Insights into effect of chloride ion on the degradation of 4-bromo-2-chlorophenol by sulphate radical-based oxidation process

ABSTRACT

Degradation efficiency of 4-bromo-2-chlorophenol (BCP) containing both chlorine and bromine substituents in Co/PMS process was investigated in the light of a wide range of substrate, oxidant, catalyst concentrations and pH value. The effects of chloride ion (Cl⁻) on degradation kinetics, total organic carbon (TOC) removal and intermediates formation during BCP depletion in Co/PMS system were studied. The kinetics results demonstrated that the dual effect of Cl⁻ on BCP depletion in Co/PMS system due to different mechanisms involved. High concentrations of Cl⁻ (>5 mM) can significantly promote the degradation of BCP, but did inhibit BCP mineralisation to a certain extent which was closely related to Cl⁻ content. High degradation rates but lower mineralisation rates were found in the laboratory experiments, owing to the fact that BCP was mainly transformed to new halogenated intermediates instead of complete mineralisation. Gas chromatograph-mass spectrometer (GC-MS) data verified that a series of chlorinated by-products were formed during BCP decomposition process involving of the participation of Cl⁻. The proposed degradation pathways of BCP and its derivatives in presence of Cl⁻ were discussed on the basis of intermediate products including the undesirable halogenated by-products recognised by GC-MS. These results might offer some new perspectives on the transformation fates of BCP by utilising Co/PMS regent.

KEYWORDS:

• 4-bromo-2-chlorophenol
• sulphate radical
• chloride
• halogenated products
• degradation pathway

Acknowledgments

This work was supported by National Key Research and Development Program of China (2016YFC0400501), Shanghai Sailing Program (19YF1459900). The present work was also financially supported by the Central-Public interest Scientific Institution Basal Research Fund (2019T13, 2019T14), Shanghai Natural Science Foundation (20ZR1421100) and Science and Technology Development Fund of Pudong New Area (PKJ2021-C01). Dr. Guo also appreciates the Project of Key Undergraduate Courses (Instrumental Analysis) from Shanghai Municipal Education Commission (A01GY21G013-03).

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No potential conflict of interest was reported by the authors.

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Funding

This work was supported by National Key Research and Development Program of China (2016YFC0400501), Shanghai Sailing Program (19YF1459900). The present work was also financially supported by the Central-Public interest Scientific Institution Basal Research Fund (2019T13, 2019T14), Shanghai Natural Science Foundation (20ZR1421100) and Science and Technology Development Fund of Pudong New Area (PKJ2021-C01). Dr. Guo also appreciates the Project of Key Undergraduate Courses (Instrumental Analysis) from Shanghai Municipal Education Commission (A01GY21G013-03).