Oxygen vacancies mediated flower-like BiOX microspheres for photocatalytic purification of methyl mercaptan odor: Significant distinction induced by halogen elements

Abstract

Odor pollution, represented by low-concentration volatile organic sulfur compounds (VOSCs), has become a difficult issue in the field of air pollution control. Photocatalytic oxidation technology is applicable for the treatment of low-concentration VOSCs. However, currently available photocatalysts often suffer from limited efficiency and severe deactivation. Herein, flower-like BiOX (X = Cl, Br, I) microspheres abundant with oxygen vacancies (OVs) were developed for the removal of the model pollutant CH3SH. BiOI exhibited the optimal CH3SH oxidation performance, with the removal efficiency stabilizing at 75% within 180-min simulated solar-light irradiation, while BiOCl and BiOBr deactivated from 38% and 55% to 20% and 22%, respectively. Mechanism analysis found, OVs and I- synergistically endowed BiOI with better CH3SH adsorption and activation, enhanced light harvesting, quicker charge transfer, and more affluent •OH and •O2- productions. Photogenerated e- and •OH took a predominantly irreplaceable part in CH3SH oxidation, followed by •O2- and h+. New pathways of CH3SH photocatalytic oxidation was proposed, and dimethyl trisulfide was firstly found as its oxidation product. Besides, the oxidation products SO42- was proved to be converted to •SO4- radicals to further promote CH3SH oxidation, and the largest production of •SO4- over BiOI might be responsible for its excellent performance. Furthermore, the strong adsorption and substantial accumulation of CH3SO3H on BiOCl and BiOBr might be the key cause of their rapid deactivation. This work would inspire the construction of more effective photocatalysts for the purification of VOSCs odor.