investigates the chemical and structural stabilities of dual-phase membranes of perovskite and fluorite phases with changes in composition, temperature (T), and oxygen partial pressure p(O₂). Lanthanum chromite-based perovskite has been doped with Sr and Fe as A- and B-site dopants, respectively. Different compositions of the perovskite phase with change in A-site and B-site dopants and A-site deficiency have been considered. There different stabilized zirconia as the fluorite phase have been examined with the perovskite phase: ScYSZ, ScCeSZ, and YSZ. The interaction between these two phases under fabrication and processing conditions have been studied through experimental and computational thermodynamics. The results reveal the correlation between Cr:Fe ratio and the formation of secondary phases. XRD results with thermodynamics calculations show that valance stabilities of Fe and Cr ion species regarding applied T and p(O₂) and defect chemistry of the perovskite phase are responsible to maintain structural integrity of composites. The formation mechanism of secondary phases and their effects have been discussed in the purpose of minimizing and controlling their formation. It is offered how to tune initial compositions of the perovskite phase to control the formation of most detrimental phases of SrZrO₃ and La₂Zr₂O₇. Owing to use of computational thermodynamics, it is discussed how applied T and p(O₂) during either fabrication or processing leave effects on chemical/structural stabilities of dual-phase membranes. In fact, computational thermodynamics provides practical guidelines about controlling composition, T, and p(O₂) to maintain structures and control desired stoichiometries. Structural stability of fluorite phases has been also examined via X-ray diffraction methods.

In the era of smart wearable electronics and compact electric transportation system, there is an urge for the development of flexible, lightweight, solid-state and efficient energy storage devices. For realizing high performance energy devices, novel electrolyte materials with high energy density at enhanced power and longer life cycle are demanding. The recent development in the field of two-dimensional (2D) materials, including graphene, hexagonal boron nitride (hBN) and transition metal dichalcogenides, have exhibited promising applications in various areas, such as electrochemistry and clean energy storage devices. In particular, 2D hBN, also known as “white graphene” is an isomorph of graphene with similar layered structure in a hexagonal lattice, which is uniquely featured by its outstanding physicochemical properties along with mechanical robustness and thermal stability. Due to its remarkable electrochemical properties, it is considered as a promising candidate that can be integrated with other 2D materials for the next generation electrochemical energy storage and conversion applications including fuel cells, batteries and supercapacitors. Moreover, hBN possess electrically insulating behavior at wide range of humidity and temperatures, which makes it more versatile to be manipulated and used as an electrolyte membrane in electrochemical energy systems.
Herein, we have developed functionalized hexagonal boron nitride (FhBN) polymer electrolyte membranes (PEMs) and presented as a potential proton exchange membrane for electrochemical energy storage and conversion devices. The dispersions and functionalization of FhBN nanosheets are produced by direct in-situ liquid phase exfoliation and functionalization. FhBN dispersions possess excellent dispersibility and stability over several months of few-layered FhBN nanosheets in the solution, which is indicated by highly positive zeta potential values of +42.5 ± 3.2 mV of the dispersion. Physicochemical properties of FhBN nanoflakes are investigated by various spectroscopic and microscopic characterisation tests, confirming strong covalent interactions/attachment in the FhBN nanoflakes between the hBN lattice and sulfonic acid groups. Further to fabricate proton conductive FhBN PEMs, high concentration of FhBN nanoflakes are blended with Nafion solution to form a stable dispersion, which are thermally and chemically treated to form the membranes. The addition of FhBN nanoflakes with sulfonic groups provides additional proton conduction sites and enhances the ion exchange capacity of the nanocomposite FhBN-Nafion PEMs with lower swelling ratio compared to that of bare Nafion. The in- and through-plane proton conductivity of the FhBN-Nafion PEMs is significantly increased under various conditions relative to that of re-casted Nafion membrane. The maximum value of in-plane conductivity of FhBN75%-Nafion PEM is observed at 80°C - 80% relative humidity (RH) condition, which is 0.41 S/cm, i.e, 7 times higher than that of the recast Nafion, under the same conditions. Moreover, at 80°C - 80% RH, the through-plane conductivity of FhBN75%-Nafion PEM is 0.1 S/cm i.e., 14 times higher than that of the recast Nafion under the same conditions. The superionic transport characteristic of highly concentrated 2D FhBN PEMs provide promising solutions for various applications in electrochemistry and clean energy devices, including supercapacitors, polymer electrolyte membrane for fuel cells and water electrolysis.

Solid electrolytes which could transport cations are widely used in energy-related and environmental applications. Herein, functionalized graphene oxide-cellulose nanofiber solid proton electrolytes (NPGOM-CNF) were successfully prepared. Based on 1D CNF and 2D dopamine-functionalized GO (NPGO), long-range 1D and 2D ionic nanochannels are constructed in the membranes with perfluorinated sulfonic acid resin (PFSA). The proton conductivity of NPGOM-10-CNF is as high as 0.4 S cm^-1 at 80 ^oC-95 %RH, two times higher than that of commercialized Nafion117. The single-cell performance of NPGOM-10-CNF-based MEA is 31% higher than that of Nafion117-based MEA at 60 ^oC-100 %RH on account of higher proton conductivities and better H₂ impedance ability. Besides, NPGOM-CNF membranes also possess outstanding stability in water and high methanol barrier performance, demonstrating great practical application potential in both proton-exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC)areas.

