The speciation of uranium bis(trifluoromethylsulfonyl)imide (TFSI) species formed from UI3(THF)4 in butyl-methylpiperidinium bis(trifluoromethylsulfonyl)imide ([BMPip][TFSI]) and [BMPip][TFSI]/HTFSI was investigated by X-ray absorption fine structure (XAFS) spectroscopy. Following the dissolution of UI3(THF)4 in the room temperature ionic liquid (RTIL), X-ray absorption near edge spectroscopy (XANES) indicates that U(III) did fully oxidize to U(VI) in [BMPip][TFSI] while a U(VI)/U(IV) mixture was obtained in [BMPip][TFSI]/HTFSI media. Extended X-ray absorption fine structure (EXAFS) results are consistent with the formation of UO2(TFSI)2(THF)3 in [BMPip][TFSI]. The U-S(TFSI) distance (i.e., 3.81(4) Å) is consistent with the presence of TFSI ligands coordinated to the UO22+ unit in monodentate mode. In [BMPip][TFSI])/HTFSI, EXAFS indicates the presence of UO2(TFSI)2(THF)3 ( 35

Storing uranium hexafluoride, UF6, is challenging due to the high chemical reactivity and volatility. Dissolution of UF6 into the ionic liquid reduces volatility while simultaneously providing stability for the dissolved species. The ionic liquid, 1-methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)imide provides a stable, non-volatile environment for the reactive dissolution of UF6. The oxidation of the bis(trifluoromethylsulfonyl)imide anion (TFSI) to form a radical facilitates dissolution. Spectroscopic analysis indicates the dissolution occurs through the one electron reduction of UF6 to produce the pentavalent UF6− species.

The thermal behavior of (NH4)(2)[ReF6] was evaluated in an alumina crucible using simultaneous thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) in an argon atmosphere. The TGA of (NH4)(2)[ReF6] is characterized by a single step decomposition while the DSC exhibits two exothermic peaks. Powder X-ray diffraction (PXRD) analyses of the decomposition products show the presence of a mixed ReO2 phase. The formation of ReO2 is driven by the reaction of (NH4)(2)[ReF6] with Al2O3 at the grain boundary of the alumina crucible. XRD peak broadenings due to the combined effect of crystallite size and lattice strain were evaluated using both Scherrer and Williamson-Hall methods.

Uranium metal is associated with several aspects of nuclear technology; it is used as fuel for research and power reactors, targets for medical isotope productions, explosive for nuclear weapons and precursors in synthetic chemistry. The study of uranium metal at the laboratory scale presents the opportunity to evaluate metallic nuclear fuels, develop new methods for metallic spent fuel reprocessing and advance the science relevant to nuclear forensics and medical isotope production. Since its first isolation in 1841, from the reaction of uranium chloride and potassium metal, uranium metal has been prepared by solid-state reactions and in solution by electrochemical, chemical and radiochemical methods. The present review summarizes the methods outlined above and describes the chemistry associated with each preparation.

The remediation of radioactive isotopes such as Cs+ and Sr2+ from water has been evaluated using sitinakites. The sorption media employed in the remediation of radioactive wastes must have thermal and chemical stability to be useful. The present study investigates the structural stability and adsorption performance of sitinakites under conditions of elevated temperatures between 50 and 550 degrees C. X-ray diffraction indicates that major structural changes are initiated with heating, reducing the crystallinity of the material. The FTIR results also indicate that simultaneous and irreversible dehydration of the materials occurs with elevated temperatures under the conditions studied. Thermal processing also influences the sorption of Cs+, which decreases rapidly as the temperature increases. Adsorption was reduced by 80% at 550 degrees C for Cs+ , when compared to the material processed at 50 degrees C and neutral pH. In contrast, the sorption of Sr2+ decreases substantially only when the processing temperature reaches 550 degrees C under the same conditions. In addition, the sorption of Cs+ and Sr2+ follow different trends as functions of pH after thermal treatment. The sorption of Cs+ decreases as a function of increased processing temperature and higher alkalinity. In contrast, the sorption of Sr2+ decreases with thermal processing; however, overall Sr2+ sorption increases as the pH becomes more alkaline. The sorption differences suggest that Cs+ uptake is structurally driven, while Sr2+ sorption is influenced by both the structure and the surface electrostatics of the material. These results suggest the effectiveness of the materials may be compromised due to changes in structure, hydration, and electrostatic interactions that occur when exposed to elevated temperatures.

