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 up lots of research possibilities and will facilitate potentially more widespread practical uses in the future.
Herein we report a low cost, energy efficient and less time-consuming solution-based synthesis of nanoparticles of various compositions in V-VI-VII materials using Bismuth-Sulfur-Iodine as the model system. In addition to separate precursors for all the required constituent elemental precursors, we have also employed a molecular precursor approach and summarized results will be presented. Synthesized nanoparticles can be dispersed well in organic/aqueous solvents and deposited in the form of homogeneous thin films. Electronic devices such as diodes, transistors and solar cells are used for a comparative study of the electronic transport properties of the synthesized materials.

Silicon nanocrystals have attracted increasing attention as light emitting materials, luminescent downshifters, and imaging sensors. Among various quantum dot materials, silicon is earth abundant, biocompatible, and has low toxicity compared with group II-VI and III-V materials. Nonthermal plasma synthesis has been successfully applied for production of quantum confined, luminescence silicon nanocrystals with narrow size distribution. However, the relatively low luminescence efficiency of silicon nanocrystals will limit their use as light emitting materials. Engineering of silicon nanocrystal surfaces is usually necessary for enhanced luminescence performances, and this is typically done by functionalization of silicon surfaces with organic ligands.
In this work, we develop an all gas-phase synthesis route that integrates nonthermal plasma synthesis, plasma-assisted functionalization and in-flight heating within one flow stream. In this approach, ligands are attached to nanoparticle surfaces in the plasma afterglow, after which the gas stream carrying nanocrystals enters a tube furnace. With the appropriate furnace temperature, the as-produced silicon nanocrystals have photoluminescence quantum yield exceeding 20%. This is a five-fold increase relative to the case when no in-flight heating is applied. We attribute the enhanced photoluminescence to a reduction of dangling bond densities and a change of surface silyl species composition associated with heating. Compared with colloidal synthesis methods, the all gas-phase approach eliminates the use of solvents, produces no by-products, and has higher process yields. With gas-phase deposition methods, silicon nanocrystals can be directly deposited as nanocrystal thin films with densities approaching the theoretical limit of random close packing. We further demonstrate that it is feasible to control the average interparticle distance in nanocrystal films by using ligands with different lengths for functionalization.
This work was supported by the DOE Energy Frontier Research Center for Advanced Solar Photophysics.

In the recent years, focus on the nanoparticle synthesis has shifted towards the clean and eco-friendly methods, for: simple, cheap, nontoxic, reusability and ecofriendly green chemical synthesize. Here, a novel, environmentally benign method for the FeCrO₃ and NiO nanoparticles is reported by using the gelling property of biopolymer pectin. The prepared powders are calcinated at different temperatures, from Transmission electron Microscope (TEM) analysis revealed the 300⁰C calcinated has the particle size of ~ 6 nm and uniformly distribution spherical shape nanoparticles. For the 500⁰C particle size was ~ 36 nm, UV-Vis spectroscopy confirmed the narrowing of the band gap for the nanoparticle. The proposing method is highly reproducible and simple for the preparation of the nanoparticles.

Controlled fabrications of porous nanostructured materials are pivotal for studying structure-property and performance relationships in energy storage and conversion devices. Regardless of great success, fully tunable nanostructures are remains elusive based upon block copolymer self-assembly. Fundamental studies of structure-performance relationship in energy devices require tunable materials with architecture control where one can tailor pore size and wall-thickness independently. A unique kinetic-controlled self-assembly based approach, termed as persistent micelle templating (PMT), recently reported establishing a custom-made block copolymer structure-directing agent, poly(ethyleneoxide-block-hexyl acrylate) and a solution processing guideline where the kinetic rates are regulated by adjusting cosolvent amount. It directs to formation of nanostructured materials with tunable 6-9 nm wall-thickness with ~2Å precision and constant pore diameters of 13 nm with a wide range of inorganic material addition. Also, interestingly, the nanoscale morphology remains constant throughout the addition of various amounts of inorganics. This approach launches a new era to fine-tune small architectural feature limiting micelle chain exchange. However, the excessive amount of cosolvent may cause the formation of secondary pores into the material wall. This is addressed by improving the PMT approach via adding major solvents of higher Hildebrand solubility parameters (δ) and minimizing the cosolvent amount. This new approach not only avoids the formation of secondary pores, it also expands the PMT window tunability. PMT control with a range of solvents will be presented here.

We are now proposing low temperature sintering copper fine particle systems. Usually, in order to sinter metal components at very lower temperature than melting temperature, nano-sized objects are frequently used. Nanoparticles or other nano-sized objects show melting point depression, which are often used for low temperature sintering. Gold and silver nanoparticles have been proposed for low temperature sintering printed electronics materials. However, they are noble metals and these materials are very expensive. Therefore, low temperature sintering system of copper is eagerly desired. However, since copper is easily oxidized even under air, its surface is necessary to be coated with organic materials and inorganic materials to prevent oxidation, so even if stable copper nanoparticles are prepared, their sintering temperature cannot be lowered according to the passivate layer. Therefore, in order to perform low temperature sintering of submicron copper fine particles, we attempted to prepare the surface stable state of specially designed copper fine particles. Detailed discussion will be done at the site.

