BiOI-SnO Heterojunction Design to Boost Visible-Light-Driven Photocatalytic NO Purification.

The efficient, stable, and selective photocatalytic conversion of nitric oxide (NO) into harmless products such as nitrate (NO) is greatly desired but remains an enormous challenge. In this work, a series of BiOI/SnO heterojunctions (denoted as %B-S, where % is the mass portion of BiOI compared with the mass of SnO) were synthesized for the efficient transformation of NO into harmless NO. The best performance was achieved by the 30%B-S catalyst, whose NO removal efficiency was 96.3% and 47.2% higher than that of 15%B-S and 75%B-S, respectively. Moreover, 30%B-S also exhibited good stability and recyclability. This enhanced performance was mainly caused by the heterojunction structure, which facilitated charge transport and electron-hole separation. Under visible light irradiation, the electrons gathered in SnO transformed O to ·O and ·OH, while the holes generated in BiOI oxidized HO to produce ·OH. The abundantly generated ·OH, ·O, and O species effectively converted NO to NO and NO, thus promoting the oxidation of NO to NO. Overall, the heterojunction formation between p-type BiOI and n-type SnO significantly reduced the recombination of photo-induced electron-hole pairs and promoted the photocatalytic activity. This work reveals the critical role of heterojunctions during photocatalytic degradation and provides some insight into NO removal.