Electropositive carbon sites and sulfur vacancies in SnS2/g-C3N4 for achieving adsorption and photocatalytic degradation of As(III) in stages by pH regulation

Highlights: • 37.4% pyrrole nitrogen doping generates electropositive carbon sites in g-C₃N_4. • Sn-based sulfide was grown on the N‒C bond framework of porous pyrrole in situ. • The Sn valence state was adjusted by β particles to obtain controllable sulfur defects. • The −CSn− interface chemical bond improves the transport of carriers. • Enhanced arsenic removal from water was achieved in stages by pH regulation. -- Abstract: In this work, a high content of pyrrole nitrogen carbon nitride (HPCN)-SnS₂ has been successfully constructed with −CSn− chemical bond as the interface framework. The charge state of Sn species was adjusted by β particles to obtain controllable sulfur defects onto the HPCN-SnS₂ through electron beam irradiation (EBI). The composites exhibited excellent photocatalytic oxidation capacity of As(Ⅲ) and adsorption capacity of As(Ⅴ). It is confirmed that the optimized HPCN-SnS_1.38 can remove the total As concentrations below 0.40 mg/L within 80 min. Additionally, the effect of various conditions (pH value and type of anions) was evaluated using degradation experiments, and HPCN-SnS_1.38 could be reused at least 5 times without an obvious reduction in the photocatalysis and adsorption performances. Based on the experimental results, the photocatalytic mechanism of As(Ⅲ) by HPCN-SnS₂ after electron beam irradiation was studied. Free radical quenching experiments and electron paramagnetic resonance (EPR) showed that the oxidation of As(III) under visible light is mainly controlled by • O₂⁻ and • OH, and • OH is converted from • O₂⁻ under acidic conditions.