The Discovery And Research Of Desert-Rose-like Graphene

The graphene, a novel 2D nanomaterial consisted of sp~2 hybridized carbon atoms located in flat honeycomb structure, has high electron transfer rate, specific surface area and stability. The above features ensure graphene could be broadly applied in microelectronics, high efficient catalyst, advanced energy materials and so on. The thesis firstly prepared Desert Rose-like Graphene vertically grown on the surface of Si C microspheres(DRG) through the pyrolysis of oligomer-Polysilane(o-PS). DRG presents the unique structure, stability and high activation of selective oxidation, which could be used as catalyst repeatedly. Based on the research of the growth mechanism of DRG, DRG or ultra-long Si C nanowires were selectively obtained due to the modulation of the reaction condition. Si C nanopaper was prepared by the Si C nanowires through a simple route, and the humidity sensing character of Si C nanopaper was further investigated.The preparation and application of DRG are important parts of the thesis. DRG can be acquired on silicon wafer and graphite substrates by the pyrolysis of o-PS, and the unique nanostructure is consisted of solid polycrystalline Si C microsphere and graphene standing on the microsphere. Most graphene are vertically grown on the Si C microsphere, and has an average lateral length of 100 nm. Similar as the graphene, a few carbon nanotubes with average diameter of tens of nanometers and length of several hunderds nanometers are vertically grown on the Si C microsphere. Si C microspheres have and average diameter of 0.9 μm, and graphite, β-Si C nanocrystals(average diameter is 3 nm) and amorphous materials inside. The β-Si C nanocrystals is mainly concentrated in the inner part and graphite nanocrystalsin the outer part.In order to impove the catalytic activity of DRG, both the method of chemical modification of DRG and pyrolysis of the mixture of o-PS and acetonitrile are applied to prepare nitrogen doped DRG. For the selective oxidation of benzyl alcohol and ethylbenzene, the conversion is 36.3% and 46.9%, respectively. But the conversions of the above two kinds of nitrogen doped graphene all exceed 90% with high selectivity.Based on the preparation research of DRG, the pyrolysis process and mechanism of o-PS is further discussed. The pyrolysis product of o-PS on silicon wafer and graphite substrate is DRG, and the product is Si C nanowires on ceramic boat and active carbon. The growth mechanism of DRG could be briefed as follow: the o-PS molecules were volatilized and formed micro drops during the temperature-rise period, then the carrier gas will transfer the suspending micro drops to the high temperature zone of a horizontal alumina tube furnace. Due to the inevitable pyrolysis process at high temperature zone, the micro drops agglomerated and precipated to the growth substrate, which developed to DRG after sintering and crystallization. The carbon-containing molecular radicals released at pyrolysis process are helpful carbon source for the growth of DRG.SiC nanowires prepared by the pyrolysis of o-PS are applied to fabricate free standing Si C nanopaper. The resistance of Si C nanopaper linearly increases with increasing humidity. The sensitivity could reach as high as 47.43% and the response time could as fast as 0.8 s(a lab-made pulse humidity sensor testing system). Based on the study of the humidity sensing mechanism of Si C nanopaper, the adsorption of water molecules on Si C nanopaper surface lead to fast electron transfer between Si C nanopaper and water layer, which reduces the carrier density of p type Si C nanopaper and results increment of Si C nanopaper resisitance.