Noble metal nanostructures have been extensively investigated owing to their morphology-dependent physical and chemical properties. In particular, a number of synthetic methods have been developed to prepare the nanostructures with various shapes and sizes. Generally, template-assisted growth methods have been widely used to synthesize the noble metal nanostructures because the morphology of the template can easily determine the shapes and sizes of the replicated nanostructures. Therefore, controlling structural properties of templates is essential to synthesize the replica metallic nanostructures having desired physical and chemical properties. Especially, nanometer-sized silver halide templates have been conventionally replicated into gold and silver nanostructures, and demonstrated excellent photocatalytic properties under visible light irradiation. In fact, the silver halide nanomaterials hardly generate hot electrons under visible light because of their wide band gap, which is a crucial disadvantage as visible light photocatalysts. On the other hand, the gold or silver metal nanoparticles on the surface of the silver halide templates can absorb light using localized surface plasmon resonance (LSPR), which consequently results in the generation of hot electrons in the silver halide templates. In spite of the aforementioned advantages of silver halides over conventional TiO₂ catalysts, limited morphologies of the silver halide templates are hurdles for many applications. In this work, we present our systematic investigation of key factors to control shapes and sizes of AgCl templates, and demonstrate their replicated noble metal nanostructures. Not only the mole ratio of silver ion and chloride ion, but also the concentration and molecular weight of polyvinylpyrrolidone (PVP) dominantly affect the shape and size of the AgCl nanotemplates. To precisely figure out the components, we analyzed several metallic replica nanostructures with different shapes and sizes using energy dispersive x-ray spectrometer. In addition, the surface-enhanced Raman scattering (SERS) properties of the replicated metallic structures were observed, which was additionally supported by theoretical simulation. Importantly, the synergistic effect of gold and silver was determined to be crucial for the SERS activity. Finally, we demonstrated the shape-dependent photocatalytic properties of the noble metal replica nanostructures under visible light for the removal of Cr(VI), which would be highly important for the environmental applications.

Semiconductors are important materials for a wide range of scientific and industrial applications.^1-4 Continuous effort are made to improve limitations in their electronic, optical and magnetic properties.^5-7. These properties are dependant on chemical composition, the type and method of synthesis. Doping – an intentional introduction of impurities (dopant) into the semiconductor (host) is often used to improve properties. The optical properties can also be tuned by introducing different impurity atoms, the concentration of these dopants determine the degree to which the band gaps are tuned.
In this work, imidodithiodiphosphinates complexes of Mn(II), Zn(II) and Pb(II) were synthesised and used deposit metal sulfide materials using melt reactions. Controlled doping of Zn²⁺ and Mn²⁺ into host PbS was carried out between 2 to 12 percent. Peak shifts in XRD and Raman indicated successful doping. The P-XRD peaks of the Mn²⁺ doped PbS shifted towards lower 2θ angles while that of the Zn²⁺ doped PbS shifted towards higher 2θ angles. The cubic structure of the PbS phase was not altered even at high dopant concentration.
References
1. B. Ferguson and X.-C. Zhang, Nature materials, 2002, 1, 26.
2. S. Wolf, D. Awschalom, R. Buhrman, J. Daughton, S. Von Molnar, M. Roukes, A. Y. Chtchelkanova and D. Treger, Science, 2001, 294, 1488-1495.
3. A. Facchetti and T. Marks, Transparent electronics: from synthesis to applications, John Wiley & Sons, 2010.
4. T. Y. Edward, III-V nitride semiconductors: Applications and devices, CRC Press, 2002.
5. W. Walukiewicz, Physica B: Condensed Matter, 2001, 302, 123-134.
6. D. A. Drabold and S. K. Estreicher, Theory of defects in semiconductors, Springer, 2007.
7. D. Redfield, Phys. Rev. Lett., 1971, 27, 730.

Two- and three dimensional arrangement of magnetic nanoparticles (NPs) enables us to control the magnetic properties and novel functions since the magnetic properties of the NPs are affected by the interparticle interactions. Liquid crystalline dendritic molecules are representative organic materials with self-assembling property by the change in the temperature. In our previous studies, ^1,2) precise modification of liquid crystalline dendrons on the surface of the functional NPs enables us to introduce self-assembling and dynamic structure-changeable abilities into the NPs.
In the present study, we focused on Fe₃O₄ NPs to introduce the dynamic functions into the NPs by the surface dense modification by the liquid crystalline dendorn.
The Fe₃O₄ NP-cores were synthesized by the thermal decomposition method in the presence of oleic acid and oleylamine as ligands. Then, oleic acid and oleylamine on the particle surface were changed to phosphonic acids by the ligand exchange reaction, followed by the introduction of the carboxyl group onto the NPs surface. In this case, dodecylphosphonic acid (DPA) and carboxyl group-terminated 16-phosphonohexadecanoic acid (PHDA) were used as a ligand. From the TEM observations, particle mean diameter of the phosphonic acid modified Fe₃O₄ NPs was assigned as 7.1 ± 0.4 nm. It is to be noted that the interparticle distance was controlled to 9.0 ± 0.8 nm and that the phosphonic acids were bound to the surface of Fe₃O₄ NPs, confirmed by the absorption at 1070 cm^-1 due to Fe-O-P bond. In addition, the ligand exchange was successfully performed with high efficiency because any peaks of oleic acid were not detected.
After modification by DPA and PHDA, amidation between carboxy group of NPs and amide group-containing dendron was carried out to obtain Fe₃O₄ NPs with double layers structure in which the inner was phosphonic acids and the outer dendron. The amount of COOH groups on the particle surface was controlled by change in the molar ratio of DPA and PHDA in feed. At the same time, the modified density of the dendrons layer was brought to form an ordered NPs array. FT-IR profile of the dendron-modified NPs showed the absorption at 1645 cm^-1 derived from the amidation bond between surface of Fe₃O₄ NPs and dendron. Further, TEM images exhibited interparticle distance increased to 11.6 ± 1.5 nm under well-ordered two dimensional array at the ratio of DPA and PHDA as 4 : 1. It indicated that self-assembling property was added to Fe₃O₄ NPs by modification with liquid-crystalline dendrons. In conclusion, the modification by liquid crystalline dendron have successfully enabled Fe₃O₄ NPs to control to give the ordered array.

References
1) K. Kanie, M. Matsubara, X. Zheng, F. Liu, G. Ungar, H. Nakamura, A. Muramatsu, J. Am. Chem. Soc., 134, 808 (2012).
2) M. Matsubara, W. Stevenson, J. Yabuki, X. Zeng, H. Dong, A. Muramatsu, G. Ungar, K. Kanie, Chem, 2, 860-876 (2017).

