Mechanistic aspects of photocatalytic degradation of Lindane by TiO2 in the presence of Oxalic acid and EDTA as hole-scavengers

Abstract

γ-Hexachlorocyclohexane (γ-HCH, Lindane) is a carcinogen and endocrine-disrupting compound. Lindane’s widespread presence in various components of the environment demands efficient methods of its remediation. Photocatalytic reduction (PCR) of γ-HCH, Lindane using P25 (TiO2) in the presence of Oxalic acid (OA) and Ethylenediaminetetraacetic acid (EDTA) as hole-scavengers (HS) was investigated. Concentrations of OA ≤25 mM could not completely suppress photocatalytic oxidation (PCO). Complete reductive dechlorination of lindane was achieved in the presence of 1 mM EDTA and 1 g/L TiO2 after 90 min of irradiation at an initial pH of 2.8. Intermediates formed during PCR were analyzed using GC-MS and complete dechlorination of lindane was confirmed by detection of cyclohexene as one of the end-products besides chloride ions. Dichloroelimination and dehydrochlorination followed by hydrodechlorination was the most likely pathway of lindane degradation. The initial pH of the solution greatly influenced the rate and pathway of lindane removal. Reductive dechlorination was favoured at pH 2.8, whereas PCO could not be suppressed at pH 5.1. Complete dechlorination of lindane was also possible under sunlight, although at a much slower rate than that under UV light. PCR of lindane using TiO2 is not reported so far.