Study on the purification and surface modification procedures of graphite encapsulated iron nanoparticles
Date Issued
2015
Date
2015
Author(s)
Li, Shang-Shih
Abstract
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.
Subjects
core/shell
ferromagnetic
suspension
surface modification
hydrophilic
refluxing
agglomeration
Type
thesis
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