隨著快速都市化與工業化，諸多工廠林立，大規模工業廢水排至水體已造成環境上嚴重水污染，台灣深受水污染的場址更為廣泛，根據環保署統計三氯乙烯(TCE)為地下水中第二常見的污染物，美國環保署及國際癌症組織亦將TCE列為對人類有害的致癌物，於諸多水污染處理技術中，高級氧化處理程序(AOP)具有高效率且生成之副產物為非毒性(CO2及H2O)之優點，而光觸媒降解即為一種AOP方式，藉由光觸媒吸收光能，激發電子從價帶躍遷至導帶，生成電子電洞對，除了本身具有強還原力及強氧化力外，亦可與水分子及氧分子反應生成不同自由基，破壞TCE。TiO2為最普遍之光觸媒材料，卻受限於僅由紫外光激發，大幅降低環境工程應用性，近年來，鈣鈦礦型(perovskite-type)觸媒經證實可被可見光激發，而LaFeO3為常見perovskite光觸媒的一種，具易改質及穩定之特性，且對光降解染料具有良好的處理效率，因此本研究開發LaFeO3作為光觸媒，並就其降解水中TCE之可行性進行探討。本研究結果成功使用sol-gel法製備LaFeO3光觸媒，其具大比表面積及良好的孔洞分布特性，提供觸媒表面更多的吸附及活性位址，除了增加TCE吸附效應外亦增加表面電子電洞對的生成，而藉由對光反應批次系統進行空白測試的結果指出本實驗設計之光反應器可提高光利用效率且具有氣密性，反應器內TCE不隨時間揮發，去除效率不因TCE揮發性而改變。此外，本研究證實於氙燈(Xe lamp)照射下LaFeO3光觸媒可於1 hr有效降解水中TCE(96%)，而光強度、觸媒添加量及pH皆對光觸媒降解帶來正面的影響，其原因為於反應過程隨三種參數的提升，光子數量、反應位址及OH自由基亦增加，使得水中TCE被破壞的機率上升，增加TCE去除效率。本研究亦對反應後的產物(HCl)進行量測，結果指出經反應後約84%TCE的氯原子生成HCl，顯示光觸媒降解速率相當迅速，毒性中間產物生成的可能性較低，更彰顯環境應用之價值。;With rapid urbanization and industrialization, anthropogenic discharge of organic compounds has led to serious water pollution. In Taiwan, water contamination has been discovered widespread, and tricholorethylene (TCE) is ranked as second common organic pollutant in groundwater. The Environmental Protection Agency (EPA) has classified TCE as a human carcinogen. Thus, there is an urgent need to eliminate TCE. Advanced Oxidation Process (AOP), which is of the highest efficiency to remove organic pollutants and produce non-toxic byproducts, is better than other traditional treatments. Photocatalytic oxidation is one of the AOPs. In recent years, perovskite-type photocatalysts have been found with high photocatalytic activity under visible light in addition to TiO2. Besides, LaFeO3 becomes a kind of potential “environmentally friendly photocatalyst” due to its advantages of abundance and non-toxicity. It can utilize the visible light efficiently and generate electron-hole pairs under visible light to photocatalytically degrade contaminants in water. LaFeO3 is prepared and applied as photocatalyst to remove TCE in liquid phase. In summary, LaFeO3 photocatalyst is successfully synthesized via sol-gel method. Furthermore, LaFeO3 photocatalyst is proved for good photocatalytic activity for the degradation of TCE in aqueous solution under continuous spectrum illumination within 1 h. In our experiment, TCE concentration can maintain the same in this system and ensures that the TCE removal is contributed by photocatalytic degradation rather than volatility. The effects of light intensity, photocatalyst loading and pH on TCE photodegradation are evaluated. By increasing the light intensity, activated sites and OH group would accelerate the formation rate of OH radical to attack TCE in aqueous phase, resulting in higher TCE removal efficiency.
