Adsorb-and-reduce VOx-Mo2C carbon material for enhanced hydrated-electron UV/S/I reduction and fast destruction of PFOA, PFOS, and GenX.

This study proposes a rice-straw-derived biochar decorated with vanadium oxides and molybdenum carbide (VOx-Mo2C@BC) as a redox-active adsorptive material for a UV/sulfite/iodide (UV/S/I) advanced reduction process that targets PFOA, PFOS and GenX. VOx-Mo2C@BC combines hierarchical porosity with well-dispersed VOx and Mo2C nanodomains, which roughly doubles PFAS adsorption capacity relative to pristine biochar and fits well to the Langmuir model (R2 ≈ 0.999). Under optimized conditions (pH11.5, C0 = 5.0 mg L-1, 0.3 g L-1 catalyst, 2.5 mM sulfite, 0.5 mM iodide, 254 nm UV), the VOx-Mo2C@BC/UV/S/I system achieves pseudo-first-order rate constants of 0.039, 0.033 and 0.045 min-1 for PFOA, PFOS and GenX, corresponding to half-lives of 21-15 min and nearly complete removal within 120 min. In a two-step configuration where PFAS are pre-adsorbed in the dark and then irradiated (adsorb-then-UV/S/I), the PFOS defluorination fraction reaches ∼0.42 after 120 min, compared with only ∼0.09 for homogeneous UV/S/I without catalyst, confirming the crucial role of interfacial adsorb-and-reduce chemistry. Radical-quenching and probe experiments show that hydrated electrons dominate PFAS destruction (≈64% contribution), followed by SO3•- and I2•-/I•, with minor roles from •OH and 1O2, and the measured electron equivalents correlate linearly with released F- equivalents (slope ≈0.8), indicating efficient utilization of reducing equivalents. The process maintains k_obs values in the 10-2-10-1 min-1 range across diverse real-water matrices (tap, surface, groundwater, wastewater effluent and seawater) and shows good operational reusability over ten consecutive cycles with low V and Mo leaching.