以陽極氧化法製備二氧化鈦奈米管光電陽極及其應用於水中染料降解之研究

Abstract

傳統染整工業所產生之廢水因含有高濃度之有機污染物及高色度等特 性，若未經處理而任意排放易導致水體之污染。而高級氧化處理程序於近年來開始發展並應用於水中染料之降解脫色，如：芬頓反應、光催化反應及電化學程序等；其中二氧化鈦光催化程序最為被廣泛研究及應用，但於二氧化鈦之應用上卻因其形態而有諸多限制，如以顆粒形式散佈雖能提高其比表面積卻易造成二次污染之疑慮，若改以覆膜之方式解決二次處理之問題卻又導致其活性位置減少而降低其光催效能；另外，於光催系統上則是因電子轉換效率不佳而使得系統效能不彰。因此，為增進二氧化鈦之光催活性，不同形式之合成方法(如：化學氣相沉積法及陽極氧化法)，開始於近年來被研究及改善；於其系統應用上之缺陷，亦由單純之光催化觸媒發展至電極應用，藉由系統協同之方式(電芬頓、光芬頓、光電芬頓及光電催化)提升整體系統之效能，且證實其應用於降解有機污染物上具有明顯成效。 因此，為提升染料廢水之處理效能，本研究開發特殊奈米鈦管光陽極 並應用於光電催化系統以評估其對染料廢水處理之可行性。以陽極氧化法於鈦網基材上長成二氧化鈦奈米管，並探討不同製備條件下，如：電場強度、陽極氧化時間及鍛燒溫度，以SEM、XRD及 XPS等分析方法分別觀察二氧化鈦奈米管之組成型態差異，並利用電化學分析等方式評估不同製備條件下二氧化鈦奈米管組成型態差異及其效能之相互關係。此外，亦將此材料作為光電陽極應用於偶氮染料廢水acid orange 10 (Orange G, OG) 之降解試驗，並嘗試不同能源協同之形式，如：光解、光催化、電催化及光電催化，評估對於整體系統之降解效能以及機制上差異。 結果顯示，製備過程中將鈦網基材以30 V之外加電場進行陽極氧化 60分鐘後，並以DI water (18.3 MΩ-cm, Milli-Q)進行超音波震盪表面清潔後處理，再進入550 oC鍛燒2小時，所得光電陽極展現最佳之光生電流0.112 mA/cm2，並具備極佳之電穩定性。於染料降解試驗中，結果顯示以光電催化為化學氧化途徑之複合式系統，於反應時間3小時能使脫色率達59 %，而於延長反應時間至24小時之情形下，更能有效礦化有機物達64%，不但具有良好之脫色效果，更可有效將系統中有機污染物大量礦化，而達成高效之水質淨化目的。

Dye wastewater is composed of high organic content which has chroma characteristics. It is prone to pollute water body and damage the aquatic ecological system if they are not treated properly prior to being discharged. Several advanced oxidation processes (AOPs), such as, Fenton process, photo-catalysis, electro-chemical process, etc., started to receive attentions in treating dye wastewater. Photo-catalysis process by using titanium dioxide (TiO2) is one of the most widely applied techniques recently. However, some drawbacks of this technique, including the dispersed particles are difficult to collect which induce the secondary pollution to environment, limited the useage of photo-ctalysis processes in pratical. Therefore, some innovative techniques including chemical vapor deposition (CVD) and anodization have been investigated to improve its photo-catalytic performance. For enhancing the electron conversion efficiency of these phto-catalysts, resent studies have also paid attentions on the degradation combined-energy system, such as, electro-Fenton, photo-Fenton, photoelectro-Fenton, and photoelectron-catalysis. Therefore, in order to improve the removal efficiency of dye wastewater treatment in this work, the titania nanotubes (TNTs) photoanode was fabricated by anodization, and the feasibility for dye wastewater treatment under photoelectro-catalytic system was also evaluated. In this study, TNTs was fabricated on Ti mesh substrate by anodization technique. The effects of different preparation conditions such as, applied voltage, anodization time, and calcination temperature on the photoelectron-chemical properties of TNTs were investigated. The surface morphology, crystal phase, and chemical composition were investigated using SEM, XRD, and XPS, respectively. Photo-electrochemical and electro-chemical properties of the TNTs were examined using voltammetry method. Furthermore, the fabricated TNTs was applied as photoanode for degrading azo dye - acid orange 10 (Orange G, OG). The dye degradation efficiency of TNTs photoanode applied in different combined-energy system, including: photolysis, photo-catalysis, electro-catalysis, and photoelectro- catalysis were evaluated. The well-fabricated TNTs photoanode in this study shows a high photocurrent (0.112 mA/cm2) and a great electrochemical-stability, was prepared under 30 V of anodization for 60 minutes followed by applying DI water (18.3 MΩ-cm, Milli-Q) sonication for surface cleaning post treatment and calcination at 550oC for 2 h subsequently. In the feasibility test for dye degradation, photoelectro-catalytic system using TNTs photoanode not only achieved high decolorization rate (59%) but also is capable to mineralize organic carbon to CO2 (64%) under extended reaction time. Therefore, these results suggest that TNTs photoanode prepared in this study is suitable for the application of dye wastewater treatment to achieve high removal efficiency in order to accomplish effective water purification purpose.