以電泳沉積法製備光電半導體電極及其應用於水中染料降解之研究

Abstract

常見用於針對染整廢水處理之高級氧化技術主要為芬頓反應、光催化反應以及光芬頓反應，然而這些反應機制於實務應用上仍有極大之限制主要因其電子轉換效率不佳而導致在操作成本上偏高，因此近年來已有許多研究以電場輔助形式協助提升其電子利用效率，常見的方法有電芬頓反應、光電催化反應以及光電芬頓反應，其中又以光電催化反應以及光電芬頓反應在污染物去除之效能上有極佳之表現。 本研究主要以電泳沉積方式製備二氧化鈦複合不鏽鋼鐵網基材，作為光電半導體電極，於製備過程中改變不同操作參數例如外部電場之電壓、沉積時間、二氧化鈦懸浮液溫度以及其離子強度等，觀察二氧化鈦之沉積行為以及其鍍層結構特性，得出結論以濃度0.64 g/L 之低溫(4℃)二氧化鈦懸浮液，在經過一高電壓(180 V)短沉積時間(1 min)之電泳沉積程序後經過350℃鍛燒60分鐘後所得之二氧化鈦複合不鏽鋼網之光電半導體電極，其二氧化鈦鍍層能有效減少裂隙現象之產生，經過循環伏安法之電化學特性分析有較穩定之電子傳遞特性。 此外，本研究將以此二氧化鈦複合不鏽鋼鐵網電極應用於光電半導體電極系統針對染料 Orange G (OG) 進行降解，以改變不同工作參數像是系統 pH值，陰極材料以及通入氣體種類進行系統最佳化之調控，並以不同能量供應形式評估系統中對應機制種類與效能如電芬頓、光催化、光電催化等氧化途徑，其中陰極材料部分選用鉑金以及石墨兩種材料針對其電化學特性分析其對於氧氣還原產生過氧化氫之效率做出評估，並在最後以改變電壓控制方式，將系統中陰極石墨電極控制於-1.0 V (vs. SCE)，此時亞鐵離子因電場強度關係將從不鏽鋼網基材表面析出，並經由擴散作用穿過二氧化鈦鍍層進入反應水溶液中，系統中之氧化途徑將由光電催化反應與光電芬頓反應結合成一複合性反應機制，有效提升系統電子利用效率而達成高效淨水之目的。

The traditional advanced oxidation processes such as Fenton reaction, photocatalysis reaction and photo Fenton reaction were all limited by its low electron efficiency in dye wastewater treatment. Recent studies have tried to enhance the electron efficiency with electrochemical methods, including electro Fenton reaction, photoelectrocatalysis reaction and photoelectro Fenton reaction. In this study, titanium dioxide coatings on stainless steel mesh regarded as photoelectric semiconductor electrode have been prepared for dye waste water treatment by electrophoretic deposition (EPD) method. Zn(NO3)2 was added as electrolyte in the suspension comprised of 0.64 g titanium dioxide particles and 200 mL 2-propanol in order to increase the positive charge on the surface of titanium dioxide particles. While the electrolyte concentration is 10-4 M and suspension temperature at 4℃, the surface of stainless steel mesh is completely covered with a homogeneous titanium dioxide layer via cathodic electrophoretic deposition which applied a high voltage electric field in the short period of deposition time. After heat treatment with 350℃for 60 min, a crack-free titanium dioxide layer is produced, and its thickness is about 2.14 μm. The azo dye Orange G degradation reaction was studied in an undivided cell with carbon felt as the cathode and oxygen gas was purged in the solution for the hydrogen peroxide electrogeneration. Titanium dioxide coatings on stainless steel mesh electrode worked as the photoanode for the photoelectro-assisted reaction under ultraviolet light irradiation. In this photoelectro-assisted oxidation reaction system, hydrogen peroxide is produced by a two-electron transfer reduction of oxygen and the ferrous ion is supplied with electrogeneration from titanium dioxide coatings on stainless steel mesh electrode while applied -1.0 V(vs. SCE) on the carbon felt. Therefore, it means the heterogeneous photoelectrocatalysis reaction and homogeneous photoelectron Fenton reaction simultaneously occurred in the same reaction system, both the degradation rate and removal ratio of total organic carbon for Orange G dye have been enhanced with comparison to other oxidation processes in this system such as photocatalysis reaction, electro Fenton reaction and photoelectrocatalysis reaction.