Recent Progress and Current Status of Photocatalytic NO Removal

Air pollution has become a globally prominent environmental problem in which nitrogen oxide (NOx, 95% NO and NO2) has been considered as one of the most serious harmful gaseous pollutants that can cause haze, photochemical smog, and acid rain. Exposure to NO (∼ppb) harms human health with a risk of respiratory and cardiopulmonary diseases. As such, much attention is focused on the throughout removal, effective control, and precise monitoring of NO, especially for those of NO with low concentration (∼ppb). Semiconductor-based photocatalysis is a practical approach for pollutant treatments, especially for low concentrations but highly toxic ones, for example, NO (∼ppb) removal in indoor and outdoor atmospheres. This work aims to introduce the main process, methods and summarize the critical scientific issues during the photocatalytic NO treatment and review the latest progress in semiconducting materials. This work also surveys the newly emerged photocatalysts such as metal oxides, Bi-based semiconductors, including Bi2O2CO3, BiOX (X = Cl, Br, and I), Bi-metal-based defective photocatalysts, and other Bi-based catalysts with well-defined surface/interface characters for the complete NO removal, specific conversion mechanisms and controlling the generation of the toxic intermediate (NO2) is highlighted. The challenges/bottlenecks of the practical applications in the field are also highlighted at the end.