Exhaustive photocatalytic lindane degradation by combined simulated solar light-activated nanocrystalline TiO₂ and inorganic oxidants

Organochlorine compounds (OCs) are very toxic, highly persistent, and ubiquitous contaminants in the environment. Degradation of lindane, a selected OC, by simulated solar light-activated TiO₂ (SSLA-TiO₂) photocatalysis was investigated. The film types of the TiO₂ photocatalyst were prepared using a dip-coating method. The physical properties of the films were investigated using X-ray diffraction, transmission electron microscopy, and environmental scanning electron microscopy. The SSLA-TiO₂ photocatalysis led to a lindane removal of 23% in 6 h, with 0.042 h^-1 of an observed pseudo first-order rate constant (k_obs). The SSLA-TiO₂ photocatalysis efficiency was greatly enhanced by adding hydrogen peroxide (H₂O₂), persulfate (S₂O₈ ^2-), or both combined, corresponding to a 64%, 89%, and 99% lindane removal in the presence of 200 µM of H₂O₂, S₂O₈ ^2-, or equimolar H₂O₂-S₂O₈ ^2-, respectively. The hydroxyl and sulfate radicals mainly participated in lindane degradation, proven by the results of a radical scavenger study. The degradation kinetics were hindered in the presence of the water constituents, indicated by a 61%, 35%, 50%, 70%, 88%, and 91% degradation of lindane in 6 h, using a SSLA-TiO₂/S₂O₈ ^2-/H₂O₂ photocatalysis system containing 1.0 mg L^-1 humic acid (HA), or 1 mM of CO₃ ^2-, HCO₃ ^-, NO₃ ^-, SO₄ ^2-, and Cl^-, respectively. The TiO₂ film demonstrated high reusability during four runs of lindane decomposition experiments. The SSLA-TiO₂/S₂O₈ ^2-/H₂O₂ photocatalysis is very effective for the elimination of a persistent OC, lindane, from a water environment.