以二氧化鈦固定化反應槽進行光催化程序處理難分解性有機物

Abstract

苯環化合物具有毒性及難生物分解的特性，若被排入自然水體中將提高環境危害的風險，因此對於如何分解此種污染物應為目前相當重要的研究課題，利用傳統的生物處理法對於難分解及高毒性物質並無法有效將其去除，然而光催化程序因為能產生更具氧化力之氫氧自由基，相較前者對於污染物的降解作用上具有更佳的操作優勢。而在異相光催化程序中則以利用二氧化鈦為光催化劑其反應性最強，但當催化劑以懸浮方式存在處理系統時，反應後需搭配過濾或離心方式分離，導致在實廠的運用上受到相當大的限制，因此目前許多研究都嘗試以固定催化劑之方式進行催化反應，避免後續催化劑再處理的問題。 本研究之目的在於開發出一種新的二氧化鈦粉末的固定化技術，能將光催化劑有效的固定在不鏽鋼基材上，在此係以Degussa P25型二氧化鈦與聚合物溶液摻合，再將其塗佈經預氧化處理之不鏽鋼基材表面，經過高溫燒結之後，即可形成表面為二氧化鈦塗層的不鏽鋼基材。此聚合物溶液是以矽酸乙酯及水為反應物，以1：2的混合比於常溫下經過水解及聚縮合反應所合成。而在光催化反應過程水中濁度監測值僅小於或略大於1NTU，表示二氧化鈦於不鏽鋼基材表面黏著性優異，因此本研究所發展之固定化方法具有相當高的技術可行性。 實驗中選擇五種難分解及高毒性的化合物，用於評估二氧化鈦固定化反應系統對於有機物的處理效能。根據實驗結果顯示上述有機物經此反應器降解後其濃度與時間之關係圖，顯示此固定化反應器之動力行為仍符合Langmuir-Hinshelwood模式，比較五種有機物經3小時後之分解效率，其中以甲烯藍的去除效率最高，於紫外光/二氧化鈦系統進行甲烯藍分解反應，其一階反應速率常數為0.407215 hr-1，而僅以紫外光照射進行直接光解反應之反應速率常數為0.192397 hr-1，顯示此固定催化劑系統能有效的將甲烯藍去除，相較於其他研究中所使用之光源在本研究所採用的光源強度較低，僅為1.4518*10-6 einstein min-1，因此若能再提高系統之光強度及光利用率將更能有效的將難分解有機物予以降解。

Treatments of toxic and refractory organic compounds have become an important issue by the environmental studies. Due to the ineffective degradation of toxic organic compounds in the traditional biological treatment processes, photocatalytic has been developed for treating these compounds. Regarding to the application of photocatalytic process, UV/TiO2 is an important means that can produce a huge amount of OH radicals. Being a sort of powerful oxidants, OH radicals can efficiently destroy several kinds of toxic organics. In this system, separating the TiO2 particulate from the solution is difficult, thus, recent the researches have tried hard to focus on the immobilization of TiO2 powders in the equipment. The major objective of this study is to develop a new technique for the immobilization of TiO2 powders on a cylindrical stainless steel support. A coating solution was prepared by mixing tetraethyl orthosilicate (TEOS) and water together in the ratio of 1 to 2. After finishing the preparation, sprinkling the Degussa P25 TiO2 powders were over the solution and coating the stainless steel support with the solution and sintering it. Then, the TiO2 film would form on its surface later. From the turbidity result (1*NTU), the adhesion of the TiO2 film was known to be excellent. According to the XRD spectrum, the crystalline phase kept the same after the sintering process. Therefore, the development of this immobilization technique is feasible in this study. In the degradation experiments of the toxic organics, five pollutants were tested in this new immobilized system. When comparing to the decomposition efficiencies of these five pollutants, methylene blue was the highest (k=0.407215 hr-1). Contrasting with its reaction to the direct photolysis (k=0.192397hr-1), it was found that most of methylene blue was decayed by the photocatalystic reaction. From the reaction profile in the reactor, the Langmuir-Hinshelwood model can be used to describe the kinetics of the photocatalystic reaction. Besides, the light intensity value (1.4518 *10-6 einstein min-1) in the study was not as high as other researches. A higher intensive light source should be used in the further studies to increase the degradation efficiency of the toxic organics.