以鉛、銅及鐵改質二氧化鈦在紫外光照射下降解全氟辛酸之研究

Abstract

全氟辛酸（PFOA，C7F15COOH）被廣泛地運用於工業和商業活動上，由於PFOA會對自然環境與水體造成嚴重危害，因此PFOA使用與處理上成為全球關注的議題。PFOA不能以傳統UV/TiO2光催化方法有效去除，因此本研究利用金屬改質TiO2觸媒進行光催化反應降解PFOA。有研究指出用金屬改質TiO2觸媒，表面上金屬顆粒具有捕捉電子效果，因此會延緩電子電洞再結合，進而提升光催化反應系統降解化合物之能力。本實驗以三種金屬改質TiO2觸媒表面(Fe-TiO2、Cu-TiO2與Pb-TiO2)與未表面改質TiO2觸媒進行光催化降解PFOA能力之比較，實驗結果顯示Pb-TiO2觸媒對PFOA光催化降解之去除率與去氟率擁有最高活性。在UV/ Pb-TiO2系統經過12 h光催化反應後，去除率與去氟率分別達到99.9%與22.4%。PFOA依序被降解為更短碳鏈著中間產物如全氟庚酸(PFHpA，C6F13COOH)、全氟己酸(PFHeA，C5F11COOH)、全氟戊酸(PFPeA，C4F9COOH)、七氟丁酸(PFBA，C3F7COOH)、五氟丙酸(PFPrA，C2F5COOH)和三氟乙酸(TFA，CF3COOH)與礦化成最終產物氟離子(F-)。利用擬一階動力(pseudo-first-order kinetics)模式對不同系統(UV/TiO2、UV/Fe-TiO2、UV/Cu-TiO2與UV/Pb-TiO2)之PFOA降解率數據進行模式分析，擬一階動力模式之反應速率kobs值分別為0.0158、0.0891、0.1837與0.5136 hr-1，在反應速率結果顯示UV/Fe-TiO2、UV/Cu-TiO2與UV/Pb-TiO2系統比UV/TiO2系統具有更高的活性針對PFOA之光催化降解之能力。本實驗金屬改質觸媒以光沉積法製備而成，之後分別利用掃描式電子顯微鏡、X光粉末繞射儀、以及紫外光-可見光光譜儀等做觸媒物化分析。實驗數據顯示，在UV/Fe-TiO2、UV/Cu-TiO2與UV/Pb-TiO2系統會產生捕捉電子效果，因此延緩光催化反應中電子電洞再結合，進而提升光催化降解PFOA之能力。

Perfluorooctanoic acid (PFOA, C7F15COOH) is widely used in industrial and commercial applications. It has become a global concern due to its widespread occurrence in water bodies and adverse environmental impact. PFOA could not be effectively removed by the conventional UV/TiO2 system. This study synthesized metal-modified TiO2 catalyst and used it as a catalyst with light irradiation for PFOA decomposition. It was found that the metal-TiO2 catalyst could produce traps to capture photo-induced electrons or holes that lead to better photocatalytic efficiencies. Comparing TiO2 and three types of metal-modified TiO2 (Fe-TiO2, Cu-TiO2 and Pb-TiO2), Pb-TiO2 exhibited the highest catalytic activity during PFOA decomposition and defluorination. After 12 h of reaction, the PFOA decomposition and defluorination efficiencies by the UV/Cu-TiO2 system reached 99% and 22%, respectively. PFOA was decomposed into fluoride ions (F-) and shorter perfluorinated carboxylic acids (PFCAs) such as C6F13COOH, C5F11COOH, C4F9COOH, C3F7COOH, C2F5COOH and CF3COOH. The pseudo-first-order kinetic was used to model the decomposition of PFOA. Rate constant values of PFOA decomposition for the UV/TiO2, UV/Fe-TiO2, UV/Cu-TiO2 and UV/Pb-TiO2 systems were 0.0158, 0.0891, 0.1837 and 0.5136 hr-1, respectively. The Fe-TiO2, Cu-TiO2 and Pb-TiO2 catalysts exhibited considerably higher activities than that of TiO2. The photocatalysts were prepared by a photodeposition synthesis method and were characterized by scanning electron microscopy with energy-dispersive X-ray, X-ray diffraction and UV-Vis spectrophotometry. The experimental results have demonstrated that the UV/Fe-TiO2, UV/Cu-TiO2 and UV/Pb-TiO2 systems could produce traps to capture photo-induced electrons, thereby reduce electron-hole recombination during photocatalytic reactions and consequently enhance the PFOA decomposition.