本研究之主要目的為將批式反應器用之由電極與電解質形成電化學迴路之概念，將外加電位施於電極上以進行液相之六價鉻光電催化還原反應。針對光陰極之光電特性進行分析，包括光觸媒披覆厚度，以作為後續反應器設計之依據。研究結果指出，光陰極在TiO2披覆厚度為6.50μm條件下，實際光催化還原液相六價鉻時展現最好的還原效率，因此後續實驗將選用此光陰極。
將製備所得之光陰極應用於液相光電催化還原六價鉻，並探討各項實驗操作變因(如：溶液pH值、光強度、初始六價鉻濃度、週期照射、外加電位以及電位形式)對六價鉻的還原轉化率之影響及反應動力行為。實驗結果顯示，於週期照射的操作條件下，還原六價鉻之效率皆優於連續式照射的操作條件，由於在長時間的亮週期條件下，不利於光觸媒表面吸附物質的脫附反應，因此降低了六價鉻的還原效率。
六價鉻的還原效率會隨著施加電壓的負值提高而上升，隨著外加電壓負值的提升，將有更多的電子累積於光陰極上以利於六價鉻的還原反應發生。六價鉻的還原效率亦可藉由光電催化的程序以提升，由於施加於光陰極上之外加電位有利於光觸媒因受光而激發出之電子累積於光陰極表面。光電催化程序引入半方波外加電位形式與直流電相比，結果顯示直流電形式的外加電位較有利於六價鉻的還原反應。由於當半方波形式的外加電壓於負值切換至零的當下，會有部分電子自光陰極經由外迴路流向陽極的現象發生，因此降低了六價鉻的還原效率。

In this study, the photoelectrocatalytic reactor constructed by the structure design of batch reactor was used for the photoelectrocatalytic reduction of hexavalent chromium (Cr(VI)) in aqueous phase. The photocatalytic properties of photocathodes with different TiO2 thickness are examined. The experimental results indicated that the 6.50 μm thickness of TiO2 film shows the highest photocatalytic activity among all the thickness investigated.
The effects of solution pH, light intensity, initial Cr(VI) concentration, periodic illumination, bias potential and driving modes of bias potential were investigated on the photocatalytic and photoelectrocatalytic processes. The kinetics parameters of photocatalytic reduction of aqueous Cr(VI) was studied and discussed. The photocatalytic reduction of Cr(VI) for experiments conducted with periodic illumination were higher than that conducted with continuous illumination at pH 2. Because the surface fractional coverage is higher than replenished surface coverage of concentration of hydroxide and oxygen during long illumination period. Therefore, the photocatalytic reduction of Cr(VI) became slower at the long illumination period.
The extent of electrolytic reduction was increased with decreasing applied bias potential. The bigger negative value of bias potential which provided more electron to reduce Cr(VI). Reduction of aqueous Cr(VI) was efficiently enhanced by photoelectrocatalytic process because the photoinduced electrons efficiently accumulate on TiO2-coated photocathode. The driving mode of half-rectified square wave mode (HR-SW) for electrolytic reduction also was investigated. However, the reduction of Cr(VI) under HR-SW mode was lower than which with constant DC mode when the negative bias potential. It is considered that when turning the bias potential from negative value to zero, the electrons which accumulating on the surface of cathode are drown to anode via external circuit under HR-SW mode.

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