Enhanced solar photocatalytic degradation of nitric oxide using graphene quantum dots/bismuth tungstate composite catalysts

Composite (GQDs/BWO) materials for enhanced photocatalysis are hydrothermally produced by combining graphene quantum dots (GQDs) with bismuth tungstate (Bi2WO6). These GQDs/BWO nanomaterials are evaluated for photocatalysis, at different GQDs loadings, for the degradation of gaseous nitric oxide with concentrations of 10–11 ppm. Results show that 10GQDs/BWO has the best photocatalytic performance among competitors for NO degradation. The NO conversion rate reaches 73% during 30 min, which is 3.84 times higher than that of pure Bi2WO6. This is because GQDs not only have a good electron transfer ability, but also form a direct Z-scheme heterojunction with Bi2WO6. These features promote electron-hole separation efficiency of the composite catalyst, and inhibit their recombination. This performance results from the increase in the surface area of the composite and to the increase in light absorption. The selectivity for the formation of NOx- (SNOx-) increased from 66 to 88%, and the DeNOx index increased from −0.003 to 0.43 after the introduction of GQDs. Active species scavenger experiment, Mott-Schottky (MS) tests and density functional theory (DFT) calculations are used to evaluate the mechanism of photocatalytic NO. Furthermore, cyclic tests show that 10GQDs/BWO catalysts maintain their chemical stability for NO degradation over 8000s.