Ultrasound-assisted decomposition of metronidazole by synthesized TiO2/Fe3O4 nanocatalyst: Influencing factors and mechanisms

Abstract This study focused on the facile preparation of TiO2/Fe3O4 catalyst prepared by the sol-gel approach as an efficient catalyst for decomposition and mineralization of metronidazole (MTN) in TiO2/Fe3O4/US process. FE-SEM, EDX, VSM, FTIR and XRD analyses were used to characterize the catalyst. The results confirmed the formation of TiO2/Fe3O4 catalyst with the average crystallite size of 32.4 nm. The influence of various factors such as solution pH, catalyst dose, initial MTN concentration and ultrasonic (US) power was examined on MTN decomposition. Also, the effect of various scavengers and inorganic anions was evaluated. In addition, mineralization of MTN, intermediates, reusability and stability tests of catalyst was also investigated. The removal efficiency of MTN by TiO2/Fe3O4 assisted ultrasonic was higher than of pure TiO2 and Fe3O4 nanoparticles. Under the optimal conditions (TiO2/Fe3O4 dosage = 1.0 g L−1, pH = 5.0, initial MTN content = 10 mg L−1, US power = 40 W and time = 90 min), 97.5% of MTN was removed. The scavenging studies expressed that •OH radicals were the main active species in the process. The GC–MS analysis showed that MTN was firstly decomposed into aromatic and aliphatic intermediates in the first stage of the reactions and then mineralized to CO2, H2O and inorganic ions. The removal efficiency of 91.2% for COD and 73.6% for TOC approved the efficient mineralization of MTN solution. The low leakage value of Fe and high reusability of the catalyst (within six consecutive cycles) indicated that TiO2/Fe3O4 had a high stability and reusability and makes it a promising catalyst for efficient degradation of antibiotics in the practical applications.