Symposium NM04 : Nanomaterials and Nanomanufacturing for Sustainability

Electrocatalytic water splitting has been considered as a viable strategy to convert and store energy renewably, but has been hampered by the slow kinetics of the oxygen evolution reaction (OER). Hence there is an urgent need to improve the performance of currently used materials and/or develop new materials. Iridium oxide is an effective stable electrocatalyst with low over-potential and high current for efficient fuel generation technologies. To further improve its activity, we developed a facile one-step molten salt synthesis process to generate ultrafine iridium oxide nanorods (IrO₂ NRs). The electrocatalytic performance of these IrO₂ NCs for OER in acidic media was compared with that of commercial IrO₂ nanoparticles (NPs) in terms of specific capacitance, total charge, most accessible charge, electrochemically active surface area, and roughness factor. Our IrO₂ NRs demonstrated enhanced electrocatalytic OER activity in 0.5 M H₂SO₄ compared to the commercial IrO₂ NPs. Moreover, compared to commercial IrO₂ NPs and previous reports, our IrO₂ NRs showed enhanced electrocatalytic activity for both OER and HER after passing either N₂ or O₂ gas in a 0.5 M KOH electrolyte, as confirmed by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Our results are comparable with, and in most cases, higher than reported data in the literature. Therefore, the current study reported a type of highly electrocatalytic efficient IrO₂ nanostructures, but also a simplistic, reliable and scalable synthetic process for them. It is expected that these IrO₂ NRs can serve as a benchmark in the development of active OER and HER (photo)electrocatalysts for various applications in the near future.

Gamma-radiation-induced synthesis of metal and metal oxide nanoparticles involves reactions of dissolved precursor metal salts with products of water radiolysis. When exposed to ionizing radiation water decomposes to form chemically reactive radicals and molecular species. The products of water radiolysis range from highly oxidizing, e.g. hydroxyl radicals to highly reducing, e.g. hydrogen radicals and solvated electrons. The oxidants and reductants produced upon radiolysis react then with solutes and change their oxidation state. These chemical changes lead to the formation and subsequent precipitation of insoluble species, since the solubility and reactivity of metal ions depend on their oxidation states. Synthesis of nanomaterials can be done by using either reductive or oxidative routes. To reach the controlled redox conditions and avoid the unwanted reactions one can add other organic or inorganic compounds which act as scavengers of the radicals. The amount of material obtained by gamma- radiation-induced synthesis can be controlled by the yield of reductive/oxidative radiolysis products formed in solution. Radiation induced synthesis is a powerful tool to produce the materials of complex shape and compositions. It has the following advantages as compared to the other methods: The nanoparticles with very narrow size distribution and uniform shape can be synthesized; there are possibilities to synthesize the nanostructure in confined media, such as porous materials, nanotubes etc. The formation of radicals stops immediately when the solution is removed from the radioactive source. Therefore the amount of reacting radicals and thus the amount of obtained precipitate is controlled by the total radiation dose with a high accuracy. Moreover, the radiation induced method is cost-effective processing, since it implies direct energy transfer without intervening media. It has low energy consumptions, since the radiation source does not require external energy supply. It requires minimal use of potentially harmful chemicals (initiators, crosslinking agents, acids etc.). Thus, radiation-induced synthesis can be considered as a green method.
In the current work we demonstrate how gamma radiation induced synthesis can be implemented to produce metal (Ag, Cu, Ni) and metal oxide (Cu₂O, Co₃O₄, CeO₂) nanoparticles having narrow size distribution for different applications. The nanomaterials are produced both free standing and on solid supports. Metal nanoparticles are synthesized using the reductive route while metal oxide particles are produced using both oxidative and reductive routes [1, 2].
References
1. C. Dispenza, N. Grimaldi, M. A. Sabatino, I. L. Soroka and M. Jonsson, J. Nanoscale and Nanotechnol., 2015, 15, 3445-3467.
2. I. L. Soroka, N. V. Tarakina, A. Hermansson, L. Bigum, R. Widerberg, M. S. Andersson, R. Mathieu, A. R. Paulraj, Y. Kiros. Dalton Trans. 2017, 46, 9995-10002.

