製備ZnO/TiO2電極以電化學氧化輔助光催化降解全氟辛酸(PFOA)

Abstract

全氟辛酸(Perfluorooctanoic acid, PFOA)為新興汙染物，近年來因具有環境持久性、生物累積性、毒性與可長距離傳輸等危害性質而備受關注。然而因PFOA本身特殊的物化特性，使得在一般傳統的淨水處理程序中無法被去除。到目前為止，PFOA降解技術仍持續在開發中，當中已有一些技術可有效的降解PFOA，然而大部分的有效去除PFOA的降解技術能耗量都較高，這使得要發展至淨水工程中成為很大的阻礙。因此，一個能有效降解PFOA且低耗能低環境衝擊量的PFOA降解技術是目前迫切需要發展的方向。本研究中，藉由製備ZnO奈米線陣列電極，及以溶膠-凝膠法並分別以含浸、迴流的方式製備ZnO/TiO2電極，並以此三種電極材料藉由電化學氧化法輔助UV光催化系統降解PFOA。電極材料的探討在本研究中係以SEM/EDX、TEM/EDX和XRD作為材料的特性分析。而在降解實驗中，已經成功且有效的將PFOA降解去除。在PFOA初始濃度30mg/L、降解時間3小時後，ZnO電極在pH=10時，PFOA降解率為78.08%、脫氟率為74.39%; ZnO/TiO2(含浸法)電極在pH=10時，PFOA降解率為75.85%、脫氟率為67.77%; ZnO/TiO2(迴流法)電極在pH=5時，PFOA降解率為78.54%、脫氟率為78.67%。由結果顯示，本研究的PFOA降解方法擁有有效且快速的降解結果。此外本研究亦結合綠色化學的概念與生命週期評估法，針對三種電極材料與參考目前較具效能的PFOA降解技術(微波法與超音波法)進行環境友善度評估。由LCA評估結果顯示，ZnO電極以電化學輔助光催化的方法是當中擁有最小環境衝擊量的PFOA處理方法。而ZnO/TiO2(含浸法) 與ZnO/TiO2(迴流法)則是有相當具發展性的潛能。本研究藉由研發新型電極材料並結合電化學氧化與光催化法已成功的降解PFOA，提供一個新型的PFOA降解技術。研究當中也以生命週期評估法作為技術評估及未來改善方向的依據。

Perfluorooctanoic acid (PFOA) is characterized by its environmental persistence, bioaccumulation, long-range environmental transport and potential toxicity to humans. PFOA is resistant to most conventional treatment technologies. Additionally, most current PFOA removal technologies are not energy-efficient. The development of a mild and highly efficient decomposition method of PFOA in aqueous solutions remains a challenge. In this study, we successfully decomposed PFOA through electrochemical oxidation-assisted photocatalysis by using particular ZnO/TiO2 anodes. The anodes were made by producing well-aligned and vertical ZnO nanowire arrays on FTO glasses with a TiO2 protective membrane. The as-made ZnO/TiO2 anodes were characterized using SEM/EDX, TEM/EDX, and XRD. The material selection was based on the degradation efficiency of PFOA. The ZnO and ZnO/TiO2 anodes were used to conduct the photoelectrocatalytic experiments to determine the effects of the initial pH value. The PFOA concentrations decreased by 78.08%, 75.85%, and 78.54% on ZnO, ZnO/TiO2 (dip-coating), and ZnO/TiO2 (reflux) anodes, respectively, at an initial 30 mg/L PFOA concentration for 180 min. The defluorination ratios of PFOA on the 3 anodes were 74.39%, 67.77%, and 78.67%, respectively. Under this optimal condition, the PFOA defluorination could be expressed as a pseudo first-order kinetic reaction, and the first-order kinetic rate constants for PFOA defluorination were 0.451, 0.368, and 0.484 h-1, respectively. It was faster and more efficient than most treatment technologies. The role of photoelectron-catalysis in the degradation process was construed to be an aid to electrochemical oxidation rather than a tool itself, based on the properties of semiconductor materials. In addition, life cycle assessment (LCA) was used to calculate the environmental impacts of environmentally-friendly processes for the degradation of PFOA including the stages of producing novel materials, ZnO and ZnO/TiO2 anodes, and decomposing procedures. The results revealed that this novel method had lower energy consumption and was thus more environmentally friendly than other treatment technologies. We therefore developed a novel and successful method for PFOA degradation, as well as a life cycle inventory of treatment technology.