Construction Of Electrochemical System For Reduction And Defluorination Of Perfluorooctanoic Acid

Perfluoroctanoic acid（PFOA）has excellent thermal stability,good hydrophobicity and high surface activity and is widely used in industrial and civil production fields.Inevitably released to the environment during its production and application,it has been detected in almost all environmental media and organisms.Because PFOA is persistent,bioaccumulative and toxic and poses a serious threat to ecosystems,there is an urgent need to find a way to effectively control and degrade it.Electrochemical method is a kind of green degradation technology with great development prospect because of its mild reaction conditions,easy operation and easy automation.Fluoride in PFOA molecules has a strong electronegativity and tends to accept electrons and undergo reduction reactions.Therefore,this paper mainly studies the electrochemical reduction and degradation effects of PFOA.The electrochemical reduction technology is essentially a heterogeneous contact reaction conducted in the surface area of the electrode.The electrode determines whether this reaction can occur and the rate of reaction occurs.Comparing electrodes prepared by rhodium/nickel,rhodium/copper,rhodium/silver,palladium/nickel,palladium/copper,palladium/silver,etc.It is found that Rhodium/nickel electrode has a good effect on PFOA reduction and removal with concentration of 100 mg/L.The effects of Rhodium load morphology,different nickel substrates and load methods on electrode preparation were studied.The electrode suitable for PFOA reduction was selected by electrochemical reduction effect analysis,stability analysis,microstructure characterization and electrochemical characteristics study.The working electrode of the Rhodium/nickel electrode was prepared by using the CHI660E electrochemical workstation as the power source,the three H-type electrolytes as the electrolysis cell,The system for PFOA reduction defluorination is explored in terms of solvents,supporting electrolytes,electron transfer media,electrolytic form and electrolytic strength,stirring speed,etc.The results showed that the constant voltage electrolysis could reduce and remove the PFOA with dimethyl formamide as solvent and dimethyl ferrocene as electron medium.Moreover,the electrochemical system was constructed to achieve better reduction removal effects for short-chain perfluorinated carboxylic acid organics,short-chain perfluorinated sulfonic acid organics and perfluorooctane sulfonic acid（PFOS）.By analyzing the defluorination form,degradation product,fluorine mass balance and nuclear magnetic resonance fluorography in PFOA reduction process,it is estimated that defluorination is mainly carried out by dehydrofluorination in the electrochemical reduction process of PFOA.The products are dominated by fluorine ions,hydrogen-substituted fluorine compounds and short-chain carboxylic acid organics,and short-chain carboxylic acid organics are formed by the gradual removal of CF₂ units from PFOA.