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

ABSTRACT

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 (e_aq^-), 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 e_aq^-. 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.

GRAPHICAL ABSTRACT

KEYWORDS:

• CCl₄
• aqueous electron
• degradation
• reduction
• mechanism

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Zhen Wang http://orcid.org/0000-0002-9573-2129

Additional information

Funding

This study was granted by the National Natural Science Foundation of China [grant number 50578151], the Major Science and Technology Program for Water Pollution Control and Treatment of China [grant number 2015ZX07406005-001], and the Fundamental Research Funds for the Central Universities (CN) [grant number 2652018187].