以奈米碳管活化過二硫酸鹽催化降解2,4-二氯酚

Catalytic Degradation of 2,4-Dichlorophenol by CNT-activated Peroxydisulfate

陳建佑(Chien-Yu Chen)

指導教授 ： 林逸彬

國立臺灣大學/工學院/環境工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201900233

摘要

近來，碳基非金屬催化劑因其優異的有機汙染物去除能力而在高級氧化程序中受到廣泛注目。此研究以奈米碳管活化過二硫酸鹽去除2,4-二氯酚，並探究其中的反應機制及奈米碳管扮演之角色。在控制組的二元系統中，過二硫酸鹽無法單獨直接氧化2,4-二氯酚，而過二硫酸鹽及2,4-二氯酚皆能吸附至奈米碳管表面。在過二硫酸鹽/2,4-二氯酚/奈米碳管的三元系統中，2,4-二氯酚的降解速率會隨過二硫酸鹽、2,4-二氯酚、奈米碳管的量及pH增加而加快，但在含有超過100 μM的過二硫酸鹽及20 μM的2,4-二氯酚的反應溶液中此降解速率會趨緩。在奈米碳管重複使用的實驗中，有75%的2,4-二氯酚在第一輪反應中降解，但在第二、三輪中都只有約21%的2,4-二氯酚降解。奈米碳管活化過二硫酸鹽之可能途徑有三:游離自由基、表面自由基及非自由基機制。自由基清除實驗及電子順磁共振光譜儀證實游離自由基並非主要之過二硫酸鹽活化產物，顯示奈米碳管之表面自由基及非自由基機制可能為2,4-二氯酚降解的主要機制且發現奈米碳管本身在此催化降解過程中也會消耗自由基。X射線光電子能譜儀也在此研究中被應用於反應前後的奈米碳管，結果指出2,4-二氯酚降解所造成奈米碳管之氯化，來自於表面自由基氧化2,4-二氯酚所產生之含氯芳香族自由基的自由基加成反應造成，而非自由基機制可造成約24%的2,4-二氯酚降解。

關鍵字

過硫酸鹽 ； 氯酚 ； 奈米碳管 ； 催化降解 ； 表面自由基 ； 非自由基

並列摘要

Metal-free carbon catalysts have drawn extensive attentions for the removal of recalcitrant organic pollutants in advanced oxidation processes (AOPs). In this research, pristine carbon nanotubes (pCNT) was employed to activate peroxydisulfate (PDS) for the removal of 2,4-dichlorophenol (DCP). In control experiments using dual-compound systems (PDS/DCP, pCNT/PDS and pCNT/DCP), PDS hardly oxidized DCP directly and both PDS or DCP could adsorb onto pCNT surfaces. The effects of PDS dosage, DCP dosage, pCNT loading and pH were investigated in the PDS/DCP/pCNT system. The DCP degradation rate increased with increasing PDS, DCP, pCNT and pH but gradually slowed down in the presence of over 100 μM PDS or 20 μM DCP. In the evaluation of service time of pCNT, the PDS/DCP/pCNT system showed 75% DCP degradation in the 1st cycle and 21% in both the 2nd and 3rd cycles. There are three possible PDS activation mechanisms for the degradation of DCP, including free radical oxidation, surface-bound radical oxidation and non-radical oxidation in the PDS/DCP/pCNT system. The results obtained from radical scavenging experiments and electron paramagnetic resonance (EPR) tests indicated that the surface reactions including surface-bound radicals and the non-radical mechanism instead of aqueous free radicals were responsible for DCP degradation. In addition, CNT was found to act not only as the PDS activator but also the radical scavenger. X-ray photoelectron spectroscope (XPS) was applied to CNTs to determine the element content before and after reactions. The results suggested that the chlorination of CNT resulted from chlorine-aryl radical addition induced by surface-bound radicals via non-reusable active sites and 24% of DCP degradation could be attributed to non-radical mechanism.

並列關鍵字

persulfate ； chlorophenol ； carbon nanotube ； catalytic degradation ； surface- bound radical ； non-radical

參考文獻

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