光電化學催化與光電芬頓反應偶合於染料廢水處理之研究

Abstract

電化學高級氧化程序(Electrochemical advanced oxidation processes, EAOP)如光電化學催化(photoelectrochemical catalysis, PEC)、電芬頓(electro-Fenton, EF)及光電芬頓(photoelectro-Fenton, PEF)等程序，因具有使用上應用性廣、高處理效能且對環境負荷低等優點，故於近年來廣泛應用於高污染之染整廢水處理。諸類電化學高級氧化程序為於系統中生成具有高氧化及低選擇性之氧化物-氫氧自由基(hydroxyl radicals, OH•)，其可與大多數的有機化合物反應生成二氧化碳、水及無機鹽類。近年來，結合多種電化學方法之偶合型(coupled)與複合型(hybrid)電化學程序因較其它單一電化學程序能提供較高的廢水處理效能，而被逐漸發展而出。因此，本研究為發展偶合光電化學催化與光電芬頓之程序，結合二氧化鈦/鈦金屬(TiO2/Ti)與不銹鋼(stainless steel)之雙陽極系統。研究於前期分別針對TiO2/Ti與不銹鋼陽極材料進行個別探討，後期則結合兩種陽極探討偶合光電化學催化與光電芬頓程序對染料廢水之處理。 本研究可分為二部分，第一部份之研究主要為探討TiO2/Ti光陽極，利用電泳沉積法(electrophoretic deposition, EPD)製備TiO2/Ti光陽極，並藉光電催化系統處理偶氮染料Orange G (OG)作為TiO2/Ti電極之效能驗證。由表面分析和電化學分析之結果得到最佳電泳沉積製備條件為180 V之沉積電壓下沉積一分鐘並於350oC鍛燒後，可得最佳的TiO2/Ti光陽極。於研究結果顯示於光電化學系統下具有光催化(photocatalysis, PC)與電化學氧化(electrochemical oxidation, EO)兩種反應之加成效應，對染料降解效能大小依序：光電化學催化程序>電化學氧化>光催化，且由反應動力分析可知對於OG染料降解為擬一階反應，且氫氧自由基為參與氧化反應之主要活性氧物種。 第二部份則為不銹鋼陽極與石墨陰極系統之電芬頓與光電芬頓之研究，系統中之亞鐵離子主要由犧牲性不銹鋼陽極提供，石墨陰極則可生成過氧化氫(hydrogen peroxide, H2O2)。研究結果指出操作電流可控制不銹鋼與石墨電極生成的亞鐵離子與過氧化氫產量，且當操作電流為45 uA/cm2可得到最佳[H2O2]/[Fe2+]莫耳比例為3.58。另外，系統使用光電芬頓程序較電芬頓對染料更具有降解能力，同樣在45 uA/cm2之操作電流下，反應時間3小時內其脫色能力可達到85%。藉由反應動力學分析可得知電芬頓與光電芬頓對染料降解為一階反應，並提出此兩種程序主要皆由氫氧自由基進行脫色反應。 為了偶合兩種光電化學催化與光電芬頓程序(coupled PEC/PEF process)，本研究採用TiO2/Ti與不銹鋼雙陽極電化學系統作染料廢水處理。由反應動力學分析得知，PEC/PEF程序主要是藉由提升亞鐵離子與過氧化氫的生成並產生更多的氫氧自由基，使系統更能有效的降解OG與其副產物，故對染料降解效能大小依序為：偶合光電化學催化與光電芬頓程序>光電芬頓>電芬頓>光電化學催化>電化學氧化>光催化，且TiO2/Ti與不銹鋼雙陽極分別在75 uA/cm2與45 uA/cm2操作電流下，經七小時反應後，其脫色及礦化能力分別可達到99.8%和70%。由反應動力學分析可得到偶合光電化學催化與光電芬頓程序頓對染料降解為擬一階反應。

In recent years, advanced oxidation techniques including electrochemical advanced oxidation processes (EAOP) have gained much attention. EAOP have been employed widely for the decontamination of wastewaters containing high-strength organic pollutants due to their versatility, high efficiency, and environmental compatibility. The effectiveness of EAOP such as photoelectrochemical catalysis (PEC), electro-Fenton (EF) and photoelectro-Fenton (PEF) are ascribed to the generation of hydroxyl radicals (OH•), which has a high redox potential that can react non-selectively with most organic compounds to produce CO2, water, and inorganic ions. Recently, many coupled and hybrid electrochemical processes have been proposed aiming developing more powerful processes for dyes removal. It provides more advantages than individual electrochemical processes owing to the high degradation performance on the treatment of wastewater via combined different electrochemical methods. Therefore, the purpose of this thesis was to develop the coupled PEC/PEF process by combining TiO2/Ti and stainless steel dual anode system. In the first parts of this study, the TiO2/Ti and stainless steel anodes would be integrated individually. After that, the combining both anodes with coupled PEC/PEF process for treatment of dye wastewater treatment was integrated in the second part of this study. The first part was the integration of TiO2/Ti photoanode, the TiO2/Ti photoanode was prepared by electrophoretic deposition (EPD) process. The performance of TiO2/Ti photoanode was tested by degradation of azo dye Orange G (OG) using a PEC system. Results of surface analysis and electrochemical analysis revealed that the optimal EPD condition was a deposition potential of 180 V for 1 min and annealed at 350oC. These results showed that the coupling effect of photocatalytic and electrochemical oxidation processes was evaluated in terms of the decolorization of OG. The degradation of OG increased in the following increasing order: photocatalysis (PC) < electrochemical oxidation (EO) < PEC. The degradation of OG follows the pseudo first-order kinetic in PEC process, which proposed the OH radical is the major player in the decolorization reaction. The second part was the integration of stainless steel (SS) anode and graphite cathode system with EF and PEF processes. In this system, the ferrous ions being derived from a sacrificial stainless steel anode and hydrogen peroxide being produced at a graphite cathode. Results indicated that the applied current controlled the rate of electrogeneration of ferrous ion and hydrogen peroxide. The optimal [H2O2]/[Fe2+] (molar) ratio was 3.58 at an applied current density of 45 uA/cm2 for the SS-graphite system. The OG degradation efficiency in the PEF process was greater than that of the EF process under otherwise identical conditions. At an applied current density of 45 uA/cm2, stainless steel anode achieved a decolorization of 85% after 3 h. The degradation of OG followed the pseudo first-order kinetics for both EF and PEF processes, which proposed that OH radical was a main species for the decolorization reaction. For coupling the PEC and PEF two processes, the dual anode electrochemical system by combining the TiO2/Ti and stainless steel was developed for OG treatment. From the result of kinetic aspect, the efficiency of the PEC/PEF process depended on the Fe2+ and H2O2 electrogeneration which yielded OH radical in the solution bulk, which could promote the oxidative degradation of OG and its byproducts. The degradation of OG increased in the following increasing order: photocatalysis < electrochemical oxidation < photoelectrochemical degradation < electro-Fenton < photoelectro-Fenton < coupling the photoelechemical and photoelectro-Fenton. After the 7 h reaction time, a decolorization of 99.8% and TOC removal of 70% were achieved at an applied current density of TiO2/Ti and stainless steel anodes were 75 uA/cm2 and 45 uA/cm2. The degradation of OG following the pseudo first-order kinetic for PEC/PEF process.