Study On Degradation Pathway Of Triclosan With Fenton Catalytic Oxidation

Triclosan [5-choloro-2-(2,4-dichlorophenoxy) phenol, TCS] is a broad spectrumantibacterial agent used in pharmaceuticals and personal care products. The used TCS willflow into sewage and natural water. It has been frequently detected in sewage and surfacewater and the concentration comes to be rising. TCS is bioaccumulative. In addition, it willtransform into higher toxicity products under certain conditions. Therefore, TCS‘s potentialecological risk should be concerned immediately. The oxidation laws of Fenton are good fortoxicity complicated organic degradation complete. But the degradation pathway of TCS withFenton has not in-depth study at present.In this study, TCS was treated by Fenton. The analytical methods of TCS and theintermediates during Fenton process were built. The optimal catalytic oxidation conditionsand the reaction pathways were studied, aiming to provide theoretical foundation ofdegradation reaction optimizing and to reduce potential harmful products.Firstly, the method for TCS determination in water by high performance liquidchromatography and mass spectrometry with atmospheric pressure chemical ionization(HPLC-APCI-MS) was established. The result showed that the recovery rate of hexaneconcentrated extract was about99.6%.The optimal conditions for TCS determination was asfollows: the detection wavelength was230nm, the mobile phase was75/25(v/v) MeCN/H2Oand the ion source was APCI (-). Under these conditions, TCS can be separated anddetermined accurately in5minutes. The Quality Assurance and Quality Control (QA/QC)studies showed that this method was accurate, precise and responsible.The effects of different reaction parameters on the catalytic oxidation were studied.The results showed that the degradation mainly occurred in the beginning10min and itchanged little after10min. In10min,87.93%TCS could be depredate under the conditionsof pH=3, Fe2+dosage of5mM, H2O2dosage of4.895mM. And it would not get significantimprove if increasing dosage.Secondly, the method for determining intermediates of TCS degradation by highperformance liquid chromatography and mass spectrometry with electro spray ionization(HPLC-ESI-MS) was established. The result showed the optimal conditions for intermediatesdetermination were as follows: the detection wavelength was280nm, the mobile phase was75/25(v/v) MeCN/H2O in0~15min, gradient rose to100/0(v/v) MeCN/H2O. Under theseconditions,9intermediates were separated with HPLC,5intermediates were detected withESI (-) and6intermediates were detected with ESI (+). Basd on the analyze results, the intermediates during the fenton process and thedegradation pathways were studied. The results showed that the main9intermediates were:2,4-Dichlorophenol;1,2,4-Dichloro-benzene;2,8-DCDD;3-Chlorophenol;4-Dichloro-1,2-dihydroxybenzenel;4-Chloro-1,2-benzoquinone; formic acid; acetic acid; oxalic acid. Thedegradation pathway of TCS was inferred as following:1) Cyclization, TCS transformed into2,8-DCDD.2) Ether bond broke. A: breaking into2,4-Dichlorophenol and4-Chloro-1,2-dihydroxybenzenel; B: breaking into1,2,4-Dichloro-benzene and4-Chloro-1,2-dihydroxybenzenel with; C: breaking into2,4-Dichloro-benzene and3-Chlorophenol.3)Chlorophenol were further attacked by·OH and transformed into chlorohydroquinone, whichsubsequently oxidized by·OH and degraded into acid formic acid, acetic acid and oxalic acid.