Oxidation of Refractory Benzothiazoles with PMS/CuFe₂O₄: Kinetics and Transformation Intermediates

Abstract

Benzothiazole (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., R ct) for this process is a constant that is related to the reaction condition and can be easily determined. The reaction rate constants of these benzothiazoles toward 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–1 s–1, respectively (pH 7 and 20 °C). On the basis of R ct 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 that are reactive toward common oxidants. For OHBT oxidation, the thiazole ring is preferentially broken down. 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 dissolved organic carbon waters like urban runoff or polluted groundwater.

Efficient degradation of Acid Orange 7 by persulfate activated with a novel developed carbon‐based MnFe2O4 composite catalyst

“…2,70 The standard redox potentials of Fe III /Fe II , Mn III/ Mn II and Mn IV /Mn III were reported as 0.77, 1.51 and 0.15 V respectively. 23,67 Therefore the conversions of Fe III /Fe II and Mn II /Mn IV /Mn III were thermodynamically favorable following Eqns (2) and (5). 67 For the generation of another species, • OH could be produced by SO 4 −• reacting with H 2 O (Eqn (7)).…”

“…Compared with traditional technologies such as adsorption, filtration, biodegradation and membrane separation, advanced oxidation processes (AOPs) have been extensively investigated for their high performance in decomposing recalcitrant organics . In addition to hydroxyl radicals ( • OH), sulfate radical‐based AOP technology has drawn increased attention in the destruction of refractory pollutants in water . With high redox potential and strong reactivity, the sulfate radical (SO 4 −• ) reacted with contaminants usually by electron transfer in the removal of pollutants .…”

“…2,3 In addition to hydroxyl radicals ( • OH), sulfate radical-based AOP technology has drawn increased attention in the destruction of refractory pollutants in water. 4,5 With high redox potential 6 and strong reactivity, the sulfate radical (SO 4 −• ) reacted with contaminants usually by electron transfer in the removal of pollutants. 5,7 More importantly, SO 4 −• exhibited a long half-life (30-40 μs) and wide working pH range (2−8).…”

“…4,5 With high redox potential 6 and strong reactivity, the sulfate radical (SO 4 −• ) reacted with contaminants usually by electron transfer in the removal of pollutants. 5,7 More importantly, SO 4 −• exhibited a long half-life (30-40 μs) and wide working pH range (2−8). [8][9][10] Thus it was significant to explore the generation of SO 4 −• for its wide application.…”

Converting Thioether Waste into Organic Semiconductors by Carbon–Sulfur Bond Activation

“…[6] Thus,different oxidation techniques,i ncluding ozonation, UV irradiation, and advanced oxidation processes (AOPs) generating hydroxyl radicals (e.g., photocatalytic oxidation, O 3 /H 2 O 2 and UV/H 2 O 2 )h ave been employed to remove this organic waste. [7] Thep roducts of these oxidization procedures are human-benign but useless.T hus,i ti sv ery attractive to develop an efficient methodology to convert this waste into valuable materials.A lso,d ifferent adsorption techniques were developed to isolate and enrich these chemicals, [8] providing the basis for their chemical conversion.…”