奈米碳管對於硝基酚與銅之競爭吸附

Competitive adsorption of nitrophenol and copper(II) from aqueous solutions on mult-walled carbon nanotubes

李向曦(Hsiang-hsi Lee)

指導教授 ： 秦靜如

國立中央大學/工學院/環境工程研究所/碩士(2012年)

摘要

本研究利用奈米碳管吸附鄰-硝基苯酚(2-NP)、對-硝基苯酚(4-NP)及銅離子(Cu2+)，探討其競爭吸附及機制。研究結果顯示，經硝酸氧化處理後，比表面積與氧化前差異不大，但在碳管表面引入官能基－COOH，使得碳管表面電荷有所改變，造成對2-NP、4-NP及Cu2+的吸附影響。等溫吸附實驗顯示，碳管的含氧官能基多寡會影響2-NP、4-NP及Cu2+之吸附量，未經氧化奈米碳管吸附2-NP及4-NP之吸附量會優於氧化後奈米碳管，和空間障礙及水簇作用有關。而氧化後奈米碳管對吸附Cu2+之吸附量會大於未氧化碳管，會因官能基的增加提高碳管表面負電荷，導致吸附量提高。2-NP與4-NP因電子分佈之影響，氧化前後奈米碳管對4-NP的吸附能力較2-NP低；不論酸氧化前後奈米碳管，對於2-NP及Cu2+之吸附皆較為符合Langmuir模式，而對於4-NP之吸附則較為符合polanyi 模式。經熱力學分析得知酸氧化前後奈米碳管吸附2-NP及4-NP均為放熱反應；而酸氧化前後奈米碳管吸附Cu2+為吸熱反應。在不同pH值下，酸氧化後奈米碳管吸附2-NP及4-NP之吸附量具有相同的趨勢，與分子解離及表面電荷有關；吸附Cu2+則與表面電荷及沉澱有關。在2-NP及4-NP存在下之競爭結果顯示，碳管吸附Cu2+之吸附量增加，因2-NP及4-NP解離後將可能與Cu2+形成新物質或錯合物，提高Cu2+之吸附百分比；但在pH值小於7時，Cu2+將對氧化後奈米碳管吸附2-NP及4-NP產生抑制作用，與水合作用產生遮蔽效應有關。

關鍵字

Polanyi model ； Langmuir model ； 競爭吸附

並列摘要

Adsorption of 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), and copper (Cu2+) by multi-walled carbon nanotubes (MWCNTs) with and without oxidation by nitric acid were investigated in this study. The adsorption capacities of 2-NP and 4-NP by A-MWCNT were larger than H-MWCNT, because of steric obstructions and water clustering. On the other hand, H-MWCNT had better adsorption capacity of Cu2+ than A-MWCNT, because the functional groups generated more negatively charged surface. Furthermore, MWCNTs had better adsorption capacity of 2-NP than 4-NP due to the electronic distribution. The adsorption of 2-NP and 4-NP by MWCNTs were endothermic while the adsorption of Cu2+ was exothermic. The enthalpy change and free energy change suggested that the adsorption of 2-NP, 4-NP, and Cu2+ onto MWCNTs were physisorptions. The adsorption at different pH values showed that the adsorption of 2-NP and 4-NP by H-MWCNT had the same trend, relating to the molecular dissociation and surface charge, while the adsorption of Cu2+ was affected by the surface charge and precipitation. When 2-NP or 4-NP were present, the adsorption of Cu2+ was promoted, because complexes of 2-NP/Cu and 4-NP/Cu may form after 2- and 4-NP dissociated. When pH values were lower than 7, the adsorption of 2-NP and 4-NP would be inhibited by Cu2+ due to the shielding from hydration of Cu2+.

並列關鍵字

competitive adsorption ； Polanyi model ； Langmuir model

參考文獻

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