A CQD/CdS/g-C3N4 photocatalyst for dye and antibiotic degradation: Dual carrier driving force and tunable electron transfer pathway

The path and mechanism of charge transfers in composite catalyst are important for degrading organic pollutants effectively. A quasi-ternary Z-scheme heterojunction photocatalyst with carbon quantum dots (CQD), CdS, and graphitic carbon nitride (g-C 3 N 4 ) (CQD/CdS/g-C 3 N 4 ) has been successfully constructed in this work, and its electron transfer path is elucidated by contrast CdS/CQD/g-C 3 N 4 photocatalyst. The built-in electric field at the interface between CdS and g-C 3 N 4 induces exciton separations. The energy barrier between CQD and CdS accelerated charge transfers and further prevents exciton annihilation. As a result, CQD/CdS/g-C 3 N 4 exhibits the greatest photocatalytic degradation, and the removal rates of Rhodamine B and sulfadiazine are 94.7 % and 76.0 %, which are 2.46 times and 1.47 times of CdS/CQD/g-C 3 N 4 , 7.02 times and 7.92 times of g-C 3 N 4 , respectively. It is further proved that CQD as the active site can promote the generation of H 2 O 2 and effectively inhibit the formation of •O 2 – in the photocatalytic reaction. In addition, the degradation pathway and products of sulfadiazine are explored by means of HPLC-MS and calculation of Gaussian software. This work demonstrates the relationship between photocatalytic activity and electron transfer path, meanwhile, provides a reference for the design of efficient heterogeneous photocatalysts for environmental remediation.