以高錳酸鹽活化溶解態全氟辛酸在超聲波系統中的分解與脱氟之研究

Abstract

高錳酸鉀首次運用於全氟辛酸在水溶液中的降解研究。全氟辛酸的降解分為分解與脫氟兩部份，超聲波振幅、高錳酸鉀劑量、溶液初始pH值及溫度為其反应速率的影響因子。全氟辛酸的分解為擬一階反應，隨著振幅的增加(20μm、40μm與 60μm)，超聲波輸出能量的提高，其速率常數(K1obs)顯著地從0.0021上升到0.0146 min-1。氟元素離子化的過程稱作全氟辛酸脫氟反應，可模擬為零階反應(K2obs)。高錳酸鉀的劑量效應說明其分別作為活化劑與氧化劑參與到全氟辛酸的分解與脫氟反應中。在本研究的劑量範圍中，以ln(K2obs)對ln([KMnO4]0)作圖，可得到一條線性回歸線。對於132μM的全氟辛酸而言，分解反應與脫氟反應的最佳劑量分別為3mM與10mM。相對於強酸性（pH=2）與中性環境，pH=4的酸性環境與pH=11的強鹼性環境最利於全氟辛酸的降解。將溫度從30℃ 升至50℃，全氟辛酸的降解速率有輕微的提升。雖然高溫能有效加速氧化過程，但同時也降低了超聲波的能量輸出。一組高錳酸鉀與雙氧水的對比試驗分別在氬氣、空氣與氧氣的氛圍下進行。曝氬氣能把溶液中的溶解氧掃除，進而把高錳酸鉀-超聲波與雙氧水-超聲波系統的K2obs分別提高1.57倍與2.40倍；而曝氧氣時則將K2obs分別降低至0.72與0.51倍。這是由於溶解氧在超聲波系統中引發的自由基鏈式反應的終止步驟。根據所有得出的實驗數據，本研究提出全氟辛酸在高錳酸鉀-超聲波系統中的分解与脱氟機制。

Permanganate was investigated for the first time as an activator for the degradation of perfluorooctanoic acid (PFOA) in aqueous solution. PFOA Degradation, consisted of decomposition and defluorination, were investigated as a function of amplitude of ultrasonic waves, permanganate dosage, pH and temperature in ultrasonic system. The decomposition of PFOA was of pseudo-first order, and the rate constant (K1obs) increased significantly, from 0.0021 to 0.0146 min-1, with raised amplitude (20μm, 40μm and 60μm) which determine the output power of ultrasonic irradiation into medium. Ionization process of fluorine, named PFOA defluorination, could be simulated with pseudo-zero order (K2obs). Dosages effect shown that permanganate act as an activator for PFOA decomposition and oxidant for defluorination. And plotting ln(K2obs) versus ln([KMnO4]0) gave a linear curve in the dosages range studied. For 132 μM initial concentration of PFOA, 3mM and 10mM permanganate is optimal for decomposition and defluorination efficiency, respectively. Reaction solution with an initial pH of 4.0 and 11.0 were most favorable for PFOA degradation activities as compare to highly acidic and neutral condition. Degradation process was observed to be promoted slightly from 30℃ to 50℃, as high temperature would accelerate the oxidation process by permanganate but abate the power output of ultrasonication. A comparative investigation between permanganate and perhydrol under oxygen, air and argon atmosphere, respectively, was carried out to study the atmosphere effect. Aeration with argon gas, which could sweep away dissolved oxygen, improved K2obs to 1.57 for permanganate-ultrasonic and 2.40 times for perhydrol-ultrasonic system; while aeration with oxygen decreased K2obs to 0.72 and 0.51 time due to the termination steps induced by oxygen molecules. With experimental results, the mechanisms of PFOA decomposition and defluorination in permanganate-ultrasonic system were proposed, respectively.