Microbial-assisted synthesis of Schwertmannite@g-C3N4 composite for bisphenol AF degradation through visible light-driven peroxymonosulfate activation

Iron-based materials are considered as excellent environmental catalysts due to the characteristics of abundant reserves, low biological toxicities, and rich chemical states for redox reactions. The sea urchin-like microscopic morphology of biosynthesized schwertmannite (Sch) with abundant surface active sites is beneficial to the environmental catalytic process. In this study, flake-type graphitic carbon nitride (g-C3N4) was introduced into the mineralization process of Acidithiobacillus ferrooxidans (A. ferrooxidans) as the additive to regulate the biomineralization process and directly control the morphology and structure of iron-based minerals. Schwertmannite@g-C3N4 composites (Sch-CN) with a desired structure of sea urchin-like well-dispersed biosynthesized Sch loaded on flaky g-C3N4 were successfully prepared by A. ferrooxidans-induced biomineralization process. A Light/Peroxymonosulfate/Sch-CN catalytic system was constructed to degrade the model organic pollutant bisphenol AF (BPAF). The system combined two advanced oxidation systems of photocatalysis and peroxymonosulfate (PMS) activation, showing excellent catalytic degradation ability and wide pH adaptability. In addition, the system was also applicable to the catalytic degradation of other bisphenol pollutants. The mechanism was deduced by the results of quenching experiments and electron paramagnetic resonance (EPR) measurements. Several degradation intermediate products were identified and the probable degradation pathways of BPAF were proposed. The toxicity activities of BPAF solution towards Raphidocelis subcapitata were largely reduced after treatment by the photochemical process. Overall, the Light/PMS/Sch-CN system has great potential in treating bisphenol wastewater.