Enhanced sunlight-driven photocatalytic removal of tetracycline via C=O-functionalized g-C3N4: band structure tuning and active site regulation

The photocatalytic performance of materials is primarily governed by their band structure, charge carrier transport, and active sites. This study introduces a surface modification strategy for graphitic carbon nitride (g-C 3 N 4 ) using C=O groups to significantly enhance its photocatalytic activity. The C=O-modified g-C 3 N 4 (CNSHQC2) demonstrated exceptional photocatalytic performance. It achieved a degradation rate of over 85 % for tetracycline hydrochloride (TC) in five different real wastewater matrices within 40 min of natural sunlight exposure. By combining quantitative structure-activity relationship analysis with site-specific blocking experiments, the C=O groups were identified as the primary active sites. Traditional functional group modifications typically improve photocatalytic performance by increasing surface area or enhancing charge transfer. In contrast, C=O modification simultaneously optimizes the band structure and introduces active sites that promote PMS activation. The results indicate that this dual modulation of electronic structure and surface chemistry facilitates efficient charge carrier separation and enhances the generation of reactive oxygen species (ROS). Additionally, C=O groups increase triplet exciton generation and promote singlet oxygen formation via energy transfer. These synergistic effects collectively contribute to a significant improvement in the photocatalytic performance of g-C 3 N 4 . This work provides a new strategy for designing high-performance photocatalysts and valuable insights into the role of C=O groups in expanding the potential applications of carbon-based materials in environmental remediation.