Hejie Qin

Perchlorate (ClO4–) reduction to benign Cl– under mild conditions remains challenging due to its kinetic inertness. Herein, we report a solid–solid catalytic system consisting of a MoS2-based composite (MoS2/NC) and nanoscale zerovalent iron (nZVI). This system achieved complete reduction of 1 mM ClO4– to Cl– in 24 h at 25 °C and pH 6.0, with a rate constant of 0.25 h–1, without noble metals or external energy input. In this physically mixed system, nZVI served as the electron donor, with electron transfer enabled by contact with MoS2/NC, while defect-rich MoS2/NC provided catalytic sites for oxygen atom transfer. Beyond the reactivity, this system provided a platform for developing a quantitative kinetic framework for solid–solid catalysis in which particle interactions and surface reaction steps are strongly coupled. With the combination of a hydrodynamic-based particle interaction simulation with a site-associated kinetic model, the framework moves beyond apparent rate analysis and distinguishes nZVI-driven catalyst activation from ClO4– reduction at catalytic sites. The model identified reduction at the catalytic sites rather than electron transfer between nZVI and MoS2/NC as the dominant rate-limiting step. This work not only provides an effective strategy for perchlorate reduction under mild conditions but also establishes a general framework for mechanistic analysis and rational optimization of kinetically complex solid–solid reaction systems in water.

Perchlorate (ClO ₄ ⁻ ) contamination in water poses global health risks, yet its efficient reduction to harmless Cl ⁻ under mild conditions remains challenging. Here, we report a donor−acceptor catalytic system comprising defective MoS ₂ on N-doped carbon (MoS ₂ −NC) coupled with zerovalent iron (Fe ⁰ ), which enables rapid ClO ₄ ⁻ reduction at near-neutral pH (rate constant, 2.36 h ⁻¹ ), yielding Cl ⁻ as the sole product. In the MoS ₂ −NC/Fe ⁰ system, Fe ⁰ acts as the electron donor, while undercoordinated Mo atoms in defective MoS ₂ serve as the active sites, and N-doped carbon mediates electron transfer and optimizes the electronic environment for ClO ₄ ⁻ reduction. The reduction proceeds via oxygen atom transfer, involving Cl−O bond cleavage, O binding to Mo sites, and hydrodeoxygenation of the Mo-bound O atoms. Our observations offer a practical strategy for ClO ₄ ⁻ reduction without harsh conditions or noble metals and underscore the promise of donor−acceptor-based, defect-engineered catalysts for reductive transformation of challenging oxyanions.

Surface engineering strategies and interfacial reaction mechanisms are of fundamental significance to the development of material-based environmental remediation technologies. Despite the tremendous efforts in manipulating the surface properties of materials exemplified by nanoscale zerovalent iron (nZVI), the interfacial reaction mechanism has scarcely been steered through modulating the surface-pollutant interaction. Herein, we demonstrate that extracellular polymeric substance (EPS) modification essentially reshapes the reactivity and selectivity of nZVI via the surface-pollutant interaction toward various nitroaromatics, based on a spectrum of degradation experiments, fluorescence quenching experiments, proton conductivity measurements, kinetic isotopic effect determination, and computational analysis. Distinctively, EPS modification diverges the nZVI reactivity with remarkable promotion, negligible change, and significant inhibition toward 4-nitrophenol (PNP), nitrobenzene, and 3-nitrobenzenesulfonate (NBS), respectively. Moreover, the corresponding interfacial reaction mechanism is fundamentally changed. The desirable proton-coupled electron transfer (PCET) route is activated via the association of hydrogen-bonding networks harnessing the phenolic group of PNP and the proton-shuttling characteristic of EPS, while the electrostatic repulsion induced by the sulfonate group of NBS significantly impedes the reaction by eliminating the PCET pathway. Through understanding and steering the surface–pollutant interaction, this study illuminates the precision design and selection of materials for efficient water decontamination and site remediation.

Various methods have been developed to enhance the performance of zerovalent iron (ZVI) for chlorinated hydrocarbon (CHC) removal, but their applicability across diverse CHCs remains limited. Here, we present a MoS₂ modification strategy to address these challenges. MoS₂-modified ZVI (MoS₂-ZVI) exhibited dechlorination rate constants that are 1.25 to 54 times those obtained with ZVI, for eight representative CHCs, with significantly fewer incompletely dechlorinated products. The electron efficiency values increased to 2.7-26.5 times, with the synchronously inhibited H₂ evolution possibly resulting from the increased hydrophobicity caused by MoS₂ modification. While H^• contributes to the reduction of certain CHCs, the enhancement by MoS₂ is mainly attributed to improved electron transfer at the surface. Characterization results revealed partial integration of MoS₂ with ZVI and the presence of sulfur vacancies on MoS₂ surfaces in MoS₂-ZVI. Electrochemical experiments with separated ZVI and MoS₂^bm in different compartments identified sulfur vacancies as the reactive sites. In situ Fourier transform infrared spectroscopy and density functional theory results demonstrated that CHCs adsorb at Mo sites exposed by sulfur vacancies, and this process is facilitated by the integrated effects of underlying ZVI. The dechlorination of CHCs subsequently occurs with the electrons transferred from ZVI to the surface-bonded CHC through the MoS₂ layer. This study provides a broadly applicable modification strategy for achieving rapid, full, and selective dechlorination of a wide range of CHCs.