Synthesis, Characterization And Photocatalystic Performance Of SiC And Its Nano-composites

In this paper, graphite, CH4and alcohol employed as carbon source respectively, under mixing gas of hydrogen and argon with different proportions, reacted with silicon powders to synthesize SiC/C (C coating SiC) and SiC(main phase)-C-Si nano-composites in situ. In addition, under0.03MPa pury oxygen, every synthetic product underwent heat-treatment at500℃and800℃, respectively. The components of the obtained products were characterized via X-ray diffraction(XRD), Raman spectrum and infrared spectroscopy(IR); the morphology and microstructure of the samples were characterized by scanning electron microscope(SEM) and transmission electron microscope(TEM); the electrical conductivity and optical absorption properties were tested via four-probe resistivity meter and UV-Vis diffuse reflectance spectroscopy, respectively; the photocatalytic activity was evaluated by the efficient decomposition of10mg/L MB solution through irradiation under UV light.The studies upon synthesis of SiC nano-composites materials show:1) the components of products using graphite as carbon source are cubic SiC (β-SiC) and a little carbon. The morphology is shell-core structure, in which graphite with60nm thick and the SiC particle aggregates with50nm in average particle size (APS) consist of its shell and core, respectively. The particle size of shell-core nano-composites ranges from0.5to1μm. The synthetic product exhibits the character of Schottky heterojunction, and its resistance and band gap are1.2×104-1.7×104Ω and2.36eV, respectively.2) the component of products using CH4as partial carbon source is cubic SiC(main phase)-Si-C, in which SiC is cubic-SiC with64.1nm in APS, constituting of nano-particles aggregating. The synthetic product appears ohmic contact characteristic and its resistance is approximately60-70Ω. After heat-treatment in500℃, only(3-SiC and Si is left and its APS is75.7nm, while in800℃there are P-SiC in synthetic products and its APS is77.2nm. The main components of products using CH4as main carbon source make no difference, compared with the products mentioned above, and the products is78.7nm in APS and composes of certain amount of graphene and amorphous carbon black and silicon particles and carbon shell layer with10nm thickness coating SiC with50nm in APS. The product exhibits the character of Rectification Effect due to forming Schottky heterojunction and its resistance and band gap are500-600Q, and2.32eV larger than bulk SiC, respectively.3) the components of products using alcohol as carbon source are SiC(main phase)-Si-C, of which there are main (β-SiC and a little amout of6H-SiC, and the APS of product is64.1nm. The products are flower-like composites which are composed of particles aggregates with several decade nanometer in APS. Rectification Effect appears in properties of the products with resistanc ranging from280to310Ω. After heat-treatment in500℃and800℃, the APSs of abtained products are88nm and94nm, respectively.In order to study the influences of the thickness of cover layer and surface morphology on photocatalytic performance, the photocatalytic activity of products synthesized from different carbon sources before and after heat-treatment were tested. The results show that:1) the products obtained using graphite as carbon source under500"C heat treatment, exhibit optimal photocatalysis performance, approximately75%degradation rate over MB,47%increase compared to pury nanocrystalline SiC;2) both of the products which were abtained using CH4as main carbon source and which underwent heat-treatment under500℃exhibit excellent adsorption property, almost not possessing photocatlysis ability, except for the product underwent800℃heat-treatment, its degredation rate77.5%over MB after150min. while all of the products which were abtained using CH4as partial carbon source or before and after heat-treatment under different situations exhibit good absorption performance, only the products after500℃have certain photocatalysis activity which reached76.5%after15()min.3) the products abtained using alcohol as carbon source show admirable absorption performance and certain photocatalysis ability, after150min, its photocalysis rate on10mg/L MB is72.1%, while the absorption property is left after heat-treatment.