NiFe Layered Double Hydroxide-Derived Catalysts with Remarkable Selectivity for the Oxidation of 5‑Hydroxymethylfurfural to 2,5-Furanedicarboxylic Acid under Base-Free Conditions

In this work, we report the exciting discovery of inexpensive and durable catalysts for the selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furanedicarboxylic acid (FDCA) under base-free conditions. A nickel-iron layered double hydroxide (NiFe-LDH) precursor was first prepared then subjected to hydrothermal sulfidation with thioacetamide at 120 °C or thermal phosphidation with sodium hypophosphite at 400 °C to produce NiFeS and NiFeP-400 catalysts, respectively. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) showed these catalysts to contain FeNi2S4 and FeNi2P, respectively, as the dominant phases. The catalytic activity of each catalyst was optimized by studying the effect of the solvent, reaction temperature, oxidant, and reaction time on HMF conversions and product distributions. Under optimized conditions (acetonitrile solvent, 120 °C, tert-butanol peroxide as an oxidant, 12 h, respectively), the NiFeS catalyst afforded 100% HMF conversion with an 83.2% FDCA selectivity with the performance of the NiFeP-400 catalyst being almost identical (HMF conversion of 100%; FDCA selectivity of 82.7%). Both catalysts showed excellent stability over five cycles of catalyst tests with the catalysts able to be easily collected after use with a magnet. Based on the experimental findings, the similar reaction mechanisms used are to be proposed for HMF oxidation to FDCA over the two catalysts. Results show that metal sulfide-based and metal phosphide-based catalysts are promising alternatives to traditional noble metal-based catalyst for the valorization of bio-derived HMF

Nanocarbon Framework-Supported Ultrafine Mo₂C@MoO_<i>x</i> Nanoclusters for Photothermal-Enhanced Tumor-Specific Tandem Catalysis Therapy

Recent advances in the synthesis of multifunctional nanomaterials create new opportunities for the rational design of multimodal chemodynamic therapy (CDT) agents. Precisely tailoring the nanostructure and composition of CDT nanoagents for maximum efficacy remains a challenge. Herein, we report the successful synthesis of nanocarbon framework-supported ultrafine Mo2C@MoOx nanoclusters (C/Mo2C@MoOx) via a pyrolysis of a Mo/ZIF-8 MOF precursor at 900 °C followed by mild surface oxidation. The developed C/Mo2C@MoOx composite demonstrated outstanding performance in photothermal-enhanced tumor-specific tandem catalysis therapy. Specifically, C/Mo2C@MoOx efficiently catalyzed the conversion of endogenous H2O2 to cytotoxic 1O2 via a Russell mechanism, while also converting the O2 byproduct to cytotoxic ·O2– via an oxidase-like mechanism. A high dispersion of active Mo5+ sites in the exposed MoOx shell enhanced the reactive oxygen species (ROS)-generating efficiency of C/Mo2C@MoOx. Moreover, the Mo2C core in the ultrafine Mo2C@MoOx nanoclusters allowed NIR-II (1064 nm)-driven photothermal heating, which significantly boosted the CDT process through photothermal effects. Additionally, the CDT process relied on a redox cycle involving Mo5+/Mo6+ species, which could be sustained by glutathione (GSH) consumption. Given these advantages, C/Mo2C@MoOx demonstrated remarkable synergistic therapeutic efficacy for cancer treatment (both in vitro and in vivo) through tumor microenvironment-stimulated generation of multiple ROS and NIR-II photothermal activity

RuO₂–CeO₂ Lattice Matching Strategy Enables Robust Water Oxidation Electrocatalysis in Acidic Media via Two Distinct Oxygen Evolution Mechanisms

The discovery of acid-stable and highly active electrocatalysts for the oxygen evolution reaction (OER) is crucial in the quest for high-performance water-splitting technologies. Herein, a heterostructured RuO2–CeO2 electrocatalyst was constructed by using a lattice-matching strategy. The interfacial Ru–O–Ce bridge structure provided a channel for electron transfer between Ru and Ce, creating a lattice stress that distorts the local structure of RuO2. The resulting RuO2–CeO2 catalyst exhibited attractive stability with negligible decay after 1000 h of the OER in 0.5 M H2SO4, along with high activity with an overpotential of only 180 mV at 10 mA cm–2. In situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), in situ differential electrochemical mass spectrometry (DEMS), and density functional theory (DFT) calculations were used to reveal that the interface and noninterface RuO2 sites enabled an oxide path mechanism (OPM) and the enhanced adsorbate evolution mechanism (AEM-plus), respectively, during the OER. The simultaneous and independent OER pathways accessible by lattice matching guides improved electrocatalyst design for the OER in acidic media

Toward More Efficient Carbon-Based Electrocatalysts for Hydrogen Peroxide Synthesis: Roles of Cobalt and Carbon Defects in Two-Electron ORR Catalysis

Electrochemical production of H2O2 is a cost-effective and environmentally friendly alternative to the anthraquinone-based processes. Metal-doped carbon-based catalysts are commonly used for 2-electron oxygen reduction reaction (2e–ORR) due to their high selectivity. However, the exact roles of metals and carbon defects on ORR catalysts for H2O2 production remain unclear. Herein, by varying the Co loading in the pyrolysis precursor, a Co–N/O-C catalyst with Faradaic efficiency greater than 90% in alkaline electrolyte was obtained. Detailed studies revealed that the active sites in the Co–N/O-C catalysts for 2e–ORR were carbon atoms in C–O–C groups at defect sites. The direct contribution of cobalt single atom sites and metallic Co for the 2e–ORR performance was negligible. However, Co plays an important role in the pyrolytic synthesis of a catalyst by catalyzing carbon graphitization, tuning the formation of defects and oxygen functional groups, and controlling O and N concentrations, thereby indirectly enhancing 2e–ORR performance

Perovskite Cs₃Bi₂I₉ Hexagonal Prisms with Ordered Geometry for Enhanced Photocatalytic Hydrogen Evolution

The synthesis of metal halide perovskite/perovskitoid (MHP) photocatalysts with well-defined morphologies and facet-specific redox activity is technically challenging. Herein, using surfactants to control the arrangement of 0D facet-shared [Bi2I9]3– dioctahedra building blocks, we successfully fabricated ordered perovskite Cs3Bi2I9 hexagonal prisms (CBI-HPs). Using Co2+ oxidation and Pt4+ reduction as redox probes, photoexcited holes were shown to spatially migrate to the edge (100) facets while photoexcited electrons migrated to the (006) basal facets, respectively. Density functional theory revealed that the built-in potential of the facet junction between (100) and (006) facets was ∼130 meV. Because of the well-separated redox facets, the photocatalytic hydrogen evolution rate of ordered CBI-HPs via hydroiodic acid splitting reached 1504.5 μmol/h/g, which is 22.1 times that of a disordered CBI photocatalyst. This work guides the rational design of high-performance MHP photocatalysts for solar energy conversion and other applications