本研究主要利用紫外光發光二極體為光源，以週期照射操作提高液相中反應物的降解率、光子利用率與總有機碳去除率。探討實驗操作變因為照射時間、暗時間、pH值、光強度、反應物的初始濃度及溶氧量。由實驗結果顯示，相較於連續照射操作下，週期照射在總照射時間為60分鐘時，可以改善反應物的降解率、光子利用率與總有機碳去除率。當暗時間增加，反應物的降解率也隨之增加，主要是因為暗時間增加時，會使反應物的觸媒表面更新提高，而進一步減少電子與電洞的再結合。此外，光電流量測實驗更再度證實電子與電洞再結合隨暗時間的增加而減少。週期照射會改變反應機制，相較於連續操作。
當溶氧量為8.5或32.0 mg/L，暗時間對降解率影響較明顯，這可能是因為氧氣會再度吸附在二氧化鈦表面上，且更多的超氧離子基會存在暗時間下，以增加反應物的觸媒表面更新。本研究提出的動力式，可以描述以週期照射操作對光觸媒程序處理水溶液中鄰苯二甲酸二甲酯反應。在總照射時間為60分鐘下，隨暗時間增加，能源使用隨之減少。

The use of periodic illumination with UV–LEDs for enhancing decomposition, photonic efficiency and total organic carbon (TOC) removal of photocatalytic processes in water has been investigated. The effect of illumination period, dark period, solution pH, light intensity, initial concentration of target compound and dissolved oxygen concentration on photodegradation, photonic efficiency and TOC removal has been studied by UV–LED/TiO2 process in a batch photoreactor. The results have shown that there are obvious effects on the decomposition, photonic efficiency and TOC removal at 60 min total irradiation time under continuous and periodic illumination. The decomposition of target compound was increased for experiments conducted with increasing dark period. It is believed that the replenished surface coverage of target compound increased and the photogenerated electron–hole recombination decreased for experiments conducted with increasing dark period. Besides, the photocurrent experiments further confirmed the decreasing photogenerated electron–hole recombination when dark period increased. There are different reaction mechanisms under continuous and periodic illumination by photocatalytic process.
When the dissolved oxygen concentration was 8.5 or 32.0 mg/L, dark period has significant effect on the degradation efficiency. The results are may be depleted O2 re–adsorb onto the TiO2 surface and more O2•- are possibly presented during dark period with these higher dissolved oxygen concentrations, which could advance the replenished surface coverage of target compound. The photocatalytic decomposition of DMP by UV–LED/TiO2 process under periodic illumination could be well modeled by the the proposed approach. The electric energy saving increased significantly for experiments conducted with increasing dark period.

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