Enhanced Remove Of Perfluorooctanoic Acid By Carbon Based Aerogel Electrode From Water And Soil Media

Per-and polyfluoroalkyl substances(PFASs)have excellent hydrophobicity,oil repellency,surface activity and thermal stability,which are widely used in many industries,such as fire protection,aerospace,automobile,construction,electronic manufacturing,textile and food processing.At the same time,the extensive use and unreasonable treatment of PFASs lead to its emission into the environment.As one of the most stable PFASs,perfluorooctanoic acid(PFOA)can hardly be degraded naturally when it enters the environment,which leads to its higher concentration in the environment,and causes persistent harm to human and biological health.Therefore,the problem of PFASs removal from the environment needs to be solved.There are many methods to remove PFOA from the environment,such as photo/chemical catalytic degradation,heat treatment and so on.However,the operation of these methods are complex and requires harsh reaction conditions.Therefore,electro-remediation,a green and environmentally friendly method was used to remove PFOA in this study.Because of the variability and complexity of soil,it was very inconvenient to directly study the remediation of contaminated soil.Therefore,the adsorption/electro-sorption behaviors of PFOA on carbon based aerogels(CAs)in water were researched,and the adsorption/electro-sorption mechanisms were also defined.The remediation process and influencing factors of PFOA in the soil were determined finally.The results of this study are as follows:(1)Four kinds of CAs,namely reduced graphene oxide aerogel(rGA),fluorine doped rGA (F-rGA),copper nanoparticles loaded rGA(Cu-rGA),and rGA modified by F elements and copper nanoparticles(Cu/F-rGA),were prepared by microbubble template method.Then the properties CAs were characterized by specific surface area measurement system,SEM,XRD,XPS and FTIR.The results showed that F elements can improve the surface area,average pore volume and average pore size of rGA from 188.92 m² g^–1,1.87 cm³ g^–1,3.54 nm to203.08 m² g^–1,2.36 cm³ g^–1,5.68 nm,respectively.Copper nanoparticles(Cu NPs)can reduce the surface area and pore volume of rGA to 151.65 m² g^–1(Cu-rGA)/133.49 m² g^–1(Cu/F-rGA)and 1.38 cm³ g^–1(Cu-rGA)/1.19 cm³ g^–1(Cu/F-rGA),but increased the average pore size to4.62 nm(Cu-rGA)/4.87 nm(Cu/F-rGA).In addition,the synergistic effect of fluorine and Cu NPs significantly increased the capacitance of Cu/F-rGA from 17.75 Fg^–1 to 47.66 Fg^–1.(2)Batch equilibrium method was used to study the adsorption kinetics,isothermal adsorption and adsorption-desorption of PFOA on the CAs.The equilibrium time of PFOA on CAs was 360 min and the adsorption rate was affected by variety factors.The isothermal adsorption showed that compared with rGA,the modified rGA,especially Cu/F-rGA can significantly increase the adsorption capacity of PFOA.When the equilibrium concentration of PFOA in solution was 2.0 mg L^–1,the adsorption capacity of Cu/F-rGA for PFOA was 4.87times higher than that of rGA.After analysis of statistical physics model,when the temperature rised from 20? to 40?,the binding amount of PFOA on adsorption sites of Cu/F-rGA increased from 0.53 to 1.41,and the site density of Cu/F-rGA decreased from 25.51mg g^–1 to 12.54 mg g^–1,and the number of adsorption layers decreased from 2.51 to 1.63.After 10 times of desorption by using ethanol,Cu/F-rGA still maintained 73.26%adsorption capacity for PFOA,which ensured the recycling performance of Cu/F-rGA.In addition,compared with response surface methodology(RSM)and artificial neural network(ANN),adaptive neural fuzzy inference system(ANFIS)can better simulate and predict the removal rate of PFOA on Cu/F-rGA under different environmental variables(adsorbent dosage,solution pH,ionic strength and temperature),and the adsorbent dosage had a significant influence on the removal rate of PFOA.The adsorption mechanisms of PFOA on Cu/F-rGA mainly included complex reaction,hydrophobic interaction and F-F interaction.(3)The electro-sorption kinetics,isothermal electro-sorption and electro-sorption desorption of PFOA on Cu/F-rGA electrode were reseached.According to the fitting results of the electro-sorption kinetic models,the equilibrium time of PFOA on Cu/F-rGA(+0.8 V)was determined to be 120 min.Compared with the open circuit state(Cu/F-rGA(OC)),the electro-sorption rate of Cu/F-rGA(+0.8 V)was increased by 3.88 times.When the equilibrium concentration of PFOA was 1.0 mg L^–1,the adsorption capacity of Cu/F-rGA(+0.8 V)was about 105.37%higher than that of Cu/F-rGA(OC).After analysis of statistical physics model,when the temperature rised from 20? to 40?,the binding amount of PFOA on Cu/F-rGA(+0.8 V)adsorption sites increased from 0.72 to 1.76,and the site density of PFOA decreases from 25.84 mg g^–1 to 17.06 mg g^–1,and the total number of adsorption layers decreases from 2.87 to 1.46.Compared with RSM and ANN,ANFIS can better simulate and predict the removal rate of PFOA on Cu/F-rGA(+0.8 V)under different environmental variables(solution pH,ionic strength,voltage and humic acid concentration),and the voltage and humic acid concentration had a significant influence on the removal rate of PFOA.The electro-sorption mechanisms of PFOA on Cu/F-rGA mainly included electric field interaction,complex reaction,hydrophobic interaction and F-F interaction.(4)The influence of electrode material,electro-remediation time,voltage intensity,electrolyte type and concentration on the removal rate and energy consumption of PFOA in soil were discussed.Compared with commercial electrodes(graphite electrode,Pt/Ti electrode),Cu/F-rGA electrode could significantly improve the removal rate of PFOA in soil.After 5 days of electro-remediation,the removal rate of PFOA in soil were 80.37%?82.31%,which met the requirements of soil electro-remediation.With the increase of voltage intensity,the removal rate of PFOA also increased,and the optimal voltage was 2.0 V.The results showed that the removal rate of PFOA in soil were 81.12%?82.08%,and the corresponding energy consumption was 17.18 Wh m^–3.By comparing the removal rate and energy consumption of different concentrations of HCl solution and Na₂SO₄ solution,the optimal electrolyte solution was 0.1 mol L^–1 Na₂SO₄,and the removal rate of PFOA in soil were80.31%?83.55%,and the corresponding energy consumption was 19.04 Wh m^–3.Moreover,Na₂SO₄ solution had little disturbance to pH value of soil and did not produce harmful gases,so it was a very suitable auxiliary reagent for soil electro-remediation.In conclusion,Cu/F-rGA electrode had excellent pore structure and electro-chemical properties,which provided a good structural basis and adsorption sites for its adsorption/electro-sorption of PFOA in water,and promoted the electro-remediation of contaminated soil.The relationship and relative contribution of various influencing factors in the process of PFOA remediation were explored,and the removal mechanism of PFOA in water and soil was clarified,which has important theoretical significance for the future large-scale removal of PFOA in the environment.