Gas-phase Photoelectrocatalysis of Benzene Vapor by TiO2 Thin Films

[[abstract]]苯(benzene)是一種典型的揮發性有機化合物，當其逸散至大氣中，對環 境污染和人體健康造成潛在的威脅。基於此，本研究旨在研發氣相光電催化 分解程序，藉以分解苯蒸氣。研究中利用磁控濺鍍技術(sputtering technology)， 製備兩種複合以氧化銦錫(ITO)之二氧化鈦(TiO2)光催化劑－單純二氧化鈦 (Ti30)和複合以氧化銅之二氧化鈦(TNCu5)，進行苯(Benzene)之光催化分解 效率之測試，並進一步探討系列環境參數(梳型電路間距、外加電壓、光源 波長、水氣含量、反應溫度等)，對氣相光電催化反應速率影響。 研究結果顯示：苯之氣相光電催化分解反應，基本上呈現一階反應動力 關係。不同間距的銀梳型電路對於苯(Benzene)分解速率的影響，針對 Ti30 系列觸媒之苯分解速率，依序為 Ti30-250＞Ti30-750＞Ti30-500，TNCu5 系 列的降解速率為 TNCu5-250＞TNCu5-500＞TNCu5-750。由於當間距縮減、 觸媒電阻降低，使電流消耗減小，電子導出速率加快，可減緩電子電動對再 結合反應，使整體反應速率增快；此外，在外加電壓影響方面，則呈現先促 進、後抑制反應速率的現象；另外，針對不同光源對於苯分解速率影響方面， 在所測試的二種光源 UV(= 365nm)和 LED(= 470nm)，對於苯蒸氣之分解 速率依序為 TNCu-250(LED)>Ti30-250(UV)，TNCu-750(LED)>Ti30-750(UV)， 以 TNCu-250 在可見光下的反應速率最快，其除了因為所提供的 LED 光強 度較大外，也顯示本研究所製備的光觸媒，可在可見光下，進行反應；在濕 度與溫度對苯分解速率的影響方面，則呈現先促進後抑制之反應特性，呈現 典型的觸媒競爭吸附反應機制。適度增加外加電壓有利於延緩電子電洞再結 合速率，提升整體分解效率；最後，就實際分解速率量化結果而言，兩種光 觸媒薄膜的最快反應速率條件，分別為：Ti30 薄膜試片在 UV 光源下，反應 溫度為 75℃、水氣濃度為 165 μM 下，給予外加電壓 1.0 V 時，反應速率常數(kTi30-250= 0.482 hour-1 )；而 TNCu5 薄膜試片則在 LED 光源下，反應溫度 為 75℃、無水氣乾燥條件下，給予外加電壓 0.8 V 時，具有最快的反應速率 常數(kTNCu5-250= 2.214hr-1 )。[[abstract]]The study applied TiO2-based photocatalytic thin-film probes as photocatalysts to decompose a volatile organic compound- benzene under various external biases. There were two series of photocatalysts, Ti30 and TNCu5, prepared with sputtering processes in this study to investigate the effects of operating parameters (electric circuit spacing, applied biases, light sources, moisture content, and reaction temperature) on the photoelectrocatalytic degradation rate of benzene.All the experiments were conducted in a bench-scale photoelectrocatalytic reactor. The experimental results indicate photoelectrocatalysisof benzene basically following the first-order reaction kinetic. Based on the observed degradation rate of benzene, both Ti30-250 and TNCu5-250 were two photocatalysts with the highest reaction rate for benzene because both of them had lower electric resistance. It is expected that the recombination rates of electro-hole pairs can be more retarded by them. For the effects of external biases on the benzene degradation rate, the degradation rateincreased with increasing biases initially but further declined with applied biases for higher biases.For the effects of different light sources on benzene decomposition rate, the experimental results indicated TNCu-250 (LED)> Ti30-250 (UV) and TNCu-750 (LED)> Ti30-750 (UV). The experimental results successfully demonstrated the achieved TNCu5 series photocatalysts can work under illumination of LED blue light. In addition, for the effects of humidity and reaction temperature on the benzene degradation rate, there was a peak reaction rate observed, showing typical reaction patterns of heterogeneous reactions. Finally, in terms of degradation rate of benzene, the highest reaction rates were observed when the reaction temperature was 75℃, the water vapor concentration was 165 M, and applied bias was 1.0 V for Ti30 sampleas irradiated by UV light (kTi30-250= 0. 4.82hr -1 ) andwhen the reaction IV temperature was 75℃, in adry condition, and applied bias was 0.8 V for TNCu5sampleas irradiated byLED blue light (kTNCu5-250= 2.214 hr -1