Catalytic degradation of perfluorohexanesulfonate by transition-metal coenzymes:Optimization of the biomimetic systems
Biomimetic systems containing transition-metal coenzymes as catalyst have been optimized for simultaneous degradation and defluorination of both linear-(L-PFHxS)and branched-perfluorohexanesulfonate(Br-PFHxS).Vitamin B12(VB12)catalyzed the reductive degradation and defluorination of both L-PFHxS and Br-PFHxS,whereas hematin did not.For cofactor 430(F430),biomimetic degradation and defluorination was only found for Br-PFOS but not for L-PFHxS.However,the removal rate and defluorination rate of technical PFHxS catalyzed by VB12 were both much higher than that catalyzed by F430.Biomimetic degradation of technical PFHxS catalyzed by VB12as well as F430 could well be described by a first-order exponential decay model,indicating that the spiked PFHxS could initially distribute between two completely separate pools with independent degradability,i.e.non-degradable and degradable fractions.The axial ligands of VB12 could impact their catalytic defluorination of PFHxS,and the highest defluorination rate was achieved by adenosylcobalamin.Nanoscale zero-valent zinc(nZn0)is the best electron-donor for the biomimetic system under the experimental conditions.At 60℃ and pH=9.0,the removal rate and defluorination rate of technical PFHxS were as high as 57.1％±2.9％and 8.19％±0.65％,respectively,with cyanocobalamin as biomimetic catalyst and nZn0as electron-donor,and then the degradable fraction accounted for about 54.6％and its depletion rate was 1.01d-1.
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