Fabricating a novel ternary recyclable Fe3O4/graphene/sulfur-doped g-C3N4 composite catalyst for enhanced removal of ranitidine under visible-light irradiation and reducing of its N-nitrosodimethylamine formation potential

A novel ternary recyclable Fe 3 O 4 /graphene/sulfur-doped g-C 3 N 4 (Fe 3 O 4 /GE/SCN) composite catalyst was synthesized and adopted in a visible-light driven catalytic system for the degradation of ranitidine, which is an important precursor of the emerging disinfection by-product of N-nitrosodimethylamine (NDMA). The addition of GE and Fe 3 O 4 significantly improved the interface charge transfer of SCN, increased the light collection efficiency and decreased the photogenerated charge recombination efficiency. Considering both the ranitidine removal efficiency and catalyst recovery, the Fe 3 O 4 mass fraction of 20% (20%-Fe 3 O 4 /GE/SCN) was recommended. Ranitidine (≤   2 mg/L) was completely removed in 60 min under the conditions of an initial pH of 7.0 and a 20%-Fe 3 O 4 /GE/SCN dose of 1.0 g/L, and its degradation fitted well with the pseudo first-order kinetics model. Electron paramagnetic resonance analysis and trapping experiments confirmed that ·O 2 − , ·OH and h + participated in the degradation of ranitidine. Ranitidine was removed through the pathways of demethylation and hydroxylation based on the analysis of the detected degradation intermediates, and 57.3% of the NDMA formation potential (FP) was reduced after the reaction. The visible-light driven 20%-Fe 3 O 4 /GE/SCN catalytic technology is a promising method not only for the control of NDMA FP but also the catalyst could be recovered and reused.