Simultaneous high transparency and high haze are necessary for high-efficiency optical, photonic, and optoelectronic applications. However, a typical highly transparent film lacks high optical haze or vice versa. Here, we report a silk fibroin-based optical film that exhibits both ultrahigh optical transparency (>93%) and ultrahigh optical transmission haze (>65%). Also, in combination with the soft lithography method, different nanostructured silk fibroin films are presented and their optical properties are characterized as well. To demonstrate its exceptional performance in both high transmission and high optical haze, we combine the silk fibroin with the silicon photodiode and show that the efficiency can be increased by 6.96% with the silk fibroin film without patterns and 14.9% with the nanopatterned silk fibroin film. Silk provides excellent mechanical, optical, and electrical properties, and the reported high-performance silk fibroin can enable the development of next-generation biocompatible eco-friendly flexible electronic and optical devices.

The (NH 4 ) 2 ReX 6 (X = F, Cl, Br, I) salts have been investigated by x-ray absorption fine structure spectroscopy. The Re-F distance determined by EXAFS in (NH 4 ) 2 ReF 6 (i.e., 1.95 Å) is in good agreement with the one determined by single crystal x-ray diffraction in A 2 ReF 6 salts (A = K, Rb, Cs). The XANES studies of (NH 4 ) 2 ReX 6 (X = F, Cl, Br, I) indicates that the positions of the absorption edge and of the white line are shifted to higher energy when moving from I to F. These shifts have been explained in terms of the crystal field splitting parameter and covalent charge carried by the Re atoms. Calculations of the XANES spectra of the ReX 6 2− (X = F, Cl, Br, I) anions at the Re-L 3 edge have been performed and the calculated shifts and intensity of the white lines reproduce well the experimental observations.

The controlled reduction of a nickel metal anion, NiCl42-, at a carbon (Grafoil) and Polyaniline (PANI) electrode is explored. The incremental increase of Ni deposits is achieved from the reduction of the metal precursor at both electrodes. The normal oxidation/reduction was used to facilitate the uptake and dispersion of the precursor using electrostatic interactions with the positively charged PANI. The controlled in-situ reduction of the dispersed Ni precursor in the polymer was utilized to produce PANI/Ni composites with variable metal content. Scanning electron microscope (SEM) analysis and energy dispersive x-ray (EDX) spectroscopy of both substrates confirm the reduction of the Ni metal precursor at both electrodes. The chemical reactivity of the Ni metal deposited was also confirmed for both substrates using surface specific electrochemical reactions including the formation/reduction of oxidized nickel species and the catalytic oxidation of methanol in alkaline solutions (pH approximate to 14). The electrochemistry associated with NiOOH/Ni(OH)(2) and the catalytic oxidation of methanol is resolved in alkaline solution for both electrodes. Furthermore, the electrochemical activity of PANI/Ni composite materials is maintained without acid doping the polymer. Finally, an alternative pathway for the inclusion of anionic transition metal species in PANI that eliminates the competitive uptake of proton and metal cation precursors commonly used in traditional acidic environments is demonstrated. (C) 2018 Elsevier Ltd. All rights reserved.

