N/S-doped biochar-loaded Bi and FeS activated persulfate-driven ¹O₂ efficient degradation of ofloxacin

Biochar-loaded Fe-based bimetals have been shown to be an effective catalyst for the activation of peroxodisulfates. However, reports on heteroatom-doped biochar-loaded Bi and FeS bimetals are scarce, and their properties and mechanisms remain unclear. In this study, NS₄-Bi₁FeS_0.75 catalysts were constructed using reductive hydrothermal and calcination methods. The results showed that the reductive hydrothermal process made Bi and FeS tightly bound, thereby promoting the stability of the catalyst. Under the optimal conditions, the NS₄-Bi₁FeS_0.75 system could completely degrade ofloxacin (OFX) within 20 min. Moreover, the NS₄-Bi₁FeS_0.75 system had excellent stability and regeneration capabilities, and was able to efficiently degrade a wide range of organic pollutants. A series of mechanistic studies and density-functional theory(DFT) calculations confirmed the existence of multiple synergistic mechanisms in the activation of PDS by the catalyst, in which N doping favors the generation of ¹O₂ and S serves to promote the rapid transfer of the metal electrons; while, the introduction of Bi and FeS enhances the adsorption capacity of the catalyst for PDS, and the presence of Bi promotes the Fe³⁺/Fe²⁺ cycle, which guarantees the continuation of the Fenton-like reaction. In summary, this study elucidated multiple reaction mechanisms in the visible light/NS₄-Bi₁FeS_0.75/PDS system, which provides new design ideas for the development of heteroatom-doped biochar loaded with metals and metal sulfides for wastewater treatment.