Synergistic decomposition of imidacloprid by TiO2-Fe3O4 nanocomposite conjugated with persulfate in a photovoltaic-powered UV-LED photoreactor

To facilitate decomposition of imidacloprid (IMD), as a persistent probe insecticide, TiO2-Fe3O4 (TF) nanocomposite was synthesized and characterized. TF particles in size of 50-60 nm with band-gap of 2.8 eV were immobilized onto glass tubes and utilized as a photocatalyst irradiated with ultraviolet-light emitting diode (UV-LED) powered by photovoltaics. Synergistic decomposition of IMD in the photocatalytic reactor injected with persulfate (PS) was investigated. Along with various control and reference tests, parametric studies to evaluate the effects of PS concentration, IMD concentration, and circulation rate on IMD decomposition kinetics and electrical energy consumption were performed. The contribution of various physical and chemical mechanisms to IMD removal was discussed, including self-decomposition, direct photolytic decomposition, chemical oxidation by PS, photolysis of PS to produce sulfate radicals, Fenton-like reaction to produce sulfate radicals, photocatalysis to generate hydroxyl radicals, and adsorption onto catalysts. TF conjugated with PS under UV-LED synergistically decomposed IMD. Additionally, results demonstrated the synergy index factor of 75%, 65%, and 60% for IMD degradation by UV-LED/TF/PS, UV-LED/Fe3O4/PS, and UV-LED/TiO2/PS routes, respectively. Outcomes also showed that utilizing TF can greatly reduce electrical energy consumption. Since all devices used in this study, including UV-LED, were powered solely by a photovoltaic module, the immobilized TF photoreactor was proposed as a sustainable, self-powered, energy-saving, and practical point-of-use decontamination system to remove organic contaminants in water under solar radiation.