Carbonaceous Silica Research Articles

In-situ synthesis of SiC nanowires on biomass carbon materials derived from cherry stones

SiC nanowires were synthesized via the in-situ carbothermal reduction of silica xerogel on biomass carbon materials. The carbonaceous silica xerogel was prepared by sol-gel method using tetraethoxysilane (TEOS) as a silicon source, and carbonized cherry stones as carbon sources. The composition, morphology, and structures of the products obtained at different reaction temperatures were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The results show that the products have different phase compositions with the reaction temperature and a large number of β-SiC nanowires were obtained at 1300 °C for 8 h. The SiC nanowires have a diameter of 40–100 nm and a length of several microns. The thermogravimetric (TG) analysis showed that the content of SiC was about 43.2% in SiC nanowires/biomass carbon materials, and the Raman spectrum indicates the carbon phase has a higher graphitic structure.

Scalable fabrication of novel SiC nanowire nonwoven fabric

Flexible papers constructed by one-dimensional nanowires have attracted much attention due to their various applications. Herein, a novel nonwoven fabric with paper-like qualities composed of zinc blende SiC (β-SiC) nanowires was fabricated by a scalable rolling process. The SiC nanowires were synthesized by the carbothermal reduction reaction of the carbon fiber and carbonaceous silica xerogel. The crystal phase, morphology and microscopic structure of the as-prepared SiC nanowires were characterized by field emission scanning electron microscope, X-ray diffraction and high-resolution transmission electron microscopy. The nanowire vapor–solid growth mechanism and preparation process for SiC nanowire nonwoven fabric were also discussed. The freestanding SiC nanowire nonwoven fabric exhibited high flexibility, high mechanical strength, excellent refractory performance and thermal stability. With high flexibility, high mechanical strength, superior nonflammability and thermal stability, the flexible paper-like 3C-SiC nanowire nonwoven fabric materials would be expected to have some potential applications, such as ceramic matrix composites, metal matrix composites, energy storage, catalyst supports, radiation-proof fabric, filtration and separation.

Self-forming salt-assisted synthesis of SiC nanoparticles and their adsorption property for methylene blue from aqueous solution

SiC nanoparticles were synthesized by the carbothermal reduction of carbonaceous silica xerogel with self-forming NaCl salt prepared from sodium silicate and sucrose as sources, and ferric nitrate as an additive. The products obtained by heating the xerogel at 1150°C for 6h in argon flow (200ml/min) were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) method. The results show that the SiC samples to be mainly composed of porous and blocky-shaped particles consisting of fine irregular particles with 50–100nm average size, high surface area (27.1m2/g) and pore volume (0.052cm3/g). The SiC nanoparticles showed excellent adsorption of MB from aqueous solutions, the adsorption efficient reaching 86.4%, and the adsorption capacity being 14.4mg/g.

A new approach to fabricate SiC nanowire-embedded dense SiC matrix/carbon fiber composite

A novel and simple sol-gel route has been used for the fabrication of composite structure composed of carbon fibers and silicon carbide nanowires embedded in dense silicon carbide matrix. The carbonaceous silica sol was impregnated in the carbon fiber preform at atmo- spheric pressure. The sol impregnated carbon preform was cured and heat treated to convert into silicon carbide. The analysis by X-ray diffraction, scanning electron micros- copy, X-ray tomography, and transmission electron microscopy indicates that the impregnated carbonaceous silica gel converts to b-silicon carbide with dense and wire morphology. Different morphological silicon carbide was uniformly distributed inside carbon fiber preform and there was no degradation in thermophysical properties of carbon composite during processing. These results reveal high efficient reinforcement of different morphological silicon carbide in carbon composite, demonstrate a new mecha- nism of carbon composite reinforcement and suggest a new direction to carbon composite reinforcement.

FeCl2-assisted synthesis and photoluminescence of β-SiC nanowires

β-SiC nanowires were synthesized by the carbothermal reduction of the carbonaceous silica xerogel prepared using tetraethoxysilane (TEOS) and sucrose as sources, and ferrous chloride as an additive. The products were obtained by heating the xerogel at 1300°C for 6h in argon flow (200ml/min). The products were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and selected area electron diffraction (SAED). The results show that the products mainly consist of crystalline β-SiC nanowires with an amorphous SiO2 shell. The SiC nanowires have a diameter of 100–300nm and a length from tens to hundreds of micrometers. The vapor–liquid–solid (VLS) mechanism was proposed to explain the formation of β-SiC nanowires, and the nanowires mainly grow along [111] direction. The photoluminescence (PL) spectrum of β-SiC nanowires at room temperature shows two emission peaks at 405nm and 436nm.

