Sonocatalytic degradation of tetracycline by BiVO₄/CuWO₄ nanocomposites: operational parameters, sonocatalytic mechanism, and degradation pathways

In this study, BiVO₄/CuWO₄ nanocomposites with S-scheme heterojunction structure were prepared firstly and the properties were analyzed by various techniques. The sonocatalytic activity was evaluated by the degradation of tetracycline (TET). Under the optimum experimental conditions of initial concentration of TET = 25 mg/L, composite ratio of BiVO₄ and CuWO₄ = 15%, catalyst addition = 1 g/L, ultrasonic time = 120 min, ultrasonic power = 500 W, pH = 7, the experiment results showed that BiVO₄/CuWO₄ sonocatalyst removed TET by 81.05 ± 2.92%. K₂S₂O₈ was verified to enhance the sonocatalytic performance of BiVO₄/CuWO₄ efficiently, and the removal ratio of TET could reach 91.25 ± 1.95% within 120 min by using BiVO₄/CuWO₄ and K₂S₂O₈. The free radical (ROS) quenching experiment and TA-PL technology proved that the main free radical of degradation was ·OH. The potential sonocatalytic mechanism showed that the enhanced catalytic efficiency was due to the construction of S-scheme heterojunctions, which improved electron–hole pair (e⁻–h⁺) separation efficiency and rapid kinetics. The speculated TET degradation route of TET included intermediate products was proposed and four reused experiments proved that BiVO₄/CuWO₄ had good recyclability. In conclusion, the prepared BiVO₄/CuWO₄ composites with S-type heterojunction mechanism have more possibilities in wastewater treatment, which provides a helpful guide for the synthesis and application of composite sonocatalysts.