利用酸氧化前後奈米碳管吸附鄰苯二甲酸酯類之特性研究; Adsorption of phthalate esters by carbon nanotubes with and without oxidation

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Title:	利用酸氧化前後奈米碳管吸附鄰苯二甲酸酯類之特性研究;Adsorption of phthalate esters by carbon nanotubes with and without oxidation
Authors:	陳珮蓉;Pei-jung Chen
Contributors:	環境工程研究所
Keywords:	奈米碳管;疏水性;π-π分散力;鄰苯二甲酸酯類;hydrophobicity;π-π interactions;phthalate esters (PAEs);single-walled carbon nanotubes (SWCNTs)
Date:	2010-12-22
Issue Date:	2011-06-04 15:05:14 (UTC+8)
Publisher:	國立中央大學
Abstract:	本研究藉由酸氧化在奈米碳管表面引入官能基，利用奈米碳管吸附不同碳數的鄰苯二甲酸酯類(鄰苯二甲酸二甲酯、鄰苯二甲酸二乙酯及鄰苯二甲酸二丁酯)，探討奈米碳管表面官能基對不同烷基側鏈之苯環衍生物吸附影響。研究結果發現，經硝酸氧化處理後奈米碳管表面引入COOH官能基，且管外或總表面積皆與酸氧化前相差不大。由動力吸附實驗發現，奈米碳管吸附鄰苯二甲酸酯類達平衡所需時間順序為鄰苯二甲酸二甲酯> 鄰苯二甲酸二乙酯 > 鄰苯二甲酸二丁酯，並遵循擬二階動力模式。等溫吸附曲線實驗結果顯示，鄰苯二甲酸二甲酯與鄰苯二甲酸二乙酯由於疏水性不同，未經酸氧化之奈米碳管對於相對疏水之鄰苯二甲酸二乙酯表現出較高之吸附能力。再者，經酸氧化後之奈米碳管因水簇效應及電子分佈之影響導致吸附量下降。不論酸氧化前後的奈米碳管，對於鄰苯二甲酸二甲酯及鄰苯二甲酸二乙酯的吸附較符合Freundlich模式。經熱力學分析得知酸氧化前後之奈米碳管吸附鄰苯二甲酸二甲酯之ΔH 0< 0，顯示此吸附為放熱反應；而酸氧化前後之奈米碳管吸附鄰苯二甲酸二乙酯之ΔH0 > 0，顯示此吸附為吸熱反應。酸氧化前與後之奈米碳管吸附鄰苯二甲酸二甲酯之ΔG0階隨溫度上升而上升，顯示在低溫有利於吸附；酸氧化前與後之奈米碳管吸附鄰苯二甲酸二乙酯為高溫有利於吸附。又由ΔH0及ΔG0得知碳管吸附鄰苯二甲酸酯類為物理吸附。在不同pH值下，未經酸氧化奈米碳管吸附鄰苯二甲酸二甲酯及鄰苯二甲酸二乙酯實驗結果為當pH ＝ 9時之吸附量比pH值為3與6高；而經酸氧化後奈米碳管吸附鄰苯二甲酸二甲酯及鄰苯二甲酸二乙酯，結果顯示與未經酸氧化奈米碳管吸附鄰苯二甲酸二甲酯及鄰苯二甲酸二乙酯相較之下，pH值為9之吸附量有下降之趨勢。其原因為未經酸氧化奈米碳管與鄰苯二甲酸二甲酯及鄰苯二甲酸二乙酯之π-π分散力增強，造成吸附量上升；而經酸氧化奈米碳管與鄰苯二甲酸二甲酯及鄰苯二甲酸二乙酯間靜電斥力較未經酸氧化奈米碳管大導致吸附量下降。 Adsorption of phthalate esters (PAEs) by single-walled carbon nanotubes (SWCNTs) with and without oxidation by nitric acid was conducted to investigate the influences of ester substitution groups on the benzene rings on the adsorption by CNTs. Dimethyl phthalate (DMP)、diethyl phthalate (DEP) and dibutyl phthalate (DnBP) were used. With proper treatment, the BET surface areas and pore size distributions of SWCNTs before and after oxidation were almost the same, thus, the influences of oxidation of SWCNTs on the adsorption of PAEs would only be contributed by the oxygen-containing surface group. The adsorption rates from the fastest to the slowest were DMP, DEP, and DnBP, and followed the pseudo-second order kinetic model. The Freundlich isotherm models fitted the adsorption of DMP and DEP by both SWCNTs with and without acid oxidation. Both SWCNTs with and without oxidation had better adsorption capacities for DEP than for DMP. This may be because that the DEP is less polar than DMP and results in stronger attraction to non-polar graphene. Furthermore, water clustering and electronic distribution of oxidized SWCNTs resulted in decreases in the adsorption capacity. The adsorption of DEP was endothermic while the adsorption of DMP was exothermic The enthalpy change and free energy change suggested that the adsorption of PAEs onto SWCNTs was a physisorption process. The adsorption capacity of PAEs by without oxidation SWCNTs at solution pH of 9 were more than those at solution pH values of 3 and 6. Dissociation of ester groups at high solution pH resulted in stronger???? interactions between the PAEs molecules and the SWCNTs. For oxidized SWCNTs, the adsorption capacity at high pH decreased, which is due to the electrostatic repulsion between the dissociated surface groups on SWCNTs and ester groups on PAEs.
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