Accurate measurement of biomass pyrolysis products can provide valuable guidance for thermal processing. However, pyrolysis generates large numbers of compounds in varying concentrations, factors that can make compound identification and quantitation difficult. In this study, Miscanthus biomass samples were analyzed using pyrolysis/two-dimensional gas chromatography/mass spectrometry (Py-GCxGC-MS), which provided a more comprehensive chromatographic separation and mass spectral compound identification. Quantitative measurement was performed for 34 calibrated pyrolysis compounds using an internal standard method. Pyrolysis efficiency was measured as a function of sample mass, pyrolysis temperature, and pyrolysis temperature ramp rate. For most of the calibrated pyrolysis products, production efficiency decreased with sample mass, increased with pyrolysis temperature, and decreased with pyrolysis temperature ramp rate. Significantly, the temperature profiles of the different pyrolysis products were variable, notably acetic acid and the vinyl and formyl derivatives of phenol and guaiacol, which were produced at lower temperatures compared to other compounds such as the syringyl derivatives and levoglucosan. Lignol ratios were compared with those generated using 1H/13C heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance spectroscopy (NMR). Lower fractions of syringyl- and guaiacyl-lignols and higher fractions of the phenol-lignols were generated by Py-GCxGC-MS compared to HSQC-NMR.

Nitroxide radicals in organic compounds such as 4–hydroxy–2,2,6,6–tetramethylpiperdinine–1–oxyl (4–hydroxy–TEMPO) are redox–active and are of interest for potential applications in redox flow batteries. The mechanisms governing charge–transfer reactions of such compounds are not well understood. Specifically, the anodic charge transfer coefficient (α_a) corresponding to the electro–oxidation of 4–hydroxy–TEMPO in an aqueous medium is ~0.9, i.e., α_a deviates considerably from 0.5 expected for a symmetric single–step one–electron transfer redox reaction. In a previous publication [J. Electrochem. Soc., 167, 143505 (2020)], we have proposed a reaction mechanism to explain such asymmetric behavior by invoking adsorption–desorption processes. In the proposed mechanism, reversible oxidation of 4–hydroxy–TEMPO leads to adsorption of the oxidation product, which then undergoes slow rate–limiting desorption from the electrode surface. In the present contribution, supporting evidence is provided for this mechanism. In situ surface–enhanced Raman spectroscopy combined with density functional theory simulations are employed to confirm the presence of surface–adsorbed species at a Au electrode during electro–oxidation of 4–hydroxy–TEMPO. Furthermore, we employ chronopotentiometry to track the gradual re–equilibration of the electrode–electrolyte interface following the electro–oxidation of 4–hydroxy–TEMPO. Analysis of the chronopotentiometry data further suggests the presence of adsorbed species, which were previously proposed and are now confirmed by direct spectroscopic evidence.

Nuclear power plants use energy-dense fuel and provide dependable baseload energy without generating greenhouse gas emissions. Despite these advantages, the long-term management of used nuclear fuel (UNF) remains a key challenge due to its lifetime (hundreds of thousands of years) and radiotoxicity. The components of UNF that contribute the most to this challenge are the actinide elements. A potential solution to this issue is to separate these radioisotopes from the bulk of the UNF and recycle them as fuel in advanced nuclear reactors. These separations can be achieved using electrochemical reprocessing, which employs electrochemical conversion and electrodeposition in a high-temperature molten salt electrolyte medium to separate the actinides from UNF. In this short perspective, we review the current status, fundamental challenges, and future prospects of electrochemical reprocessing as they relate to UNF recycling.

Special nuclear material, like enriched uranium and plutonium, can contaminate environmental soils and water because of weapons development and testing or improper waste storage. To remediate affected lands and design long-term waste storage solutions, it is crucial to understand uranium speciation in the environment which depends on its complexation, oxidation state, and associated adsorption mechanisms. These phenomena are complex and poorly understood because they depend on many variables including the environmental pH, water or soil composition, uranium concentration, and surface chemistry of the minerals or soils. In previous studies, the proposed mechanism for adsorption of the hexavalent uranyl species, UVIO2 2+, on metal-oxide surfaces follows these general steps: 1) adsorption of UVIO2 2+ on the mineral, followed by 2) reduction to UVIO2 2+ due to the coupled reaction of a redox active species within the mineral. To gain better mechanistic insight into coupled electron transfer and adsorption phenomena associated with uranyl species, we demonstrate here a novel technique to probe an electrochemical interface to detect adsorbed uranium species under reducing conditions. In this technique, we monitor the transient response of the electrode potential immediately after electrochemical reduction of UVIO2 2+ on a rotating disc electrode is halted. This potential relaxation rate, when analyzed, contains information on presence and coverage of surface adsorbed species. In combination with electrochemical quartz crystal microgravimetry (e-QCM), these experiments confirm the presence of an adsorbed layer of uranium ions during the reduction of UVIO2 2+. To simulate uranyl adsorption on minerals under environmental conditions, future work will aim to probe adsorption onto a metal-oxide film prepared on an e-QCM electrode under varying redox and pH conditions.

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