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

Abstract

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.