Photoreductive degradation of CCl4 by UV-Na2SO3: influence of various factors, mechanism and application

Due to the strong electron-withdrawing nature of Cl atom in CCl4, CCl4 could not readily be degraded by oxidation process. In the present study, aqueous electron (eaq-), a powerful reducing agent generated in UV-Na2SO3 system, was applied to reductively degradation of CCl4. The effects of several crucial factors (e.g. Na2SO3 concentration, solution pH, inorganic ions and NOM) on CCl4 degradation as well as degradation mechanism and pathway were systematically investigated. Results indicated that CCl4 was efficiently degraded in UV-Na2SO3 system and the process could be well described by pseudo-first order kinetic model. The degradation rate increased with the elevated Na2SO3 concentration (0–10 mmol/L) and solution pH (6.0–8.0), while remained approximately constant in alkaline conditions (pH = 8.0, 9.0 and 10.0). Nevertheless, O2, inorganic ions and NOM exerted a negative effect on CCl4 degradation and the removal efficiency of CCl4 in groundwater was only 31.7%. Mechanistic study implied that degradation of CCl4 was primarily induced by eaq-. CCl4 (10 mg/L) was almost completely dechlorinated within 60 min and the predominant intermediate products were CHCl3, C2Cl4 and C2HCl3. CHCl3 and CH2Cl2 were also rapidly degraded in the UV-Na2SO3 system.