Synergistic effect of cyano defects and CaCO3 in graphitic carbon nitride nanosheets for efficient visible-light-driven photocatalytic NO removal

Photo-oxidation with semiconductor photocatalysts provides a sustainable and green solution for NOx elimination. Nevertheless, the utilization of traditional photocatalysts in efficient and safe photocatalytic NOx removal is still a challenge due to the slow charge kinetic process and insufficient optical absorption. In this paper, we report a novel porous g-C3N4 nanosheet photocatalyst modified with cyano defects and CaCO3 (xCa-CN). The best performing sample (0.5Ca-CN) exhibits an enhanced photo-oxidation NO removal rate (51.18 %) under visible light irradiation, largely surpassing the value of pristine g-C3N4 nanosheets (34.05 %). Such an enhancement is mainly derived from an extended visible-light response, improved electron excitation and transfer, which are associated with the synergy of cyano defects and CaCO3, as evidenced by a series of spectroscopic analyses. More importantly, in-situ DRIFTS and density functional theory (DFT) results suggest that the introduction of cyano defects and CaCO3 enables control over NO adsorption and activation processes, making it possible to implement a preference pathway (NO → NO+ → NO3¯) and reduce the emission of toxic intermediate NO2. This work demonstrates the potential of integrating defect engineering and insulator modification to design highly efficient g-C3N4-based photocatalysts for air purification.