Delicate Construction of Z-Scheme Heterojunction Photocatalysts by ZnS Quantum Dots Wrapped CoWO₄ Nanoparticles for Highly Efficient Environmental Remediation

In recent times, the fabrication of Z-scheme heterostructures has gained popularity as an effective strategy for developing composite catalysts with photogenerated carriers that possess high redox capacity. This study introduces a novel type of direct Z-scheme heterojunction photocatalysts known as ZnS quantum dots wrapped around CoWO₄ nanoparticles (ZnS-QDs@CoWO₄). The results of the experiments and analysis indicate that these heterojunction photocatalysts demonstrate superior degradation of tetracycline hydrochloride in wastewater compared with individual ZnS-QDs or CoWO₄. Notably, the 30ZS-CWO catalyst, with a mass ratio of 30:1 between ZnS-QDs and CoWO₄, exhibited the highest photocatalytic reaction rate constant (k = 0.03427 min^-1), which is 3.5 times greater than that of ZnS-QDs (k = 0.00969 min^-1) and 214 times higher than that of CoWO₄ (k = 0.00016 min^-1). The enhanced photocatalytic performance can be attributed to two main factors. First, the use of CoWO₄ nanoparticles as carriers helps in better dispersing the ZnS quantum dots, leading to increased catalytic reaction sites. Second, the formation of Z-scheme heterojunctions in the composite photocatalysts significantly boosts the redox capability of the photogenerated carriers. Furthermore, the excellent stability and recyclability of ZnS-QDs@CoWO₄ heterojunction photocatalysts were validated through five-cycle experiments. This research introduces a promising approach for developing QDs-based Z-scheme photocatalysts for highly effective environmental remediation.