Patterned metal film is an inevitable component for wide range of electronic devices, and it is fabricated by standard photolithography and vacuum deposition methods in general. These conventional fabrication methods have achieved tremendous success to date, but also possess a number of limitations such as requirement of high vacuum environment, high processing temperature and the use of toxic chemicals. As a consequence, the need for alternative method is growing continuously in the area of low cost, large area electronics in particular.
Regarding this matter, selective laser sintering (SLS) of silver (Ag) nanoparticle (NP) ink has been reported recently to create metal pattern through all-solution process in low temperature and non-vacuum environment. In the previous studies, Ag NP ink is firstly coated on the target substrate and selectively sintered to create continuous metal patterns at micron scale by utilizing the focused laser as a localized heater, while the other NPs are removed by a simple cleaning procedure with the solvent. The entire process can be conducted in a relatively low-temperature owing to the melting temperature depression of the Ag NP from its size effect. However, despite these advantages, SLS process is often not compatible to highly dense patterns due to its direct writing nature: the processing time increases proportionally to the pattern density.
In this study, instead of the previous additive SLS process which turns Ag NP ink into conductive layer upon the scanning, we introduce subtractive laser patterning of Ag NP ink that removes the Ag NP ink selectively based on the thermocapillary effect for high density metal patterns. The laser-induced thermocapillary effect was already examined in the previous studies on the SLS process of metal nanoparticles, but it has been considered as unwanted phenomenon since the thermocapillary flow either displaces the NP ink to the sides or create secondary microstructures such as elevated rims. In contrast, we utilize more drastic laser-induced thermocapillary effect in order to thrust Ag NP out of the laser scanning path entirely.
According to our experimental results, the most significant parameter in the subtractive laser patterning of Ag NP ink is its coating condition. Coating condition changes the thickness, the viscosity, which are highly related to the physical events that happen during the laser irradiation including sintering, evaporation and thermocapillary flow. At the optimum spin coating condition of 500 rpm for 300 seconds, we found that the Ag NP ink is selectively removed from the scanning path of the focused laser beam at 0.3W power and 1mm/s speed with the smallest amount of heat affected zone. Through the proposed method, two types of negative photomask – single slit and alphabetic letters – which are difficult and time-consuming to achieve with the conventional SLS process are created successfully and tested through optical means.

In the last a few years, research using water-borne organic semiconductor nanoparticles (NPs) has intensified as an eco-friendly route to electronic materials without toxic chlorinated-solvents. The water-processable NPs are so far the most environmentally friendly outcome. In syntheses of the NPs, typically sodium dodecyl sulfate (SDS) is used as a surfactant. However, they suffer limited charge carrier behavior particularly for the charge separation owing to their confined structure, a randomly blended core of p- and n-type materials surrounded by a surfactant shell. To overcome this phenomenon, we introduced a new surfactant, PC60, which comprises an n-type semiconducting fullerene molecule grafted with a polyethylene glycol (PEG) chain. We found that the PC60 has a spherical micelle structure with double-layer formation, which allows specific shell structure in the heterojunction NPs. Consequently, unique p-n heterostructured NPs with precisely phase-separated core (p-type)-shell (n-type) morphology were obtained when combined with p-type semiconducting polymer, and they showed superior photo-induced charge separation characteristics. Furthermore, we could control the shell morphology of the NPs through one- or two-phase methodology, and the resulting water-borne NPs showed not only shell-morphology-dependent carrier quenching effect but also ultra-stable colloidal property under thermal- and long-term conditions. Out NPs, thus, can open up and provide a new paradigm in the current fields of water-based organic semiconductor colloids.

Ternary III-V semiconductor alloys, such as InGaP and AlGaAs, play vital roles in many nanoelectronic, optoelectronic, and photovoltaic devices. However, these materials are often plagued by a variety of nanomanufacturing difficulties that stem from either detrimental or incompatible top-down etching, or expensive bottom-up growth techniques. Here, low-cost, high-throughput, and lean nanofabrication processes are demonstrated via metal-assisted chemical etching (MacEtch), with the potential to revolutionize wafer-scale III-V nanomanufacturing. Specifically, novel Au-catalyzed etching approaches are defined for fabrication of suspended InGaP nanofoils and ordered arrays of AlGaAs nanopillars. MacEtch methods show promise as robust, solution-based alternatives for fabrication of high aspect-ratio nanostructures with smooth surfaces. These methods rely on catalytic oxidation of a semiconductor directly beneath a metal catalyst layer, followed by site-specific dissolution of the selectively oxidized material. MacEtch techniques combine many of the advantages of other top-down etching approaches, such as the anisotropic nature of reactive ion etching (RIE), and the fabrication simplicity and cost-efficiency of conventional wet chemical etching. Additionally, many of the corresponding disadvantages are not present, including surface damage from high-energy ion bombardment and use of hazardous gases associated with RIE, and the crystallographic dependences or isotropic nature of traditional wet etching. While MacEtch research has been predominantly focused on silicon processing, these techniques have been recently adapted to overcome fabrication challenges associated with III-V nanomaterials synthesis. In this work, Au-enhanced inverse-MacEtch (I-MacEtch) of heteroepitaxial InGaP/GaAs systems is presented, and differential etch rates between epilayer and substrate are exploited as a viable method to produce suspended III-V nanofoils. A comparison of vertical etch rates (VER) between nominally undoped, p-type, and n-type InGaP is detailed, showing VER in the I-MacEtch regime is independent of doping type. Au-enhanced I-MacEtch of AlGaAs is also demonstrated, and the VER and lateral etch rates (LER) are shown to be tunable with Al fraction and etching temperature. Control over the VER/LER ratio allows for etch conditions to be tailored to provide ordered AlGaAs nanopillar arrays with predefined aspect ratios. The work detailed here provides efficient means to customize nanomanufacturing processes for specific needs, such as tuning MacEtch process parameters to achieve a desired ternary III-V nanostructure geometry. It is anticipated that these processes can be utilized for adaptable and versatile manufacturing of nanomaterials for LEDs, lasers, HEMTs, and multijunction solar cells applications.

