Tunable band structure of synthesized carbon dots modified graphitic carbon nitride/bismuth oxychlorobromide heterojunction for photocatalytic degradation of tetracycline in water

In this study, graphitic carbon nitride (CN) decorated with carbon quantum dot (CQD) and bismuth oxychlorobromide (BiOCl_xBr_1-x) was fabricated by calcination and hydrothermal methods. The morphology characterization of the synthesized photocatalyst revealed that CQD and BiOCl_xBr_1-x solid solution were deposited on the CN surface. CQD served as the electron reservoir, which could reduce the recombination of electron-hole pairs, thus improving the overall photocatalytic performance. The synergistic effect of 1 wt% CQDs and BiOCl_0.75Br_0.25 markedly improved the interfacial charge transfer efficiency and light-harvesting capacity of the composite. The degradation rate of tetracycline (TC) over CN/CQD/BiOCl_0.75Br_0.25 was 83.4 % after 30 min and favorable stability with near-initial capacity under visible light irradiation. Meanwhile, the reaction mechanism of the photocatalytic performance was demonstrated by the analysis of the surface adsorption sites, efficient utilization of visible light, and charge carrier transfer. The degradation by-products and potential degradation pathways were also analyzed using liquid chromatography-mass spectrometry. Finally, the toxicity estimation software tool (T.E.S.T) analysis indicated that the toxicity of most intermediates was lower than TC. This work provideed a strategy for fabricating visible light (VL) photocatalyst with excellent photocatalytic activity, furnishing a new insight for interface charge transfer.