利用針鐵礦催化過氧化氫分解2-氯酚

Abstract

本研究以針鐵礦(Goethite; α-FeOOH)催化過氧化氫分解2-氯酚，內容可分為四個部份包括背景實驗、控制因子之探討(2-氯酚濃度、過氧化氫濃度、Goethite濃度、Goethite粒徑、溶液pH值、溶液溫度、不同氯酚化合物及背景離子種類之效應)、反應作用機制與2-氯酚反應動力模式之探討。 實驗結果顯示，降低2-氯酚的初始濃度、加高過氧化氫初始濃度與Goethite添加濃度則2-氯酚分解速率愈快。但Goethite添加量達至0.4g.l以上時則反應速率下降。粒徑大小對2-氯酚的去除影響相當大，Goethite粒徑愈小，2-氯酚分解速率愈快。反之則愈慢。Goethite/過氧化氫氧化程序分解2-氯酚，最佳反應pH值介於2∼3之間。分解不同氯酚類化合物，其分解速率快慢順序為2-氯酚＞4-氯酚＞2,4-二氯酚。而在不同背景離子條件下分解2-氯酚，影響程度依序為H2PO4-＞Cl-＞NO3-＞ClO4-。本系統在酸性條件下，而Goethite中鐵離子溶出是以亞鐵離子型態溶出可以表示如下: α-FeOOH＋1/2H2O2＋2H+ → Fe2+＋l/2O2＋2H2O Goethite/過氧化氫氧化程序作用機制，是由於亞鐵離子的生成，再與過氧化氫作用形成Fenton反應。藉由Fenton反應所產生的氫氧自由基，氧化2-氯酚而達到去除2-氯酚的目的。Goethite/過氧化氫氧化程序去除2-氯酚，在前後100分鐘呈現出兩種不同分解速率階段，反應在100分鐘後較明顯成為主要反應階段，並且可以利用零階反應動力去模擬2-氯酚的分解反應。

Catalytic degradation of 2-chlorophenol has been investigated in the α-FeOOH/H2O2 process. There are four parts in this research. First, a background test was carried out. Second, controlling factors, such as initial 2-chlorophenol concentration, hydrogen peroxide concentration, goethite concentration, goethite particle size, pH, temperature, different chlorophenol compounds and electrolytes were investigated. Third, the reaction mechanism in this process was studied. Finally, the reaction kinetic model of 2-chlorophenol degradation was also proposed. The results are shown as follows. The rate of 2-chlorophenol oxidation increases with decreasing 2-chlorophenol initial concentration and increasing initial hydrogen peroxide and goethite loading. Effect of goethite particle size on the 2-chlorophenol oxidation is very signficant; the smaller goethite particle size, the faster 2- chlorophenol oxidation. The rate of 2-chlorophenol oxidation is highest at pH=2~3 . Three lands of chlorophenols were degraded compounds by α-FeOOH/H2O2, and the oxidation rate of these chlorophenols is shown as below : 2-CP>4-CP>2,4-DCP This process is sensitive to electrolytes. It was found that the effect of electrolytes on the oxidation rate follows the order: H2PO4- > Cl- > NO3- > ClO4- Goethite can be dissolved to produce ferrous ions and the dissolution reaction can be shown as follows: α-FeOOH＋1/2H2O2＋2H+ → Fe2+＋1/2O2＋2H2O Ferrous ions can produce Fenton reaction with hydrogen peroxide, and hence 2-chlorophenol can be degraded by Fenton reaction. The oxidation of 2-chlorophenol with α-FeOOH/H2O2 in this study is a two-stage reaction. In the first stage, 2- chlorophenol oxidation is limited by the amount of ferrous ions forming in the reaction solution. In the second stage, after 100 minutes of reaction time, the rate of 2- chlorophenol oxidation suddenly increases, and can be described with a zero-oder kinetics.