| 摘要: | 由於奈米碳管多方面運用於各材料上的發展，必定會造成排放之問題，造成水體的汙染及生態環境上的變遷影響，故本研究為進一步了解其內部特性及吸附機制，挑選四種常見之化學氧化法(HNO3、piranha、NH4OH 25 %: H2O2 30 % = 50:50加熱迴流；KOH高溫氧化)作為碳管改質的方式，進行對於同樣被廣泛利用且被間接排入水體中的雙酚A之吸附實驗，探討其吸附行為與機制，有助於解決自然水體環境汙染問題。 研究發現經過氧化後之碳管其表面積、純度與官能基皆有增加之趨勢，動力吸附實驗方面，達吸附平衡時間由快至慢為A-MWCNTs(原始購得碳管)、N-MWCNTs(經HNO3氧化後碳管)、K-MWCNTs(經KOH氧化後碳管)，且其飽和吸附量各為0.3116、0.2039、0.5919 mmole/g，且皆較符合擬二階動力學模式。而在pH值之影響方面，發現主要受到雙酚A本體之解離作用影響，當雙酚A解離後帶負電與帶有負電官能基之奈米碳管表面定性正好相同，故雙酚A與碳管間形成靜電斥力，使得各種碳管之吸附環境pH值越高，有吸附量下降之趨勢。 等溫吸附實驗方面，主要影響吸附量多寡的原因為碳管的比表面積，尤其是K-MWCNTs，其氧化之強破壞力產生的高表面積而造成高吸附量，但吸附力仍受各氧化程序後產生之表面酸含氧官能基作用，而使吸附量下降，這也是A-MWCNTs之表面積雖高於N-MWCNTs，但相對吸附量卻相反之原因。在15、25、35℃下A-MWCNTs與N-MWCNTs皆符合Langmuir isotherm model，而K-MWCNTs則無法判定。且△Ho皆小於零，表示吸附過程為放熱反應，△Go亦皆小於零，可判定吸附反應為自發性。 Due to various applications of carbon nanotubes, their discharge into natural water is expected and their adsorption phenomena should be studied to understand their fate and transport. In this study, four common chemical oxidation methods were chosen to modify multi-walled carbon nanotubes (MWCNTs), they are, HNO3, piranha, NH4OH 25 %: H2O2 30 % = 50:50, and KOH. Bispenol A (BPA) were adsorbed to investigate the influences of different oxidation methods of MWCNTs on the adsorption mechanisms. It was found that, with proper oxidation parameters, nitric acid could introduce significant amount of oxygen-containing surface groups without altering the surface structure. Oxidation by KOH increased the surface area of MWCNTs dramatically and introduced oxygen-containing surface groups of the amount similar to that nitric-acid-treated MWCNTs. Thus the adsorption of BPA was only conducted by A-MWCNTs (as-purchased MWCNTs), N-MWCNTs (oxidized by HNO3), and K-MWCNTs (oxidized by KOH). The adsorption rates the fastest to the slowest were A-MWCNTs, N-MWCNTs, and K-MWCNTs and could be described by the pseudo-second order kinetic model. The adsorption capacities of A-MWCNTs, N-MWCNTs, and K-MWCNTs were 0.3116, 0.2039, and 0.5919 mmole/g, respectively. Comparison between the adsorption capacities of A-MWCNTs and N-MWCNTs showed that the oxygen-containing group hindered the π-π interactions and reduced the adsorption of BPA. The adsorption capacity was affected by solution pH, mainly due to the dissociation of BPA. Deprotonation of BPA leaded to electrostatic repulsions between BPA molecules and the surface of MWCNTs at high solution pH and, thus, reduction in the adsorption capacity.The enthalpy and free energy showed that adsorption of BPA on MWCNTs were exothermic and spontaneous. |
