- 學位論文
鋅結合二氧化鈦複合二氧化矽光觸媒降解多氯聯苯之研究
The degradation of PCBs using zinc and titanium dioxide composite with silicon dioxide photocatalyst
摘要
光解是污染物質於環境中自然降解的重要途徑，特別是藉由光感物質吸收日照光能所進行的間接性光解，其優點為處理效率高、操作設備小、操作程序簡單、能源消耗少、可利用自然光等。多氯聯苯(Polychlorinated biphenyls﹐PCBs)因具有穩定性高、不易被生物分解的特性，釋放至環境中經由空氣、水體、動植物以及土壤等介質之傳輸，累積於生物體中，進而對人體及自然生態產生危害。 二氧化鈦與鋅皆有成本低、無毒性的特性，將鋅粒子嵌入二氧化鈦於光照後使電荷分離產生電子-電洞對，具有較高效能的光催化能力，而二氧化矽則可以提高其熱穩定性。本研究以溶膠-凝膠法(Sol-Gel process)製備鋅結合二氧化鈦複合二氧化矽光觸媒，並比較純TiO2、純SiO2、TiO2- SiO2/ Zn (0.5、0.7、1.0 wt％)及不同結合順序的Zn- SiO2/TiO2 (0.5、0.7、1.0 wt％)改質光觸媒之光催化能力，使其提高可見光之吸收區域，並進一步探討處理亞甲基藍與多氯聯苯水溶液光降解效能之研究。 研究結果顯示複合之觸媒能加速日光下降解速率，經場發射掃描式電子顯微鏡(Field Emission Scanning Electron Microscope﹐FE-SEM)之結果指出，鋅的摻雜對其表面不會造成影響；於X-ray繞射分析儀 (X-Ray Diffraction, XRD)分析結果經資料庫(JCPDS)驗證，本研究所製備之觸媒皆為具有高度光催化活性的銳鈦礦(anatase)型為主要優勢物種；從光降解試驗可知，在自然日光照射2小時，除了純TiO2及純SiO2兩種觸媒，其餘降解率皆達100%。以上述實驗之最佳條件針對多氯聯苯在自然日光下進行降解，其去除率可達43.52 %、礦化率為15.55%；經過五天的持久性試驗，以溶膠-凝膠法製備之0.7與1.0 wt% Zn- SiO2/TiO2，經鍛燒600℃其可重複利用且較符合目前環境保護之經濟效益。
並列摘要
Photodegradation is one of the most important mechanisms of natural degradation for organic pollutants in environment especially through the indirect photodegradation. The advantage of indirect photodegradation can be an efficient method with low equipment cost, less complicated operation processes, low energy consumption, and capable of using solar energy. Polychlorinated biphenyls (PCBs) have been widely used in industries. PCBs are highly stable man-made organic matters. However, PCBs are not easily biodegradable, a group of persistent organic pollutants. When PCBs released to the environment through the transportation of atmosphere, water, organisms and soil in the various environmental media they can be accumulated in organisms because of the contamination in the environment. Titanium dioxide (TiO2) and Zinc (Zn) have low cost and non-toxic properties. After Zn particles embedded TiO2 the charge separation producing an electron-hole pairs under the exposure of the lights. TiO2 has a high performance light catalytic ability. The silicon dioxide (SiO2) can improve TiO2 thermal stability. The sol-gel preparation of Zn and TiO2 composite with SiO2 with defferent amounts of Zn are used to form pure TiO2, pure SiO2, TiO2-SiO2, TiO2- SiO2/ Zn (0.5、0.7、1.0 wt％) and different binding order of Zn-SiO2/TiO2 (0.5、0.7、1.0 wt％). Zn was applied to enhance the photocatalytic capacity to improve the visible light absorption and to further explore the treatments of methylene blue and PCBs aqueous solutions. The results found that the catalyst complex can accelerate the degradation efficiency of pollutants under natural sunlight. The findings of FE-SEM tests showed that the doping of Zn did not affect its surface. The XRD analytical results were used to compare the JCPDS authentication database used in this study. The main dominant species comfirmed the catalyst types with all highly photocatalytic activity of TiO2. Degradation percentages of methylene blue were 100 % under natural sunlight after 2 hours exposure except for the sample of Pure TiO2 and Pure SiO2. The degradation percentages of PCBs were up to 43.52% and 15.55% of mineralization. PCBs concentration decreased with increasing illumination times. The results indicated that 0.7 and 1.0 wt% Zn-SiO2/TiO2 calcined at 600℃ by sol-gel method can be reused, and it confirmed their economical benefits of environmental protection techniques.