Facile synthesis of Mn-doped BiOCl for metronidazole photodegradation: Optimization, degradation pathway, and mechanism

Manganese-doped bismuth oxychloride (Mn-BiOCl) photocatalysts were facilely synthesized for the photo degradation of metronidazole (MTZ), and the as-prepared Mn-BiOCl was systematically characterized. The results show that the introduction of Mn2+ to BiOCl increases its MTZ removal efficiency through increasing its specific surface area, broadening its light absorption region, and facilitating photoinduced carrier separation. The enhancement of the optical properties is ascribed to the generation of an intermediate Mn 3p-O 2d energy level in the forbidden gap of Mn-BiOCl based on the density functional theory calculations. Mn-BiOCl also exhibited favorable stability and recyclability after four cycles. Moreover, the results of the quenching experiments indicate that superoxide radicals (O2(center dot-)), hydroxyl radicals (OH center dot) and holes (h(+)) participated in MTZ degradation over Mn-BiOCl, and the electron spin resonance (ESR) test demonstrated that more OH center dot was generated in the Mn-BiOCl process than the BiOCl process. This was explained by the H2O adsorption energy and bond parameter on the photocatalyst's surface. Finally, the photodegradation pathway of MTZ was elaborated based on the intermediate analysis, and a mechanism for the promotion of MTZ photodegradation through Mndoping BiOCl was proposed.