Efficient degradation of lindane by visible and simulated solar light-assisted S-TiO2/peroxymonosulfate process: Kinetics and mechanistic investigations

Abstract

Organochlorine pesticides (OCPs) are toxic and the most potent endocrine disrupting chemicals in the environment. Most OCPs are resistant towards oxidation by OH due to presence of electron-withdrawing chlorine group in their molecular structures. Here, we investigated a visible and simulated solar light-assisted sulfur doped TiO2 (S-TiO2)/peroxymonosulfate (HSO5−) process to eliminate a selected OCP, lindane. Initially, visible and simulated solar light-assisted S-TiO2 photocatalysis resulted in 31.0 and 63.4% removal of lindane (C0=1.0μM), respectively in 6h. The photocatalytic activity of S-TiO2 was dramatically increased in the presence of 0.2mM HSO5−, leading to 68.2 and 99.9% lindane removal under visible and simulated solar light illumination, respectively in 6h. The observed pseudo first-order rate constant for simulated solar light-assisted S-TiO2/HSO5− decreased with increasing initial concentration of lindane, corresponding to 8.98×10−1, 6.58×10−1 and 3.84×10−1h−1 at [lindane]0 of 0.5, 1.0 and 2.0μM, respectively. The degradation kinetics were significantly affected by solution pH, leading to 88.2, 99.9 and 71.4% removal of lindane in 6h at pH 4.0, 5.8 and 8.0, respectively. S-TiO2 film exhibited a high mechanical strength with only 3.3% loss of efficiency after four repeated cycles. Based on the detected reaction intermediates, a possible reaction mechanism was proposed, suggesting dechlorination, dehydrogenation, and hydroxylation via OH, SO4− and O2− attack. The results suggest that visible and simulated solar light-assisted S-TiO2/HSO5− is a promising alternative for treatment of water contaminated with most OCPs.