Surface, interface, and bandgap engineering play a pivotal role for designing tandem photoelectrodes for photoelectrochemical water splitting to potentially realize solar-to-hydrogen efficiencies >20%. III-nitride semiconductors, e.g. GaInN, have emerged as one of the most promising materials to realize high efficiency photoelectrodes: their fundamental bandgap can be varied across nearly the entire solar spectrum by changing the alloy compositions and the band edge positions straddle water oxidation and reduction potentials under visible light irradiation. In this context, we have performed, both theoretically and experimentally, a detailed investigation of the structural, electronic, and photoelectrochemical properties of Ga(In)N/Si heterostructures. Detailed X-ray photoelectron spectroscopy (XPS) measurements reveal that the conduction band edge of GaN and Si are near-perfectly aligned, which enables efficient extraction of photo-generated electrons from the underlying Si wafer to GaN nanowires. Band diagrams were constructed from the measured valence band minimum (VBM) and the observed core-level shifts between different thickness GaN/Si samples. Deposition of 2-3 nm of GaN evidently passivates the Si surface and induces a small amount of upward band bending (BB). The interfacial valence-band offset calculated from measured VBMs and core-level shifts was 2.52±0.1 eV. This value, in combination with the individual band gaps of Si and GaN, leads to a conduction band offset of -0.22±0.1 eV, where the negative sign indicates that the CBM of GaN is lower than that of Si. It is to be noted that n⁺-(In)GaN acts like a hole blocking layer which helps in charge carrier separation and thereby reduce the surface recombination of the photo-generated carriers. With the incorporation of Pt co-catalyst nanoparticles on Ga(In)N surface, we have demonstrated solar water splitting on Ga(In)N/Si photocathode with a maximum current density of >35 mA/cm² and an applied bias photon-to-current efficiency >10% in 0.5 M H₂SO₄ under AM1.5G one-sun illumination. This work shows the use of GaN nanowires as a multi-functional protection layer as well as excellent charge extraction of the photogenerated electrons from the underlying Si wafer.

Zinc oxide (ZnO) nanoparticle, an active ingredient of bactericides, has potential applications in treating citrus greening disease owing to its unique properties. Here, employing density functional theory we study the structures and reactivity of sub-nanometer-sized ZnO nanoparticles. Examination on the propensity of binding of water, urea, salicylic acid and citric acid molecules to the surface of ZnO nanoparticle (diameter ~14Å), indicates that the molecules bind strongly at Zn atoms at the nanoparticle edges. Strikingly, the binding of urea, salicylic acid and citric acid through their O (O=C) atoms at the Zn sites can be traced to the electronic structures. We also investigate the solvation effects on the binding characteristics of these molecules. Finally, we compare the structures and energetics of molecules adsorbed on the nanoparticle with those on extended ZnO(10-10) surface, and find that the edge Zn sites of the nanoparticles are more active than the surface Zn sites of the extended surface. Overall, our results provide insights into the reactivity of ZnO nanoparticle in different local environments, and may offer guidelines to design the ZnO-nanoparticle-based material as an antibacterial agent for agricultural applications.

*This work is supported by USDA NIFA under grant FLAW-2014-10120.

Water and energy are two of the world’s most valuable resources. In the near future, as the industrial sector expands, demand for water and energy will be even greater than it is today. Recently, advanced materials have been widely implemented in energy and water areas. Here, hybrid nanostructures composing of graphene-like film and bamboo-like carbon nanotubes have been synthesized in a simple, one-pot, catalyst-free chemical vapor deposition process. Pre-sputtered carbon coating on a copper substrate is considered as the key factor contributing to the final morphology. Furthermore, this hybrid nanostructure product has been shown to be a potential alternative material in solar cell and water desalination applications for sustainability.

Smart gels-based materials can response external stimulus, such as temperature, pH value, light, electric, magnetic etc., via significant volume phase transition, have attracted a great amount of attentions.¹ Recently, organic/inorganic hybrids have been developed as a novel platform for design of gels-based materials with diverse scales and dimensions, showing multi-functions to broad their applications in smart sensing and biomedical fields. Here, combing our long-term research, series of organic-inorganic hybrid gels-based materials with diverse dimensions to meet practical applications requirements have been designed and prepared. In details, we prepared zero-dimensional (0D) nanogels, functionalizing with photothermal agents and anti-cancer drugs to deal with cancer.^2-4 As for 1D fiber, we obtained hydrogel fibers continuously with high efficiency based on a novel dynamic-crosslinking-spinning technology, the hydrogel fiber could be functionalized with conductive agents using a subtle coaxial spinneret, provide promising candidate for artificial nerves.⁵ Furthermore, several 3D smart bulk hydrogels were synthesized by in-situ introduction of functional nanoparticles into hydrogels, which could be used in fields of sensors including micro-channel valves and temperature switches.^6-9

Acknowledgement: This work is financially supported by National Key Research and Development Program of China (2016YFA0201700/2016YFA0201702), Project of Shanghai International Science and Technology Cooperation Fund (14520710200) and Program for Changjiang Scholars and Innovative Research Team in University (T2011079, IRT_16R13), and the Program of Talents of Discipline to University (111-2-04), and Innovation Program of Shanghai Municipal Education Commission (2017-01-07-00-03-E00055).