Pharmaceuticals and personal care products (PPCPs) have recently been recognized as emerging contaminants that pose potential hazards to environment and human health. Conventional nanofiltration membranes relies heavily on the size exclusion and charge repulsion for the separation of contaminant from water and herein are less effective in rejecting neutral micropollutants. In this research, graphene oxide (GO) nanosheets were stacked into 50 nm thin film as a tight nanofiltration membrane to remove pharmaceuticals and PPCPs in water. The layer-stacked GO membranes has sub-nanometer-sized channels that enhance the interactions between GO and the targeting contaminants which lead to hindered diffusion of neutral micropollutants. The diffusion and partitioning coefficient of three representative PPCPs were for the first time characterized based on their adsorption kinetics into the GO thin films using quartz crystal microbalance with dissipation (QCM-D). The results suggest that the diffusion coefficient of caffeine, acetaminophen and carbamazepine in the confined GO nanochannels are more than four magnitudes slower than that in the bulk water. By comparing the solute flux measured experimentally using a nanofiltration system and the theoretical values calculated from the diffusion and partitioning coefficient, we can confirm the transport of neutral micropollutants in the GO membranes are dominated by the diffusion process.

Water is our planet’s most precious resources and life’s most basic indispensable component. Reverse osmosis (RO) filtration is highly adopted, growing technologies to produce clean water by removing undesired (charged or uncharged) solute species. However, polymer and ceramic membranes suffer from low permeability, structural breakdown and fouling. Graphene, a form of carbon, provides the foundation for the production of highly permeable membranes as an emerging technology for RO desalination. Adding oxygen to few-layer graphene nanosheets, i.e. graphene oxide (GO), opens allows efficient adsorption of charged ionic species (selectivity) and augmented flow of water molecules (ultrafast permeability). This works reports on the development of novel graphene oxide thin film nanocomposite (G-TFNC) membranes embedded with a thinner active polymer layer via interfacial polymerization to tackle the trade-offs among water flux transport and salt ionic species rejection, robustness and anti-fouling characteristics. This study overcomes the gap between drinkable freshwater demand and supply through nanotechnology-enabled high performance graphene composite membranes.

The demand of water is increasing along with population growth, where fresh water sources are decreasing and improved methods for water reclamation are needed. This is fundamental in order to create self-sustaining societies. Graphene oxide (GO) membranes have been widely studied for water desalination, pigment filtration and solvent separation, however there are few scalable methods to produce large membranes for water filtration. In addition, chemical stability and antifouling properties are needed in order to be promising candidates for real applications. In this work, we present a spray-coated GO membrane for water filtration. Its desalination performance was measured for a mixture of GO/few-layered graphene and only GO, where salt rejection can reach between 80% and 90% and a permeate flux of 0.1 - 0.4 m³m^-2day^-1. The membranes were kept in a solution of sodium hypochlorite (200 pm), a typical agent for industrial cleaning of filtration membranes. Here, the membranes with few-layered graphene exhibited an increased chemical resistance. Furthermore, protein fouling against negative and positive charged proteins bovine serum albumin and lysozyme, respectively, was carried out by monitoring variations in permeate flux and microscopy. The GO membranes demonstrated excellent anti-fouling against both membranes due to electrostatic interactions, hydrophilicity and surface smoothness. The present membranes have excellent scalable fabrication method, chemical resistance and anti-organic fouling necessary for real-world applications in water reclamation, desalination, food industry, etc.

Membrane separation technology plays an important role in various fields including water treatment, chemicals and gas separation in many industrial processes, and food processing. There has been a renewed focus on 2D material for membrane application since their atomic thickness and confined interlayer spacing could theoretically lead to enhanced separation performance.Indeed, multilayer assembly of single nanosheets – forming nanolaminate membranes – creates 2D capillaries that can efficiently sieve chemical species depending on their size. Selectivity- and size controlled diffusion of these nanochannels can be modified to tune the transport mechanism within the structure. For instance, chemical modifications of the surface of 2D nanosheets via functionalization have opened new avenues for tuning the membrane properties in both fields of molecular³ and gas sieving.
Among the different building blocks of the nanolaminate membranes made of two-dimensional materials (2D), graphene oxide (GO) has been studied as a candidate for molecular sieving via size-limited diffusion in the 2D capillaries¹. Unfortunately the high hydrophilicity of GO nanosheets make GO membranes unstable in water, while the poor control of the capillary width between the nanosheets limits the water permeance of membranes. Exfoliated nanosheets of transition metal dichalcogenides (TMDs) constitute attractive platforms for the realization of nanolaminate membranes. Recent works carried out on nanolaminate membranes made of molybdenum disulfide (MoS₂) have demonstrated improved stability. Here, we report a novel type of nanolaminate membranes with well-controlled surface chemistry of the nanosheets. We will notably present our recent investigations on the performance of lamellar membranes based on chemically functionalized MoS₂ nanosheets toward water desalination and micropolutant removal. Our results open novel directions for fine tuning the sieving behavior of membranes based on 2D materials.

