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[Display omitted] • Removal of lindane was studied by visible and simulated solar light-assisted S-TiO 2. • Efficiency of S-TiO 2 photocatalysis dramatically increased in the presence of HSO 5 −. • Operational parameters such as pH, concentration of lindane and HSO 5 − were optimized. • Degradation mechanism was proposed based on identified intermediates and final products. • S-TiO 2 photocatalysis is an effective AOP to treat lindane contaminated waters. 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 TiO 2 (S-TiO 2)/peroxymonosulfate (HSO 5 −) process to eliminate a selected OCP, lindane. Initially, visible and simulated solar light-assisted S-TiO 2 photocatalysis resulted in 31.0 and 63.4% removal of lindane (C 0 = 1.0 μM), respectively in 6 h. The photocatalytic activity of S-TiO 2 was dramatically increased in the presence of 0.2 mM HSO 5 −, leading to 68.2 and 99.9% lindane removal under visible and simulated solar light illumination, respectively in 6 h. The observed pseudo first-order rate constant for simulated solar light-assisted S-TiO 2 /HSO 5 − decreased with increasing initial concentration of lindane, corresponding to 8.98 × 10−1, 6.58 × 10−1 and 3.84 × 10−1 h−1 at [lindane] 0 of 0.5, 1.0 and 2.0 μM, respectively. The degradation kinetics were significantly affected by solution pH, leading to 88.2, 99.9 and 71.4% removal of lindane in 6 h at pH 4.0, 5.8 and 8.0, respectively. S-TiO 2 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, SO 4 − and O 2 − attack. The results suggest that visible and simulated solar light-assisted S-TiO 2 /HSO 5 − is a promising alternative for treatment of water contaminated with most OCPs. [ABSTRACT FROM AUTHOR]

Degradation of lindane, a highly persistent and potentially carcinogenic pesticide, by iron (II) activated peroxymonosulfate (Fe 2+ /HSO 5 − ) was investigated. The efficiency of this process was found to increase with UV light irradiation, probably due to an improved regeneration of Fe 2+ for a fast generation of highly reactive OH and SO 4 − . A greater mineralization and dechlorination efficiency was also observed by UV/Fe 2+ /HSO 5 − , with a 92.2% total organic carbon removal and 96.4% chloride ion release after 180 min UV illumination. Removal of lindane by such a photochemical process was further promoted with increasing the initial concentration of either Fe 2+ (10–1000 μM) or HSO 5 − (50–1000 μM). The initial degradation rate of lindane increased while the observed pseudo first - order rate constant ( k obs ) decreased with increasing the initial concentration of lindane. Higher pH (>4) resulted in a lower efficiency of UV/Fe 2+ /HSO 5 − , attributable to the complexation or precipitation of Fe 2+ /Fe 3+ . A Fe 2+ level of 50 and 500 μM showed a comparable effect on lindane mineralization, probably due to the scavenging of SO 4 − and OH or the faster decomposition of the oxidant by excess Fe 2+ . Additionally, potential activation of Fe 2+ /HSO 5 − by fluorescence light was evaluated. Despite an enhanced degradation of lindane, no significant mineralization of lindane was observed. The results indicate that UV/Fe 2+ /HSO 5 − is effective and has a strong application potential for the degradation of lindane and other chlorinated pesticides. [ABSTRACT FROM AUTHOR]

• Degradation of lindane by UV/persulfate based AOPs was investigated. • Mechanism involved H-abstraction by SO 4 •− accompanied by C-Cl bond cleavage via UV-C. • Both less and more toxic by-products than lindane were produced, but vanished at high UV dose. • Natural organic matter and inorganic ions considerably affect degradation efficiency. • H 2 O 2 had significant synergistic effects on UV/persulfate process. Sulfate radical-advanced oxidation processes (SR-AOPs) are emerging technologies for decomposing organic pollutants in water. This study investigated the efficiency of UV/persulfate (UV/S 2 O 8 2−) process to degrade lindane in water, showing 93.2% lindane removal ([lindane] 0 = 3.43 μM, [S 2 O 8 2−] 0 = 100 μM) at a UV fluence of 720 mJ/cm2. The lindane degradation followed first order kinetics and mechanistic studies suggested H-abstraction by SO 4 •− and Cl removal via C-Cl bond cleavage by UV-C light. Toxicity assessment using ECOSAR program showed toxicity gradually decreased and eventually no significant toxicity remained when all by-products vanished at high UV dose. Removal efficiency of lindane decreased from 93.2% to 38.4, 45.5, 56.0, 84.3 and 88.6%, by adding 1.0 mg/L humic acid or 1.0 mM CO 3 2−, HCO 3 −, Cl− or SO 4 2−, respectively. Coupling of H 2 O 2 with UV/S 2 O 8 2− showed a significant synergistic effect with 99.0% lindane removal at a UV fluence of 600 mJ/cm2, using [S 2 O 8 2−] 0 = [H 2 O 2 ] 0 = 50 μM while UV/H 2 O 2 resulted in only 36.6% lindane removal ([lindane] 0 = 3.43 μM, [H 2 O 2 ] 0 = 100 μM) at a UV fluence of 720 mJ/cm2. The results indicate that SR-AOP has potential for consideration as a remedial technology to treat persistent chlorinated pesticides such as lindane in contaminated water. [ABSTRACT FROM AUTHOR]

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 (kobs). The SSLA-TiO2 photocatalysis efficiency was greatly enhanced by adding hydrogen peroxide (H2O2), persulfate (S2O82−), or both combined, corresponding to a 64%, 89%, and 99% lindane removal in the presence of 200 µM of H2O2, S2O82−, or equimolar H2O2-S2O82−, 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/S2O82−/H2O2 photocatalysis system containing 1.0 mg L−1 humic acid (HA), or 1 mM of CO32−, HCO3−, NO3−, SO42−, and Cl−, respectively. The TiO2 film demonstrated high reusability during four runs of lindane decomposition experiments. The SSLA-TiO2/S2O82−/H2O2 photocatalysis is very effective for the elimination of a persistent OC, lindane, from a water environment. [ABSTRACT FROM AUTHOR]