Earthquakes are lethal natural disasters frequently burying people alive under collapsed buildings. Tracking entrapped humans from their unique volatile chemical signature with hand-held devices would accelerate urban search and rescue (USaR) efforts.¹ Here, a compact and orthogonal sensor array has been designed to detect the breath- and skin-emitted metabolic tracers acetone, ammonia, isoprene, CO² and RH, all together serving as sign of life. It consists of three nanostructured metal-oxide sensors (Si-doped WO₃², Si-doped MoO₃³ and Ti-doped ZnO⁴), each specifically tailored at the nanoscale for highly sensitive and selective tracer detection along with commercial CO₂ and humidity sensors. When tested on humans enclosed in plethysmography chambers to simulate entrapment, this sensor array rapidly detects tracers of human presence with low parts-per-billion (ppb) level accuracy and precision, unprecedented by portable detectors but required for USaR.⁵ These results were validated by bench-top selective reagent ionization time-of-flight mass spectrometry (SRI-TOF-MS). As a result, an inexpensive nanostructured sensor array is presented that can be integrated readily into hand-held or even drone-carried detectors for first responders to rapidly screen affected terrain.

[1] Mochalski, P.; Unterkofler, K.; Teschl, G.; Amann, A., Trac-Trend Anal Chem (2015), 88-106.
[2] Righettoni, M.; Tricoli, A.; Gass, S.; Schmid, A.; Amann, A.; Pratsinis, S. E., Anal Chim Acta (2012), 69-75.
[3] Güntner, A. T.; Righettoni, M.; Pratsinis, S. E., Sensor Actuat B-Chem (2016), 266-273.
[4] Güntner, A. T.; Pineau, N. J.; Chie, D.; Krumeich, F.; Pratsinis, S. E., J. Mater. Chem. B (2016), 5358-5366.
[5] Güntner, A. T.; Pineau, N. J.; Mochalski, P.; Wiesenhofer, H.; Agapiou, A.; Mayhew, C. A.; Pratsinis, S. E., Anal Chem (2018), 4940-4945.

TiO₂ has attracted much attention because of potential applications in photocatalytic degradation of pollutants and hydrogen generation. TiO₂ deposition on organic templates has been regarded as a feasible route to fabricate TiO₂ nanostructure catalyst. Compared with conventional deposition methods, atomic layer deposition (ALD) can improve the catalytic properties of TiO₂ nanostructures because of the conformal coating behavior and precise thickness control. Therefore, it is worthwhile to develop low-temperature ALD for growing TiO₂ nanostructures by using organic templates. Previously, we found that the TiO₂ nanotubes prepared at low temperature contained residual chloride from the ALD reaction using TiCl₄ and H₂O precursors. The existence of residual chloride would lead to a lower efficiency of catalytic reaction. In this study, a chlorine-free and low-temperature ALD process was developed to grow TiO₂ films. H₂O and tetrakis(dimethylamino)titanium (TDMAT) were used as the co-reactant and titanium precursor of TiO₂ ALD, respectively. Each cycle consisted of a precursor pulse for 0.1 s and a purge with N₂ for 10 s. The growth rate of TiO₂ prepared by ALD at 110 ^oC is 0.06 nm/cycle. The growth rate of TiO₂ would decrease to 0.053 and 0.043 nm/cycle at a growth temperature of 150 and 200 ^oC, respectively. The appearance of hydrocarbon residue in the X-ray photoelectron spectroscopy (XPS) reveals that the low process temperature of ALD would result in incomplete reaction of TDMAT.

Zinc oxide (ZnO) films, as well as Ag-doped, Ni-doped, and (Ag,Ni) co-doped ZnO thin films were grown on glass substrates using pneumatic spray pyrolysis. Zinc acetate, silver nitrate, and nickel acetate were used as precursors. Ni doping was performed for the atomic concentrations 1, 3, 5, 7%. Silver doping was carried for the atomic concentrations 1, 3, 5, 7 and 9% (until the solubility limit). Ag-Ni co-doping was executed by various combinations of Ag and Ni concentrations (5:5, 5:9, 7:9 at.%). The fabricated films were further characterized to understand the structural and morphological properties. The structural and morphological studies showed that films were of polycrystalline and grown with nanostructures like nanospikes, nanocombs, hexagons and trigonal flakes, respectively. Photocatalytic activities of these films were tested using a solar simulator lamp on indigo carmine dye (which is being used widely in textile and cosmetic industries). The photocatalytic results were analyzed using UV-Vis spectra. The degradation of peaks of indigo carmine behaved differently with respect to the films with different dopants conditions. The 100% discoloration of indigo carmine occurred for Ag-Ni co-doped ZnO thin films in less than one hour, whereas the Ag-doped ZnO, Ni-doped ZnO, and undoped ZnO achieved only 30-50% of discoloration in one hour. In this work, we propose the possible degradation mechanism of indigo carmine dye with respect to dopants type and their concentration.

Semiconductors quantum dot (QDs) are fluorescent nanocrystals with a ranging diameter of 2 nm - 10 nm. Due to their intrinsic optical properties, which are dependent of their size, these nanoparticles have many industrial and bio-medical applications e.g. bio-imaging, diagnostic, LED’s (light emitting diode) production, and photocatalyst of organic compounds. More recent applications are based on their potential use as photosensitizer to generate cytotoxic reactive oxygen species (ROS) when activated by light. The factors that govern the cytotoxicity associated to the generation of ROS include the particle size, shape, surface chemistry, the presence of lattice defects, degree of aggregation, among others. Based on these considerations, the present work was focused on: (i) the development of a synthesis protocol of water dispersible pure and doped ZnS-based QDs, (ii) modify their surface chemistry with biocompatible molecules and, (iii) evaluate their potential capacity to generate ROS under light irradiation. QDs were synthesized in water using a microwave reactor system under controlled temperature and reaction time in presence of 3-mercaptopropionic acid (MPA) as sulfide supplier. ZnS QDs were also doped with Mn²⁺ or Cu²⁺. As-synthesized ZnS QDs, as evidenced by XRD, were optically characterized by X-ray Diffraction (XRD), HRTEM, UV-Vis and Photo-luminescence spectroscopy techniques. UV-Vis analyzes evidenced the presence of excitonic peaks around 310 nm, 314 nm and 315 nm for ZnS, Cu-ZnS and Mn-ZnS, respectively. The band gap energy of the pure ZnS QDs was estimated at 3.70 eV that indicates a strong quantum confinement effect, as evidenced by this high value compared to the bulk (3.54 eV). In addition, the photoluminescence analyses of the QDs showed a strong emission peak (438nm for pure ZnS) that was red-shifted when Mn²⁺(487nm) or Cu²⁺ (521nm) were used as dopant species. The incorporation of these transition metals into the ZnS lattice should have created new intermediate energetic levels between the valence and conduction bands of the ZnS particle. The effect of doping on the crystal size and the corresponding capacity of ZnS-based QDs to generate ROS, via the photo-degradation of specific organic dyes, will also be presented and discussed.

