| Perfluorooctanoate(PFOA) and Perfluoroctansulfonate(PFOS) are two typical perfluorinated compounds(PFCs), with the chracteristics of persistent, recalcitrant, bioaccumulative and widespread. Currently, few studies are focused on the degradation of PFOA, PFOS, and other perfluorinated organic pollutants. As so far, only these methods, such as pyrolysis, UV photolysis, plasma oxidative degradation, persulfate or ozone degradation, have been used to decompose the PFC contaminants. However, these methods have the disadvantage of cumbersome process, technically complex, high energy consumption and cost, and low defluorination efficiency. Therefore, it urgently need to develop a highly efficient method to degrade the PFCs. The electrooxidation method has currently been applied to the degradation of PFCs, because of its low energy consumption and strong selectivity.In this study, we synthesized the novel Ti/Sn O2-F, Ti/Sn O2-Cl, Ti/Sn O2-Br, Ti/Sn O2-I electrode and traditional Ti/Sn O2-Sb electrode by a sol-gel process. Their surface morphology, composition and crystalline of Ti/Sn O2-X(X = Sb, Cl, Br, I, or Sb) electrode were investigated by SEM-EDX, XRD and other characterization methods. The electrode life and oxygen evolution potential(OEP) of Ti/Sn O2 anode doped by Sb or halogen were investigated by accelerated life test and Linear Scan Voltammetry(LSV). After investigating the effect of different doping elements on the electrooxidation degradation efficiency of PFOA, it indicated that the optimal electrode for electrochemical decomposition of persistent perfluorooctanoic acid(PFOA) was the Ti/Sn O2-F electrode The Ti/Sn O2-F electrode has a significantly longer service life, higher oxygen evolution potential and good degradation efficiency, so the Ti/Sn O2-F electrode was taken to explore the characteristics and mechanism in electrooxidation degradation of PFOA.Subsequently, the electrode preparation conditions were optimized by investigating the effects of annealing temperature, F doping amount, aging time, and dip coating times on the removal efficiency of PFOA. The effects of current density, p H, and the electrolyte type on the removal efficiency of PFOA were also investigated to improve the efficiency. These results showed that under the optimal conditions, namely annealing temperature at 500 oC, 14 day of aging time and 20 times of dipping and coating, initial p H of 3.7, 20 m A/cm2 of current density, and using Na Cl O4 as the electrolyte, the removal efficiency of PFOA could reach 99.8% after 30 min electrolysis. Finally, the electrochemical degradation pathway of PFOA was proposed according to the intermediate analysis.After preparing the novel high efficiency Ti/Sn O2-F electrode, we investigated the effect of increasing P, V, Ni, Fe, Er, Pr, Sb doping and using Ti O2-NTs, Sn-Sb, Mn as intermediate layer on the stability of Ti/Sn O2-F electrode, associating with the effect of different electrodes on the electrooxidation degradation efficiency of PFOS. As a result, the prepared Ti/Sn-Sb/Sn O2-F-Sb electrode presented a longer service life and higher degradation efficiency. Subsequently, the effects of Sb doping amount, current density and p H on the removal efficiency of PFOS were investigated. These results show that the optimal Sb doping amounts were Sn:F:Sb = 9:0.25:1, 20 m A/cm2 of current density and 6.48 of initial p H, the removal efficiency of PFOS reached 99.6% after 120 min electrolysis. Finally, we proposed an electrochemical degradation pathway of PFOS according to the intermediate analysis and the removal ratio of TOC and fluorineion. |
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