石墨包裹奈米鐵晶粒的純化及表面改質程序之研究

Study on the purification and surface modification procedures of graphite encapsulated iron nanoparticles

李尚實(Shang-Shih Li)

指導教授 ： 鄧茂華

國立臺灣大學/理學院/地質科學研究所/博士(2015年)

https://doi.org/10.6342/NTU.2015.01009

摘要

石墨包裹奈米金屬晶粒(Graphite Encapsulated Metal nanoparticles, GEM)是一種在1993年偶然間發現的核/殼奈米結構材料，外層由吸附效果佳的多片石墨層所組成，內核則包裹有奈米金屬晶粒，而由於鐵、鈷和鎳等鐵磁性金屬具有催化碳變為石墨的能力，故以合成石墨包裹奈米鐵磁性金屬晶粒的研究最為普遍。本研究係以石墨包裹奈米鐵晶粒(FeGEM)做為主要研究材料，針對該材料的合成純化步驟及表面改質程序，進行操作條件的分析改良。
本研究團隊利用注入液態醇類作為碳源配合改良之電弧系統，已成功將FeGEM顆粒的生產良率由10 wt%提升至40-50 wt%，並經由本研究分析發現使用鹽酸做為純化處理之酸液，不僅可有效減少氧化鐵雜質的產生，並能保留高比例包裹良好之產物及維持該材料在10K時具有97 emu/g的飽和磁化強度。然而，保留了FeGEM材料高的鐵磁性質，顆粒之間存在磁力及凡得瓦力等吸引力，加上外殼石墨(數層石墨烯)層之親油特性，導致FeGEM顆粒在極性溶劑中產生快速團聚而沉澱，此現象對於材料所應具有的高比表面積、顆粒滲透反應和鍍膜的均勻分佈等優異特性都造成很大的阻礙。
本研究利用硝酸進行FeGEM顆粒迴流程序，利用升溫至80℃的條件成功將顆粒親油表面改質為親水性，使FeGEM顆粒可穩定懸浮於去離子水或乙醇等極性溶劑中超過24小時，克服FeGEM顆粒團聚問題，同時依序利用亞硫醯氯和四乙烯五胺迴流改質FeGEM顆粒表面，使其接枝上不同官能基團，並利用表面電位、元素分析、傅利葉紅外光譜以及超導量子干涉磁量儀等設備進行分析，輔以分光光譜儀定量檢測奈米顆粒於膠體系統中之懸浮程度，有效說明本研究改質程序之結果，不僅成功克服FeGEM顆粒團聚問題，亦增加材料在應用上的潛能。

關鍵字

核殼結構 ； 鐵磁性 ； 懸浮 ； 表面改質 ； 親水性 ； 迴流 ； 團聚

並列摘要

Graphite encapsulated iron metal nanoparticles (FeGEM) are a core/shell nanostructured material. The novel ultrafine material of graphite encapsulated metal (GEM) nanaoparticles was first discovered in 1993. The outer shells of GEM material are composed of graphitic layers with superior adsorbing property and the inner core is composed of nanocrystalline metal. Due to the excellent catalytic ability of ferromagnetic metal to transform carbon to graphite, the researches about synthesizing graphite encapsulated ferromagnetic metal nanoparticles are most common. In this study, we focused on the purification and surface modification procedures of FeGEM. By introducing various liquid alcohols as carbon source during modified arc-discharge synthesis procedures, we succeeded in raising the yield rate of FeGEM from 10 wt% to 40-50 wt%. It is found that the purification steps with hydrochloric acid can reduce the impurities of oxides and preserve high percentage of well-encapsulated nanoparticles and the best magnetic property. However, the hydrophobic outer graphite (graphene) shells and the strong magnetic attraction between inner ferromagnetic iron cores can easily lead to rapid agglomeration and precipitation of FeGEM nanoparticles in a polar solvent such as water. As a result, it may impede many potential applications of FeGEM nanoparticles in numerous fields.
To overcome the problem, it is necessary to change the hydrophobic surface of FeGEM nanoparticles to a hydrophilic one. In this work, we show that progressive sequential refluxing in nitric acid, thionyl chloride and tetraethylenepentamine (TEPA) can modify FeGEM nanoparticles with different functional groups. After refluxing with nitric acid solution at 80℃, the grafted FeGEM is able to disperse in polar solvent, such as deionized water or ethanol for over 24 h. Zeta potential analysis, EA, FTIR and SQUID were used to characterize the grafted FeGEM at the refluxing step, and ultraviolet-visible spectrophotometry was used to quantify the suspension ability of modified FeGEM nanoparticles in a colloidal system continuously. The modification processes not only overcome the agglomeration problem of FeGEM nanoparticles but also enhance the potential applications of the material.

並列關鍵字

core/shell ； ferromagnetic ； suspension ； surface modification ； hydrophilic ； refluxing ； agglomeration

參考文獻

[8] 陳永得 (2006) “以人造鑽石及噴氣式電弧法合成石墨包裹奈米鐵晶粒之初步結果”，碩士論文，國立台灣大學地質科學系。

[37] 李雱雯 (2013) “以退火改善石墨包裹奈米鐵晶粒之包裹良率”，碩士論文，國立台灣大學地質科學系。

[39] 蔡少葳 (2007) “石墨包裹奈米鎳晶粒的緻密化之初步研究”，碩士論文，國立台灣大學地質科學系。

[40] 蕭淵隆 (2010) “甲醇之蒸散速率效應對石墨包裹奈米鎳晶粒緻密化之研究”，碩士論文，國立台灣大學地質科學系。

[71] 吳俊人 (2007) “利用聚乙二醇和葉酸接枝於石墨包覆鐵磁性奈米粒子做癌症之熱治療”，碩士論文，國立台灣大學醫學工程學系。