[1] W. Kim, S. Nair, Chem. Eng. Sci., 2013, 104, pp 908-924
[2] D. Voiry, M. Chhowalla, Nature Chemistry, 2015, 7, pp 45–49
[3] M. Deng, H.G. Park, Nano Lett., 2017, 17 (4), pp 2342–2348
[4] L. Sun, X. Peng, ACS Nano, 2014, 8 (6), pp 6304-6311

Two-dimensional (2D) materials such as molybdenum disulfide (MoS₂) present tremendous opportunities in membrane-based molecular separation. Compared to graphene oxide, MXene and other 2D inorganic materials, MoS₂ show exceptional stability in organic solvents. A few studies have reported the preparation of MoS₂ membranes for separation in aqueous solutions. However, there have been no investigations on the application of MoS₂ membranes for organic solvent separation. In addition, multi-layer and mono-layer MoS₂ nanosheets may be prepared by different approaches and have both been used for membrane preparation. Though studies have revealed that monolayer MoS₂ structure is unstable in the ambient conditions, there have been no reports on the stability of MoS₂ membranes.
This presentation covers our recent progress in 2D MoS₂ membranes for organic solvent separation. In the first part, we prepared both multi-layer and mono-layer MoS₂ nanosheets using different methods, and compared their structure, stability and performances after made into membranes. It’s found that multi-layer MoS₂ membranes are looser in structure, and hence result in higher permeability to isopropanol and lower rejection to dyes. On the other hand, though mono-layer MoS₂ membranes show better rejection to dyes in the short tests (within 3 hours), the rejection keeps decreasing over a 5-day tests, which is attributed to the limited stability of such nanosheets that lead to aggregation and breakage. To achieve high rejection and good stability, a ‘bridging’ agent is employed to regulate the interlayer spacing and nanosheet alignment of multi-layer MoS₂ membranes, leading to improved rejection and stable performances over one week.

In the second part, mixed matrix membranes containing MoS₂ nanosheets based on a 3-step layer-by-layer (LbL) method have been prepared, which provides a more cost-effective and scalable way to fabricate 2D membranes. Very interestingly, while the original LbL polyelectrolyte layer is impermeable to organic solvents, mixed matric membranes containing MoS₂ nanosheets open the pathways to solvents while rejecting solutes whose molecular weight is around 300 Dalton. The phemonena is attributed to the lower of surface energy by MoS₂ and its bridging effects. With a thin layer of < 50 nm, the mixed matrix membrane can achieve ethanol permeance –selectivity that surpasses the hypothetical upper bound, e.g., 92.9 % rejection for Victoria blue B (VBB, MW 506.08) with an ethanol flux of 11.4 L m^-2 h^-1 bar^-1.

Kraft black liquor (BL) is a corrosive (pH >12), high total solids (> 15 wt%), and high-volume byproduct (~500 million tons/yr worldwide) of biomass pretreatment for pulp and paper production [1]. BL contains lignin, hemicellulose, organic acids, inorganic salts, and water. Dewatering of BL is currently performed by multi-effect evaporators, which is highly energy-intensive (about 0.2 Quads/year in the US alone). Membrane-based concentration of black liquor [1,2] is attractive as an energy-efficient alternative, but challenging due to the harsh operating conditions, complex feed composition, and high fouling potential of BL. This talk will discuss our pursuit of chemically and mechanically robust, low-cost, and scalable GO membranes for black liquor concentration. We will discuss in detail the development and properties of graphene oxide (GO) nanofiltration and reverse osmosis membranes for rejection of lignin, other dissolved organics, and inorganic salts; including their operation in long-term testing under real BL conditions. We will overview our efforts for scale-up of GO membranes, and the development of an overall process for membrane-based concentration of BL streams with simultaneous production of usable process-quality water. A brief summary of the technoeconomic analysis for membrane-based BL concentration will also be presented.

References:

Kevlich, N. S.; Shofner, M. L.; Nair, S., Membranes for Kraft Black Liquor Concentration and Chemical Recovery: Current Progress, Challenges, and Opportunities. Separation Science and Technology 2017, 52 (6), 1070-1094.

Rashidi, F.; Kevlich, N. S.; Sinquefield, S. A.; Shofner, M. L.; Nair, S., Graphene Oxide Membranes in Extreme Operating Environments: Concentration of Kraft Black Liquor by Lignin Retention. ACS Sustainable Chemistry & Engineering 2017, 5 (1), 1002-1009.

Nanoporous graphene is a promising candidate material for gas separation membranes, due to its atomic thickness and low cross-membrane transport resistance. The mechanisms of gas permeation through graphene nanopores, in both the large and small pore size limits, have been reported in the literature. However, mechanistic insights into the crossover from the small pore size limit to the large pore size limit are still lacking. In this study, we develop a comprehensive theoretical framework to predict gas permeance through graphene nanopores having a wide range of diameters using analytical equations. We formulate the transport kinetics associated with the direct impingement from the bulk and with the surface diffusion from the adsorption layer on graphene, and then combine them to predict the overall gas permeation rate using a reaction network model. We also utilize molecular dynamics simulations to validate and calibrate our theoretical model. We show that the rates of both the direct impingement and the surface diffusion pathways need to be corrected using different multiplicative factors, which are functions of temperature, gas kinetic diameter, and pore diameter. Finally, we utilize our newly developed model to predict the permeances of CO₂, CH₄, and Ar through graphene nanopores. We show that as the pore diameter increases, gas transport through graphene nanopores can transition from being translocation dominated (pore diameter < 0.7 nm), to surface pathway dominated (pore diameter 1–2 nm), and finally to direct pathway dominated (pore diameter > 4 nm). The various gas permeation mechanisms outlined in this study will be particularly useful for the rational design of membranes made out of two-dimensional materials like graphene for gas separation applications.

