Reductive Degradation Of Perfluorohexanesulfonic Acid Catalyzed By Transition Metal Coenzyme In A Bionic System

Perfluoroorganic acids?PFAs?have been widely used in metal electroplating,foam fire extinguishing agents and other industries due to their unique physical and chemical properties.After the production of perfluorooctane sulfonic acid?PFOS,C8?was restricted,alternatives such as perfluorohexyl sulfonic acid?PFHxS,C6?with shorter chain lengths were more frequently produced and used,and currently show higher pollution,but people are not paying enough attention to it.PFHxS has stable properties,and it is difficult to remove it by conventional methods.Existing degradation technologies have problems such as harsh reaction conditions and high removal costs.In this study,suitable electron donors were introduced,transition metal coenzymes were used to catalyze the degradation of industrial grade PFHxS?linear isomers accounted for 78.2%?,and the influence of key influencing factors on the defluorination of PFHxS in water was investigated.The results show that the use of transition metal coenzyme vitamin B₁₂(VB₁₂)to catalyze titanium citrate can not only degrade branched PFHx S,but also degrade linear PFHxS at the same time.This is the first report of bionic reduction degradation of linear PFHxS.The process of reducing and degrading PFHxS in VB₁₂/titanium citrate system can be fitted with a quasi-first-order kinetic model.When the temperature is 75?,at a relatively mild initial pH?pH=8.30?,the degradation rate constant of industrial grade PFHxS is 0.07d^-1 and the half-life is 9.9d.Liquid chromatography-triple quadrupole mass spectrometry?LC-MS?analysis showed that no standard PFAs products were produced during the PFHxS reduction and degradation process.After PFHxS defluorination and hydrogenation,there is no standard product as a control.Based on the previous research results,the potential defluorination pathways of PFHxS branched and linear isomers are speculated.Based on the determination that transition metal coenzymes can catalyze the reduction and degradation of PFHxS,by controlling the reaction conditions?electron donor type and its dosage,coenzyme type,temperature,coenzyme dosage,initial pH value,etc.?single factor experiment,the analysis of Under the similar bionic system,the defluorination effect of main environmental factors on PFHxS in water.The results show that the use of nano-zero copper?nCu⁰?as electron donor has no defluorination effect,and the use of heme as a metal coenzyme has no defluorination effect.Under VB₁₂ catalysis,both nano-zero-valent zinc?nZn⁰?and nano-zero-valent iron?nFe⁰?can reduce and degrade PFHxS.As the dosage of nZn⁰ increases,the defluorination rate of PFHxS per unit time is higher,but the dosage of nZn⁰ After reaching a certain value,it has little effect on the defluorination effect,and the high concentration of nFe⁰ has an inhibitory effect on the defluorination of PFHxS.Take the VB₁₂/titanium citrate system as an example.Increasing the temperature can significantly increase the defluorination rate of PFHxS.After 9 days of reaction,the defluorination rates of PFHxS at 75?are 1.6 times,6.4 times,17.1 times,32.8times at 60?,45?,35?,25?.The concentration of VB₁₂ is in the range of 25-300?mol/L.Increasing the dosage is beneficial to the reduction and defluorination of PFHxS,and the reduction activity of the system is stronger.When the dosage is300?mol/L,the fluoride ion in the solution after 9d The concentration was 189.5?mol/L and the defluorination rate was 7.29%.The initial pH value has a significant effect on the reduction activity of similar bionic systems.The degradation rate of PFHxS increases with the increase of the initial pH.When the pH is 9.10,the degradation rate is 49.63%after 8 days of reaction,which are 2.63 times,1.53 times,1.63 times,1.26 times and 1.11 times of the degradation rates when the pH is 4.94,6.65,7.13,7.80,8.30,respectively.At the same time,this study also tracked the changes of the oxidation-reduction potential?ORP?and pH of the system.