References
¹ Jones, C. D.; Steed, J. W. Chem. Soc. Rev. 2016, 45, 6546.
² Chen, Z. G.; Wang, H. P.; Zhu, M. F. Advanced Materials, 2015, 28, 245.
³ Chen, Z. G.; Zhu, M. F. Adv. Mater. 2013, 25, 2095.
⁴ Chen, Z. G.; Zhu, M. F.; Hu J. Q. Adv. Mater. 2011, 23, 3542.
⁵ Hou, K.; Zhu, M. F. Macromol. Rapid Commun., 2016, 37, 1795.
⁶ Zhang, Q.H.; Zhu, M. F. Carbon, 2011, 49, 47.
⁷ Xia, M.; Zhu, M. F. Aust. J. Chem., 2014, 67, 112.
⁸ Liu, Y.; Zhu, M.F. Soft Matter, 2012, 8, 3295.
⁹ Xia, M.; Zhu, M. F. Macromol. Rapid Commun., 2015, 36, 477.

CO₂-derived fuels present an attractive way towards a sustainable energy system. Mimicking natural photosynthesis by synthesizing carbon-based energy carriers using renewable energy allows for closing the anthropogenic carbon cycle and therefore represents an attractive way to store intermittent power, a challenge that has not yet found a satisfying solution.
Using solar power as the energy source for fuel synthesis will require large surfaces of absorbers and efficient catalysts, which should be fabricated from abundant materials. In this context, we show the application of cheap and scalable Cu₂O photocathodes in combination with molecular rhenium catalysts, both in solution and covalently bound to the nanostructured photoelectrode surface. Both systems feature substantial photocurrents and photovoltages, demonstrating protected Cu₂O photocathodes as viable candidates for solar-driven CO₂ reduction processes.
Moving from organic solvents into aqueous systems, we demonstrate the unassisted and sustainable splitting of CO₂ into CO and O₂ using perovskite photovoltaics as light absorbers and nanostructured gold and IrO₂ as catalysts, reaching an efficiency of 6.5 %. Building up on this work, we show how ALD modification of CuO nanowires can lead to a bifunctional and low-cost catalyst both for CO evolution from CO₂ and for the oxygen evolution reaction. By ALD modification, the wide product distribution of Cu-based catalysts could be narrowed to yield predominantly CO. Investigations into the microkinetics on these electrodes indicate that the selectivity change is due to the suppression of H₂ evolution, while the rate of CO production remains similar. Together with the use of a bipolar membrane, allowing for separating product gases while maintaining a sustained pH gradient, we used these electrodes demonstrate long-term solar CO production at an efficiency of 13.4 %, driven by a single 3-junction photovoltaic.
Going beyond the production of CO, a novel approach was used to gain insight into the mechanism of hydrocarbon formation at copper electrocatalysts. Studying this process in nonaqueous electrolytes at low temperatures allows for fine-tuned control of the proton donor and the CO binding strength, enabling activation-controlled kinetic studies over an extended parameter range. From these measurements, we are able to show that the rate of methane and hydrogen formation is governed by the competition of CO and H for surface sites while ethylene formation remains weakly impacted by this effect.
The presentation illustrates the pathway to ever more insight and to efficient catalysts and devices for the reduction of CO₂, first to CO and subsequently to hydrocarbon fuels such as methane and ethylene.

Inspired from natural surfaces such as lotus leaves, water strider legs, the Namib desert beetle, and geckos’ feet, the past few decades have seen significant research and development in the design and manufacturing of water repellent or superhydrophobic surfaces. For superhydrophobicity, surfaces need to be fabricated in two steps, initially creating micro/nanostructures, thereby providing roughness to the primary substrate, followed by the deposition of a low surface energy coating. The low surface energy leads to higher advancing and receding contact angles with water droplets, lower contact angle hysteresis, and hence easy droplet removal, promoting dropwise condensation and enhancing heat transfer. Recent studies have focused on chemical oxidation of metallic surfaces to form conformal micro/nanoscale structured metal oxide layers at the solid-air interface. The process is usually self-limiting, with both the oxide layer thickness and structure length scale ranging from 10 nm to 100 µm. Despite enabling efficient dropwise condensation, the metal oxide layers create a significant conduction parasitic thermal resistance due to their lower thermal conductivities (around 10 W/m.K) when compared to their pure metal counterparts (around 100 W/m.K). Furthermore, the application of metal oxide structures for industrial applications remains a challenge due to their poor durability. Here, we develop micro/nanostructured surfaces via direct electrolytic etching of metals. Different length scale surface structures and roughness are obtained by controlling the etching time and supply voltage of the electrolytic process. The etched metallic structures are made of the base metal, enabling higher thermal conductivity and lower parasitic resistance. Furthermore, the uniform metallic composition of the base metal and etched structures enables greater durability from thermo-mechanical stresses. Linear abrasion tests revealed greater durability of our etched metal structures when compared to metal oxides. After coating the developed surfaces with a low energy self-assembled monolayer using vapor deposition, these surfaces show water droplet contact angles greater than 160°. Our work not only develops metal etched structured surfaces for durable condensation of steam and enhancement of condensation heat transfer coefficient, it enables a scalable manufacturing technique for durable superhydrophobicity.