Enhanced fluid transport in single-walled carbon nanotubes (SWCNT) promises to enable major advancements in several membrane applications, from efficient water purification¹ and low-cost recovery of high-value components, to advanced protective garments². Realization of the SWCNT-membrane potential in practical applications has been hampered so far by the challenge of fabricating large-area membranes with a high density of open, small-diameter, SWCNT pores. A high tube density is required to achieve flow rates outperforming those of commercial membranes, whereas small diameters enhance both size and charge based selectivity.
To demonstrate ultrapermeable large-area SWCNT membranes, we optimized the growth of vertically aligned SWCNTs to maximize number density (up to 2x10¹² tubes/cm²) and minimize average diameter (down to <2-nm) while simultaneously scaling up growth area (up to 4-in diameter).³ By filling the intertube gaps with a chemically resistant polymer and then opening the SWCNT caps with dedicated etching steps, we demonstrated wafer-scale SWCNT membranes with water permeances up to 250 LMH/bar, which greatly surpass those of commercial loose nanofiltration / tight ultrafiltration membranes. These SWCNT membranes display high rejection of nm-sized dyes (e.g., Rose Bengal) while permitting complete passage of salts like NaCl or Na₂SO₄. Contrary to conventional membranes for water treatment, aggressive cleaning methods did not affect detrimentally SWCNT membrane performances. This efficient fractionation and recovery of dyes/salts at modest applied pressures (far below the salt osmotic pressure) suggests that SWCNT membranes hold great promises for sustainable textile-water treatment. Together with their ultrahigh permeance, the demonstrated chemical resistance of these membranes offers opportunities for energy-efficient nanofiltration/ultrafiltration processes in chemically demanding environments.

References
1. F. Fornasiero, H. G. Park, J. K. Holt, M. Stadermann, C. P. Grigoropoulos, A. Noy, O. Bakajin, Proc. Natl. Acad. Sci. U. S. A. 105 (2008) 17250.
2. N. Bui, E. R. Meshot, S. Kim, J. Peña, P. W. Gibson, K. J. Wu, F. Fornasiero, Adv. Mater., 28 (2016) 5871.
3. E. R. Meshot, S. J. Park, S. F. Buchsbaum, M. L. Jue, T. R. Kuykendall, E. Schaible, L. B. Bayu Aji, S. Kucheyev, K. J. Wu, F. Fornasiero, submitted (2019).

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Membrane-based processes are becoming increasingly popular for water treatment due to their relatively high energy efficiency and low cost compared to other treatment methods. However, the advantages of membranes are mitigated by the need for additional pre-treatment steps that are required to maintain their effective operation. The treatment and prevention of membrane fouling, in particular, constitutes a large fraction of typical membrane operational costs. One potential approach to combat fouling is to design conductive membrane coatings that can prevent the attachment and growth of biofoulants both electrostatically and via electrochemical generation of reactive oxygen species. Despite their potential, these conductive membrane coatings are often expensive, requiring additional chemicals and non-scalable methods to produce, e.g. carbon nanotube mats or other graphitic coatings deposited by vacuum filtration. In this work, we explore the use of laser-induced graphene (LIG) for the creation of conductive ultrafiltration membranes. Porous polyethersulfone (PES) membranes are first coated in a thin layer of alumina using atomic layer deposition (ALD) before being irradiated with an infrared laser. We show that this alumina film, which can be scalably produced using spacial ALD, can localize LIG formation to the surface of the membrane, preventing the buried, un-lased areas of PES from melting and losing their porosity during the lasing process. This allows the top-most layer of the PES to be a conductive coating that can be used to charge the membrane surface and used to improve membrane performance (e.g. fouling mitigation). The formation of LIG is verified by scanning electron microscopy and Raman spectroscopy. The conductive layer is also shown to possesses relatively high conductivity, which is important for reducing power consumption in devices. Insight into the mechanism behind the improved stability to melting provided by ALD is provided by thermogravimetric analysis, differential scanning calorimetry, and Fourier-transform infrared spectroscopy. The effect of ALD film thickness and the use of sequential infiltration synthesis will also be explored. These insights are used to discuss the potential application of this approach to creating conductive coatings on other polymers using ALD-based approaches.

