Template-free synthesis of oxygen-containing ultrathin porous carbon quantum dots/g-C3N4 with superior photocatalytic activity for PPCPs remediation

Abstract

The development of facile and environmentally compatible synthetic strategies for broad-spectrum response photocatalysts is a primary goal for researchers in this area. For this study, we report on a template-free thermal treatment strategy for the synthesis of an oxygen-containing ultrathin porous carbon quantum dots/polymeric carbon nitride metal-free composites (CQD/OUPCN). Morphology characterization revealed that the thermal treatment induced bulk CQD/g-C₃N₄ (CQD/BCN) to transform to porous ultrathin 2D nanosheets with a high specific surface area. Chemical structure characterization revealed that O atoms were involved in the chemical composition of C₃N₄ following the introduction of CQD and subsequent thermal treatment. Optical and electrical characterization, as well as density functional theory (DFT) calculations, confirmed that the introduction of O atoms and CQD enabled the tuning of the intrinsic electronic state, and improved the charge transfer capacity of C₃N₄. Together with the up-converted fluorescence properties of CQD, the CQD/OUPCN exhibited remarkable broad-spectrum activity toward the degradation of PPCPs. Under visible light irradiation, the CQD/OUPCN-0.5% showed an 18.5 fold higher indomethacin (IDM) degradation rate than did g-C₃N₄. Further kinetics studies, including reactive species (RS) and degradation intermediate detection, indicated that RS, particularly O₂˙⁻, was generated during the photocatalytic process, which could lead to the decomposition, and finally mineralization of IDM.