Highly efficient (BiO)(2)CO3-BiO2-x-graphene photocatalysts: Z-Scheme photocatalytic mechanism for their enhanced photocatalytic removal of NO

NO removal is one of the most important issues in dealing with air pollution. In this report, Z-scheme (BiO)(2)CO3BiO2-x-graphene (BOC-BiO2-x-GR) composite photocatalyst was designed for NO removal under simulated solar light irradiation. Characterizations of physical properties of the ternary composites revealed extended light absorption and high efficient electron-hole separation. Through the optimization of the BiO2-x content, we observed that the BOC-BiO2-x(35wt%)-GR composite exhibited superior photocatalytic activities in NO removal as compared to pure BOC, BiO2-x, and BOC-BiO2-x binary composites. Detailed microstructural observation showed that the BOC-BiO2-x heterojunction was formed between BOC (013) and BiO2-x(111) planes. The density of state (DOS) calculation revealed that due to the different hybridization conditions in the energy bands of BOC and BiO2-x the Z-scheme charge transfer should be dominant at the heterojunction interface. The density functional theory (DFT) computation on the Fermi level results confirmed that energy band structure between BOC and BiO2, is more in favor of the transfer of photo-generated electrons from CB of BOC to the VB of BiO2-x, which can be further enhanced by highly conductive GR sheets. The electron spin resonance (ESR) experiments results show that O-2(center dot-) and HO center dot were produced during the photocatalytic process, which further provided evidences that the BOC-BiO2-x(35wt%)-GR composite works as a Z-scheme photocatalyst. This work indicates that Bi-based nanomaterials can be employed as a stable and high efficient solar light active photocatalyst for NO removal in air pollution control.