Synthesis And Properties Of Silicon Carbide Nanowire Film

Silicon carbide (SiC) is a material with some outstanding properties such as wide band-gap,high hardness, high thermal conductivity, high breakdown voltage, high electronic mobility,superior oxidation and corrosion stability. One-dimensional SiC nanomaterials exhibit even moreexcellent characteristics in mechanics, electricity, and optics due to its nanometer size effect,special morphology, internal crystal structure and defect. SiC nanowire film, as bulk structure ofone-dimensional SiC nanowire material, has promising application in the high-temperatureseparation membranes, photoelectrocatalytic water splitting, catalyst carriers, high temperaturesensors, nanocomposites and photoelectric nanodevice.In this paper, SiC namowire film has been prepared via carbothermal reduction method. Theexpandable graphite, silicon metal powder and tetraethoxysilane were used as the raw materials,and graphite paper and alumina plate were used as the substrate. The crystalline phase,morphologies and microstructure of the products were characterized by X-ray diffraction,scanning electron microscope and transmission electron microscope. The compositions andoptical performance of film were characterized by Fourier infrared spectrometer, Ramanspectrometer and fluorescence spectrophotometer. The electrochemistry, photoelectrocatalysisperformance and photocatalytic degradation of methylene blue solution were also investigated.Some conclusions are listed as follows:The SiC nanowire film has been synthesized on graphite paper substrate with expandablegraphite and silicon metal powder as raw materials. The morphologies and structure ofnanowires are affected by the temperature, C/Si molar ratios and holding time. The film,prepared at1500℃for6h and the molar ratio of C/Si=2:1, possesses a thickness of100-200μm. The nanowires have uniform diameter of20nm and length of hundreds micrometers tocentimeters. The growth mechanism of graphite paper-supporting SiC nanowire film wasdiscussed. SiC nanowires grow on graphite paper by two steps of vapor–solid (VS) growthmodel. First, silicon react with residual oxygen in the furnace to produce SiO, and the initial SiCcrystal nucleus is formed by the heterogeneous nucleation of SiO gas with the carbon on graphitepaper substrate. Second, SiC generated by the vapor–solid reaction of gaseous SiO and CO continuously deposits on the crystal nucleus and at the tips of the nanowires, making thenanowires preferentially grow in one-dimensional direction.The electrochemical performance of graphite paper-supporting SiC nanowire film has beeninvestigated. Electrochemical measurements were carried out with the SiC nanowire film aselectrochemical electrode. The cyclic voltammograms show the film electrode has excellentcapacitance performance and reversibility in0.1M H2SO4solution at10mV s1scanning rate.The galvanostatic charge-discharge tests indicate the specific capacitances are25.6mF cm2at0.2A cm2,37mF cm2at0.3A cm2,28mF cm2at0.5A cm2and28mF cm2at2.0A cm2,and the discharge capacity retention ratio exhibits no decrease after2000cycles.The photoelectrocatalytic water splitting activity of the graphite paper-supporting SiCnanowire film has been investigated. Conspicuous photoelectrocatalytic water splitting tohydrogen production process is observed in0.1M H2SO4solution when exposed to theirradiation of500W visible lighter. The response current of the visible light irradiation is2.8mAcm-2, whereas the response current is much lower and no water splitting process can be observedin the darkroom. The response current and hydrogen production efficiency are improved by theincreasing of positive potential. The photoelectrocatalytic water splitting process is discussed bythe reverse Volmer-Heyrovsky mechanism. The photoelectrocatalytic efficiency is also effectedby electrolyte, different film substrate, and the condition of film surface loading Pt particles.The SiC nanowire film has been synthesized on alumina substrate via sol-gel andcarbothermal reduction method with expandable graphite and tetraethoxysilane as the rawmaterials. The factors affecting film growth are investigated, including temperature, C/Si molarratios and holding time. The SiC nanowire film is prepared at1500℃for6h and the molarratio of C/Si=1:1, possessing thickness of80μm. The diameter of nanowires is20-40nm. Thegrowth mechanism has been analyzed. The reduction reaction between SiO2and carbon inC/SiO2xerogel produces the reductive vapor of CO and SiO, then the film nucleates and growson alumina crucible cap by vapor-solid model. The photocatalytic degradation performance ofSiC nanowire film has been investigated. The film exhibits high photocatalytic activity and after6h irradiation of the visible light, the decolorization rate of the methylene blue solution reachesapproximately76%. Methylene blue molecules would be oxidized and degraded by thephotogenerated holes, superoxide radicals and activated hydroxyl radicals.