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.