Sodium titanate nanomaterials (nanotubes, nanorods and nanobelts) synthesized by the Kasuga method have already been tested as catalysts for biodiesel production from vegetable oil and methanol giving good results. In the present work, we modified sodium titanate nanotubes (STN) by the addition of different amounts of sodium carbonate in order to increase their basicity and, consequently, improve their performance in the transesterification reaction. Catalysts with sodium carbonate loadings between 1 and 10 wt. % were prepared. Hereinafter, these catalysts will be denoted as STN-x, where x represents nominal Na₂CO₃ weight loadings in the samples. Synthesized catalysts were characterized by N₂ physisorption, X-ray powder diffraction (XRD), FT-IR, scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM), and CO₂ temperature-programmed desorption (CO₂-TPD). The STN reference had high sodium content (10.3 wt. %) and attractive textural characteristics (surface area of 222 m²/g and pore volume of 0.46 cm³/g). Addition of sodium carbonate to STN resulted in a slight decrease in the specific textural characteristics of the STN materials. However, all of them maintained a characteristic nanotubular structure and showed the presence of only the sodium trititanate crystalline phase (Na₂Ti₃O₇). No agglomeration of sodium carbonate was detected by XRD. Addition of sodium carbonate to the STN allowed us to obtain 1D nanostructured materials with a higher amount of sodium, which resulted in an increase in the total amount of basic sites and especially in the proportion of strong basic sites. Thus, STN-3 and STN-5 materials had about 18 – 19 % of strong basic sites, which represents a noticeable increase in comparison with the starting STN reference (13 % of strong basic sites). Catalytic activity tests were performed in transesterification of soybean oil with methanol. Reactions were performed in a batch reactor, at 80 ^oC, 1 h reaction time, 1 wt. % of the catalyst, using methanol:oil molar ratio of 20:1. The best results were obtained with the catalysts containing 3 and 5 wt. % of sodium carbonate, which gave methyl esters (ME) yields of 90-91 %. In the same conditions, the reference STN catalyst resulted only in a 53 % of ME yield. Such a strong increase in the catalytic activity of Na₂CO₃-containing sodium titanate nanotubes was attributed to a sinergetic effect between the impregnated sodium salt and 1D nanostructured STN material.

During the last years, an enormous variety of nanomaterials with different shapes and compositions have been developed for a broad range of applications including optics and electronics but also for their employment in health care and foods. However, many of these fabrication processes still rely on the employment of toxic and environmentally hazardous substances, offering potential risks to manufacturers and customers. Therefore, alternative synthetic procedures are focus of current research to allow for the synthesis of nanomaterials under the important aspects of biosafety and environmental compatibility.
Herein we report a green and facile one-pot synthesis for the preparation and in situ functionalization of water-dispersible and biocompatible iron oxide nanoparticles (IONPs) for their employment as contrast agents for magnetic resonance imaging (MRI). Two classes of naturally available nutrients namely ascorbic acid (vitamin C) and green tea were employed. In the first approach, easily water-dispersible crystalline IONPS were produced in a hydrothermal synthesis using ascorbic acid as reducing agent whereby the oxidation product instantly formed a protecting and stabilizing layer around the particles. As-obtained particles were not only highly biocompatible, but demonstrated enhanced r2/r1 ratios compared to the clinically approved contrast agent Sinerem. In this context we further developed the synthesis of iron oxide nanoparticles using green tea catechins. Green tea is a promising material which additionally exhibits beneficial antioxidative, anticancer and anti-inflammatory effects. Similar to vitamin C, green tea functionalized IONPs were long-term stable in water and highly biocompatible. Moreover, in vivo studies revealed accumulations of the particles in tumor tissues similar to clinically approved contrast agents. Indeed, a strong contrast enhancement was visible based on high relaxivity values, which further support their employment as novel MRI contrast agents in clinics.

Platinum (Pt) based catalysts are widely used in petrochemical refinery, automotive emission control, and fuel cell applications (1). However, the catalytic activity of Pt nanoparticles (NPs) catalysts tends to decrease drastically as a result of the loss of active surface area via sintering at high temperature (2). TiO₂ is an earth-abundant and chemically stable material and has been extensively studied as support for Pt-based catalysts (3). However, for the precursors of TiO₂, such as layered protonated titanates (LPTs), the sintering resistance effects on noble metal NPs are not well studied. The high surface area and cation exchange capacity of LPT make it the ideal supports for catalytically active materials (4). In this work, the promotional effects of the support structures on the hydrothermal stability of the TiO₂ nano-array supported Pt catalysts were studied. Two types of TiO₂ nano-array supported Pt catalysts were prepared with different initial support structures, namely the anatase TiO₂ and LPT nanowires. Pt NPs were loaded onto both types of supports and went through the same hydrothermal aging at 800 °C for 50h. The evolution of the Pt NPs before and after the hydrothermal aging was studied by scanning transmission electron microscope and CO oxidation was employed as a probe reaction to compare the catalytic performance of these catalysts. According to the microstructural evolution of the Pt NPs and the catalytic activity of the sample before and after hydrothermal aging, the LPT nano-arrays based Pt catalysts showed better hydrothermal stability than the crystalline anatase nano-arrays based ones. The better hydrothermal stability of the LPT nano-array supported Pt NPs might be due to the greater interaction between the Pt NPs and the LPT surfaces formed during the dip-coating process through ion-exchange. The sintering resistance of the Pt NPs is therefore enhanced by the potentially better anchoring effect from the LPT nano-array supports. Considering the wide application of TiO₂ supported Pt catalysts, this new finding may provide a new pathway to design highly stable Pt-based catalysts for different gas phase reactions.
Keywords: Pt-based catalysts; Hydrothermal stability; Layered protonated titanates; Sintering resistance; CO oxidation.
1. H. F. Rase, Handbook of commercial catalysts: heterogeneous catalysts. CRC press: 2000.
2. Y. Nagai et. al., J. Catal. 242 (2006), 103.
3. S. Hoang et. al., Catal. Today 2017, doi.org/10.1016/j.cattod.2017.11.019.
4. Á. Kukovecz, K. Kordás, J. Kiss and Z. Kónya, Surface Science Reports, 2016, 71, 473-546.

