Qingze Chen

Ferrihydrite (Fhy) is a metastable iron (oxyhydr)oxide whose transformation into more stable crystalline phases is an important manifestation of its reactivity. However, whether nominally identical 2-line Fhy samples retain formation-dependent differences in short-range structure and how these differences control subsequent phase transformation behavior remain poorly understood. Here, Fhy was synthesized at different pH levels to establish formation-pH-dependent variations in the structure and phase transformation. Although all products were identified as 2-line Fhy by conventional X-ray diffraction, low-pH Fhy contained more hydroxyl-related components and exhibited lower structural order, while the local Fe coordination environments varied with the formation pH. These structural differences strongly affected the subsequent transformation. Under aqueous conditions, Fhy formed at pH 3.0 showed a greater tendency toward dissolution-mediated transformation to goethite, whereas Fhy formed at higher pH values generally yielded a greater relative proportion of hematite. Under nonaqueous conditions, the greater hydroxyl content of low-pH Fhy facilitated dehydroxylation and promoted hematite formation at a lower temperature and shorter reaction time. These results demonstrate that the formation pH leaves a persistent structural imprint on Fhy that governs hydroxylation degrees, Fe coordination environments, and phase transformation pathways. This work establishes formation-controlled short-range structures as a vital determinant of the transformation behavior of metastable materials.

Strong iron–arsenic (Fe–As) coupling in iron tailings hinders selective As separation during Fe recovery, posing risks of secondary contamination and limiting tailings valorization. This study developed a nitrate–biomass hydrothermal treatment that enables selective Fe–As decoupling from iron tailings through As(V) reduction. The proposed strategy achieved ~90% Fe recovery in the solid phase for valorization and ~90% As separation to the liquid phase for safe management. Recovered Fe was predominantly retained as Fe(II)–O species associated with hydrochar. Notably, nitrate addition markedly enhanced the electron-donating capacity of the hydrothermal system, resulting in a six-fold increase in As(V) reduction efficiency and thereby promoting As release from the solid phase. Nitrogen transformation analysis indicated that nitrate was first reduced to ammonium and subsequently condensed with biomass-derived intermediates, forming pyrrolic-N doping within the hydrochar matrix. Density functional theory (DFT) calculations revealed that pyrrolic-N sites facilitated As(V) reduction by shifting its interfacial interaction energy from +1.2 eV to -2.57 eV and enhancing electron transfer from carbon matrices to As(V) (Bader charge from -0.08 e to -0.15 e). Overall, this study establishes a nitrate-driven electron transfer system for selective Fe–As decoupling, providing mechanistic insights into nitrogen-mediated reductive transformation and a sustainable strategy for resource recovery from complex solid wastes.

Noble metal nanocrystals with high‐index facets exhibit superior catalytic activity but are challenging to synthesize on solid supports due to thermodynamic preference for low‐energy facets and uncontrolled metal‐support interactions. Here, we propose a pre‐amination‐directed strategy wherein grafting amino‐silanes onto supports fundamentally redirects the in situ growth of high‐index faceted nanocrystals. The pre‐installed amino groups coordinate with metal precursors to form stable surface complexes which, upon thermal activation, generate localized reducing environments that orchestrate facet‐selective nucleation and growth. Through synergistic regulation via coordination chemistry, electrostatic stabilization, and steric effects, this approach yields ultrasmall polyhedral nanostructures (4∼7 nm) enriched with abundant high‐index facets, effectively addressing the fundamental limitations of conventional synthetic routes, which tend to yield oversized particles (>50 nm) and are prone to ligand‐induced surface contamination. The strategy proves universally applicable across Pt, Pd, and Au‐based systems, delivering nanocrystals with remarkably low coordination numbers (4.0∼7.2) and superior catalytic performance (e.g., T ₉₀ = ∼150°C for toluene oxidation by Pt‐based catalysts). Our work establishes pathway engineering through pre‐amination as a general principle for designing supported high‐index faceted noble metal nanocrystals for diverse catalytic applications.

Probing the molecular-level redox behavior and mechanism of oxides is essential to developing innovative applications in different fields such as catalysis, but remains a challenge for the scientific community. Using in-situ transmission electron microscopy, here we provide an overall reduction view of single-crystalline α-Fe₂O₃ with different characteristics from the conventional wisdom of oxide reduction. Specifically, the formation of epitaxial nanoislands with concomitant oscillatory phase transitions (α-Fe₂O₃→defective γ-Fe₂O₃→α-Fe₂O₃) at the subsurface is observed during reduction. The dynamic equilibrium of lattice oxygen at the surface and the limited oxygen replenishment from the deep layer drive the α-Fe₂O₃→defective γ-Fe₂O₃ transformation in the subsurface, while the polymorphic transition (defective γ-Fe₂O₃→α-Fe₂O₃) spontaneously occurs under heating conditions. Such oscillatory phase transition is accompanied by the release of asymmetric stress, inducing the extension of epitaxial nanoislands. Our work highlights the complexity of reduction by providing an integral picture of oxide reduction, which contributes to the understanding of the site evolution of oxide-based catalysts in their working state.

The reduction of volatile organic compounds (VOCs), especially the oxidation of highly toxic and chemically resistant toluene, remains a challenge in environmental catalysis. In this research, a porous TiO ₂ /SiO ₂ support was initially fabricated through titanium pillaring of montmorillonite and then calcined and acid-leached as an efficient platform for Pt nanoparticle immobilization to yield Pt–TiO ₂ /SiO ₂ . The experimental data showed that the catalyst loaded with 0.37 wt.% Pt (0.37Pt–TiO ₂ /SiO ₂ ) exhibits superior toluene oxidation performance, reaching a T ₉₀ of 190°C. Moreover, the catalyst exhibited remarkable water resistance, maintaining high efficiency even in the presence of 10% water vapour and outstanding long-term stability, with no substantial deactivation after 48 h of continuous operation. The performance improvement is explained by the high dispersion of Pt nanoparticles on the support and the metal–support interaction between Pt and TiO ₂ , characterized by electron transfer from TiO ₂ to Pt. This interaction facilitates the adsorption and activation of reactant molecules. In situ diffuse reflectance Fourier-transform infrared spectroscopy explained the catalytic mechanism: toluene is sequentially transformed into benzyl alcohol, benzaldehyde and benzoate intermediates, which are subsequently converted to maleic anhydride by opening the ring and eventually mineralized into CO ₂ and H ₂ O. This work developed a high-performance, durable catalyst using cost-effective and abundant natural minerals, offering promising prospects for practical abatement of industrial VOCs.

Nanosilicon (Si) holds exceptional promise for next-generation high-energy-density lithium-ion batteries, yet its practical application is hindered by costly and complex synthesis. Here, we present a universal and scalable strategy to synthesize porous nano-Si from natural clay minerals via ball-milling-assisted magnesiothermic reduction, without pretreating clay or external heating. The self-heating ball-milling process enhances energy efficiency while enabling uniform reactions. The inherent aluminum-oxygen octahedral layers in montmorillonite inhibit Si nanocrystal aggregation and buffer temperature by self-decomposition. Moreover, only 0.4 equiv of NaCl relative to the precursor are sufficient to suppress high-temperature byproduct formation, while simultaneously promoting the fragmentation of montmorillonite layers to accelerate the reaction. The obtained nano-Si features a small crystalline size (∼26 nm), hierarchical porosity, and a moderate specific surface area. After carbon-encapsulating and blending with graphite, the Si@C/G composite delivers 699 mAh g^-1 with a high initial Coulombic efficiency of 87.1%, and retains 90.0% capacity over 200 cycles.