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

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 O-center dot(2)- and (OH)-O-center dot radicals are active for the oxidation of NO to NO3- under light irradiation, which is due to the Z-scheme heterojunctions of Mn3O4/BiOCl.

Automated summary

The Mn3O4/BiOCl heterojunction photocatalyst shows excellent performance in removing NO under simulated solar light irradiation, with stable optical properties and morphology. Mn3O4 acts as an electron acceptor to promote photogenerated carrier separation and increase surface oxygen vacancies, which are key factors in NO photocatalytic removal.