"以奈米碳管活化過一硫酸氫鉀複合鹽藉由電子轉移途徑去除2,4-二氯酚 "

Abstract

近年來，過硫酸鹽高級氧化程序因具備高效力的有機污染物降解能力而受到廣泛的關注。許多研究陸續提出了非自由基的降解途徑及相關證明。為了更直接地探討非自由基機制中的電子轉移途徑，本研究使用賈法尼電化學氧化程序(Galvanic oxidation process) ，以多壁奈米碳管作為活化劑，塗佈於石墨片上作為電極，並將2,4-二氯酚及過一硫酸鹽分別置於以鹽橋和銅線連接的陰極反應槽和陽極反應槽中，以排除自由基或具反應性表面錯合物對2,4-二氯酚的降解貢獻。在10 µM 2,4-二氯酚和25 mM 過一硫酸氫鉀複合鹽條件下，連接與未連接鹽橋和銅線的賈法尼氧化程序控制試驗中， 22 % 的2,4-二氯酚去除是源於吸附作用，而幾乎所有的2,4-二氯酚去除是由吸附和電子轉移途徑所貢獻。此外， 2,4-二氯酚的去除速率隨著過一硫酸鹽用量、2,4-二氯酚濃度、多壁奈米碳管塗佈量以及2,4-二氯酚陰極溶液pH的增加而提升。測得的電流大小也隨著2,4-二氯酚去除速率的提升而變大。於電極耐久性評估試驗中，2,4-二氯酚於第八次的循環使用中仍有92 % 左右的去除效率，顯示多壁奈米碳管電極具備良好的重複使用性及穩定性。最後，應用X射線光電子能譜儀（XPS）及拉曼光譜儀對使用過的多壁奈米碳管進行分析，多壁奈米碳管結構上減少的缺陷或紊亂及增加的氧原子含量說明其結構於過程中有吸附、活化及電子轉移的反應發生，有可能會影響更長期2,4-二氯酚的去除效率。

Persulfate advanced oxidation process has gained increasing attentions in recent years due to its high capability to degrade organic contaminants. In addition to free radicals produced, studies suggested that the degradation of organic contaminants can be proceeded via the non-radical mechanism. In order to specifically investigate the electron transfer pathway of the non-radical mechanism, the galvanic oxidation process (GOP) was employed, in which the target contaminant 2,4-dichlorophenol (2,4-DCP) and peroxymonosulfate (PMS) were separated into two individual anodic and cathodic cells that were connected by a salt bridge and external copper wire. The separated cells can exclude the contributions of radicals and reactive surface complexes generated from the PMS activation toward the degradation of 2,4-DCP. Multi-walled carbon nanotube (MWCNT) was used as the PMS activator and was coated on the graphite sheet as electrodes. In the GOP control system that is connected or disconnected to salt bridge and external copper wire in the condition of 10 µM 2,4-DCP and 25 mM PMS, it was observed that 22% of 2,4-DCP removal could be attributed to adsorption on the electrode, while almost all of the 2,4-DCP was removed via the adsorption and direct electron transfer pathway in 7 h. The 2,4-DCP removal was enhanced by the increasing of PMS concentration, 2,4-DCP concentration, MWCNT coating and the pH of 2,4-DCP solution in the anodic cell. The magnitude of current measured was higher at a higher 2,4-DCP removal rate. In the electrode reusability test, the 2,4-DCP removal remained about 92% after 8 cycles, indicating the good reusability and stability of the MWCNT electrodes. X-ray photoelectron spectroscope (XPS) and Raman spectroscopy were applied to analyze the used MWCNT. The results of decreasing defects or disorders on MWCNT and the increasing of oxygen content suggested that the adsorption, activation and electron transfer did occur in the process and could gradually restrict the activation ability of MWCNT. These changes may affect the long term performance of the electrode and may require further investigation.