Nanoscale step structures have attracted recent interest owing to their importance in both fundamental and applied research, for example in adsorption, in catalysis, and in directing nanowire growth. In this in situ study, self-ordered vicinal-like surface structures were obtained by annealing of thin films of gold deposited on ultraflat Si/SiO2 substrate. Annealing at temperatures ≥200 °C efficiently promoted the formation of vicinal-like structures on the inner gold/substrate interface. Gold grains near the inner surface exhibited an orientation with the [111] direction very close to the substrate normal. Furthermore, the step periodicity depended on the grain/substrate orientation angle. Smaller misorientation resulted in a larger average step periodicity, similar to that seen in regular vicinal surfaces of gold single crystals. Formation of low-index terraces and atomic steps at the inner gold interface (while the silica surface remains ultraflat) can be considered as a kind of solid−solid dewetting. We suggest that the formation of vicinal-like structures could be attributed to the thermally activated surface reconstruction driven by minimization of the total surface energy, which includes the gold/substrate cohesion energy and the GB energies. The process is controlled by diffusion of gold from the inner gold/substrate interface, most probably to the grain boundaries and then to the outer surface of the film. Substantial bulk diffusion across the film during annealing at 400 °C for 4 h can also provide a required mass transport from the inner to the outer surface. This work contributes to the understanding of the atomic step structure formation at the gold/substrate interface, which will be helpful in the use of vicinal-like surfaces as templates for growing of regularly spaced nanostructures. It also offers a method for the in situ investigation of both the grain orientation and the grain interface step periodicity in a given grain, and then can be utilized for further explorations of vicinal-like surfaces.

Water-reactive nanostructured metals and metalloids such as nano-Mg, nano-Al, nano-Zn and nano-Si with minimum surface oxide coverage have a broad range of potential applications. They can serve as catalysts for combustion, as active materials in hydro-powered spaceship engines, and as materials for onboard hydrogen production to power portable devices and hydrogen fuel-cell vehicles. The degree of reactivity of this class of materials with water is linked directly to their nanoscale size and to the extent in which the surface of these nanomaterials is covered with oxide. For example, smaller nanostructures exhibit faster kinetics in their reaction with water to produce hydrogen. Nearly oxide-free, ultrafine nanoscale structures with characteristic sizes in the range of 10-20 nm are commonly required for effective reactivity with water. Nanofabrication of these highly-reactive materials with such ultrafine structure sizes and minimum surface oxide coverage is still a fundamental challenge due to their high chemical reactivity. In this talk, I will present a novel, cost-effective, and scalable route to sustainable hydrogen for on-board application. Our new route involves: (i) the hydrolysis of neutral water with nanoporous aluminum to produce hydrogen and aluminum hydroxide without the typical use of catalysts, and (ii) the recycling of aluminum hydroxide back to aluminum metal without any CO₂ footprint. While over 95% of hydrogen used worldwide is produced by steam reforming of natural gas, this method is not sustainable because CO₂ is co-produced during the process. Sustainable hydrogen can be generated by electrolysis of water into hydrogen and oxygen, but this method is relatively expensive (~40-53 kWh of energy is needed to produce 1 kg of H₂) and not very efficient (40-60% yield). The new method presented in this talk requires only 24-47 kWh of energy to produce enough nanoporous aluminum to generate 1 kg of hydrogen with 50-85% yield by hydrolysis in neutral water. [1,2]

References:
[1] Eric Detsi and John S. Corsi: “Bulk Nanoporous Aluminum for On-board Hydrogen Generation by Hydrolysis”. Patent Application, #18-8558-104377.000203
[2] John S. Corsi, Jintao Fu, Zeyu Wang, and Eric Detsi: “Sustainable Hydrogen Solution Enabled through Hydrolysis of Nanoporous Aluminum in Neutral Water” (Under review)

High temperature processing can provide sufficient activation energy for materials’ compositional, structural, and morphological evolutions, and is essential for various kinds of reactions, synthesis, and post-treatment. However, the current high temperature heating sources, mostly furnaces, are far from satisfying for nanomaterials processing owing to their bulky size and limited temperature and ramp range (~1300 K, ~10 K/min). Here we have focused on the study of electrical triggered Joule heating as a new route for high temperature engineering of nanomaterials toward nanomanufacturing. We developed facile, highly stable and controllable heating strategies for micro/nanoscale high temperature engineering. Ultrahigh temperature annealing (>2500 K) is applied to carbon nanomaterials to address the defects and poor interfacial problems. Ultrafast thermal shock (~2000 K in 55 ms) is applied to metal salt loaded carbon substrates for in-situ synthesis of ultrasmall, well-dispersed nanoparticles. The high temperature engineering on nanomaterials is highly facile, energy-efficient, and reliable toward scalable nanomanufacturing. More exciting results and products are expected for various nanomaterials during/after the unique high temperature engineering.

