The Catalytic Synthesis And Self-assembly Of Carbon Microspheres

Because of their unique spherical structure and special properties in electronics, magnetic, chemistry and so on, zero-dimensional carbon materials, such as C₆₀, onion-like fullerenes (OLFs), and carbon microspheres (CMSs), have attracted much research interest. Among these materials, C₆₀ is the simplest OLFs and CMSs are giant OLFs with low graphitized degree. Photonic crystals are artificially arranged periodic structures of materials with different dielectric constants in optical wavelength scale. The transmittance of light is forbidden in a wavelength range called photonic band gap. Photonic crystals have broader application prospect than common optical materials. It is promising to prepare photonic crystals using carbon materials as building blocks. The research in this area is becoming hot.In this paper, OLFs and CMSs were prepared by chemical vapor deposition (CVD) using acetylene as carbon source and the effects of the catalysts on the products were studied. Then the products were modified and the magnetic property of the products was measured. CMSs were used as building blocks of self-assembly. The effects of solvent, assembly method, substrate, pH value of the suspension, concentration of suspension and reaction temperature were investigated. Field emission scanning electron microscopy, high resolution transmission electron microscopy, thermogravimetry, Raman spectroscopy, X-ray diffraction, and atomic force microscopy were employed to characterize the samples. The ferromagnetic property of the products was measured with a vitrating sample magnetometer (VSM). The results are as follows:1. Metal-encapsulating OLFs were prepared using Fe/NaCl and Co/NaCl as catalysts by CVD at 420℃, while carbon nanotubes (CNTs) were prepared using Ni/NaCl as catalyst. The influence of catalyst content on the products was further discussed using Co/NaCl as catalyst. Lots of cobalt-encapsulating OLFs were prepared when the content of cobalt was 2wt.%. In absence of catalyst, no products were obtained at 420℃, while CMSs were prepared at elevated temperature of 950℃. After immersing in concentrated HCl, cobalt nanoparticles encapsulated by carbon shells were not removed. It means that carbon shells can protect the encapsulated cobalt cores against acid. When the products were further heat-treated at 900℃, cobalt-encapsulating OLFs with higher graphitization degree were obtained. Moreover, the results from the measurement of VSM also showed a unique magnetic property.2. CMSs oxidized by HNO3 and H2O2 (volune ratio 1:1) had better dispersion than as-synthsized CMSs. Suspension of oxidized CMSs was prepared using NaOH as solvent. Vertical deposition method was adopted for the self-assembly of CMSs into films using glass slide as substrate. Film with a more compact array was obtained by self-assembly at a fixed temperature when pH value of the suspension was about 13. The thickness of the film increased with increasing suspension concentration under fixed temperature and pH value. When suspension concentration was 2wt.%, a more dense film was prepared. Further investigation on the reaction temperature showed that the suitable temperature was 50℃. Sample showed a good reflection of light with uniform color, which indicates the formation of uniform CMSs film and thus good potential for preparation of photonic crystals.