Recent Advances and Roles of Oxygen Vacancies for Photocatalytic Nitrogen Oxide Removal

Air pollution has become a globally prominent environmental problem, in which nitrogen oxide (NOx, ~ 95% NO and NO2) is one of the most serious pollutants, how to remove low-concentered NO from the air without producing secondary pollution is becoming a challenging task. Environmental nanomaterial based photocatalytic technique is considered as a green technology for the removal of dilute NO (~ ppb) due to its low costs, high efficiencies and environmental friendless. Photocatalysts with certain surface defects, e.g., oxygen vacancies (OVs) have attracted huge interests with appreciable effectiveness for the NO removal as they affect essential steps of the photocatalytic reactions. Considering the advantages of OV for the NO conversion, this review systematically summarizes the methods of defect creation (e.g., OVs), characterizations, detailed reaction mechanisms during the photocatalytic NO removal. This review presents the state-of-the-arts, applications and vital roles of OVs including extending light absorption, promoting carrier separation, strengthening the surface-interface reactions in the photocatalytic NO oxidations. Based on these, several challenges and prospects of surface defect engineering in semiconducting materials are proposed for the further application of OV for NO conversion as well as the removal of other potential atmospheric hazardous.