One of the major worldwide concerns nowadays is the use of chemical warfare agents (CWAs) in events of terrorism or war. One of the compounds used as CWA is the sarin gas. Sarin is a nerve agent capable of bringing a person to death in about 15 minutes. This and other CWA gases are so toxic and lethal that their use is very limited even in research. In view of the need to find out safety protocols both for the handling and storage of this gas and for its detection, filtering and chemical transformation, it is important to develop new and effective methods of researching CWA properties. In particular, theoretical methods are very welcome to study the chemical and physical properties of CWAs at different physical conditions. In this work, we present the results of a computational study of the interaction of sarin molecules and graphene, towards the characterization of sarin-filtering properties of nanoporous graphene. Classical molecular dynamics (MD) are employed here in order to study relatively large system sizes and number of molecules as well as some conditions of concentration and temperature that are prohibitive in ab initio studies. A graphene structure of about 32 by 34 Å of lateral sizes with a relatively large hole of about 15 Å is placed in the middle of an 80 Å length environment separating two regions, one with the presence of gas molecules and the other with vacuum, so creating a pressure difference between the two regions. Two sets of gas molecules are considered, one which has only sarin molecules and the other which has sarin and air (a mixture of 1% of Ar, 78% of N₂ and 21% of O₂) molecules. The aim of the study is to find out at which combinations of sarin concentration and temperature, the sarin molecule remains on one side or pass through the hole, as compared to the passage of air molecules. The MD simulations were carried out at four values of temperatures, 300 K, 500 K, 700 K, and 900 K, and two concentrations of sarin, 5% and 10% with respect to the total number of gas molecules. After 10 ns of simulation time, the results show that not a single sarin molecule went through the porous graphene for T = 300 K, regardless of sarin concentration. This is a remarkable result because the size of the hole is about three times the length of the sarin molecule. For the other values of temperature, the number of sarin molecules that crossed the hole was shown to depend on both temperature and concentration. In all MD simulations, the air molecules passed easily through the hole in graphene, and an interesting accumulation of sarin molecules around graphene structure was observed. We discuss these results on possible applications of porous graphene as a nanofilter of sarin gas.

Carbon dioxide and methane are the main greenhouse gases and their accumulation is responsible for worldwide environmental repercussions. In addition to the efforts to reduce their emissions, it is imperative to establish effective ways of capturing these compounds. The first step in this respect is to develop an understanding of what mechanisms are important for the interaction with potential sorption materials, with a goal of developing suitable capture materials with particularly high selectivity for CO₂ or CH₄.^1,2. A possible solution to reduce anthropogenic CO₂ emissions is through enhanced gas recovery (EGR) operations, by releasing trapped CH₄ through an exchange process with CO₂. By employing such a process, some estimates suggest that additional gas recovery through CO₂ injection may have an indirect value of nearly 1 T$³. The presently unrecoverable methane in shale reservoirs is retained through interactions with organic content and clay minerals. To employ such strategies, the fundamental interactions between clay, methane and carbon dioxide needs to be investigated.
We have studied (Li, Na, Cs, Ca, Ba, Ni)-fluorohectorite⁴ with a capillary based high-pressure cell with synchrotron X-ray powder diffraction and by volumetric adsorption. Here we show how the kinetics of the adsorption depends on the specific cation, clay layer charge, temperatures and pressure. Our studies show crystalline swelling of Ni-Fh within seconds in response to CO₂ exposure. We have investigated CO₂ capture for three different layer charges, 0.3, 0.5, 0.7 per formula unit (Si₄O₁₀F₂), where we observe crystalline swelling for 5-10 bar, 10-15 bar and 30 bar respectively at room temperature. In our experiments Cs-Fh, Ca-Fh and Ba-Fh does not show any sign of crystalline swelling when exposed CO₂. However, when Ni-fluorohectorite is exposed to methane up to a pressure of 60 bar at -20°C we observe no intercalation. Our results show the selectivity of CO₂ over CH₄ in fluorohectorite clay.

1 Sircar, Sh. "Applications of gas separation by adsorption for the future." Adsorption Science & Technology 19.5 (2001): 347-366.
2 Lu, An-Hui, and Guang-Ping Hao. "Porous materials for carbon dioxide capture." Annual Reports Section" A"(Inorganic Chemistry) 109 (2013): 484-503.
3 Davidson, Casie L., et al. "Modelling the deployment of CO2 storage in US gas-bearing shales." Energy Procedia 63 (2014): 7272-7279.
4 Stoter, Matthias, et al. "Nanoplatelets of sodium hectorite showing aspect ratios of≈ 20 000 and superior purity." Langmuir 29.4 (2013): 1280-1285.

Water treatment using membranes have emerged as a critical technology in solving societally important problems such as waterborne diseases caused by poor water quality and sanitation issues. This high energy consumption technology confronts key challenges for the technology to drive such as membrane selectivity and permeability, fouling and membrane lifetime. Functional nanomaterials can be a solution to these challenges by changing the membranes’ mechanical and bactericidal properties by enhancing these properties in a synergistic way. The ultra-dispersed diamond (UDD) is a versatile carbon allotrope with a small particle size range (4-5 nm), with easy surface functionality and biocompatibility properties, ideal for use in water treatment processes. This research studies UDD’s bactericidal and functionality properties embedded in membranes for water purification systems. Scanning and electron transmission microscopy (SEM) and Fourier Transmission IR (FTIR) techniques were performed to study the membrane surface and identify functional groups present in the nanoparticle. Tensile strength test was done to measure the nano composite membrane mechanical properties. Coliscan Membrane characterization was performed to obtain fecal coliforms forming units CFU on filtered samples and microorganism reduction significance was obtained using T-test analysis at a 95% level of confidence. This research aims to demonstrate how current water purification membranes can be enhanced by adding nano diamond particles to reduce bio-fouling problems, strengthen its mechanical stability, and increase its lifetime for water purification.