Polyaniline (PANI) is extensively studied due to its unique electrochemical properties. Its conjugated structure makes PANI highly conductive. This conductivity can be fine-tuned by changing the electrolyte used for polymerization or the pH of its environment1. With a high chemical stability below 100°C, mechanical strength, and large surface area, the applications of PANI are numerous – from chemical sensing to corrosion inhibition coatings to light emitting diodes2. Another application for PANI is its use as a substrate for catalysts. Previous work has thoroughly investigated the electrochemical polymerization of PANI, electrochemical insertion of Pd and Au into PANI to form PANI/Pd3 and PANI/Au4composites, and the resulting composites’ catalytic activities for alcohol oxidation. Unfortunately, each of these composites has shown a significant amount of surface poisoning during alcohol oxidation, reducing its viability as an efficient catalyst. In an effort to reduce surface poisoning, scientists have been examining the effects of adding a second metal to well-known, commonly-used catalysts. These bimetallic catalysts have been shown to reduce surface poisoning and increase catalytic activity. One possible explanation for this phenomenon is an electronic effect - the interaction of the two metals causes a shift in the electronic structure of the catalyst’s surface, resulting in a weakened interaction with poisoning species5. Another possibility is that it is due to a bifunctional effect. In one case different metals adhere to different functional groups in the molecule allowing for a more stable transition state and thus more efficient catalysis6. In the case of oxidation in alkaline media, hydroxide groups from the solvent adsorb to the secondary metal, then react with poisoning species on the primary catalytic metal to form molecules that are more easily removed from the catalyst surface7. Most likely some combination of these three phenomena results in reduced poisoning and increased efficiency. This presentation will expand PANI research into the area of bimetallic PANI composites, specifically focusing on the simultaneous deposition of Au and Pd into PANI films. Three composites were prepared, each using a metal precursor solution with a different Au to Pd molar ratio (1:1, 2:1, or 1:2). Electrochemical data from metal deposition, surface oxide formation and reduction, and oxidation of 1-propanol provide insights into how metals interact with each other and their environment within the polymer. SEM/EDX data show morphology and composition of the composites. Overall the bimetallic composites show reduced surface poisoning and increased catalytic efficiency in comparison to their monometallic counterparts. References (1) D. W. Hatchett, M. Josowicz, and J. Janata, J. Phys. Chem. B103 (1999) 10992-10998. (2) A. A. Syed and M. K. Dinesan, Talanta38 (1991) 815-837. (3) D. W. Hatchett, N. M. Millick, J. M. Kinyanjui, S. Pookpanratana, M. Bär, T. Hofmann, A. Luinetti, and C. Heske, Electrochim. Acta56 (2011) 6060-6070. (4) D. W. Hatchett, M. Josowicz, J. Janata, and D. R. Baer, Chem. Mater.11 (1999) 2989-2994. (5) A. A. Rodriguez, C. T. Williams, and J. R. Monnier, Appl. Catal. A475 (2014) 161-168. (6) A. A. Rodriguez, C. T. Williams, and J. R. Monnier, Catal. Lett.145 (2015) 750-756. (7) X. Wang, B. Tang, X. Huang, Y. Ma, and Z. Zhang, J. Alloys Compd. 565 (2013) 120-126.

The controlled electrochemical uptake and reduction of metal precursors, AuCl4−, PdCl42−, and PtCl42− in polyaniline (PANI) is used in the synthesis of variable metal content composites. The potential and current associated with the initial electrochemical deposition of each metal precursor into pristine PANI is unique when compared to subsequent reduction in the composite materials. Deposition into the polymer and at existing deposits is resolved in the voltammetry for the reduction of Au and Pd in PANI. In contrast, distinct processes for Pt reduction into the polymer and at existing metal deposits are not resolved. After the initial reduction of the Pt precursor, the peak current continues to shift to more positive potential and diminishes as a function of increasing metal content. The PANI/metal composites are characterized using FTIR spectroscopy, thermal gravimetric analysis, and conductivity measurements to evaluate the interactions between the metal and polymer, the total metal content, and the electronic properties of the composites. The Au, Pd, and Pt metals deposited in PANI are evaluated using surface specific electrochemical reactions including the formation/reduction of metal oxide and the catalytic oxidation of n-propanol in alkaline solutions (pH ≈ 14). Furthermore, the electrochemical studies demonstrate that the oxidation/reduction of the polymer directly influences the polarization and reactivity of the metal surface in the organic matrix. The results confirm that PANI/metal composite materials containing Au, Pt, and Pd remain conductive in alkaline environments thereby expanding their use outside traditional acid solutions.

