Synthesis of highly conductive carbon quantum dot-enhanced Z-scheme BiOBr/g-C3N4 heterojunction for effective photocatalytic degradation of tetracycline hydrochloride

BiOBr can effectively mitigate the ecological and environmental problems caused by pollution with antibiotics, and its photocatalytic properties can be improved by utilizing heterojunction structures and cocatalysts. In this study, the Z-scheme heterojunction ternary photocatalyst BiOBr/g-C3N4/CQDs (BCCx) was obtained by using an uncomplicated electrostatic self-assembly process. The incorporation of carbon quantum dots (CQDs) with high conductivity provided a conduit for charge transfer between g-C3N4 and BiOBr. The loading density of CQDs on BiOBr/g-C3N4 could be rapidly adjusted by changing the concentration of the CQD precursor in solution. The presence of CQDs enhanced the absorption of visible light and inhibited the synthesis of photogenerated charge carriers, thereby resulting in a synergistic effect on the Z-scheme heterojunction and improving the photocatalytic properties under visible light. In particular, BCC50 had the highest catalytic performance, with a tetracycline pollutant degradation efficiency of 100% within 60 min. The degradation efficiency remained above 95% even after repeated use in five cycles. The principles of semiconductor energy bands and internal electrostatic field generation are applied to explain the photocatalytic mechanism responsible for tetracycline degradation using BiOBr/g-C3N4/CQDs.