Mo2C-Induced Adsorbed Sulfate Radicals Mitigate Surface Carbon Accumulation and Enhance Pollutant Mineralization

The design of conventional heterogeneous catalysts for advanced oxidation processes (AOPs) predominantly targets pollutant removal efficiency, often overlooking precise control over oxidation pathways and the crucial capability for complete mineralization. This oversight can lead to the misleading accumulation of degradation intermediates on catalyst surfaces via the organic carbon transfer process (OCTP), rather than their true mineralization. Herein, we constructed an iron-loaded molybdenum carbide catalyst (Fe-Mo2C) and demonstrated its superior performance in the peroxymonosulfate (PMS) activation system for the efficient mineralization of organic pollutants, compared to a high-surface-area Fe-Fe3C catalyst. Despite its lower specific surface area (88.9 vs 321.9 m2/g) and adsorption capacity, the Fe-Mo2C/PMS system achieved a chemical oxygen demand (COD) removal efficiency of 1.08 mg/L per mg PMS, which is 3.5 times higher than that of the Fe-Fe3C/PMS system (0.309 mg/L per mg PMS). Mechanistic investigations revealed that the Mo2C substrate facilitates the rapid reduction of Fe3+ to Fe2+, thereby promoting the generation of surface-adsorbed sulfate radicals (SO4•-). These adsorbed radicals, confirmed through fluoride-ion-mediated desorption experiments and density functional theory calculations, are identified as the key species responsible for deep oxidation while effectively suppressing OCTP. This work challenges the conventional paradigm that prioritizes high surface area in catalyst design and highlights the pivotal role of adsorbed radicals in achieving efficient mineralization, providing a new strategic direction for developing advanced oxidation technologies for sustainable water remediation.