Indium phosphide (InP) quantum-dots (QDs) have attracted as most promising luminescent material for developing cadmium-free QD light-emitting diodes (QLEDs). However, the performance such as efficiency, maximum luminance and operational lifetime of InP QLEDs is still far behind that of CdSe QLEDs [1, 2]. This is mainly attributed to unoptimized synthesis of InP QDs and device structure. InP QDs have relatively low electron affinity (EA), so the electron injection barrier is quite large with conventionally available electron transporting materials, thereby resulting in low electron injection [2]. In this work, we will demonstrate that thermal annealing of zinc oxide nanoparticle (ZnO NPs) electron transport layer and the QD emissive layer can lead to enhanced QLED performance. The current density of electron-only devices with ZnO NPs increases and exhibits trap-free space-charge-limited-current (SCLC) characteristics after thermal annealing. Furthermore, the photoluminescence (PL) quantum yield of the QD layer increases with thermal annealing due to increased packing density of QDs, as previously reported [3]. Optimizing annealing temperature of inverted green InP QLEDs results in increased external quantum efficiency from 2.32% to 3.61% and maximum brightness over 10,000 cd/m². The half-lifetime (LT₅₀) at an initial luminance of 1000 cd/m² increases up to nearly 2 hours. Therefore, thermal annealing process can be effectively utilized to optimize the device performance of InP QLEDs.

Reference
[1] Lim J.; Bae W. K.; Lee D.; Nam M. K.; Jung J.; Lee C.; Char K.; Lee S., InP@ZnSeS, Core@Composition Gradient Shell Quantum Dots with Enhanced Stability. Chem. Mater. 2011 23, 20, 4459-4463
[2] Lim J.; Park M.; Bae W. K.; Lee D.; Lee S.; Lee C.; Char K., Highly Efficient Cadmium-Free Quantum Dot Light-Emitting Diodes Enabled by the Direct Formation of Excitons within InP@ZnSeS Quantum Dots. ACS Nano 2013 7, 10, 9019-9026
[3] Niu Y. H.; Munro A. M.; Cheng Y. J.; Tian Y. Q.; Liu M. S.; Zhao J. L.; Bardecker J. A.; Plante I. J. La; Ginger D. S.; Jen A. K. Y., Improved Performance from Multilayer Quantum Dot Light-Emitting Diodes via Thermal Annealing of the Quantum Dot Layer. Adv. Mater. 2007, 19, 3371-3376

We report here the characteristics of PbS formed by bacteria. X-ray diffraction (XRD) measurements and transmission electron microscope (TEM) revealed clear diffraction peaks and lattice fringes, respectively, revealing that the bacteria synthesized polycrystalline PbS. Current-voltage (I-V) measurements showed that the electric current along the PbS increased linearly with increasing applied voltage, and the amount of the current increased with increasing the area of crystalline PbS.
Biomineralization have been actively studied for more than 20 years. It can be performed to form such as magnetite, silica, calcium carbonate, hydroxyapatite, metal particles and so on under ordinary temperature and normal pressure. This can develop material synthesis techniques with low power consumption at low cost. Under this kind of circumstances, microbial synthesis for sulfide semiconductors such as CdS and PbS has been explored in some previous studies. The studies have already demonstrated the formation of nanocrystallite of these sulfide semiconductors by some yeasts. However, it has not been clarified whether they can have crystalline quality that may be applied to the semiconductor devices or not. In this study, we aim to reveal their crystalline qualities and semiconductor characteristics by focusing on PbS towards the future fabrication of the biogenic semiconductor devices.
We established bacterial strains involved in PbS formations and confirmed micro structures and crystalline quality of PbS formed by the bacteria using a X-ray diffractometer and a JEOL JEM-2010 TEM equipped with an energy dispersive X-ray spectroscopy (EDS) system, operated at 200 kV. XRD spectra of the PbS samples exhibited clear diffraction peaks, and there were good agreements with experimental data and theoretical ones of polycrystalline PbS on peak diffraction angles on each crystal plane of PbS. TEM images and EDS analysis for the samples also showed that the materials consisted of Pb and S, and lattice fringes and electron diffraction patters corresponding to crystalline PbS. I-V characteristics were measured using prober after Indium electrodes were formed on the surface of the PbS samples mounted on semi-insulated InP substrate. When the shape of PbS was formed to be spherical nanocrystallites, the amounts of the current were in the range between 0 and 17.5 pA with applied voltage was in the range between -1 and 1 V. On the other hand, the shape of crystalline PbS was changed to be thin film, the amounts of the current were changed to be in the range between 0 and 18.5 μA. The former amounts of the current increased to be 0 - 25.0 pA under light irradiation. These results suggested that the biogenic PbS have bandgaps and it exhibited general fundamental characteristics of the semiconductors.

