以合成之氧化鐵催化過氧化氫分2-氯酚之探討

Abstract

本研究之主要目的係以合成之氧化鐵催化過氧化氫分解2-氯酚之程序中，對相關影響因子及反應動力模式之探討。研究內容分為三大項，首先製備合成不同的氧化鐵，分別鑑定出其物種，並對個別之表面特性在氧化鐵/過氧化氫系統中造成的影響進行瞭解。之後選定針鐵礦為本研究系統中的催化劑，再探討反應中不同條件因子對過氧化氫催化與2-氯酚分解之影響及其主要反應作用機制。 研究結果發現，實驗中所使用的氧化鐵催化過氧化氫的能力依序為水合鐵礦＞針鐵礦＞赤鐵礦。在中性pH值條件下，三者對2-氯酚的分解去除率為針鐵礦＞赤鐵礦＞水合鐵礦，但在pH值為3的酸性環境中，由於水合鐵礦的表面會有鐵離子的溶出現象而形成Fenton反應，加速了2-氯酚的分解，此時對2-氯酚的氧化分解效率則為水合鐵礦＞針鐵礦＞赤鐵礦。 針對針鐵礦/過氧化氫之異相催化系統的研究顯示，針鐵礦表面催化過氧化氫的分解情形可以一階反應動力模式來表示。在低過氧化氫初始濃度時，分解速率會隨著濃度增加而加快，且過氧化氫之一階反應速率常數與針鐵礦的添加量間存在著一個線性關係。此外，過氧化氫在pH值愈高的環境下，其分解反應速率也愈快。 至於本研究中對2-氯酚分解之最佳加藥劑量為1g/L的針鐵礦添加量及初始濃度為8.8mM之過氧化氫，此時對2-氯酚可有49.2%的去除率。在添加量未到最佳加藥劑量時，2-氯酚的分解效率會隨著針鐵礦添加量與過氧化氫增加而提高；但當兩者的添加量超過最佳加藥劑量時，2-氯酚的氧化分解率已達極限值而不會再增加。研究中並發現本系統對2-氯酚之分解反應並不受pH值影響，因此可改善傳統Fenton法受限於酸性環境下操作的缺點，而提昇其應用上的可行性。

The essential purpose of this research was to explore the relevant impact factors and reaction kinetic pattern in the process of the degradation of 2-chlorophenol with hydrogen peroxide and synthesized goethite. The research consisted of three major parts. First, we synthesized different iron oxides, and determined the species individually. Second, the influence caused by the individual surface properties during the system with iron oxide and hydrogen peroxide was interpreted. Finally, using designated goethite as the catalytic in the reaction system to explore the different condition factors involved in the consequence that was by degradation of 2-chlorophenol with the catalytic decomposition of hydrogen peroxide, and the main reaction mechanism. From the results discovered in the research, the order was determined as ferrihydrite > goethite > hematite, according to the catalytic ability of iron oxides in the decomposition of hydrogen peroxide during the experiment. In comparison with the degradation rate of 2-chlorophenol for the three species under the condition of neutral pH, it was goethite > hematite > ferrihydrite. Under the acidic condition, due to the Fenton reaction resulting from the dissolution of ferric ions at the surface of ferrihydrite, the degradation of 2-chlorophenol was therefore accelerated. At this point, the degradation efficiency with 2-chlorophenol for the three iron oxides will be ferrihydrite > goethite > hematite. The decomposition of hydrogen peroxide due to the catalysis of goethite could be described as the first-order reaction. When the initial concentration of hydrogen peroxide was low, the decomposition rate increased with increasing its concentration, and there existed a linear relationship between the first order reaction rate constant and the amount of goethite. Besides, the decomposition rate of hydrogen peroxide increased with higher pH value. The optimal addition amounts of goethite and hydrogen peroxide in the system were 1g/L and 8.8 mM, respectively. Under this condition, 49.2% of 2-chlorophenol was degraded. Before the optimal addition amount was reached, the degradation rate rose with increasing the amount of goethite and hydrogen peroxide. Besides, the pH value did not influence the degradation rate of 2-chlorophenol in this system. Thus the disadvantage caused by the control under the acidic condition of the conventional Fenton synthesis will be improved/avoided to elevate its feasibility for practical application.