奈米碳管在鄰苯二甲酸酯類溶液與腐植酸溶液中之分散與絮凝;Stability of carbon nanotubes in phthalate esters and humic acid solutions

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Title:	奈米碳管在鄰苯二甲酸酯類溶液與腐植酸溶液中之分散與絮凝;Stability of carbon nanotubes in phthalate esters and humic acid solutions
Authors:	吳瑋羚;Woei-ling Wu
Contributors:	環境工程研究所
Keywords:	奈米碳管;吸附;空間位阻;溶解度/分散性;solubility;steric repulsion;adsorption;carbon nanotube
Date:	2012-01-19
Issue Date:	2012-06-15 19:39:52 (UTC+8)
Abstract:	奈米碳管在環境中之流佈，會受到自然水體中存在的天然與人為排放之有機汙染物質，以及水體中水質條件的改變，影響其表面特性與傳輸宿命。本研究選用HNO3 與KOH 對單壁與多壁奈米碳管(A-SWCNT、A-MWCNT)進行改質，探討其在鄰苯二甲酸酯類(phthalate ester, PAEs) (鄰苯二甲酸二甲酯(DMP)、鄰苯二甲酸二乙酯(DEP)、鄰苯二甲酸二丁酯(DnBP))與腐植酸(humic acid, HA)中的分散與絮凝現象。經由定性分析結果顯示，奈米碳管經改質後會使碳管末端產生開口與管壁多處缺陷，增加其比表面積、孔洞體積、及改變碳管之結構完整性，其總表面積大小比較為H-SWCNT>A-SWCNT>K-MWCNT>H-MWCNT>A-MWCNT，改質亦會引入羧基、羥基、羰基等含氧官能基，使碳管表面帶負電位且增加分散穩定作用。奈米碳管在PAEs 與HA 中之穩定性主要受產生靜電穩定與空間位阻影響，並受到PAEs 碳鏈長度、分子量、疏水性及吸附量影響。原始奈米碳管隨著吸附PAEs 與HA 濃度升高，碳管懸浮液濃度升高。但當吸附質為高濃度時，又可能產生多層吸附及分子間吸引等現象導致凝絮，使碳管沉澱而分散性降低。利用酸鹼溶液改質之奈米碳管，多壁奈米碳管由於其多層結構，以及改質後造成破壞程度與長短不一，因此難以控制其分散性。而單壁奈米碳管經酸氧化後分散性不佳，但由於其單層管壁結構，與吸附質濃度之相關性較為確定。水質參數亦會影響碳管之懸浮穩定性，當pH為3 時， A-SWCNT 與H-SWCNT 在DEP 溶液中之溶解度極低。當pH=6與pH=9 時，A-SWCNT 在DEP 溶液中之溶解度差異不大，而H-SWCNT表面之含氧官能基會受到pH 上升而增加其解離，並增加負電荷增強靜電斥力作用，因此其在DEP 中之溶解度隨pH 上升而升高。增加離子強度會導致碳管產生電雙層壓縮作用，減少碳管表面之帶電，使得A-SWCNT 與H-SWCNT 之溶解度均降低。Stability of pristine and modified (by HNO3 and KOH ) carbon nanotubes (CNTs)phthalate esters (PAEs) and humic acid (HA) solutions were investigated in this study. It is shown that modification would damage the structure of CNTs and, thus, increasetheir surface area and pore volume. The surface area from the largest to the smallest were H-SWCNTs> A-SWCNTs> K-MWCNTs> H-MWCNTs> A-MWCNTs, modification would also introduce carboxyl, hydroxyl, carbonyl and otheroxygen-containing functional groups, which may lead to negative charged surface and enhance the solubility of CNTs. It is found that the solubility of CNTs is mainly affected by the electrostatic and steric repulsions. The solubility of CNTs might be further affected by the carbon chain length, molecular weight, hydrophobicity, and the concentration PAEs and HA.The solubility of the pristine CNTs were improved as the concentrations of PAEs and HA increased. However, at high concentration of PAEs, the solubility of the CNTs decreased, which may due to the multi-layer adsorption or phase separation of PAEs. The H-MWCNTs and K-MWCNTs had excellent solubility and concentration and chain length of PAEs have no significant effects. The solubility of H-SWCNTs was poor and was affected by the concentration of PAEs. The effects of pH and ionic strength of the solubility of CNTs in PAEs solution was investigated by dispersing A-SWCNTs and H-SWNCTs in DEP solution. It is found that both A-SWCNTs and H-SWCNTs have very poor solubility at pH of 3. When the solution pH values were 6 and 9, the solubilities of H-SWCNTs increased and are similar. This may be resulted from the dissociation of the oxygen-containing surface groups, which increase the negatively charge and the electrostatic repulsions between H-SWCNTs. The solubility of H-SWCNTs in DEP solution was found to be decreased with increasing ionic strength, which may also be resulted from the double layer compression. In conclusion, the electrostatic repulsions played a more important role than the steric repulsion in the dispersion of CNTs in organic solution.
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