Embedded iron and nitrogen co-doped carbon quantum dots within g-C3N4 as an exceptional PMS photocatalytic activator for sulfamethoxazole degradation: The key role of Fe N bridge

The covalent modification of graphite-phase carbon nitride (g-C3N4) by carbon quantum dots (CQDs) is a promising way to improve its photocatalytic performance. Although CQDs can act as charge mediator for electrons storage and transfer, it is crucial to construct efficient interfaces, which serves as active sites for tight connect with g-C3N4 and fast release of electrons. Herein, a novel iron and nitrogen co-doped carbon quantum dots (Fe, N-CQDs) assembled g-C3N4 composite (FNCCN) was constructed via FeN bridge by hydrothermal and thermal polymerization methods. The FNCNN rivaled popular nitrogen-doped carbon quantum dots (N-CQDs) combined with g-C3N4 composites for peroxymonosulfate (PMS) activation and degradation of sulfamethoxazole (SMX). The SMX degradation rate (0.0963 min−1) is 5.38 and 3.15 times higher than that of g-C3N4 and N-CQDs/g-C3N4. The characterization and DFT calculation results suggest that Fe, N-CQDs was successfully incorporated into carbon matrix of g-C3N4 via FeN covalent bond, which joints the two counterparts closely and creates electron transport channels for higher electrons transfer efficiency. The FeN coordinated structure promotes PMS reduction on Fe2+ of FeN sites for HO and SO4- production and expedited photo carries separation through Fe3+/Fe2+ cycling. In addition, the degradation efficiency, ROS identification, EPR test and degradation pathway of SMX was determined, and the intermediate toxicity of degradation products was predicted. This work constructed a tight atomic-level connection between hydrophobic g-C3N4 and hydrophilic CQDs, which improved an effective strategy for accelerating electron transport and efficient photocatalytic activation of PMS.