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Abstract: Metal–organic frameworks (MOFs) hold immense potential for applications from separations to catalysis, yet their long-term behavior across real-world environments remains unclear. Here we introduce a hierarchical exposure framework that tracks the structural and chemical transformations in the archetypal zirconium MOF UiO-66 across sequential compartments─atmospheric gases, air, aqueous media and a biological host─and resolves how prior exposures condition or prime subsequent transformations. Using synchrotron-based spectroscopy, we find that oxidative/reactive gases leave the Zr-carboxylate nodes essentially intact, whereas exposure to environmentally relevant aqueous media initiates partial shifts in local Zr coordination and introduces oxygen into the pores─with transformation extent governed by the chemistry of the environmental matrices. Strikingly, acute exposure (24 h) to the water flea Daphnia magna drives profound framework degradation and respeciation to Zr hydroxide species. Microfocus XRF maps show that Zr is highly localized in the animal’s digestive tract, and region-specific XANES confirms uniform speciation across its tissues. Our findings establish a paradigm shifting cross-compartment transformation hierarchy in which biological processes can dominate the fate of stable MOFs even when abiotic exposures appear benign. Thus, organism-level biotransformation should be performed as a necessary part of environmental safety assessments and materials design.

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Abstract: Green hydrogen production is limited by the thermodynamic energy requirement of water splitting. By decoupling the anodic and cathodic reactions using redox mediators, alternative feedstocks such as lignocellulosic biomass can yield comparable hydrogen purity with around half the total electrical energy input of conventional water electrolysis. Keggin-type heteropolyacids such as phosphomolybdic acid (H3PMo12O40) are increasingly of interest as mediators in decoupled electrochemical energy conversion applications, due to their reversible redox characteristics. However, the redox behaviour of heteropolyacids in aqueous solution during this process is still poorly understood. X-ray absorption spectroscopy (XAS) techniques offer the opportunity to directly probe changes in oxidation state and local structure of the mediator in-operando, allowing unprecedented insight into redox processes in a flow cell environment. Here, for the first time, we demonstrate operando XAS of reduced phosphomolybdic acid as it undergoes oxidation in a proton exchange membrane electrolyser with bespoke 3D-printed flow-fields. Changes in the time-resolved XAS were correlated to structural changes in the Keggin anion, which were closely related to the state-of-charge of the mediator, laying the groundwork for future studies of solution-phase Keggin-type heteropolyacid redox states. Furthermore, reduction of the phosphomolybdic acid via mild thermal digestion of either pure lignin or real agricultural biowaste is compared, in a step towards real-world applications. This work contributes significantly to the efficient and low-cost production of green hydrogen from waste biomass feedstocks, as well as providing insights into similar decoupled electrolysis processes.

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Abstract: Understanding the redox behavior and structural stability of aliovalent substituents in ionic conductors is critical, as their variable oxidation states can inadvertently introduce electronic conductivity and alter transport mechanisms under different atmospheric conditions. Here, we report the atmosphere-dependent redox behavior and local coordination of Mo in LaNb0.9Mo0.1O4.05, focusing on its influence on phase transition and transport properties, where the as-sintered LaNb0.9Mo0.1O4.05 was systematically annealed under pure O2, pure N2, vacuum (∼1.6 × 10–8 mbar), and 5% H2/N2 at 800 °C for different dwell times. Electron paramagnetic resonance (EPR) spectroscopy results demonstrate the emergence of Mo5+ under 5% H2/N2. In situ X-ray absorption near edge structure (XANES) measurements reveal the reversible redox behavior of Mo, where Mo5+ formed under 5% H2/N2 reoxidizes to Mo6+ upon exposure to static air, while complementary in situ extended X-ray absorption fine structure (EXAFS) analysis shows that the Nb coordination environment also transitions from prototypical LaNbO4 structure under reducing conditions back to the Mo-substituted LaNbO4 structure upon reoxidation. This change of the oxidation states of Mo could correspondingly alter the band structure of the sample, which further enhances charge transport: the sample annealed in 5% H2/N2 for 24 h exhibits a reduced activation energy and increased electronic conductivity. These results highlight a strong coupling among substituent redox flexibility, local structure, and transport properties, providing an understanding of tailoring the properties of ionic conductors through controlled redox environments.

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Abstract: Metal nanoparticles are widely considered for heterogeneous catalysis due to their high atomic efficiency and tunable active microenvironment, but their specific functional tendencies are still unclear. Here, we report that a Rh@ZrO2/NC catalyst with only 0.1 wt% Rh exhibits exceptional catalytic performance and high selectivity (p-nitroacetophenone conversion-98.6 %, p-aminoacetophenone selectivity-100 %, r-56.4 molp-nitroacetophenone/(molRh·min)) towards the hydrogenation of the -NO2 group in nitroarene to -NH2. This is because the interaction between Rh species and “ZrO2-N” results in significant hydrogen spillover in the catalyst, as supported by DFT calculations. Extensive characterizations from TG, DTG, NAP-XPS, in-situ Raman spectroscopy, in-situ DRIFT spectroscopy and DFT calculations further confirm the adsorption, activation and dissociation of hydrogen on Rh nanoparticles. The H* species migrate readily over ZrO2-NC, to facilitate the catalytic activity and selectivity for the hydrogenation of nitroarene. This study presents a new approach to develop highly efficient and selective metal nanoparticle-catalysts for cost-effective hydrogenation reactions.

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Abstract: Aims: To investigate the phase changes of bismuth oxide in contact with sodium hypochlorite responsible for tooth discolouration. Methodology: Bismuth oxide (monoclinic α−phase; C) was mixed with sodium hypochlorite at 20°C, 37°C, and 60°C (B20, B37, B60) for a period of 24 weeks with weekly refreshing of solutions. The products were imaged by scanning electron and optical microscopy and characterized by thermographic analysis (TGA), phase analysis by X-ray diffraction (XRD) using Bragg Brentano geometry and Pilatus detector, infrared spectroscopy (FT-IR), and X-ray absorption fine structure (XAFS). Results: The interaction of bismuth oxide with sodium hypochlorite resulted in a change in microstructure and colour. The thermographic assessment showed a change in mass (5%–10% weight change) and colour reversal to the yellow bismuth oxide at ~450°C. Phase changes dependent on temperature were demonstrated with δ-bismuth oxide, sodium bismuthate and bismuth oxychloride formed as by-products at the different temperatures. Conclusions: The δ-phase bismuth oxide formation led to the material darkening which will cause tooth discolouration in a clinical setting. Due to the phase changes, the material chemistry after the interaction is different from that of the material placed in the tooth. The by-products of the reaction have not been tested for use in patients. It is recommended to ban the use of bismuth oxide from dental materials and other clinical use due to its instability. The clinical guidance for endodontic treatment needs to be changed to reflect this.