Mediated peroxydisulfate activation at oxygen vacancy sites: Synergistic degradation of norfloxacin by radical pathway and non-radical pathway

The synergistic treatment of pollutants in water by radical and non-radical pathways based on photo-like Fenton-activated peroxydisulfate (PDS) has received much attention from researchers. However, clarifying the structure–activity relationship between the photocatalyst structure and the dual-pathway degradation mechanism is difficult. Herein, the flower-like nickel–iron layered double hydroxide containing oxygen vacancy (NiFe-LDH-VO) was constructed by dual-hydrothermal method. The NiFe-LDH-VO/PDS/light system exhibited excellent degradation performance (93.1%) for norfloxacin (NOR). Notably, the apparent rate constant exceeded pristine NiFe-LDH by 2.6 times. The results of experiments, characterization and DFT calculations indicated that the enhanced degradation activity was attributed to the dual-pathway of radical and non-radical induced by VO on the catalyst surface. VO can not only improve the migration and separation efficiency of photogenerated carriers, which ensures the energy base of PDS activation, but also act as the active site of both radical pathway and non-radical pathway. In particular, VO can change the adsorption conformation of PDS, which enhances the adsorption of PDS on the catalyst and significantly reduces the energy barriers of the two activation pathways of PDS. The reasonable pathways for NOR degradation were proposed based on HPLC-MS and DFT calculations. In addition, the toxicity analysis of intermediates indicated lower developmental toxicity and mutagenicity compared to NOR. The present work provides innovative insights into the study of photocatalysts with dual degradation pathways and their mechanistic elaboration.