Synthesis and characterization of Si3N4 wires from binary carbonaceous silica aerogels

Silicon nitride ultrafine powders were synthesized from a binary sol–gel route, in which tetraethoxysilane (TEOS) and saccharose were used to prepare a carbonaceous silica xerogel, and ferric nitrate was employed as an additive. The influence of reaction temperature and mass ratio of C to Si (CSi=0.1, 0.5, 1) on the synthesis of Si3N4 wires was studied. After purification, the Si3N4 sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectrum and Fourier transform infrared spectroscopy. The results show that the Si3N4 was fully formed with two kinds of morphologies including globular and wire with a diameter of 100–500nm and a length of several microns at reaction temperature of 1400°C for 10h in nitrogen flow (200ml/min) by employing the mass ratio of CSi=0.5.

Preparation and photoluminescence of netlike and curved β-SiC nanostructures

The netlike and curved β-SiC nanostructures were synthesized by the carbothermal reduction of the carbonaceous silica xerogel, in which tetraethoxysilane (TEOS) and phenolic resin were used to prepare a carbonaceous silica xerogel and magnesium nitrate was employed as additive. The products were obtained by heating the xerogel at 1300°C for 6h in argon flow (200ml/min). The products mainly consist of netlike β-SiC nanostructures and curved β-SiC nanowires. The netlike SiC nanostructures have a novel pore structure of lotus root, and the diameter of circular hole is 500–1000nm. The curved β-SiC nanowires have a diameter of 300–500nm and a length of hundreds microns. The photoluminescence (PL) spectrum of netlike and curved β-SiC nanostructures at room temperature shows three emission peaks at 486nm, 494nm and 503nm, which may be due to the effect of the morphology, size confinement effects and the oxygen vacancy in the amorphous SiO2, respectively.

Hybrid UV-cured organic–inorganic IPNs

Hybrid organic–inorganic UV-cured coatings based on interpenetrating polymer networks (IPN) were prepared starting by an equimolar methacrylate-epoxy UV-curable mixture (bisphenol-A-diglycidyl dimethacrylate/bisphenol-A-diglycidyl ether, abbreviated as BisGMA/BADGE), in the presence of tetrafunctional silane monomer tetrakis(methacryloyloxy-ethoxy)silane (TetMESi) as inorganic precursor. The photocuring kinetics of the BisGMA/BADGE IPN monomer mixture were strongly affected by the order of the cure of the individual components. Addition of TetMESi resulted in higher degrees of reaction. DMTA of the BisGMA/BADGE IPN suggest a two phase structure. The rubbery modulus of the hydrolysed BisGMA/BADGE/TetMESi systems increased as the level of TetMESi was raised in the formulation due primarily to the significant reinforcing effect of the nano-silica particles. TGA of the BisGMA/BADGE IPN showed three degradation stages with no residual char but the hydrolysed BisGMA/BADGE/TetMESi systems formed a carbonaceous silica char which increased in mass as the level of TetMESi was raised. The two phase morphology of the BisGMA/BADGE IPN was confirmed by FE-SEM analysis. For IPNs prepared with TetMESi, SiO2 particles are evident in the FE-SEM image and have diameters in the nanometric size range.

Fabrication and Photoluminescence of Hierarchical SiC Nanowires

Hierarchical single-crystalline β-SiC nanowires were synthesized by simply heating carbonaceous silica xerogel. A fairly high density of stacking faults was observed perpendicular to [111] growth direction of the hierarchical nanowires. A possible vapor-solid growth mechanism for the hierarchical nanowires was discussed. The photoluminescence spectrum of hierarchical SiC nanowires at room temperature shows two emission peaks at 406 nm and 432 nm. The blue emission at 432 nm may be related to 3C-SiC, while the emission peak at 406 nm may be attributed to 6H-SiC segments formed by stacking faults in 3C-SiC nanowire matrix. Keywords: Silicon carbide nanowires, photoluminescence, microstructure, electron microscopy

The role of polymethylhydrosiloxane in the sol-gel synthesis of high surface area porous silicon carbide

Abstract High surface area porous silicon carbide was synthesized via a modified sol-gel method. In the sol-gel method, furfuryl alcohol and tetraethoxysilane were used respectively as carbon and silicon precursors, polymethylhydrosiloxane (PMHS) was employed as a pore-adjusting agent for preparing a carbonaceous silica xerogel. SiC was obtained by the carbothermal reduction of the carbonaceous silica xerogel at 1 300 °C in argon flow and then purified by removing excess silica, carbon and other impurities. Depending on the amount of PMHS added in the sol-gel process, the SiC products are found to have high specific surface area ranging from 120 to 167 m2 g−1 and pore volume ranging from 0.49 to 1.01 cm3 g−1. It is therefore suggested that PMHS enhances the production of mesoporous pores in the SiC products.

