Magnetic visible-light activated photocatalyst CuFe₂O₄/Bi₂WO₆/mpg-C₃N₄ for the treatment of natural organic matter

Despite growing interest in research on visible-light-driven photocatalysts, reusable photocatalysts have not been extensively developed for the treatment of natural organic matter (NOM), because such development requires an understanding of the complex NOM structures. In this study, we combined the individual benefits of CuFe2O4, Bi2WO6, and mesoporous graphitic carbon nitride (mpg-C3N4) to prepare a magnetic, visible-light-driven photocatalytic composite, CBC-5, for effectively removing NOM in a short period of time. The degradation mechanisms were further explored at the molecular level through ultra-high-resolution mass spectrometry. Broad light absorbance and charge transmission based on a dual S-scheme pathway allowed CBC-5 to generate multiple active agents, [rad]OH (49.7 %), [rad]O2− (27.6 %), and h+ (24.8 %), which ultimately led to the removal of 7.9 mgC of NOM per 0.9 g of CBC-5 in 6 h. Humic-like fluorophores were preferentially degraded, followed by the generation of simple phenolic components as by-products. Molecular-level investigation revealed that the NOM structures with high degree of unsaturation and functionalization were preferentially attacked by the radicals. Oxygenic groups were formed upon the oxidation of the unsaturated bonds and the functional groups having a low oxidation state of carbon (OSc) before the degradation of the carboxyl-rich alicyclic molecules. NOM degradation was prioritized in the following order: CHON > CHO > CHOS. Oxidative deamination is attributed to the preferential degradation of N-containing compounds, which are partially transformed to CHO compounds. CHOS compounds enriched with aliphatic organosulfates were recalcitrant to photocatalytic oxidation. Thus, CBC-5 demonstrated convenient magnetic recovery, stable performance, and high recyclability and can be applied as a promising NOM treatment agent.