Ion-exchange membrane technologies used for water purification, in flow batteries for energy storage. To improve the transmission characteristics of the membranes, various methods are used, such as passivation of dangling bonds, increase inlet pressure, use of reverse osmosis, the design of optimal geometry, taking into account natural convection conditions and etc. We have investigated the impact of high-frequency acoustic pressure on the convection rate capacity of the membranes. This study is a continuation of previous works [1, 2]. Typically, vortex shedding takes place in the vicinity of the slit region. At medium to high sound pressure levels, the local particle velocity in the narrow region of the perforate or slit can be so large that the linear assumptions of acoustics break down. Thus, non-linear characteristics of acoustic waves interacting with the membrane simulated using advanced approached of finite-element modelling (FEM). FEM packages used to solve equations for unsteady state two-dimensional fluid flow coupled with acoustic pressure, species transport. In this work, we present our findings relating to increasing the convection rate using acoustic waves. Experimental test for flow rate increasing and simulating performance of the process done by using FEM. Acoustic waves Influencing approach offers interesting solutions for low cost increasing performance of water filters or Vanadium Redox Flow Battery energy storages.
1) Z. Insepov, D. Wolf, A.Hassanein, Nanopumping using carbon nanotubes, 2006 Nano Letters 6(9), 1893-1895
B. Berdenova, A. Ainabayev, Z. Insepov,etc. Modeling of liquid pumping via microchannels. (2014). Technical Proceedings of the NSTI-Nanotech 2014. 136-140

Utilization of abundant source of solar energy to generate steam has a broad range of applications such as power generation, desalination, water purification, and sterilization. Micro/nanostructured Janus photothermal materials with asymmetric surfaces and thermal properties have been widely sought for use in high-performance solar steam generators. Many approaches to constructing Janus structures that incorporate graphene based light absorbing materials fulfil the requirements of self-floating solar steam systems, such as light absorption, thermal insulation, and capillary action. However, achieving multiscale-structured materials remains a challenge due to processing requirements of high thermal/chemical energy, and lengthy period of time consumption. Herein, we demonstrate a simple and scalable laser-based photothermal method for directly producing monolithic Janus membranes of hierarchically porous graphitic carbon and polyimide foam for use in floating solar steam generators. Our monolithic Janus membrane performs not only outstanding solar steam generation, with an energy conversion efficiency of 84%, but high salt rejection ratios of 99.9% in the solar desalination systems. The laser photothermal method to obtain monolithic bilayer membrane has future potential to substantially reduce the cost of high-efficiency solar-thermal systems for scalable solar steam generations.

A bipolar membrane (BPM) can be used to maintain a pH difference in an electrolysis cell, which provides freedom to independently optimize the environments and catalysts used for paired redox reactions. A BPM consists of two physical layers, of which one is selective for the exchange of cations and the other for anions. The water dissociation reaction (WDR) splits water into protons and hydroxide ions under an electric field that concentrates at the interface of the two membrane layers. However, salt ions in commonly used electrolytes influence this WDR when they are present at the interface. Using electrochemical impedance spectroscopy (EIS), we observed the rate of water dissociation decrease in the presence of salt ions while also observing the diffusion and migration of these salt ions, showing a clear link between the peaks observed in EIS and ion crossover.

Our work comprises the first detailed impedance study using modern, commercial BPM’s in different electrolytes while varying the current density. This unique series of experiments allows the ability to obtain important fundamental knowledge of a BPM, i.e. insights on the voltage behavior around the plateau current density. This information shows a direct correlation between ion crossover and electrolyte composition, which is a highly debated and controversial topic in the BPM field. In addition, we have found that using electrochemical impedance spectroscopy, it is possible to observe the degradation of individual components of a BPM, which has immense implications for industrial applications.

References
Blommaert, et al. (2019). doi:10.26434/chemrxiv.8068238

Carbon-based stationary phases for chromatographic separation are known to be highly resistant to aggressive mobile phases and extreme pH values of solvents and eluents, a significant advantage compared to commercial silica-based alternatives. We report on a new variant of carbon-based stationary phases for liquid chromatography, specifically developed for chiral separation.
The recent interest in carbon-based chiral separators is related to the implementation of new forms of carbon: graphene, graphene oxide (GO) and reduced graphene oxide (rGO)¹. Recent papers^2-6report on the attempts of chiral separation and sensing, where GO or rGO was used as one of components of modified electrodes or as a part of (quasi)stationary phases for capillary electrochromatography. We have to mention recent suggestions of separation membranes made out of chemically functionalized graphene-based materials. including the idea of using holes in planar graphene for transport of chiral compounds across graphene layers⁷, reports about the usage of L-glutamic acid-functionalized GO membranes for the separation of phenylalanines^8, ,andattempts of making intrinsically chiral mesoporous carbon synthesized via carbonization of chiral ionic liquids⁹.
Despite the achieved progress, no previous reports have so far demonstrated carbon nanotubes- or graphene-based CSPs for use in high performance liquid chromatography that are fully competitive with commercial silica-based immobilized CSPs. In our work, mesoporous three-dimensional graphene nanosheets (3D GNS), functionalized with tetracyanoethylene oxide (TCNEO) and (S)-(+)-2-pyrrolidinemethanol, used as Chiral Stationary Phases (CSPs), demonstrate separation performance parameters competitive to currently commercially available CSPs¹⁰. The modification of graphene withtetracyanoethylene oxide (TCNEO) introduces reactive cyano groups to the material, opening a wide spectrum of possible secondary modifications and uses. Demonstrated graphene-based CSPs are chemically stable, and up to an order of magnitude less expensive comparing to commercial silica-based analogues.
References
1. Liang, X., et.al. TrAC Trends in Analytical Chemistry98, 149-160 (2018).
2. Li, J. et al.. Microchim. Acta180, 49–58 (2013).
3. Tang, J. et al. Electroanalysis26, 2057–2064 (2014).
4. Upadhyay, S.S., et.al. Electrochim. Acta248, 258-269 (2017).
5. Liu, X. et al.. Electrophoresis34, 1869–1876 (2013).
6. Liu, Z., et.al..Microchim. Acta184, 583–593 (2017)
7. Hauser, A.W. et al. Angew. Chem. Int. Ed.53, 957-960 (2014).
8. Meng, C., et.al. J. Membrane Sci.526, 25-31 (2017).
9. Fuchs, I., et.al. Angew. Chem. Int. Ed.55, 408–412 (2016).
10. L. Candelaria, et.al., Scientific Reports 8 (2018)14747

