US-assisted catalytic degradation of paraquat using ZnO/Fe3O4 recoverable composite: Performance, toxicity bioassay test and degradation mechanism

In this study, the ZnO/Fe₃O₄ catalyst was used as an active catalyst for the oxidation of Paraquat (PQ) herbicide in aqueous solution under ultrasonic (US) waves. FTIR, XRD, FE-SEM, and VSM analyses were performed to characterize the synthesized catalyst. Studies on the effect of radical scavengers were also carried out and the amount of organic matter degradation was determined by measuring the TOC. Under the optimized conditions (catalyst concentration = 0.75 g/L, herbicide concentration = 10 ppm, US power = 70w), the degradation and mineralization rates of the herbicide were acquired as 96.1% and 68% within 60 min, respectively. The quenching tests showed that the hydroxyl (oOH) radical was the most effective oxidant agent in the degradation process of the PQ under ZnO/Fe₃O₄/US system. The toxicity of treated effluent assayed by Daphnia Magna was decreased from %73.16 in raw samples to %7.2 in the treated samples, during 96 h. Finally, it can be concluded that ZnO/Fe₃O₄/US process can be successfully performed as an effective process to herbicides in aqueous solutions, due to the high efficiency and excellent catalytic activity.