Perfluorooctanoic Acid Degradation And Mechanisms Under γ-ray Irradiation And UV Photocatalysis

Perfluorooctanoic acid (PFOA, C7F15COOH), one of perfluorochemicals, PFCs, is extensive used in manufacturing industry, medical and commercial products. It has been gaining increasing interests because it is a ubiquitous environmental contaminant and resistant to the most conventional treatment processes. Due to its persistance to biodegrdation, more and more attention has been paid on the development of novel methods with high efficiency for PFOA degradation. In this work, y-ray irradiation and UV photocatalysis were used to mineralize and defluorinate PFOA. The intermediate products were identified and the degradation pathway was also proposed.The main conclusions of this thesis are listed as below:1) The rapid and complete mineralization of PFOA and simultaneous defluorination were achieved by y-ray irradiation with a60Co source. After4h the degradation efficiency of PFOA was nearly100%, and after8h irradiation the PFOA was defluorinated completely, meanwhile the mineralization efficiency was more than80%based on the decrease in TOC content. The degradation of PFOA followed pseudo-first-order kinetics. The high degradation rate could be achieved at N2-satured condition and pH13.0, with the degradation rate constant k=0.654h-1and the half-time τ1/2=1.06h.2) In this work, the degradation intermediate products were identified, and the degradation pathway was also proposed. The possible mechanism was also examined by DFT calculations for validation. Both the experimental results and quantum chemical calculation confirmed that two radicals, i.e., hydroxyl radical (-OH) and aqueous electrons (eaq-), were responsible for the degradation of PFOA.3) The GaOOH precursor was synthesized by hydrothermal method to prepare Ga2O3photocatalyst. Ga2O3with uniform size was obtained and its photocatalytic activity for PFOA decomposition were evaluated. In anaerobic condition, Ga2O3show remarkable photocatalytic activity to degrade PFOA compared to commercial TiO2powder under UV irradiation. After8h irradiation, about57.1%PFOA was degradated, and the defluorination ratio was19.8%.