Accompanied by the fast world population growth, the depletion of energy resources and environmental pollutions have become two major issues that pose serious threats to the survival of human beings. As a clean and renewable alternative, hydrogen has been given special attentions in the past decades and is believed to be a high gravimetric energy density carrier for fuel cells. Nonetheless, most of the hydrogen in earth is still generated through energy intensive industries such as steam reforming which unavoidably makes the energy resource shortage and environmental problems even worsen. In contrast, generating hydrogen in the cathode through water electrolysis is a green chemical route in which pollutant free and zero carbon emissions can be realized. Additionally, the energy sources driving water electrolysis can also be renewable, further making water electrolysis a promising strategy to produce hydrogen. However, the sluggish kinetics and high energy barriers of oxygen evolution reaction (OER) in the anode have largely restricted the overall efficiency of water electrolysis, and thus limited the hydrogen production. Different catalysts have been investigated so far to address the limitations of OER. Iridium oxides, for example, are found to exhibit a great OER activity but the high costs of iridium become the barrier of their large-scale application. Developing inexpensive catalysts is critical but to boost their activity is still challenging, as most of the OER catalysts still require an overpotential around 250 to 300 mV to achieve the geometric current density of 10 mA/cm². In this work, we synthesized Fe incorporated β-Ni(OH)₂ nanosheets on macroporous nickel foam through a facile one-pot hydrothermal method. The as-synthesized Fe incorporated β-Ni(OH)₂ nanosheets are found to be composed of mixed crystal and amorphous structures. Along the boundary of crystal and amorphous structures are enriched defect sites. By virtue of these structural merits and electronic structure modification of Fe dopants, the as-prepared Fe incorporated β-Ni(OH)₂ nanosheets exhibit a low and competing overpotential of 219 mV at a geometric current density of 10 mA/cm², demonstrating a high total electrode activity. In addition, at the overpotential of 300 mV, a electrochemical surface area current density of 6.25 mA/cm² has also been obtained, which represents the highest value among the reported NiFe based OER catalysts at the same or higher overpotentials, indicating its high intrinsic activity.

Literature has many examples of semiconducting materials as photocatalysts for degradation of water contaminants. Despite a large concentration in TiO2 and TiO2-based materials, other semiconductors have gained attention due specific aspects that promote higher photoactivity (e.g., in visible light, reduced electron-hole recombination) but few was done to understand the role of surface acidity in these process. A study-of-case is Nb2O5, which is a wide-band semiconductor, with similar electronic properties to TiO2 but with very acidic surface. This feature indicates that the way that Nb2O5 plays its photooxidative role is different from other semiconductors, depending of the equilibrium of charges in degradation medium. We developed a method to produce this semiconductor through a peroxocomplex formation, which is further de-stabilized in hydrothermal conditions to promote oxide precipitation in a controllable manner. This synthesis, despite very simple, was easily controlled to produce different surface features, as well as heterostructures based on T/TT Nb2O5 phases. This material has showed a considerable photoactivity in UV light for degradation of different pollutants, but also a good versatility: the mixture with g-C3N4 (a polymeric semiconductor) in adequate pH conditions has lead to a self-organized heterostructure, with also remarkable photoactivity. However, these materials did not present only photooxidative activity: measuring their potential for photoreduction, we have observed that modifications with other semiconductors (e.g. CuO) allows this system to promote Cr(VI) reduction and, more interesting, promote the CO2 reduction to CO in significant yields, despite the acidic surface suggest that this reaction would not be favored. Therefore, the knowledge about this material for environmental remediation is now opening other application for this material in renewable energy production, which needs be deeper investigated.


Acknowledgements: FAPESP; CAPES; CNPq; FINEP; National System of Nanotechnology Laboratories – SISNANO/MCTI; Rede Agronano/Embrapa

Investigation of the interplay of metal-organic chemistry will enrich the state-of-the-art of chemical vapor deposition (CVD) and atomic layer deposition (ALD) technology and open new possibilities for the applications of new Ir-based materials. Therefore new heteroleptic Janus-typed compounds exhibiting high volatility and defined thermal decomposition under CVD and ALD conditions are reported to elaborate the precursor chemistry – materials synthesis – functional property chain. The new precursors unify both reactivity and sufficient stability through its heteroleptic constitution to provide a precise control over compositional purity in CVD and ALD deposits. CVD- and ALD-grown materials were tested towards their (electro)catalytic applications, particular in the oxygen evolution reactions. In this work functional characterization of deposited materials will be reported and their catalytic behavior is examined. The deposition on various substrate materials without the need of additional reactant gases underlines the potential of this heteroleptic precursor class for CVD and ALD of metallic thin films. The presented CVD data opens new possibilities in the vapor phase synthesis of materials facilitating the application of such films, for example, as electro- or photocatalyst in oxygen evolution reaction (OER) and oxygen reduction reaction (ORR).

Organic Photovoltaics (OPV) has in recent years emerged as a low cost alternative to silicon photovoltaics. The solution processability of polymer based photovoltaics is particularly interesting owing to her potential scalability at mass printing production compared to her vacuum processed counterpart. Albeit the continuous breakthrough in non fullerene OPV system, which the latest research reported an excellent PCE of > 14% single junction devices, yet the main hurdles of OPV to commercialization has been linked to its lower performance PCE <7% when fabricating the large area OPV module. Clearly, the OPV device cell to modules's loss in PCE is linked to the integration of a suitable solution processable interface layers. The optimization of hole transporting layer is imperative in the inverted device architechure. Here, we report on a newly designed non fullerene OPV system, using low bandgap small molecule Acceptor and a wide bandgap polymer donor and achieved PCE >13% using green solvent and a matching proprietary solution processed hole transporting layer (HTL) to minimize the gap from cell to modules. The proprietary HTL formulations consist of Pedot which is widely used in large area coating for large area OPV module. and a specific additives which serve as the energy bridge between the donor polymer and the Pedot. We achieved PCE>9%, and it is the first time of a complete total solution processed Non fullerene OPV with PCE exceeding 9%. Also, we have completed the environmental reliability tests of such OPV devices stack. i.e. the light soaking, damp heat and humidity freeze tests were made according to IEC61646 which show positive outcomes and strongly echoed that our total solution stack of OPV device could now meet the industry's expectation when coating for large area OPV modules.

