Highly efficient (BiO)2CO3-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)2CO3-BiO2-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-x 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 O2− and HO 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.