The terms “nonmanufacturing” and “nanofabrication” are often used interchangeably. Recently, Liddle et al. have distinguished between nanomanufacturing and nanofabrication by using the criterion of economic viability. Nanomanufacturing, which utilizes efficient and cost-effective nanofabrication methods to manufacture nanostructures and functional devices, has the characteristic of being a source of money, while nanofabrication is often a sink. Nanomanufacturing is indispensable in today’s “nano-world” as the devices keep shrinking in size. The functional devices with internal building blocks at the nanoscales have intriguing and extraordinary properties for many applications. For example, the color of gold nanoparticles distributed in a material does not appear yellow its familiar color for bulk gold; instead, the color of nano-gold changed to ruby red. The melting point of gold at the nanoscale is also significantly lower than its bulk counterparts.

There are a large number of nanofabrication approaches available, but only a few are suitable for large-scale nanomanufacturing. Therefore, the exploration of new technology is desperately needed to expand the nanomanufacturing toolbox. Here, we demonstrate a method that can be used for affordable nanomanufacturing at the ambient conditions. A low-cost continuous-wave (cw) laser is used to directly kick and transfer nanostructures from one substrate to another in ambient conditions. Unlike the direct laser ablation method, where expensive pulsed lasers are typically used to ablate the materials disruptively, the method demonstrated here has no damage on the nanostructures, therefore, this method can maintain the geometry of nanostructures and transfer them selectively in an additive manner.

Nanomanufacturing is the fabrication of nano-scale building-blocks (nanomaterials, nanostructures), their assembly into higher-order structures, and the integration of these into larger scale systems with manipulation and control at nano-scale. Typically, the scale ranges from 1-100 nm. Processes can be top-down (additive/subtractive) or bottom-up (self- and directed-assembly) or an integration of the two. Manufacturing processes need to be scalable, controllable, reproducible, efficient and low cost. The combination of large-scale production and nano-scale products raises environmental and sustainability issues. Questions needing answers are: 1) How can industry develop new nanotechnologies in a responsible and sustainable manner; 2) How can it be ensured that nanomanufacturing processes are safe for producers and products are safe for consumers and the environment. This talk discusses NSF-supported projects in sustainable nanomanufacturing that address life-cycle analysis, recycling, environmentally-benign nanomaterials and processing, green nanomanufacturing, clean energy, wastewater treatment, among others. It will conclude with a discussion on future directions and their implications.

During the last decades new methods or materials have been developed looking for better photocatalytic activity to TiO₂ such as addition of dopant, construction of heterojunctions like TiO₂/SrTiO₃. These modifications are based on charge transfer, heterojunctions shown a good alternative that present synergy of intrinsic conduction potential bands. In this way the composites TiO₂/SrTiO₃ present as good alternative in that one, SrTiO₃ shows band gap of 3.4 eV. In this work, the composite was obtained recovering SrTiO₃ nanoparticles with titanium sol gel. This procedure showed up easy and fast compared to current methods used to obtain composites with both ceramics phases. To obtainment the TiO₂/SrTiO₃ heterojunction the SrTiO₃ particles (1% and 5% m/m) was insert into titanium sol-gel solution resulting a suspension, which remained on soft stirring at room temperature 24 hours. Than the gel was dried at 100 ^oC for 24 hours, after that was thermally treated at 400 ^oC for 2 hours. The interface showed interesting characteristics those results in defects at medium range. The appearance of the intermediate phases observed in the interface region is due to the cubic structure of SrTiO₃ which offer lower free energy of crystallization, and thus the growth of the monoclinic and rhombohedral TiO₂ phases. The heterojunctions TiO₂/SrTiO₃ presents unusual photoluminescent as a result of these intermediate phases that promote structural defect. The new route to the formation of heterojunction allowed a solid-solid interface between TiO₂ and SrTiO₃ particles which is responsible for promote electronic, optical and photocatalytic properties due to improvement in charge carrier transfer in this region. Acknowledgments (FAPES- 2013/07296-2) and CNPq-PIBIC

The use of nanoparticles in nanomedicine is dependent of their bio-compatibility, size, physicochemical stability, absence of aggregation in aqueous phase and capacity to generate toxic species at controlled doses. It is expected that nanoparticles with intrinsic optical properties and stability in water can be ingested by cells and generate toxic species like reactive oxygen species (ROS). Selenium is commonly used as an anti-fungal agent, and as a nutritional supplement in its inorganic and organic form. The use of selenium-based nanoparticles in the biomedical field builds the basis of a new type of treatment based on bio-essential elements that will be inherently less toxic to normal cells. Based on these considerations, this research is focused on the size-controlled synthesis of selenium based-nanoparticles, its conjugation with proteins in order to improve its stability in water and the evaluation of their capacity to generate ROS in aqueous phase. The synthesis of selenium nanoparticles was achieved in a single step through microwave-assisted synthesis by reduction of sodium selenite (Na₂SeO₄) to elemental selenium in presence of ethylene glycol, sodium chloride and polyvinylpyrrolidone (PVP) at basic pH conditions. UV-vis spectra of the suspension of Se nanoparticles produced at different times of reaction (i.e. 3, 5 and 8 minutes) and constant temperature (180°C) exhibited strong absorption peaks centered on 260nm. These peaks are attributed to the excitation of the localized surface plasmons that causes strong light scattering by the electric field at a wavelength (260 nm), where resonance occurs. These nanostructures are then conjugated with albumin via a ligand exchange approach to improve its stability in water and protect the integrity of the core.
The capacity of generation of ROS by these size-controlled selenium nanoparticles will be determined and compared to well-known CdSe/S photosensitizer, also conjugated with albumin.

