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Defluorination Of Aqueous Perfluorooctanoic Acid In Photocatalytic System Over Supported Phosphotungstic Acid

Posted on:2018-01-22Degree:MasterType:Thesis
Country:ChinaCandidate:L H ZhangFull Text:PDF
GTID:2321330533966939Subject:Environmental Engineering
Abstract/Summary:PDF Full Text Request
Perfluorooctanoic acid(PFOA)has been widely used in industry such as chemical,textile and household goods because of its unique physical and chemical properties.Researchers had detected PFOA in various environmental media,organisms and human.PFOA has stable properties and biological accumulation,as well as potentially toxic to organism and human body.Therefore,how to effectively control PFOA becomes a focus problem in the field of environmental science.Phosphotungstic acid(H3PW12O40xH2O)has been widely used in medical drug,magnetic material and catalyst due to its strong acidity and reducing oxide.The SBA-15 with mesoporous materials is a kind of high specific surface area,good thermal stability,skeleton,an orderly and easy to modified material.Hence,it is often used as substrate materials in recent years.This research adopts sol-gel and the hydrothermal synthesis methods to synthesize composite HPW/SBA-15,studying the effect of different loading on HPW.And the materials were characterized using XRD,SEM,TEM etc.;A photocatalytic system with the vacuum ultraviolet lamp and HPW/SBA-15 was build to study defluorination of PFOA.The influence of loading HPW/SBA-15,initial pH and initial concentration of the PFOA on defluorination were investigated.The importance order of influence factors and operation control stragies were determined through the response surface method(RSM)in HPW/SBA-15-VUV system.PFOA and the intermediates were dectected using LC-MS/MS,and the material balance of fluorine was calculated to explore the mechanism of PFOA decomposition in HPW/SBA-15-VUV system.The results showed that HPW/SBA-15 were successfully prepared.HPW/SBA-15 have retained the orderly channel of mesoporous material,and HPW kept the Keggin structure.PFOA could be obviously defluorinated using HPW/SBA-15-VUV system.Under the condition of optimization,the defluorization rate of PFOA could reach 31.66% for 120 min reaction in HPW/SBA-15-VUV system.The defluorization rate of PFOA was only 12.73% in separate VUV system.The defluorization rate of PFOA growth curve was consistent with first order kinetics reaction in the VUV and HPW/SBA-15-VUV system.And the kinetics rate constant was 0.00105 min-1 and 0.00325 min-1 in the VUV and HPW/SBA-15-VUV system,respectively.Compared eith VUV system,the kinetics of constant of PFOA increased by 3.1 times in HPW/SBA-15-VUV system.Response surface analysis indicated that the fitting of regression equation was available.The pH was the most important factor affecting defluorination of PFOA in followed by dosing of HPW/SBA-15 and initial concentrations of PFOA.Initial pH had strong negative correlation with defluorination efficiency of PFOA at intial pH value of 4~5.Initial concentrations of PFOA and dosing of HPW/SBA-15 with defluorization efficiency of PFOA was weak positive correlation and negative correlation,respectively.The F-and the short-chain perfluorinated carboxylic(PFCAs,C2~C7)were main interdemidates in HPW/SBA-15-VUV system.PFOA is a gradual process of fluorine in HPW/SBA-15-VUV system.The mechanisms mainly reflected in two aspects,direct photolysis and photocatalytic degradation in the presence of HPW/SBA-15.
Keywords/Search Tags:Perfluorooctanoic acid, Phosphotungstic acid, Mesoporous materials, Defluorination rate, Vacuum ultraviolet
PDF Full Text Request
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