Photocatalytic Defluorination Of Aqueous Perfluorooctanoic Acid By VUV/HPW/BMMs System

Perfluorinated compounds?PFCs?are synthetic organic compounds with unique physical and chemical properties that have been widely used in industrial and consumer products.Perfluorooctanoic acid?PFOA?is the main perfluorocarbon pollutant in environmental and has been frequently detected in various environmental media,wildlife and human body.PFOA has a very strong carbon-fluorine bond,making it not only difficult to break down naturally,but also resistant to both conventional and some advanced oxidation processes.In this study,we took PFOA as the research object,chose vacuum ultraviolet as the light source,and selected the supported phosphotungstic acid?HPW/BMMs?as the photocatalyst to build the photodegradation system of VUV/HPW/BMMs,the defluorination effect and degradation pathway of aqueous PFOA were studied in detail.HPW/BMMs catalysts were prepared by supporting HPW on BMMs via inpregnation method.The characterization results showed that HPW/BMMs were in the form of particles and the surface morphology of the samples had no obvious changes,and the double-hole structure of the bimodal mesoporous materials?BMMs?was maintained,with a pore size of 3nm and a secondary pore size of 16 nm.The specific surface area was 566⁸96 m²·g^-1.With the increase of HPW loading rate,the specific surface area and particle size of HPW/BMMs gradually decreased,and the degree of mesoporosity decreased.A combined process of vacuum ultraviolet?VUV?and the catalyst HPW/BMMs was built to explore the defluorination of aqueous perfluorooctanoic acid?PFOA?,and the influence of HPW loading amounts,PFOA concentration,HPW/BMMs dosage and solution pH on the defluorination of the photocatalytic system were discussed.The defluorination rate of PFOA in VUV/HPW/BMMs system was 1.7 times,1.9 times and 1.0 times higher than that of VUV,VUV/BMMs and VUV/HPW systems,respectively.Within the scope of the reaction design,the initial concentration of PFOA negatively affected the defluorination of the system,the loading rate of HPW was controlled to 30%,the dosage of HPW/BMMs was 0.2g·L^-1,and the reaction solution was adjusted under acidic conditions?p H=3⁴?,which was beneficial to the system's defluorination of PFOA.Based on the Box-Behnken response surface method,the significance of each influencing factor was pH>PFOA initial concentration>HPW/BMMs dosage.The synergetic effect of pH with HPW/BMMs dosage and PFOA concentration on defluorination were all significant.In the design range,the premise of improving the defluorination rate of VUV/HPW/BMMs system was to control the initial pH of PFOA within the optimum range.According to the regression model,the optimal simulation was carried out.Under the optimal operating conditions,the actual defluorination rate was 51.4%in 4 h,which was only 1.2%lower than the predicted value.The intermediate products of PFOA degradation in VUV/HPW/BMMs system were mainly C2^C7 short chain PFCs.And the PFOA degradation was a stepwise defluorination process.In the VUV/HPW/BMMs system,PFOA was defluorinated by direct photolysis and photocatalytic degradation.Under the irradiation of VUV??=185 nm?,PFOA was excited and directly photodegraded.Under the irradiation of UV??=254 nm?,HPW was excited and photocatalytic degradation of PFOA was induced.