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Boosting exciton dissociation and molecular oxygen activation by in-plane grafting nitrogen-doped carbon nanosheets to graphitic carbon nitride for enhanced photocatalytic performance

Dong, Shanshan, Liu, Chao, Chen, Yinguang
Journal of colloid and interface science 2019 v.553 pp. 59-70
carbon nitride, dissociation, energy, graphene, hydrogen peroxide, irradiation, light intensity, nanosheets, oxygen, photocatalysis, photocatalysts, photooxidation, polymers, remediation, solar energy, solar radiation, sulfamethoxazole, superoxide anion
The metal-free graphitic carbon nitride (g-C₃N₄) polymer is a promising photocatalyst for energy production and environmental protection. However, attempts to intrinsically improve its low activity in photooxidation are rarely effective for the poor molecular oxygen (O₂) activation. Here we report a synthesis of directionally nitrogen-doped in-plane metal-free heterostructure, through coplanar grafting nitrogen-doped carbon nanosheets (NDCN) to g-C₃N₄. The in-plane grafted NDCN not only promoted exciton dissociation and charge transfer but also enhanced activating O₂ to reactive oxygen species, including superoxide radicals (O₂⁻) and H₂O₂. The optimal C₃N₄-NDCN coplanar heterojunction (C₃N₄-NDCN-3) photocatalytically degraded 96.3% of sulfamethoxazole (SMX) under visible light irradiation at a low light intensity of 14.5 mW cm⁻² in 4 h, whose SMX degradation rate was 37.7-fold higher than that of pure g-C₃N₄. Furthermore, C₃N₄-NDCN-3 exhibited 95.3% removal of SMX under sunlight irradiation (59.8 mW cm⁻²) in 1 h, higher than the 58.0% of pristine g-C₃N₄. First-principles calculations and material characterizations demonstrated that the coplanar NDCN served as electron sink and catalytic center for hot-electron involved O₂ activation. The improved charge carrier separation and O₂ activation promoted generation of photoexcited hole and superoxide for photocatalytic degradation of SMX. The design strategy in this work inspires a new approach for high-performance polymer photocatalysts in solar energy storage and environmental remediation.