There is a constant requirement to diversify the energy matrix due to the socio-environmental and economic impacts caused by the use of fossil fuels. In this context, renewable energies, such as solar cells, stand out as a possible solution to this problem and a good path towards sustainability. In order to make real this possibility, it is necessary to develop or optimized the properties of the structured materials used in this task. In this context, zinc oxide (ZnO) is a promising candidate for solar cells photoelectrode. ZnO is a broadband semiconductor with a band gap of 3.3 eV at 300 K and large exciton binding energy (60 meV). The zinc element (Zn) is extremely abundant on the planet and has high electronic mobility. On the other hand, hematite (α-Fe₂O₃) has been widely used as photoelectrode materials due to its exceptional properties such band gap energy (2.1 eV), maximum theoretical efficiency (12.9%), good electrochemical stability, abundance and non-toxicity. Considering all these aspects, in this work, we present the preparation and characterization of the optical and electrochemical properties of Fe2O3 nanoparticles decorated ZnO particles for future application of photoelectrode in dye-sensitized solar cell (DSSC). A hydrothermal assisted microwave method was used to produce the ZnO and the Fe₂O₃ nanoparticles. After that the ZnO and ZnO/Fe₂O₃ film was produced. A viscose paste of pure ZnO and ZnO/Fe₂O₃ (0,20g/20μmol) was prepared and 80 μL of the paste mixture was placed on FTO (Fluorine doped oxide) substrate and the films was calcined at 400°C for 1h. A typical electrochemical cell system was assembled with 3 electrodes, work (FTO/ZnO; FTO/ZnO/Fe₂O₃ films), reference (Ag/AgCl) and counter electrode (Pt) immersed in an electrolytic solution. The films were characterized by X Ray Diffraction, nitrogen adsorption–desorption isotherms, Linear Sweep Voltammetry (LSV), Chronoamperometry, Scanning Electron Microscopy, Micro Raman and FTIR spectroscopy technics. The microscopy images revels that the Fe₂O₃ nanospheres decorated with extreme efficiency the flower structure of ZnO. A significant increase in the surface area is observed with the addition of the α-Fe₂O₃ in the ZnO flowers and also significantly alters the pore volume of this material. The LSV showed a high current density of the FTO/ZnO/Fe₂O₃ (0,58mA.cm-2) film being superior to the FTO/ZnO (0,16mA.cm-2) film in light condition. The analysis showed that these materials are promising photoelectrode for DSSC applications, characterizing them Fe₂O₃ nanoparticles improving the ZnO photoelectrochemical properties. Simultaneously with this the method that was used to produce the nanoparticles adds to the production process of the same, a methodology that does not require the need for high technology equipment, not have a high energy demand or time to run it and does not generate waste, that is, a highly practical, economically viable and environmentally friendly method.

The performance of concentrating solar power (CSP) receivers is limited by thermal losses, particularly at concentrations <100 suns. Existing CSP receivers rely on spectrally selective surfaces placed within vacuum glass enclosures to minimize heat loss due to radiation and convection. However, using spectrally selective coatings and maintaining a high-quality vacuum at high temperatures (400 °C) increases cost and significantly limits longevity. We have developed a high-temperature solar-transparent thermal insulation that enables high-efficiency heat collection and obviates the need for selective coatings and vacuum in CSP receivers. We use silica aerogels, a class of highly porous (porosity >90%) materials known for their thermally super-insulating properties, which we have engineered to achieve extremely high solar transparency. The optimized aerogel nanostructure has reduced pore sizes of 2-50 nm that minimizes scattering losses at low wavelengths, increasing the solar-weighted transmittance to >95% for an 8 mm thick sample compared to <85% typically reported in literature. The low near-UV scattering, high infrared absorption, and high porosity of our aerogels maximizes solar transmittance and minimizes heat loss due to conduction, convection and radiation, enabling CSP receiver efficiencies >80% even at concentrations <50 suns. In this work, we report the results of optical and high-temperature thermal characterization of the fabricated solar-transparent silica aerogel. We compare experimental results with a numerical model based on the spectral equation of radiative transfer that predicts the optical and thermal properties of silica aerogel. Finally, we model the performance of a linear CSP receiver comprising of our solar-transparent aerogel and optimize its thickness, density and pore-size to maximize receiver efficiency.

Electrochemical supercapacitors are important energy storage devices that bridge the gap between electrostatic capacitors and batteries. A critical component of supercapacitor design is the electrode material. We have been developing electrode materials and fabrication strategies for conventional electrochemical capacitors as well as micro-supercapacitors (in-plane devices fabricated on-chip). Pseudocapacitive materials in particular hold promise of significantly higher capacitance than carbon-based materials and hence have recently become a subject of intense investigations. These materials can store charge through both surface redox reactions and fast intercalation process leading to intercalation pseudocapacitance. We will discuss strategies that we have developed to rationally design pseudocapactive materials, including oxide and chalcogenides. Material structure, conductivity, electrochemical activity, defect concentration, and dimensionality are critical parameters to maximize both ion and electron transport within the electrode material, and hence improve capacitor performance. Selected examples from our work will be presented to show how dramatic improvements in electrode performance can be achieved through rational approaches. For micro-supercapacitors, we also show that collector material type, geometry (e.g., 3D and macroporous structures), and microfabrication techniques can be used to improve the kinetics and capacitance of devices. Recent integration of microsupercapacitors in energy harvesting and sensing devices will also discussed.

Because of the low gravimetric capacity of conventional graphite anode (theoretical value ~ 372 mAh/g), and massive structural changes and volume expansion of silicon anode (on the order of 300%); extensive research has been carried out during last few decades to develop stable and high-capacity anode materials. Moreover, large-volume expansion leads to stress built-up at the interface between the Si film and the current collector, leading to delamination at the interface. We, therefore, examined the possibility of 2D materials for application of high-capacity anode materials. By first-principle calculations based on density functional theory (DFT), we investigated the adsorption of lithium (Li), sodium (Na), and calcium (Ca) on graphene with divacancy and Stone-Wales defects. We find that with controlled defect topology, we can achieve a maximum storage capacity of approximately 1675, 1450 and 2900 mAh/g for Li-, Na-, and Ca-ion batteries respectively. However, despite enormous opportunities, we need to concern about several challenges such as adatom trapping at the defect sites, the effect of defects on adatoms diffusivity, microstructural changes, e.g., mechanical degradation at defect sites, etc. In addition, our recent work shows that for the Si-based anode, we can achieve far better electrochemical stability by simply coating the current