ZnO/BiOI p–n Heterojunction Composites for Enhanced Photocatalytic Degradation of Antibiotic Metronidazole

The extensive use of antibiotics has led to their persistent presence in aquatic environments, posing potential risks to ecosystems and human health. In this study, ZnO/BiOI heterojunction composites were synthesized via a two‐step hydrothermal method and applied to the photocatalytic degradation of metronidazole (MNZ). The effects of key experimental parameters on degradation efficiency were systematically investigated, including pH, catalyst dosage, and initial pollutant concentration. Under optimal conditions, the photocatalytic performance of a series of ZnO/BiOI composites toward MNZ degradation was evaluated. All composite samples exhibited markedly higher photocatalytic activity than the individual components. The ZB 0.2 composite achieved an MNZ degradation rate of 90.7% after 4 h of light irradiation, which was 19.8% and 14.9% higher than those of ZnO and BiOI, respectively. The enhanced photocatalytic performance was attributed to the formation of a p–n heterojunction in ZnO/BiOI, which promoted efficient charge separation and transfer. Three coexisting reaction pathways were proposed to account for the efficient mineralization of MNZ.