Novel in-situ composites of chlorine-doped CQDs and g-C3N4 with improved interfacial connectivity and accelerated charge transfer to enhance photocatalytic degradation of tetracycline and hydrogen evolution

The photocatalytic performance of graphite-phase carbon nitrides (g-C3N4) composites is severely limited by poor interfacial connectivity and a narrow visible light response range. Although carbon quantum dots (CQDs) can enhance the visible light absorption of g-C3N4, it is difficult to produce effective interfacial connectivity due to their different properties. Herein, a novel “in-situ composite modified by chlorine-doped CQDs” strategy was proposed to further enhance the photocatalytic redox capability of g-C3N4. Specifically, chlorine-doped CQDs (Cl-CQDs) were prepared from mulberry branch powder and sulfoxide chloride directly, and the novel metal-free photocatalyst (Cl-CCN) was prepared by in-situ compounding the Cl-CQDs with g-C3N4. Cl-CCN shows superior photocatalytic tetracycline degradation rate (0.0269 min−1) and hydrogen production rate (1397.5 µmol g−1h−1), which are 14.9 and 2.75 times higher than those of g-C3N4, respectively. The characterization and DFT calculation results reveal that the C − Cl covalent bonds serve as fast electronic channels to bridge the hydrophilic Cl-CQDs and hydrophobic g-C3N4 and significantly enhance the interfacial coupling and charge transfer. On this basis, a possible mechanism for tetracycline degradation and hydrogen production photocatalyzed by Cl-CCN is proposed. This study provides a concise and economical method for modifying and enhancing the photocatalytic activity of composites CQDs/g-C3N4.