In-situ generation of oxygen vacancies and metallic bismuth from (BiO)₂CO₃ via N₂-assisted thermal-treatment for efficient selective photocatalytic NO removal

In this study, a N₂-assisted thermal treatment method is proposed for in-situ formation of a series of oxygen vacancies (OVs)-rich Bi⁰/Bi-based photocatalysts, including OVs-(BiO)₂CO₃, Bi⁰/OVs-(BiO)₂CO₃, Bi⁰/OVs-(BiO)₂CO₃/β-Bi₂O₃, Bi⁰/OVs-β-Bi₂O₃, Bi⁰/OVs-β-Bi₂O₃/α-Bi₂O₃ and Bi⁰/α-Bi₂O₃. Mechanisms of in-situ formation of Bi⁰ nanoparticles and generation of OVs in Bi-based photocatalysts are clarified. Apart from their contribution to the effective separation of photogenerated charge carriers and enhancement of light absorption, the effects of Bi⁰ nanoparticles and OVs on selective photocatalytic oxidation of NO are also investigated. Among the synthesized Bi-based photocatalysts, Bi⁰/OVs-(BiO)₂CO₃ shows the best photocatalytic activity and stability for photo-oxidative removal of NO. The systematic study of photocatalytic mechanism demonstrated that the Ohmic contact between OVs-(BiO)₂CO₃ and Bi⁰ gradually promote the formation of •O₂^– and •OH species. It is found that •O₂^– plays an important role in the photocatalytic NO removal process, while •OH species can effectively inhibit the formation of NO₂ during the NO removal process. The new approach demonstrated in this study can be applied for the in-situ formation of wide-solar-spectrum-responsive photocatalysts with efficient photocatalytic activity.