In this work, we developed interconnected network of mesoporous graphene-based electrodes to achieve optimal desalination during capacitive deionization (CDI) of brackish water, attributed to higher specific surface area, electrical conductivity, good wettability of water, environmentally safe, efficient pathways for ion and electron transportation, as potential successor of current filtration membranes. While the pressure driven transport data on highly ordered, continuous, thin films of multi-layered graphene oxide and holey graphene is expected to demonstrate faster transport for salt water, higher retention for charged and uncharged organic probe molecules with hydrated radii above 5Å as well as modest retention of mono- and di-valent salts for ~150 nm thick membranes. The highly ordered graphene nanosheets and nanoscaled porous graphene in the plane of the membrane make organized, molecule-hugging cylindrical and spherical channels, respectively, thus enhance the permeability and hydrodynamic conductivity. The results illustrate that both the mesoscale and nanoscale pores are favorable for enhancing CDI performance by buffering ions to reduce the diffusion distance from external electrolyte to the interior surfaces and enlarging surface area analogous to electrochemical double-layer supercapacitors where in electrical energy storage is through concurrent surface ion adsorption and electron transfer. We determined the salt ion species rejection by composite CDI electrodes by > 65% for actual seawater in one cycle which can be further increased through use of nanoparticles for ion selectivity. This work is supported in parts by KY NSF EPSCoR and WKU Research Foundation internal grant.

Nano-scale patterns have been intensively studied in wide range of fields because they provide enhanced performance or new functions that cannot be observed in macro- or micro-scale patterns. However, conventional nano-patterning process based on lithographic methods have limited wide-spread of nano-patterns due to complex process steps requiring expensive equipment. To fully open the possibility of nano-patterns in various fields, an alternative method is required to fabricate nano-patterns in a facile way that secures significantly improved cost-effectiveness, and versatility allowing large-area fabrication or various form-factors such as fllexbility.Here, we proposed an additive nano-patterning process from solution route using selective-wetting phenomenon in response to such requirements.
The proposed process proceeds to 1) nano-imprinting on to hydrophobic/hydrophilic bilayers and 2) solution dragging. Appropriate post-processes such as annealing can be followed. The former step results in 3D structures consisting of nano-scale engraved hydrophilic parts and embossed hydrophobic parts. Then, by dragging a solution on top of the surface, the solution is automatically confined in the engraved hydrophilic parts without residue on the embossed hydrophobic top surface by selective-wetting phenomenon. The 3D engraved structure is also essential to cause nano-patterns with sufficient amount of target materials. The results verified that the yield of the nano-patterning process is almost perfect once the imprinting onto the bilayer is successful. 150 nm-diameter dot arrays of Ag over the area of 10 cm × 10 cm were successfully fabricated with high yield, and was served as a plasmonic color filter of uniform magenta color. The mechanism of the proposed nano-pattering process was analyzed using fluid-dynamics simulation, and verified control parameters aiming at higher process speed and smaller pattern size.
Virtually, any kind of solutions can be applied to the process, and nano-patterns of Ag, metal-oxide, and organic materials could be fabricated by using a metal-nano-particle ink, a sol-gel solution, and organic solvent. In terms of throughput, the dragging speed of solution could be over 4.5 m/min. The selective-wetting phenomenon also enables self-aligned multiple deposition of nano-patterns, thus allows thickness controllability and multi-layer nano-patterns consisting of different materials. Thanks to the simple and facile process, the proposed method could efficiently make nano-patterns on various substrates including plastics and papers. According to the aforementioned advantages, we believe the proposed process significantly improves the usefulness of nano-patterns in wide range of fields, especially if they require nano-patterns over large-area with various form-factors fabricated by a cost-effective way.

