Study On The Degradation Of Three Novel Chlorinated Disinfectants By Two Fenton-like Systems In Aqueous Solution

Widely used as active agents in household cleaning and pharmaceutical and personal care products(PPCPs),chlorinated disinfectants(TCS,CF,and DCF)belong to a group of broad-spectrum antibacterial agents.Extensive use of products containing them has made them inevitably enter into the environment.Recently,with the development of analytical instruments,they become frequently detected in soil,surface water,freshwater streams,wastewaters,and sediments.In addition,they were ubiquitously detected in biotic samples such as fish,human plasma,and breast milk The potential detrimental to human health and the ecological environment they pose has drawn increasing attentions,because of their similar structure with OH-PBDEs and PCBs.To date,TCS,CF,and DCF can be transformed via photolysis,electro-Fenton,biodegradation,enzyme catalytic degradation,and adsorption.However,the drawbacks regarding these treatment techniques limit their wide application.In recent years,Fenton-like systems with transition metal ions and hydrogen peroxide(H2O2)are usually employed to remove various kinds of organic contaminants.Compared with Fenton system,Fenton-like systems have the advantages of function well at a broad pH range and low dosage of transition metal ions,they can remove the organic contaminants under neutral conditions.It has been proved that Fenton-like systems are relative simple,economic,efficient,and environmental friendly methods of pollutants abatement.The degradation processes of TCS,CF,and DCF by two Fenton-like systems were investigated at length.The main research conclusions of present study are as follows:(1)Catalytic effect of low concentration carboxylated multi-walledcarbon nanotubes(MWCNTs-COOH)and grapheme oxide(GO)on the oxidation of chlorinated disinfectants by a Fenton-like system.It was found that the reaction kinetics of TCS,CF,and DCF followed pseudo-first order kinetics under the optimal conditions:pH 4.0,[Fe3+]=0.04 mmol/L,[H2O2]=0.6 mmol/L,[MWCNTs-COOH]=2.0 mg/L,and their rate constants were 0.1208,0.0395,and 0.0761 min-1,respectively.Meanwhile,the structure and chemical composition of MWCNTs-COOH did not show significant change after the oxidative reaction process,which has been characterized by TEM,Raman spectroscopy,XPS,and FT-IR.Mechanism study showed that the reduction rate of Fe3+ ion to Fe2+ion and the decomposition rate of H2O2 were both increased in the presence of MWCNTs-COOH,thus lead to the enhanced production of hydroxyl radicals(·OH),which is the single reactive oxygen species(ROS)responsible for TCS oxidation.Major oxidation pathways including hydroxylation,dechlorination and cleavage of the ether bond were tentatively proposed,and detailed underlying mechanisms were also discussed.(2)Bicarbonate(HCO3-)enhanced removal of triclosan by copper(?)catalyzed Fenton-like reaction in aqueous solution.It was found that the reaction kinetics of TCS,CF,and DCF followed pseudo-first order kinetics under the optimal conditions:[Cu2+]=0.01 mmol/L,[H2O2]=1.0 mmol/L,[HCO3-]=2.0 mmol/L,and their rate constants were 0.0323,0.0298,and 0.0224 min-1,respectively.In order to explore the reaction mechanism,radical scavenging technologies,molecular probe compound p-Chlorobenzoic acid(PCBA)and cyclovoltammetric(CV)experiments were employed to determine the reactive oxygen species(ROS),the steady-state concentrations of ·OH([·OH]ss)and[Cu(HCO3)]+,respectively.The results suggested that the[Cu(HCO3)]+formed between Cu2+and HCO3-could catalyze H2O2 to produce ·OH and O2-·,which were responsible for the removal of TCS,CF,and DCF.Their reaction pathways were proposed including the cleavage of the ether bond,hydroxylation,and polymerization.Finally,evaluation on the toxicity change of reaction solution with the freshwater green alga Scenedesmus obliquus showed significant detoxification after 120 min treatment.(3)Oxidation of chlorinated disinfectants by a Fenton-like system Cu2+/H2O2 and analysis on their structure-reactivity relationship.The oxidative degradation of TCS,CF,DCF,and other 14 chlorophenols(CPs)with different chlorine substitution by Cu2+/H2O2 system were examined.The degradation rate constants of the above 17 compounds followed pseudo-first-order kinetics under the investigated conditions.Fourteen molecular descriptors including structural and thermodynamic parameters were calculated using Gaussian 09 program.A quantitative structure-activity relationship(QSAR)model was established using SPSS software with measured rate constant(k)as dependent variable and calculated molecular descriptors as independent variables.A three-parameter model including energy of HOMO(Ehomo),molar heat capacity at constant volume(Cv?),and the most positive net charge of hydrogen atoms(qH+)was selected for k prediction,with correlation coefficient R2=0.878 and cross-validation correlation coefficient q2=0.805.Variance analysis,standard t-value test,and q2 were used to validate the model,the results of which suggested that the three parameters in the model possessed statistical significance,the model was reliable,and stable,respectively.