Reactive Innovations, LLC and the University of Nevada, Las Vegas (UNLV) have demonstrated an innovative improved process for extracting and separating light rare earth metals (La, Ce, Sm, Nd, Pr) from solution. Rare earth metals are valued for their unique magnetic, optical and catalytic properties. These materials are used in many clean energy technologies including wind turbines, electric vehicles, photovoltaic thin films and fluorescent lighting. Currently, China produces 95-97% of the world supply of rare earth metals and oxides, but is reducing exports and increasing prices to foreign consumers. The global impact of these restrictions is greatest in countries with large high-tech manufacturing sectors such as Japan, the USA and Germany. Lanthanides are typically found in mineral deposits. While the mining of the mineral deposits is fairly straightforward, the separation and purification of the individual lanthanide elements is laborious and energy intensive. New technologies are sought to enable more rapid, flexible, efficient, environmentally-friendly extraction and separation of individual lanthanides from aqueous mixtures with the goal of increasing the domestic supply of rare earth elements and decrease the costs of processing high purity metals. Our approach to extraction and separation of individual lanthanide metals involves selective electrodeposition from an ionic liquid media. Cyclic voltammograms taken for each of these systems clearly show multiple oxidation and reduction peaks which are characteristic of multi-valent electron transfer processes for these species as shown in Figure 1. Using this data, separate experiments were performed to electrodeposit individual rare earth metals using a constant potential method. Visually, we observed material deposited on grafoil substrates for each of the rare earth-IL systems. Further analysis by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) confirmed rare earth elements in the deposit. For illustrative purposes, Figure 2 is a representative SEM micrograph of a lanthanide deposited onto grafoil showing bulk deposition. We also demonstrated selective electrodeposition from binary mixtures in limited studies. By overlaying the individual CVs of rare earth oxides we selected two rare earth systems and reduction potentials to use in a mixture for demonstration of selective deposition of one or the other rare earth metal. Based on the differences in these CVs we utilized different deposition potentials to preferentially deposit one of the rare earths from an equimolar mixture of lanthanum and praseodymium precursors. The SEM image for deposits obtained at one voltage are provided in Figure 3 along with the EDS spectra taken for that sample. The EDS analysis indicated that preferential deposition of La occurred at this potential with ~80% of the total deposits associated with this species (Figure 3). In separate experiments, we changed the potential to shift the composition to 68% La and 32% Pr. The ability to concentrate, or selectively extract rare earth metals directly from a mixture of oxides in an environmentally benign solution (ionic liquid), could potentially replace the very laborious solvent extraction processes which produce oxide or carbonate species. We envision that our technology has potentially multiple insertion points into rare earth mining processes. Future work will focus on developing and optimizing these methods to result in a high efficiency process for rare earth metal recovery. Acknowledgements This work was accomplished with support from the Office of the Secretary of Defense (OSD) under contract no. N00014-13-P-1139.

The formation and reduction of gold oxide in wet ionic liquid (IL), N-trimethyl-N-butylammonium bis(trifluoromethanesulfonyl) imide, ([(Me3NBu)-Bu-n][TFSI]) is examined. The water concentration is determined using both the charge and peak current from the reduction of gold oxide and compared directly with Karl Fischer data. The quantitative determination of water in the IL is demonstrated for concentrations between 0.09 and 0.74 by weight (w%). The treatment of wet IL with dry nitrogen or molecular sieves reduces the water below background levels. Finally, methods for acid neutralization and the reduction of water with molecular sieves are conducted to minimize their impact on subsequent electrochemical measurements.

Ionic liquids (ILs) are solutions comprised of cation/anion pairs that are not limited by the electrochemical side reactions common to aqueous solution. The high stability of the ionic liquid provides large potential windows that can encompass the thermodynamic potentials for the reduction of f-elements such as cerium to metal. The direct dissolution of Ce2(CO3)3·xH2O into the ionic liquid trimethyl-n-butylammonium bis(trifluoromethanesulfonyl)imide [Me3NBu][TFSI] using conjugate acid bis(trifluoromethanesulfonyl)imide [HTFSI] is demonstrated. The displacement of carbonate ligand and formation of carbonic acid facilitates the in situ dissolution. The subsequent coordination of Ce with the TFSI ion in the IL is monitored using UV/vis spectroscopy and emergent ligand to metal transitions below 300 nm. Further evidence of the coordination of Ce in the ionic liquid is based on changes in the IR spectra for absorbance bands related to the sulfonyl functional groups of the TFSI anion. The reduction/oxidation of soluble Ce in IL is examined at Au, Pt, and GC (glassy carbon) electrodes. Multi-wave voltammetry at all three electrodes is consistent with the reductive deposition of Ce species from the IL solution. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) confirm the deposition of Ce species at mica/Au electrodes.

