Purification Of Onion Like Fullerenes And XRD Structural Refinement

As a new member of the fullerenes family, onion like fullerenes (OLFs) show particular characteristics in light, electricity, magnetism fields and so on, which have attracted strong attentions and great interests, and become focus of studies in the new materials field since were reported in 1992. However, the application studies of OLFs develop slowly just because of the lack of effective preparation methods. And up to date, though several methods are used to prepare OLFs, many problems lie in them, such as high cost and low yield. In this paper, systemic studies on preparation, purification and structure characterization of OLFs were investigated, and the possible affecting factors were analyzed. All of these cast a basis for the study of properties and applications of OLFs.Preparation of OLFs: The synthesis of OLFs by the two-step vacuum heat-treatment of pure graphite powders was investigatedusing Al as catalyst. High resolution transmission electron micro -scopy (HRTEM) and x-ray diffraction analysis (XRD) were used to characterize the morphologies and micro-structures of the products. Results indicate that lots of graphite pieces, amorphous spherical carbon and metal particles exist in sample after vacuum heat treatment at 800℃. After vacuum heat treatment at 1800℃, OLFs in sample is perfectly structured and highly graphitized, with external diameter between 15nm and 35nm. Moreover, the growth mechanism of OLFs and metal encapsulating OLFs were also discussed.Purification of OLFs: Resultant OLFs was purified by removing impurities using CS2 separation treatment and air oxidation methods. HRTEM, XRD and thermogravimetry(TG) were applied to analyze samples before and after purification. Results indicate that CS2 treatment can effectively remove metal catalyst particles, after calcination of sample at 610℃ for 200 min in air, most of amorphous carbon and graphite pieces can be removed, the purity of OLFs is thus greatly improved.XRD simulation of C60 structure of C60 molecule crystal was investigated using Rietveld powder diffraction profile fitting technique so as to analyze its structure further. Results of Rietiveid analysis show that C60 crystal has a faced-center cubic structure of the space group Fm3m(225) , and the lattice parameters are a=b=c= 1.416nm, α= β=γ=90°.