Since the discovery of the colloidal perovskite nanocrystals three years ago, they have rapidly grown to become one of the most promising classes of nanomaterials for large-scale applications in optoelectronic devices. Anion exchange reactions of the highly luminescent cesium lead halide perovskites (CLHPs) provide a facile post-synthetic route for the tuning of the absorption/emission band-gap of CLHPs. These post-synthetic reactions allow the utilization of CLHPs in various optoelectronic applications including third-generation photovoltaic cells and light emitting diodes. Studies of anion-exchange reactions are typically conducted using the time- and material-intensive flask-based synthesis approach. Batch scale synthesis strategies are notorious due to (a) batch-to-batch variation, (b) inefficient and irreproducible mixing timescales, (c) manual sampling and characterization at room temperature, and (d) poor size distribution of the resulting nanocrystals after scale-up. Here, we present a modular multiphase microfluidic strategy with an in situ spectral monitoring capability that enables the systematic kinetic study of anion-exchange reactions of CLHP nanocrystals. Utilizing the microfluidic nanocrystal synthesis platform, we monitor absorption and emission spectra of CLHPs, in real-time, over residence times ranging between 100 ms and 17 min. In-situ monitoring of the optoelectronic properties of CLHPs over different synthesis conditions enables fundamental and applied studies of structural tuning of CLHPs via anion-exchange reactions. The enhanced mixing feature of the multiphase flow along with the novel anion-exchange framework using ZnX2 (X=I or Cl) facilitates on-demand bandgap tuning of high-quality CLHPs (i.e., narrow size distribution with high quantum yield) via a positive feedback loop in which synthesis parameters are varied until the target optoelectronic characteristics are achieved.

Climate change and an increase in endangered species, are examples of technological advances negatively impacting the environment. As technology demands increase, an earnest effort to reduce the environmental impact of processing and manufacturing related activities is critical. From a business perspective, minimizing or removing toxic chemicals from processes, is a high impact area that can increase work environment safety and decrease waste management costs. This work presents processing considerations when transitioning to greener alternative polymer resist solvents, for applications in nanomanufacturing with sustainability considerations. Within government contracting, process modifications that change product form, fit, or function require qualification and at minimum justification. This work presents the conversion from a chlorobenzene to anisole based solvent using a 495 kMW polymetheyl methacrylate polymer resin, without impacting form, fit, or function of the intended device. Resist conversion is of interest as the difference in the substituents of the two solvents, impact the effective toxicity of the materials. Specifically, the oral median lethal dose (LD₅₀) for chlorobenzene is 1110 mg/mL, while anisole is 3700 mg/mL. Developing a process that utilizes anisole as opposed to chlorobenzene, addresses this safety concern and contributes to green initiatives worldwide. Within this work, an electron beam lithography fabricated transistor consisting of a source, drain and gate were converted from a chlorobenzene based resist to a process utilizing an anisole solvent; while maintaining process of record specifications. The purpose of this work is to provide a starting platform for individuals seeking to convert from a chlorobenzene solvent to an anisole based resist, for sub-micron lithography steps.

Approved For Public Release #18-1367; Unlimited Distribution

SrTiO₃ has a well-known perovskite crystalline structure and exhibits excellent dielectric, electro-optic and catalytic properties, being the leading candidate in many cutting-edge technological applications. We report here on the rational synthesis of SrTiO₃/TiO₂ nanodimensional heterostructures by using TiO₂ colloidal nanocrystals as sacrificial templates under different reaction conditions, with the main goal of achieving control over the morphology (size, shape), internal structure and surface composition of the resulting nanoparticles. Both the synthesis of TiO₂ nanocrystals and their subsequent conversion into SrTiO₃ were performed using a hydrothermal method. These nanostructures were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrational spectroscopy (Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy) and optical absorption measurements. Various reaction parameters have been finely tuned in order to optimize the reaction conditions. A detailed characterization of the dielectric properties of these nanopowders was carried, revealing that dielectric permittivity has a value around 120 at room temperature with a low loss, which make these nanomaterials desirable for applications in energy storage and as dielectrics. Moreover, the photocatalytic properties of SrTiO₃-TiO₂ heterostructures were analyzed by using dye degradation method under ultraviolet light. An enhanced photocatalytic activity was observed, which can be ascribed to the improved charge separation between photogenerated electrons and holes in conduction and valence bands of SrTiO₃ and TiO₂. Thus, this synthesis strategy of nanoscale heterostructures is useful to develop functional materials with superior efficiency for implementation into functional electrical devices, as well as photocatalysts.

