以維生素 B12 及零價銅金屬催化檸檬酸鈦(III) 進行全氟辛酸還原脫氟之應用

Reductive Defluorination of Perfluorooctanoic Acid by Titanium(III) Citrate with Vitamin B12 and Copper Nanoparticles.

陳沂珮(Yi-Pei Chen)

指導教授 ： 駱尚廉

國立臺灣大學/工學院/環境工程學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201601100

摘要

全氟辛酸 (perfluorooctanoic acid, PFOA) 為環境中持久性新興污染物。其具有良好之穩定性及相容性、表面活性、低表面張力以及疏水、疏油性等特性，作為含氟表面活性劑廣泛應用於乳化劑、表面處理及防水材料。近年來，隨著 PFOA 使用量的增加，其廣泛分佈於全球環境系統中，因 PFOA 在環境介質中的穩定性、持久性和生物累積性所造成的污染問題備受關注。由於 PFOA 化學穩定性甚強，其於自然環境中不會降解，傳統之生物處理、氧化處理、Fenton 法、光解及光催化對其皆無良好之去除效率。
於簡易操作條件下，以檸檬酸鈦(III) 作為電子提供者之還原系統對 PFOA 之去除及礦化效率皆比過硫酸鹽之氧化系統佳，因氟原子之高電負性使其具有強烈接受電子的傾向，故還原途徑更利於 PFOA 礦化脫氟。結合奈米零價銅金屬與採用維生素 B12 作為吸附與催化劑促進還原系統硼氫化鈉、零價鐵及檸檬酸鈦(III) 對全氟辛酸進行還原降解，結果顯示，檸檬酸鈦(III) 對 PFOA 之還原脫氟效率高且穩定性佳，且將檸檬酸鈦(III) 結合維生素 B12與奈米零價銅金屬，於溶液初始 pH、檸檬酸鈦(III)、維生素 B12與奈米零價銅金屬分別為 9.0、45 mM、0.2 mM 及 2 g/L，於 70°C 之厭氧條件下，此簡易仿生系統可達到 65% 之 PFOA 去除率。
產物以 X 光繞射儀 (X-ray Diffractometer, XRD)、掃描電子顯微鏡 (Scanning Electron Microscope, SEM) 與X 射線光電子能譜儀 (X-ray Photoelectron Spectroscopy, XPS) 進行分析，檸檬酸鈦(III) 還原系統可直接脫除 α - position 之氟原子，產生氫取代全氟羧酸進一步降解，而 HPLC 無偵測出短鏈之全氟羧酸物質，以質量平衡與偵測氟離子之濃度符合 PFOA 之降解結果。
故於此低毒性、可生物降解性、仿生且對環境造成之衝擊度低檸檬酸鈦(III) 還原系統能夠提高全氟辛酸之可生物分解性，降低含 PFOA 廢水的生物毒性，反應機制主要為 PFOA 吸附於銅金屬表面後經由還原脫氟降解。

關鍵字

催化脫氟 ； 奈米零價銅 ； 全氟辛酸 ； 還原 ； 維生素 B12

並列摘要

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.

並列關鍵字

Catalytic defluorination ； Copper nanoparticles ； Perfluorooctanoic acid ； Reductive ； Vitamin B12

參考文獻

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