| Summary: | 碩士 === 國立臺灣大學 === 環境工程學研究所 === 104 === Perfluorooctanoic acid (PFOA) has been considered as emerging persistent organic pollutants. It is a fluorosurfactant, widely used as emulsifying agents, surface treatment ingredients and water repellents due to its unique high stability, compatibility, high surface-active effect, low surface tension as well as both hydrophobic and oleophobic properties. In recent years, as the use of PFOA has increased, it is globally present in the environment. The stability, persistence and bioaccumulative properties of PFOA make it have an adverse effect on human health and ecosystem, and has drawn considerable interest from the public and regulatory agencies. It is thus crucial to evolve effective methods for the degradation of PFOA. This compound shows high chemical stabilization and it is not degraded in the natural environment or by conventional treatment methods, such as biology, ozonation, Fenton processes, photolysis, or photocatalysis. Using persulfate and Ti(III) citrate as reaction medium for oxidation and reduction degradation of PFOA, reductive defluorination of PFOA is more efficient than oxidative defluorination. Due to its strong electronegativity, the fluorine atom has high electron withdrawing capability, and acts as the reaction center. Thus, reductive defluorination of PFOA is more practical than oxidative defluorination. Catalyzed by vitamin B12 and copper nanoparticles was examined in batch systems using sodium borohydride, nano zero valent iron and titanium (III) citrate as the bulk reductant, a very efficient reduction for the conversion of PFOA to less-noxious compounds was achieved with Ti(III) citrate. A maximum removal was observed with an copper dose of 2 g L-1, Ti(III) citrate (45 mM), vitamin B12 (0.2 mM) at an initial pH of 9.0 and 70°C. In anoxic aqueous solution, the biomimetic reduction system was effectively removed 65% of PFOA. The products characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). The mass balance of fluoride matched the observed degradation of PFOA, while no short-chain perfluorocarboxylic acids byproducts were detected using HPLC. Consequently, highly efficient enhanced reduction systems were constructed for remediation of PFOA contaminated water. The removal of PFOA by TC/VB12/Cu can be attributed to the following main mechanisms: (i) adsorption onto copper surface and (ii) reduction via defluorination.
|
|---|