The world is facing several challenges related to climate and environmental issues. Current research is focused on solutions such as CO₂ reduction and polymer electrolyte membrane fuel cells (PEMFC), which have the potential to address such issues. These technologies can enable clean and affordable energy. Among the latest innovations, PEMFCs are quite promising, due to their low operating temperature and high-power output. Commercialization is one of the major challenges due to high cost. One potential cost reduction method under research is using the electrospinning technique to fabricate nanofibers which are rich in catalytic material. Nanofibers fabricated with intra-fiber porosity result in well distributed catalyst and ionomer, which has high surface area for electrochemical reaction and catalyst mass activity (1). Such electrospun cathodes are highly durable (2) and promising for cost reduction. However, to achieve our goal of fabricating nanofibers with high electrochemical surface area and high catalyst mass activity we are studying the impact of polymer solution properties and electrospinning process parameters on spinnability. The presence of carboxylic acid groups in poly (acrylic acid) (PAA), enhances polymer chain entanglement and is known for adding viscosity to the polymer solvent solution (3). We have studied the fabrication of PAA by itself and with a blend of Nafion ionomer and catalyst, such as Pt-Vulcan, in this work. These experiments improve our understanding of the morphology and diameter of these different blends of polymer solvent solutions with respect to their viscosity at different polymer concentration, and different processing and ambient parameters of electrospinning.
This study was conducted to better understand the morphology and diameter of fibers with different concentration of PAA, ranging from 5 – 20 wt.%, with and without Nafion and the catalyst (Pt-Vulcan). The PAA polymer was dissolved in a 2:1 ratio of isopropanol and water solvent. This work will be conducted at different processing conditions (ranging from needle-to-drum distance of 8-12 cm, voltage of 10- 20 KV, and flow rates of 0.75ml/hr. and 1 ml/hr.). Further, these conditions will be then tested at different humidity condition ranging from (25-45 % RH). The polymer solvent solution with and without Nafion and catalyst were mixed for approximately 72 hours. Fiber size and morphology were measured using scanning electron microscopy, and the Image J software (NIH, Bethesda, MD, USA) was used for automated fiber diameter determination and statistics.
This work demonstrates the effect of ink (e.g. viscosity) and process parameters with respect to spinnability of the fibers at different weight percent (ranging from 5-20 wt.%) of poly (acrylic acid) (PAA) polymer solvent solution with and without blend of Nafion and catalyst.
Reference:
1. Brodt, M., Wycisk, R., & Pintauro, P. N. (2013). Nanofiber electrodes with low platinum loading for high power hydrogen/air PEM fuel cells. Journal of the Electrochemical Society, 160(8), F744-F749.
2. Zhang, W., & Pintauro, P. N. (2011). High Performance Nanofiber Fuel Cell Electrodes. ChemSusChem, 4(12), 1753-1757.
3. Chen, H., Snyder, J. D., & Elabd, Y. A. (2008). Electrospinning and solution properties of Nafion and poly (acrylic acid). Macromolecules, 41(1), 128-135.

Hyperbranched polymers constitutes a category which fundamentally outlines as polymers with multiple covalent branching points of structural arrangement, rendering an intrinsically spherical-like conformation. We present hyperbranched polyglycerols multi-functionalized with tuneable degrees of unsaturated groups utilized for click cross-linking and ionic groups for electrolytic properties. The resulting ‘dendrolyte’ polymers have been applied in organic electronic devices in a one-step process to achieve free-standing monolithic ion-selective membranes for controlled electrophoretic ion delivery¹. This new generation of organic ion-conductive materials showcase the capability of performing selective electrophoretic transport of large charged aromatic compounds, coupled with the opportunity for miniaturized manufacturing² and processing for applications in organic (bio)electronic devices, broadening the possibilities for communication with biological systems³ with specificity and high spatiotemporal resolution.

