二氧化鈦奈米光觸媒薄膜之光催化活性與光電效應相關性研究 / Investigation on the relationships between photocatalytic activities and photoelectric effects of TiO2 thin films

[[abstract]]本研究旨在利用非平衡磁控濺鍍法技術，製備二氧化鈦(TiO2)光觸膜薄膜，並根據TiO2半導體之光電效應與光催化活性，進行相關效能之探討，以瞭解光催化活性與光電效應之關係，並期望藉此建立一套快速篩選觸媒活性之機制。本研究所使用的觸媒，係先於氧化鋁基板上鍍上梳型銀電極，再利用濺鍍技術鍍上TiO2薄膜，相關製備之觸媒可同時進行光催化分解污染物與實氣體感測驗。本研究之主要實驗參數包括：觸媒類型、污染物(MtBE，Methanol、Acetone)、反應溫度(60~120oC)和反應溼度(0~3712 μM)等進行相關實驗測試，相關之實驗係於批分式光催化反應中進行。 研究結果顯示：MtBE，Methanol、Acetone有機物呈現典型之氣相光催化氧化反應特性，三種揮發性有機物之光催化分解反應，皆呈擬一階分解速率關係，光觸媒表面之平衡吸附量，為反應溫度60~120oC範圍的速率限制步驟；三種揮發性有機物中，以methanol的反應速率為最快，其擬一階反應速率常數為4.3 min-1•m-2；此外，當反應溫度介於60~120oC時，有機物之光催化分解速率，隨溫度增加而下降；另外，適當的水氣含量，具有促進光催化分解的作用，但當水氣濃度過高時，因水氣與反應物競爭活性位址，反而導致分解速率降低；本研究應用L-H反應動力模式，模擬相關之分解動力關係，模擬成效不錯。模擬結果可發現，不同觸媒之反應速率常數值(kLH)差異不大，但催化活性較高的觸媒，其對於揮發性有機物與水氣之吸附平衡常數(Kc與Kw)也較大，驗證污染物之吸附難易程度為整體反應之反應速率限制步驟。 在氣體感測結果方面，本研究藉由以UV(365nm)作為活化光觸媒薄膜的光源下，成功地將光觸媒可感測溫度降至60 oC，而且偵測極限濃度可達ppb濃度範圍。本研究經由針對不同污染物、檢測溫度、光觸媒等實驗條件的測試，已建立相關性相當不錯之有機物濃度與感應值檢量關係，可針對不同溫度下對MtBE、methanol、aceton進行感測。此外，本研究也發現，當環境溫度溫度介於90~105 oC時，相關製備之光觸媒具有較佳的靈敏度，其可視為最佳的檢測溫度；另外，水氣含量對於不同揮發性有機物之感測影響方面，其影響趨勢大致相同，皆呈現先促進後抑制之現象，此與水氣分子干擾污染物光催化分解反應速率的效應一致。最後，本研究也發現，在相同參數條件下，當光催媒具有較高的促進氧化分解能力時，其氣體感測效能反而較不理想。顯示光觸媒薄膜之光電效應，可作為觸媒活性初步篩選之選項。 / [[abstract]]This study aims to investigate both photocatalytic activities and photoelectric sensing effects of thin-film TiO2 prepared by an unbalanced magnetically sputtering technology The relationships between the photocatalytic activities and photoelectric sensing effects were especially interested in the study for the particular purposes of developing a fast evaluation method of photocatalyst activities The photocatalysts were produced by depositing thin-film TiO2 on Al2O3 substrates on which comb-shaped Ag electrodes had been coated before the deposition of TiO2 Under the illumination of near-UV light series of experiments including both photocatalysis of volatile organic compounds and change in electric resistances of the thin-film photocatalysts was monitored Some typical experimental variables including four types of photocatalysts there kinds of organic compounds (MTBE methanol and acetone) four reaction temperatures (60~120oC) and different water vapor contents were examined Some important results were observed in this study For the photocatalytic oxidation of volatile organic compounds typical heterogeneously photocatalytic oxidation reactions were observed which followed pseudo-first-order reaction kinetics It is also found that their degradation rates were decreased with the increase in reaction temperature and the rates were also enhanced while some water vapor can be involved in the reaction But the reactions were inhibited when too much water vapor were present in the reaction system The adsorption of organic compounds onto photocatalyst was considered as the rate determining step A typical photocatalytic reaction kinetic model Langmuir-Hinshelwood kinetics was applied to simulate the photocatalysis of them and showed well prediction of the experimental results For the gas sensing experimental results this study successfully demonstrated the prepared samples keeping well sensing effects at 60 oC while under the illumination of 365-nm near UV light instate of proving high-temperature conditions The prepared thin-film photocatalysts can be sensitive sensing materials for measuring organic vapors with ppb-level concentrations The experimental results also indicated that the photocatalysts could be more sensitive at about 90~105 oC for monitoring the concentrations of tested volatile organic compounds but too much water vapor presenting in the reaction systems could reduce the sensing sensitivities An interesting result was also observed in the study showing the photocatalyst achieving high oxidative capabilities with relatively poorly photo sensing effects for the organic vapors