Boosting peroxymonosulfate activation over Bi2MoO6/CuWO4 to rapidly degrade tetracycline: Intermediates and mechanism

In peroxymonosulfate (PMS) activation processes, sluggish kinetics of Cu2+/Cu+ redox rate has been the weakness of photocatalytic conversion efficiency. In this work, Bi2MoO6/CuWO4 photocatalysts were synthesized via a facile hydrothermal method, which significantly boosted the Cu2+/Cu+ cycle and promoted PMS activation for the removal of tetracycline (TC) under visible light irradiation. Bi2MoO6/CuWO4 with the mass ratio of 4:1 displayed significantly enhanced photocatalytic activity toward TC degradation with the assistance of a low concentration of PMS, which was 1.95 and 2.24 times as those of CuWO4 and Bi2MoO6, respectively. The influence of initial pH values, PMS dosage and different inorganic anions during the photodegradation process was systematically investigated and demonstrated that Bi2MoO6/CuWO4 could perform photocatalytic reactions in the wide pH range of 2.0-10.0. Also, Bi2MoO6/CuWO4 showed excellent reusability and stability in the cycling experiments. Additionally, the possible degradation pathways in the PMS system were proposed according to the determination of generated intermediates during the degradation process. According to the band structures together with active species trapping experiments, a possible type-II photocatalytic charge transfer mechanism of Bi2MoO6/CuWO4 was reasonably proposed. XPS analysis of the fresh and used samples indicated that constructing type-II heterojunction significantly boosted the Cu2+/Cu+ cycle and promoted PMS activation, thereby accelerating the TC degradation. In conclusion, this work could shed more light on promoting PMS activation for the practical removal of organic pollutants in wastewater.

Automated summary

In this study, Bi2MoO6/CuWO4 photocatalysts were synthesized to enhance the Cu2+/Cu+ cycle and promote PMS activation for the degradation of tetracycline (TC) under visible light. The photocatalytic activity of Bi2MoO6/CuWO4 was significantly higher than CuWO4 and Bi2MoO6. The pH, PMS dosage, and inorganic anions were investigated, and Bi2MoO6/CuWO4 showed excellent performance in a wide pH range. The recycling experiments and analysis of intermediate products confirmed the reusability and proposed the degradation mechanism. The study sheds light on PMS activation for practical removal of organic pollutants in wastewater.