碳氣凝膠電容吸附水中重金屬; Electrosorption of Heavy Metal Ions from Aqueous Solution Using Carbon Aerogel Electrodes as the Capacitor

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题名:	碳氣凝膠電容吸附水中重金屬;Electrosorption of Heavy Metal Ions from Aqueous Solution Using Carbon Aerogel Electrodes as the Capacitor
作者:	鄭喬薇;Chau-wei Zheng
贡献者:	環境工程研究所
关键词:	電吸附;碳氣凝膠;重金屬;Eelectrosorption;Carbon aerogel;Heavy metal
日期:	2007-07-10
上传时间:	2009-09-21 12:18:00 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	過去研究大多著墨於運用電容去離子技術(Capacitive deionization, CDI)，並以碳氣凝膠紙(Carbon aerogel)為電極，處理淡海水脫鹽。碳氣凝膠具有奈米級尺度之細微孔洞和高的比表面積等優點，可提高電吸附之效率。本研究利用碳氣凝膠為電極材料吸附水中重金屬離子，以鉛(Pb2+)、鎘(Cd2+)、銅(Cu2+)和鉻(Cr3+)等氯化物為待吸附離子，探討離子半徑、離子價數之大小、改變施加的電壓和起始離子濃度之改變，對於電吸附之效率影響。實驗所使用之電吸附單元由五組電容所構成。研究過程中，以Labview程式控制電壓的施加與監測溫度、導電度、pH，並以火焰式原子吸收光譜儀檢測重金屬離子濃度和離子層析儀檢測氯離子濃度。本研究所使用之碳氣凝膠電極，其比表面積為390 m2/g，且擁有COOH-之官能基。研究結果顯示，未施加電壓初期，因特定吸附之原因，其離子濃度會有些微的下降，導電度伴隨下降，約經過一小時後施加電壓1.2 V。電吸附期間，離子濃度隨時間變化而下降，導電度亦有明顯遞減趨勢。當導電度斜率趨於0，移除施加之電壓進行電極再生試驗，此時離子濃度回升且導電度伴隨快速攀升。除了PbCl2電吸附系統，其餘電吸附試驗之重金屬濃度變化和導電度趨勢呈線性關係。起始濃度為0.5mM之PbCl2和CuCl2兩電吸附系統中，由於施加之電壓1.2 V已超過其金屬離子的沉積電壓，在負極的電極表面觀察到斜方晶狀(orthorhombic crystals) PbO和規則晶狀(polygonal crystals) CuO沉積物，但在沉積電壓小於1.2 V的CdCl2和CrCl3電吸附系統中，負極表面並未發現沉積物。探討離子半徑試驗中，以Pb2+、Cd2+和Cu2+等價數相同且離子半徑相異之重金屬為例，結果顯示離子半經越小者，其電吸附效率越佳；相同離子半徑，但價數相異之Cu2+和Cr3+實驗中，價數較大者，其去除效率較好。探討改變電壓試驗，分別為0.4 V、0.8 V和1.2 V之起始濃度0.5mM的CrCl3溶液，0.8 V電壓中的離子去除效率大約為0.4 V的兩倍，但實際由濃度變化換算電容量與理論電容值相異甚大。電壓改變實驗中，進行電壓移除再生時，濃度與導電度並無快速上升之現象。起始濃度之變化，以0.5mM、1mM和2mM之CrCl3實驗中，起始濃度越高者，其去除效率越差。 Carbon aerogel papers have been used in electrosorption as a capacitor to remove inorganic compounds in the aqueous solution. However, little of the studies discussed about the electrosorption of heavy metal ions in a solution by carbon aerogel. The characterization of carbon aerogel electrodes are analyzed by Accelerated Surface area and Porosimeter System (ASAP), Scanning Electron Microscopy (SEM), and Fourier Transform Infrared (FTIR). The surface area of the carbon aerogel paper is about 390 m2/g. Carbon aerogel are consisted of carbon fibers and the width of carbon fiber is about 6 μm. From the FTIR measurement, there are COOH- functional groups on the surface of the carbon aerogel. When the voltage was 1.2 V during the electrosorption and the initial concentration was 0.5 mM for PbCl2 and CuCl2 system, because the voltage is higher than the redox potential, there are some precipitates, such as orthorhombic crystals and polygonal crystals, formed on the negative electrodes. While applied voltage for different ionic radius of the same ionic charge, such as Pb2+, Cd2+, and Cu2+, the electrosorption efficiency increases with decreasing ionic radius. For the effect of ionic charge, the removal efficiency of Cr3+ is greater than that of Cu2+. The effect of applied voltage was examined by giving 0.4 V, 0.8 V, and 1.2 V in CrCl3 system, and the electrosorption efficiency increases with increasing applied voltage. Also, the removal efficiency increases with decreasing initial concentration. The conductivity of all the experiments are drops and the raise with the concentration of the heavy metal ions during the electrosorptive and the regeneration, except when the initial concentration was 1 mM, 2 mM, and the applied voltage of 0.4 V for Cr3+.
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