Oxidation of Refractory Benzothiazoles with PMS/CuFe2O4: Kinetics and Transformation Intermediates
KAUST DepartmentWater Desalination and Reuse Research Center (WDRC)
Biological and Environmental Sciences and Engineering (BESE) Division
Environmental Science and Engineering Program
Water Desalination & Reuse Research Cntr
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AbstractBenzothiazole (BTH) and its derivatives, 2-(methylthio)bezothiazole (MTBT), 2-benzothiazolsulfonate (BTSA) and 2-hydroxybenzothiazole (OHBT), are refractory pollutants ubiquitously existing in urban runoff at relatively high concentrations. Here, we report their oxidation by CuFe2O4-activated peroxomonosulfate (PMS/CuFe2O4), focusing on kinetics and transformation intermediates. These benzothiazoles can be efficiently degraded by this oxidation process which is confirmed to generate mainly sulfate radicals (with negligible hydroxyl-radical formation) under slightly acidic to neutral pH conditions. The molar exposure ratio of sulfate radical to residual PMS (i.e. Rct) of this process is a constant which is related to reaction condition and can be easily determined. Reaction rate constants of these benzothiazoles towards sulfate radical are (3.3 ± 0.3) × 109, (1.4 ± 0.3) × 109, (1.5 ± 0.1) × 109 and (4.7 ± 0.5) × 109 M-1s-1, respectively (pH 7 and 20 oC). Based on Rct and these rate constants, their degradation in the presence of organic matter can be well predicted. A number of transformation products were detected and tentatively identified using triple-quadruple/linear ion trap MS/MS and high-resolution MS. It appears that sulfate radicals attack BTH, MTBT and BTSA on their benzo ring via electron transfer, generating multiple hydroxylated intermediates which are reactive towards common oxidants. For OHBT oxidation, it prefers to break down the thiazole ring. Due to competitions of the transformation intermediates, a minimum PMS/pollutant molar ratio of 10-20 is required for effective degradation. The flexible PMS/CuFe2O4 could be a useful process to remove the benzothiazoles from low DOC waters like urban runoff or polluted groundwater.
CitationOxidation of Refractory Benzothiazoles with PMS/CuFe2O4: Kinetics and Transformation Intermediates 2016 Environmental Science & Technology
SponsorsThis research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST). We thank Prof. Jean-Philippe Croué (Curtin University, Australia) for the gift of HOPA and efOM. The assistance of Ms. Tong Zhan and Dr.Julien Le Roux (WDRC, KAUST) and Mr. Salim Sioud (Analytical Core 467 Lab, KAUST) in MS analysis is gratefully acknowledged. We also appreciate the anonymous reviewers for their revision suggestions which significantly improved the quality of this work.
PublisherAmerican Chemical Society (ACS)
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