In the last three decades, solid oxide fuel cells (SOFCs) have garnered significant interest for viable alternative energy systems owing to their high electrical efficiency and fuel flexibility. In this work, we introduce a novel synthesis of cathodes in SOFCs, wherein oxygen reduction occurs in two steps—adsorption and electronation, and surface/bulk diffusion to incorporation sites. Transition metal oxides such as strontium-doped lanthanum manganite (LSM) and strontium-doped cobalt iron oxide (LSCF) have been used as cathode materials, however both individually lack the key characteristics to successfully complete oxygen reduction. Furthermore, the accumulation of chromium (chromium poisoning) on SOFC cathodes is known to significantly hinder the performance of the cells. Incorporating core-shell composites as the cathode material could alleviate this problem: effectively combining the functionalities of both materials and providing a nanoscale protection from Cr poisoning with a shell such as Cr-doped LSM (LSCM). Core-shell oxide composites have broad applications in fuel cells, catalysis, magnetic devices, spintronics, nanophotonics, and many more fields. However, synthesizing core-shell composites previously has proved difficult requiring multiple steps, resulting in non-uniform core-shell structures. In this work we propose utilizing a molten salt synthesis process to create core-shell composites with precise composition with relative ease. The core is synthesized using high-temperature calcination and ball milled with the precursors of the target shell material. The milled powder mixtures are added to a LiCl-KCl eutectic melt to form core-shell hetero-structures via heterogeneous nucleation. Prior results have shown the successful formation of LSM and LSCF using the molten salt synthesis, along with the formation of core-shell LSCF-LSM hetero-structures. Synthesis temperatures dropped from the conventional 1000 ^οC to 500 ^οC, with dwell times as low as 10 minutes. Furthermore, SOFC cathodes consisting of LSCM were found to have stable polarization resistances, whereas the polarization resistance in LSM cathodes steadily increased. This result provides a strong motivation to further explore LSCM as a shell for core-shell cathodes to ensure protection from chromium poisoning. In essence, this work demonstrates an inexpensive, sustainable method to synthesize core-shell cathodes that can simultaneously provide high power densities and low rates of degradation arising from Cr-poisoning.

Paper electronics is receiving great interest because it is one of the best candidates for next generation devices with many useful features such as low cost, disposability, and flexibility. In this work, we demonstrate the fabrication of zinc oxide nanowire (ZnO NW) field-effect transistors (FETs) on paper with facile, low-cost and large area manufacturing. This was achieved using the high absorption property of paper. By absorbing silver nanowire (AgNW) solution into the paper, AgNW network formed on the paper surface that acts as a gate electrode with low sheet resistance (9±5 Ω/sq) and low RMS roughness of 120±20 nm. Then, a dielectric layer was deposited by injecting poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) solution on top of the gate. This enabled precise control of the dielectric layer thickness by controlling the concentration of the solution according to pore size of the paper. As a result, a uniform thin dielectric layer of less than 10 mm was formed. The ZnO NWs were self-assembled on a dielectric layer by a simple dipping and pulling method. Afterwards, electrodes were formed via inkjet printer. The all solution-processed flexible FETs on paper exhibit electrical performance with charge carrier mobility of 0.1 cm² V^-1 s^-1, and current on/off ratio of 2×10³. Furthermore, even after 100 bending cycles, only a 10% decrease in mobility was observed. By utilizing simple equipments such as a vacuum chamber and a syringe pump alone, we could produce outstanding FETs that are desirable for cheap flexible electronic applications.

Europium Titanate is one of the most interesting materials used in various applications such as sensors, memory devices and energy storage. Its unique features are due to its rich properties, mostly in the area of magnetic properties, which is a result of its seven unpaired spins in its 4f orbital.
There are several methods in order to synthesis Europium Titanate compounds, most of which are among solid state reactions. In this work we have synthesized Europium Titanate compounds both in Perovskite and Pyrochlore crystal structure using gel-collection method. This method is based on the sol-gel transition of metal alkoxide in alcohol, controlled by water. Followed by hydrolysis, the crystallization process initiates to give a fully crystalline material. Despite the solid state reactions, the gel-collection is a simple, green and high yield process producing uniform and aggregate free nanocrystals.
The synthesized material was heat treated both in air and in Argon. XRD of the samples heated in different temperatures indicated interesting results. A dramatic change observed in X-ray diffraction at 750°C indicates a dramatic transfer from amorphous to crystal. While the heated samples in air proved to be pyrochlore structure with interesting electrical properties which make them good candidates as dielectric materials, the sample heated in tube furnace indicates a perovskite structure.
In conclusion we could make europium titanate both in perovskite and pyrochlore structure using the gel-collection method. PDF analysis was done and proved that our perovskite structure is likely to be cubic pm3m, while our pyrochlore structure is in good agreement with the refinement for cubic Fd3m.

V-VI-VII compounds are semiconductor materials consisting of elements from group V, VI and VII of the periodic table. These materials usually consist of at least one metal, one chalcogen and one halogen. The recent discovery of BiSI and SbSI as efficient solar cell materials has stimulated research interest from different disciplines to explore various interesting (opto-)electronic properties and applications for V-VI-VII materials.
Traditionally, V-VI-VII compounds are synthesized at high temperature following an elemental reaction/flux method using specifically designed and dedicated experimental apparatuses. Unfortunately, both the solid state as well as solution phase synthesis suffers from the formation of V-VI and V-VII phase binary products and phase pure material can only be synthesized under specific experimental conditions. Simultaneously, specific precautionary/safety conditions are required, making the synthesis of these systems only accessible to experts.
In order to further study of these materials in terms of applied, as well as fundamental research, the development of a robust synthetic methodology is therefore highly desirable. Specifically, a low temperature solution based synthesis route with easy-to-handle precursors will open u