Enhanced Visible-Light-Driven Peroxydisulfate Activation by a Waste-Derived Fly Ash-Supported TiO ₂ /BiO _{1– <i>x</i>} Br _0.5 I _0.5 Photocatalyst for Degradation of Sodium Isopropyl Xanthate

Environmental pollution induced by tailing water containing sodium isopropyl xanthate (SIPX) necessitates efficient wastewater treatment strategies. Photocatalytic activation of peroxydisulfate (PDS) is a promising route. Here, a stabilized municipal solid waste incineration fly ash (FA)-supported TiO2/BiO1–xBr0.5I0.5 (FT-BiO1–xBr0.5I0.5) photocatalyst was designed for visible-light-driven PDS activation to degrade SIPX. FT-BiO1–xBr0.5I0.5 achieves >99% removal of SIPX (100 mg L–1) within 50 min. FA serves as a robust support that suppresses photocatalyst agglomeration, provides active sites, and facilitates interfacial charge transfer and redox kinetics. Incorporation of Br and I to form a solid solution, together with oxygen vacancies, tailors the electronic structure, as confirmed by experiments and density functional theory (DFT) calculations, revealing an S-scheme heterojunction. This synergy enhances light absorption, accelerates charge separation, and boosts PDS activation. Quenching tests and electron paramagnetic resonance (EPR) analysis show that photocatalytically generated O2•- is the key species initiating the rapid formation of 1O2, •OH, and SO4•-, which jointly contribute to efficient SIPX degradation. SIPX degradation pathways are elucidated by combining experiments with DFT calculations. Low heavy-metal leaching during preparation and reaction demonstrates the stability and low environmental risk of FT-BiO1–xBr0.5I0.5, offering a feasible strategy for simultaneous tailing water treatment and solid waste reutilization.