This project introduces a new, efficient and inexpensive strategy for achieving ambient NOx photoreduction to environmentally friendly N2 gas through solar/visible-light-driven photoelectrocatalysis, giving insight into a way to use solar energy to solve air pollution without deactivation and creation of secondary pollution in application.

Abstract Photocatalytic oxidation (PCO) is one of the best-known approaches to decomposing NOx at room temperature and ambient pressure. Conventional photocatalysts such as TiO2 primarily oxidize NO to nitrogen dioxide (NO2) which is still a toxic air pollutant, as well as other nitrate species that do not spontaneously desorb and deactivate the catalyst. Compared with the oxidation products, the photocatalytic reduction of NOx to nitrogen (N2) neither causes secondary pollution nor leads to catalyst poisoning. However, in the reaction process of NOx removal, the selectivity for NOx to generate N2 through photocatalytic reduction is extremely low. Thus, the removal of NOx from ambient air without deactivation and secondary pollution is an urgent and demanding challenge. This proposal suggests a new strategy to couple the photocatalysis with an electrochemical system in NOx reduction. In this hybrid process, the inherent challenges of heterogeneous photocatalysis are largely resolved. The new photoelectrocatalytic system not only significantly suppresses this recombination of the photogenerated charge carriers, i.e., of electrons and holes by gradient potential during the photocatalytic process, but also offers synergistic benefits in the treatment process and reduced energy utilisation. Its overall lower cost is advantageous. Also, the cathodic potential needed in a typical photoelectrocatalytic system is lower compared to that required for electrochemical reduction of pollutants. This project will focus specifically on the design of relatively complicated reaction devices for photoelectrocatalysis in NOx reduction, such as gas, solid, and liquid threephase reaction interfaces. Our preliminary results show that NOx can be significantly reduced under this photoelectrocatalytic system. The effects of the surface chemistry on both oxidative and reductive photoelectrocatalytic reaction processes, NOx gas adsorption, visible light absorption, band structure, interfacial charge transport mechanism, and NOx removal products, and its mechanism, in combination with density functional theory (DFT) calculations, will also be systematically investigated. This is also the first study on the application of photoelectrocatalysis system with high selectivity for the continuous reduction of nitrogen oxide to nitrogen in gas-phase under ambient conditions. This project introduces a new, efficient and inexpensive strategy for achieving ambient NOx photoreduction to environmentally friendly N2 gas through solar/visible-light-driven photoelectrocatalysis, giving insight into a way to use solar energy to solve air pollution without deactivation and creation of secondary pollution in application.