Preparation Of Carbon Nanomaterials By Template Method And Their Structure Characterization

Since their discovery, carbon nanotubes (CNTs) and onion-like fullerenes (NOLFs), with their unique structure and excellent electronic, magnetic, mechanical, and chemical properties, have developed into a new science research with ever-broadening application prospects in the areas of engineering, electronics, information, energy, biomedicine, chemical engineering, and national defense.Firstly, zeolite Li-ABW was synthesized via a simple route, and MCM-41 was synthesized by traditional hydrothermal method, vapor phase method under and unconventional conditions of extremely dense system, respectively. Secondly, CNTs were prepared by chemical vapor deposition (CVD) from acetylene using Fe-loading mesoporous molecular sieves as catalysts. Moreover, NOLFs were prepared by a two-step method including polymerization pre-molding and heat-treatment. The high-pressure properties of NOLFs were investigated by diamond anvil cell (DAC) method. The main results and conclusions are as follows:1. Synthesises of molecular sieves1) Synthesis of template Li-ABWThe characteristics of as-obtained zeolite Li-ABW (Li/Si=1.5) and mixed phase Li-ABW+Li2Si03 (Li/Si=2.5) crystallized at 150℃, such as crystal structure, phase transformation and morphology upon calcination, was investigated. The results show that Li-ABW was directly synthesized from silica gel and aluminum isopropxide as the starting materials at lower temperature (150℃). The optimum synthesis conditions for ABW were:molar composition 1.5Li2O:Al2O3:2SiO2:154H2O, and crystallization at 150℃for 7d. The phase transformation from zeolite ABW to a mixed phase of ABW+Li2Si03 was observed at the molar ratio of Li/Si=2.5.2) Synthesis of template MCM-41The mesoporous MCM-41 molecular sieve with the pore size of 1.5-4 nm was synthesized in M2O (M=Li, Na, K)-Al2O3-SiO2-CTAB-H2O hydrothermal system. The relative crystallization rate was in the sequence of K-MCM-41>Na-MCM-41>Li-MCM-41. The results show that the crystal structure, adsorption characteristics and thermal stability of K-MCM-41 molecular sieve were close to or better than those of Na-MCM-41 molecular sieve.The mesoporous MCM-41 molecular sieve was synthesized in the hydrothermal system of NaX-Na2O-Al2O3-SiO2-CTAB-H2O. The results show that introducing F- ions accelerated the crystallization of MCM-41 molecular sieve, while introducing Br- hindered the crystallization.The mesoporous MCM-41 molecular sieve with larger d100 value was synthesized in the hydrothermal system containing alkanes (n-hexane, n-heptane, isooctane) and d100 value increased with the number of carbon atoms in alkane. Petroleum ether played a similar role to alkane. For MCM-41 molecular sieve, adding alkane into hydrothermal system decreased its degree of order and lowered its specific surface area and porosity.The MCM-41 molecular sieve was also synthesized in extremely dense system from Na2O-SiO2-CTAB-H2O amorphous gel. Reducing CTAB/Si ratio to 0.0125 effectively reduced the consumption of CTAB in synthesizing MCM-41 molecular sieve.Si-MCM-41 and Al-Si-MCM-41 pure phase were synthesized by vapor phase method, which obviously decreased the CTAB consumption. Si-MCM-41 molecular sieve with appropriate Al content had higher thermal stability than Si-MCM-41.2. The CVD growth of CNTs from acetylene in Ar using Fe-loading mesoporous molecular sieves (Fe/ABW, Fe/MCM-41 and Fe/SBA-15) as catalysts was investigated. The effects of the reaction temperature, reaction zone, catalyst kind and catalyst pretreatment were discussed. The molecular sieves without Fe loading or without H2 reduction as catalysts were also investigated. The results show that CNTs with uniform diameter of 20-30 nm and good crystallization degree were obtained at 700℃using H2-reduced catalysts.3. The template synthesis was suggested for the first time as a novel synthesis method for NOLFs, which, with organic monomeric compound (such as styrene and acryl acid) as carbon source, forms NOLFs precursors around metallic nanoparticles through polymeration of the monomers, and gives well-graphitized NOLFs encapsulating Fe nanoparticles of about 60 nm in diameter. The characterization of the microstructure by field emission scanning electron microscopy and high resolution transmission electron microscopy revealed that the formation of NOLFs through pre-molding synthesis is effective in producing NOLFs with uniform size distribution and high degree of graphitization, thus realizing the controllability in the morphology and size of NOLFs, which are important for the research on property and application of NOLFs.4. The high-pressure Raman spectra of high-purity NOLFs and metal-encapsulating NOLFs prepared by arc discharge in liquid were investigated by diamond anvil cell experiments. The pressure coefficient and elastic behavior of NOLFs were found to be very similar to those of multiwalled CNTs. No detectable collapse of the concentric graphite layers was observed at pressures as high as 20 GPa, demonstrating that the NOLFs had significant hardness to sustain very high pressures. However, the increase in the ID/IG ratios for NOLFs after applying pressure demonstrates that some destruction occurred at the interface between graphite layer and metal core.