Build-in internal electric field in vacancy engineered CdS@ZnIn2S4 type-II heterostructure for boosting photocatalytic tetracycline degradation and in-situ H2O2 generation

The efficient type-II heterostructures hold great interest in the development of photocatalysts that respond to ultraviolet-(UV) to visible light (Vis) and possess numerous advantageous physicochemical properties that can enhance their ability toward robust environmental decontamination upon exposure to solar light. Herein, we designed a range of type-II n-n photocatalysts comprising immobilized CdS on sulfur-vacancy-rich ZnIn2S4 (CdS@V-ZIS) through the two-step synthesis approach. The catalytic activities of CdS@V-ZIS heterostructures were evaluated for the photocatalytic degradation of tetracycline (TC) and in-situ production of H2O2 under simulated solar-light irradiation. Benefiting from the extended light-absorption edge, well-aligned band structure, and built-in electric field, the optimum heterostructure sample (CdS@V-ZIS-0.5) achieved an impressive removal activity of 98.6 % and mineralization efficiency of 65.1 %. Through the electron spin resonance and reactive radical-scavenging techniques, it was determined that the primary active species responsible for the removal of TC were hydroxyl and superoxide radicals. The transport path of charge carriers and possible photocatalytic mechanism were thoroughly investigated by the analyses of ultraviolet photoelectron spectroscopy, valence-band X-ray photoelectron spectroscopy, and diffusion reflectance spectroscopy. Regarding the photo catalytic experiments, the in-situ hydrogen peroxide generation rate over CdS@V-ZIS-0.5 attained 4.012 mmol L-1, which was 1.62 and 2.99 times higher than that of V-ZIS and CdS, respectively. We expect that our research will open up new avenues toward the development of novel heterojunctions along with interfacial engineering, which can significantly enhance the effectiveness of water purification systems.