Comparison of the Oxidative Activities and Photoelectric Effects for various type of TiO2 Semiconductor Thin Films

[[abstract]]結合光催化氧化程序去除污染物為近年來相當熱門的研究議題，許多研究也致力於提昇光觸媒的活性，以符合其特定用途的需求，但這些光觸媒活性改良成效的評定，仍有賴於繁複且冗長的化學活性測試，其時效性有待提昇。由於光觸媒本質上屬於金屬半導體氧化物，當吸附污染物時，會導致其導電率的改變，產生光電效應的現象。基於此，本研究旨在開發一快速篩檢TiO2光觸媒氧化的方法，期能在較短的檢測時間下，篩選出活性較佳的光觸媒。本研究以非平衡磁控濺鍍技術，製備含有梳型電路之光觸媒半導體薄膜，利用二氧化鈦的光電效應與二氧化鈦的光催化活性，分別以MtBE、Methanol、Acetone為污染物，配合以反應溫度等參數進行相關探討，以瞭解光催氧化活性與光電效應之關係，期望藉此建立一套快速篩選觸媒氧化活性之機制。 研究結果顯示：光觸媒半導體(T1、T2、T3、T4、CT1)對MtBE、Methanol、Acetone等分解反應，皆為一階反應動力關係，分解MtBE以T4光觸媒具有較高的氧化活性、分解Methanol、Acetone以T1光觸媒具有較高的氧化活性；在環境濕度對光催化反應速率之影響方面，則是呈現先促進後抑制之典型競爭吸附反應機制；各有機物之分解速率，普遍隨反應溫度升高而遞減，提高反應溫度雖然會提升光觸媒表面上的反應速率，但降低有機物吸附於光觸媒上的吸附量，據此推測反應物之吸附速率為整體反應之速率限制步驟；本研究利用L-H反應動力模式模擬相關有機物之分解速率，顯示各個光觸媒之KC(有機物吸附平衡常數)及KW(水氣吸附平衡常數)，皆隨著溫度之增加而減少，驗證污染物之吸附難易程度為整體反應之速率限制步驟。 本研究嘗試利用光觸媒半導體，進行光電效應之電阻值量測，可成功量測電阻值，並針對不同污染物、溫度以及光觸媒半導體，建立相關性頗高之關係式。測試結果顯示，於不同反應溫度及MtBE、Methanol、Acetone環境下，在伴隨提供適當之光照強度時，於60-105℃間，相關觸媒試片有一較靈敏的電阻比值，可視為最佳之檢測條件。[[abstract]]TiO2 assisted photocatalytic oxidation process is a very popular research topic in recent years especially for the control of many organic pollutants Many studies have also committed to produce more efficient catalysts for their specific purposes However the assessment of the effectiveness and photocatayst activities still is depended on complicated and lengthy chemical testing procedures Since many photocatalysts are essentially semiconductor metal oxides the adsorption of pollutants by photocatalysts is the essential step for the accomplishment of photocatalytic oxidation reaction which will also lead to changing conductivity of the photocatalyst The major advantage of the conductivity measurement is much faster than conducting chemical experiments Accordingly instead of chemical tests this study aims to develop a rapid screening method for determining photocatalytic activities of the home-made TiO2 thin-film photocatalysts In this study a magnetron sputtering technology was applied to preparing thin-film TiO2 photocatalyst on the Al2O3 plate substrates on which comb-type semiconductor thin film circuits has been immobilized Three organic compounds including MtBE methanol and acetone were applied as target organic compounds Both photocatalytic oxidation activities and the photoelectric effects of the prepared thin film photocataclysts under various experimental parameters including types of pollutants reaction temperature and water vapor contents were examined for investigating the relationship between photocatalytic activities and electric conductivity of them The results showed that: the photocatalytic oxidation of MtBE methanol acetone followed typical heterogeneous photocatalytic reactions following pseudo-first-order reaction kinetics Water vapor could typical suppress the degradation of the examined organic compounds due to adsorption competition for the active sites on the photocatalysts surfaces between water vapor and organic compounds On the other hand more fast decomposition rates were observed in higher temperature conditions The adsorption of pollutants was proved to be the reaction rate limiting step by simulating the experimental results with a LH kinetics model The results also demonstrated higher photocatalytic reaction rate of organic compounds with higher adsorption rate but lower “resistance ratio” for the tested photocatalysts A working temperature range between 60~105 ℃ is suggested for achieving more sensitive results by the prepared thin-film photocatalys