ZnFe2O4-N-BC Bifunctional Catalyst in Visible Light−Peroxydisulfate Coupled System in Norfloxacin Degradation

Using norfloxacin (NOR) as the target pollutant, the synergism and degradation mechanism of ZnFe2O4-N-BC (MNBC), a nitrogen (N) and zinc ferrite (ZnFe2O4) co-doped biochar bifunctional catalyst (BC), in visible light (VIS)−peroxydisulfate (PDS) coupled system, were elucidated, and the synergistic mechanism was further supported by optical absorption and photo-induced charge transfer analyses. The results indicate that the degradation rate constant of the ZnFe2O4-N-BC/Vis-PDS system is 22.7 and 17.4 times higher than that of the ZnFe2O4-N-BC/Vis and ZnFe2O4-N-BC/PDS systems, respectively. More importantly, an apparent enhancement factor of 26.3% was obtained relative to the internal control systems. In addition, the coupled system showed a wider pH adaptation range. Furthermore, the radical quenching experiment and EPR analysis further revealed that multiple reactive species (including SO4−, O2−·, ·OH, h+, and 1O2) were involved in the degradation of NOR, and their relative contributions followed the order: 1O2 > SO4− > O2−·> ·OH > h+. Finally, HPLC-MS analysis was performed to identify the key degradation intermediates of NOR, and thus to propose its possible transformation pathways.