Construction of ZnO quantum dots anchored in oxygen-doped g-C3N4: A novel Z-type heterojunction with boosting photocatalytic performance for tetracycline degradation

Photocatalysis is widely acknowledged as a promising approach for eliminating antibiotic pollutants in the environment. This study introduces a novel Z-type heterojunction composed of ZnO quantum dots (QDs) anchored in oxygen-doped g-C3N4 (OCN), obtained by a straightforward one-pot calcination method. The degradation efficacy of the resulting catalysts was evaluated by the photocatalytic degradation of tetracycline (TC). The ZnO/OCN composites exhibit excellent photocatalytic activity in comparison with the individual catalysts. Notably, ZnO/OCN-2 achieves an optimal degradation efficiency of 92.4 % and the reaction rate constant is calculated to be 0.0406 min-1, which is approximately 5.72, 6.06 and 4.02 folds higher than that of pure ZnO, OCN and their mixtures, respectively. This enhanced photocatalytic activity is attributable to the synergistic effects of oxygen doping and the formation of a heterostructure between the ZnO QDs and OCN, leading to an enhanced visible light capture and an accelerated separation of photoexcited charges, which is conducive to more center dot O2-, photoexcited h+ and center dot OH production involved in the degradation process. Furthermore, a Z-type photocatalytic mechanism was suggested, supported by radical trap tests and electron spin resonance (ESR) analysis. In summary, this work presents a simple and effective one-pot synthesis strategy for constructing g-C3N4-based heterojunctions, significantly boosting the photocatalytic degradation of antibiotic contaminants.