1. T Abrahamsson et al. Formation of monolithic ion-selective transport media based on ‘click’ cross-linked hyperbranched polyglycerols. Front. Chem. (under revision) (2019).
2. DJ Poxson et al. Capillary-Fiber Based Electrophoretic Delivery Device. ACS Appl. Mater. Interfaces 11, 14200 (2019).
3. DJ Poxson et al. Regulating plant physiology with organic electronics. Proc. Natl. Acad. Sci. 114, 4597 (2017).

The high capital and energetic costs of reverse osmosis based water desalination technology limits its adoption in remote communities. Furthermore, the immense capital costs associated with constructing and maintaining a national scale water distribution make this technology practically irrelevant to considerable parts of the world. For this reason, a small scale, energy efficient water desalination technology is called for. Electrodialysis and capacitive deionization technologies were suggested as technologies that can fill this gap. However, the need for energy intensive chemical reactions in electrodialysis and the capacitance limitations in capacitive deionization technologies impose significant barriers to these technologies. Hence, an ion pumping technology that can operate in steady state without requiring lossy chemical reactions can provide a significant step forward towards a viable, small scale water desalination technology. We have demonstrated a first of its kind ratchet based, all electric ion pump.
Electronic ratchets are devices that utilize modulation in a spatially varying electric field to drive steady state current. Similar to peristaltic pumps, where the pump mechanism is not in direct contact with the pumped fluid, electronic ratchets induce net current with no direct charge transport between the power source and the pumped charge carriers. Thus, electronic ratchets can be used to pump ions in steady state with no electrochemical reactions between the power source and the pumped ions resulting in an “all electric” ion pump. In this contribution we analyze the applicability of this technology, its challenges and its advantages for small scale water desalination. The pumping efficiency is shown to be limited by series resistance and is heavily affected by the pore size.

Carboxycellulose nanofibers (CNFs) promise to be a sustainable and inexpensive alternative material for polymer electrolyte membranes compared to the expensive commercial Nafion membrane. However, its practical applications have been limited by its relatively low performance and reduced mechanical properties under typical operating conditions. In this study, citric acid cross-linked carboxycellulose nanofiber (CA/CNF) membranes were prepared by solvent casting method. Carboxycellulose nanofibers were derived from wood pulp by using chemical oxidation of hydroxy group present on C6 position of the cellulose chain. Results from FT-IR spectroscopy, ¹³C NMR spectroscopy, and XRD reveal a chemical crosslink between the citric acid and CNF, and the optimal fuel cell performance was obtained crosslinking 70 mL CNF suspension with 0.3 mL of 1.0 M citric acid solution. The membrane electrode assemblies (MEAs), operated in oxygen atmosphere, exhibit maximum power density of 27.7 mW/cm² and maximum current density of 111.8 mA/cm² at 80 °C and 100% relative humidity for the CA/CNF membrane with 0.1 mg/cm² Pt loading on anode and cathode, which is approximately 30 times and 22 times better respectively than the uncrosslinked CNF film. The surface morphology of Carboxycellulose nanofibers and corresponding membranes were characterized SEM, EDX, TEM, and AFM techniques.
Acknowledgments: We gratefully acknowledge support from the Louis Morin Charitable Trust and NYS Department of Economic Development.

References:
(1) Klemm, D.; Kramer, F.; Moritz, S.; Lindström, T.; Ankerfors, M.; Gray, D.; Dorris, A. Nanocelluloses: A New Family of Nature-Based Materials. Angew. Chemie Int. Ed. 2011, 50 (24), 5438–5466. https://doi.org/10.1002/anie.201001273.
(2) Bayer, T.; Cunning, B. V.; Selyanchyn, R.; Nishihara, M.; Fujikawa, S.; Sasaki, K.; Lyth, S. M. High Temperature Proton Conduction in Nanocellulose Membranes: Paper Fuel Cells. Chem. Mater. 2016, 28 (13), 4805–4814. https://doi.org/10.1021/acs.chemmater.6b01990.
(3) Zhu, H.; Luo, W.; Ciesielski, P. N.; Fang, Z.; Zhu, J. Y.; Henriksson, G.; Himmel, M. E.; Hu, L. Wood-Derived Materials for Green Electronics, Biological Devices, and Energy Applications. Chem. Rev. 2016, 116 (16), 9305–9374. https://doi.org/10.1021/acs.chemrev.6b00225.
(4) Sharma, P. R.; Joshi, R.; Sharma, S. K.; Hsiao, B. S. A Simple Approach to Prepare Carboxycellulose Nanofibers from Untreated Biomass. Biomacromolecules 2017, 18 (8), 2333–2342. https://doi.org/10.1021/acs.biomac.7b00544.

Iron-electrocoagulation (Fe-EC) is a method producing in-situ iron (oxyhydr)oxide nano-particles which attach with contaminants such as Arsenic and other heavy metals, coagulate and settle down- thus making water safe for use. Fe-EC is rate limited by amount of dissolved oxygen which is key in oxidizing Fe(II) dissolving from sacrificial anode to Fe(III). We present an improved process using gas-diffusion cathode or air-cathode, which generates in-situ hydrogen peroxide, a stronger oxidant than dissolved oxygen. We investigate the iron-oxides in conventional Fe-EC and air-diffusion cathode enabled Fe-EC. The findings from this research will guide future development of the Fe-EC process.