The direct dissolution of UO2CO3 in neat and “wet” ionic liquid (IL) trimethyl-n-butylammonium bis(trifluoromethansulfonyl)imide [Me3NnBu][TFSI] is examined. The ionic liquid serves as both the solvent for the direct dissolution of UO2CO3(s) and the electrolyte solution for the electrochemical analysis of the soluble uranyl species. The solubility data indicate that displacement of the CO32− occurs slowly due to the low concentration of protons available from residual water in the pristine IL. Enhanced dissolution of UO2CO3 through the formation of carbonic acid H2CO3 is achieved after the addition of acid, bis(trifluoromethanesulfonyl)amide (HTFSI) and water. The soluble uranyl cation can then coordinate with the TFSI anion in place of the displaced CO32− anion following the decomposition of carbonic acid and purging of CO2(g) and water from the IL. The solubility of UO2CO3 was examined using liquid scintillation counting of 233U for the pristine ionic liquid. The “wet” ionic liquid containing HTFSI and soluble UO2CO3 was evaluated using UV/vis spectroscopy before and after dissolution. The electrochemical deposition of uranium species from ionic liquid was evaluated using cyclic voltammetry. The potential mediated deposition of uranium species was achieved and verified using scanning electron microscopy (SEM) and the solid uranium deposits were evaluated using energy dispersive X-ray emission spectroscopy (EDX).

Design and development of improved low-cost hydrogen fuel cell catalytic materials and high-capacity hydrogenn storage media are paramount to enabling the hydrogen economy. Presently, effective and durable catalysts are mostly precious metals in pure or alloyed form and their high cost inhibits fuel cell applications. Similarly, materials that meet on-board hydrogen storage targets within total mass and volumetric constraints are yet to be found. Both hydrogen storage performance and cost-effective fuel cell designs are intimately linked to the electronic structure, morphology and cost of the chosen materials. The FCAST Project combined theoretical and experimental studies of electronic structure, chemical bonding, and hydrogen adsorption/desorption characteristics of a number of different nanomaterials and metal clusters to develop better fundamental understanding of hydrogen storage in solid state matrices. Additional experimental studies quantified the hydrogen storage properties of synthesized polyaniline(PANI)/Pd composites. Such conducting polymers are especially interesting because of their high intrinsic electron density and the ability to dope the materials with protons, anions, and metal species. Earlier work produced contradictory results: one study reported 7% to 8% hydrogen uptake while a second study reported zero hydrogen uptake. Cost and durability of fuel cell systems are crucial factors in their affordability. Limits on operatingmore » temperature, loss of catalytic reactivity and degradation of proton exchange membranes are factors that affect system durability and contribute to operational costs. More cost effective fuel cell components were sought through studies of the physical and chemical nature of catalyst performance, characterization of oxidation and reduction processes on system surfaces. Additional development effort resulted in a new hydrocarbon-based high-performance sulfonated proton exchange membrane (PEM) that can be manufactured at low cost and accompanied by improved mechanical and thermal stability.« less

The controlled uptake and electrochemical reduction of metal precursors PdCl 4 2− and PdCl 6 2− in polyaniline (PANI) is demonstrated. The formation of PANI/Pd composites is achieved with a reduction in proton doping and an increase in the oxidation of the polymer with Pd deposits physically blocking the nitrogen groups. High surface area filaments (PdCl 4 2− ) or a rough encapsulation (PdCl 6 2− ) of Pd metal on PANI are obtained. The structural differences highlight the influence of the metal precursor oxidation state on the morphology of the Pd deposits in PANI. Thermal gravimetric analysis provides an estimate of the Pd content for each composite of ∼40%. X-ray Photoelectron Spectroscopy and X-ray-excited Auger Electron Spectroscopy analyses confirm the deposition of Pd metal. The catalytic oxidation of methanol was demonstrated for both PANI/Pd composites in alkaline solutions that prohibit proton doping of the polymer. The data indicates that Pd metal acts as a solid-state dopant that may delocalize the charge on the polymer backbone to maintain conductivity. Methanol oxidation at PANI/Pd composites produced using PdCl 4 2− was enhanced relative to the composite produced using PdCl 6 2− and a planar Pd electrode. Comparison of PANI/Pd composite produced using PdCl 4 2− with other Pd catalysts from the literature indicates surface poisoning is reduced when Pd is coupled with the polymer. The composite is robust and stable in alkaline solution with the charge density decreasing by 5% on the positive scan and 13% on the negative scan after 200 voltammetric cycles. The data also indicates that the reductive desorption of surface contaminants is possible, minimizing the catalytic loss due to surface poisoning.