Photocatalytic removal of NO by light-driven Mn3O4/BiOCl heterojunction photocatalyst: Optimization and mechanism

Abstract A Mn3O4/BiOCl heterojunction photocatalyst was synthesized via a facile one-step hydrothermal synthesis method and characterized. The optical properties and electron characteristic are also investigated. The prepared Mn3O4/BiOCl was used to remove NO under the simulated solar light irradiation, and the long-period and multiple-cycles, capture experiments, ESR and in situ DRIFTS were used to investigate the stability of Mn3O4/BiOCl, the main active species and reaction products. The results showed that Mn3O4 nanoparticles are successfully deposited on micro-flower BiOCl to form a heterojunction interface between Mn3O4 and BiOCl. Compared with pure BiOCl, the surface oxygen vacancies of Mn3O4/BiOCl increases, and Mn3O4 acts as an electron acceptor to promote the transfer of electrons from BiOCl to Mn3O4. The enhancement of the optical properties is ascribed to a good energy band structure of Mn3O4/BiOCl, facilitating photogenerated carrier separation. Mn3O4/BiOCl achieves about 75% of NO removal efficiency within 10 min and exhibits superior inhibition ability for NO2 under light irradiation, but the photocatalytic activities gradually decrease due to the accumulation of products. When 5 or 10 vol% H2O is added into the simulated gas, the NO removal efficiency has been increased over Mn3O4/BiOCl, but the inhibition effect of NO2 is slightly weakened. The heterojunctions, optical properties and morphologies of Mn3O4/BiOCl are stable but the oxygen vacancies increase after reaction. The produced O2− and OH radicals are active for the oxidation of NO to NO3− under light irradiation, which is due to the Z-scheme heterojunctions of Mn3O4/BiOCl.