Synthesis of High Surface Area Porous Silicon Carbide by a Modified Sol-Gel Method

High surface area porous silicon carbide was synthesized by employing polymethylhydrosiloxane (PMHS) as soft template in the sol-gel process. In the sol-gel method, furfuryl alcohol and tetraethoxysilane were used respectively as carbon and silicon precursors for preparing a carbonaceous silica xerogel. PMHS was employed as pore-adjusting agent in the sol-gel process. The purified SiC sample was characterized by XRD、FTIR、SEM、HRTEM and BET. The results show that the SiC products are found to have high specific surface area of 125 m2 /g and an average pore diameter of about 17 nm. PMHS has important effect on the surface area of the SiC products.

Large‐scale synthesis of ultralong single‐crystalline SiC nanowires

AbstractA large number of cotton‐like ultralong β‐SiC nanowires (NWs) were successfully synthesized via a simple catalyst‐free carbothermal reduction approach using a carbonaceous silica xerogel as raw materials. The length of the NWs is in the millimeter range and the diameter of the NWs is about 130 nm. The ultralong NWs are bamboo‐like single‐crystalline β‐SiC NWs. A vapor–solid mechanism was proposed to elucidate the growth process of the NWs, and the large length and high‐yield of the SiC NWs may be ascribed to the stable release of SiO and CO gases form the carbonaceous silica xerogel. The simple method provides a promising candidate for industrial fabrication of β‐SiC NWs.

Synthesis of High Surface Area Porous Silicon Carbide by Employing Soft Template in the Sol-Gel Process

High surface area porous silicon carbide was synthesized by a modified sol-gel method. In the sol-gel method, furfuryl alcohol and tetraethoxysilane were used respectively as carbon and silicon precursors for preparing a carbonaceous silica xerogel. Polymethylhydrosiloxane (PMHS) was employed as pore-adjusting agent in the sol-gel process. SiC was obtained by the carbothermal reduction of the carbonaceous silica xerogel at 1300 oC in argon flow and then purified by removing excess silica, carbon and other impurities. XRD、FTIR、SEM、HRTEM and BET were used to characterize the SiC samples. The results show that the SiC products are found to have high specific surface area of 135 m2 /g. PMHS has important effect on the surface area, pore volume of the SiC products. It is therefore suggested that PMHS plays the role of structure-directing agent that enhances the production of mesoporous pores in the SiC products.

Band gap characterization and photoluminescence properties of SiC nanowires

β-SiC nanowires were synthesized by a simple carbothermal reduction of carbonaceous silica xerogel. The morphology and structure of the nanowires were investigated by X-ray diffraction, scanning electron microscope and transmission electron microscopy. The results showed that the nanowires were hexagonal prism-shaped hierarchical nanostructures. The typical stacking faults and twin defects of SiC nanowires were also observed. Band-gap characterization and photoluminescence properties of SiC nanowires were investigated by UV-vis absorption spectroscopy and fluorescence photometry, respectively. The results showed the SiC nanowire was an indirect transition semiconductor and the band gap energy for the SiC nanowires was 2.85 eV. The photoluminescence peak value at 470 nm (2.64 eV) originating from the SiC nanowires was a little higher than the value of band-gap energy.

Influence of the pH on the Morphology of Sol–Gel‐Derived Nanostructured SiC

This investigation deals with the use of the carbothermal reduction reaction of carbonaceous silica xerogel for synthesizing nanostructured SiC. The effect of the pH of the early‐prepared gel (EPG) on the properties of the finally obtained nanostructured silicon carbide was investigated. The produced silicon carbide samples were characterized by X‐ray diffraction, fourier transform infrared spectroscopy, transmission electron microscopy, and N2 porosimetry. The results revealed that the variation of EPG pH greatly affected the structural properties of the finally obtained nanostructured silicon carbide. The morphology of the produced nanostructured silicon carbide was changed from nanoparticles to nanorods and vice versa with changing the pH values of the gel. The nitrogen adsorption–desorption isotherms of the samples are of classical type IV, characteristic of mesoporous materials. The BET surface areas of the nanostructured silicon carbide are increased from 68 to 106 m2/g with increasing the pH of the EPG from 3 to 5, respectively.

Periodically twinned SiC nanowires

Twinning has been recognized to be an important microstructural defect innanoscale materials. Periodically twinned SiC nanowires were largely synthesizedby the carbothermal reduction of a carbonaceous silica xerogel prepared fromtetraethoxysilane and biphenyl with iron nitrate as an additive. The twinnedβ-SiC nanowires, with a hexagonal cross section, a diameter of 50–300 nm anda length of tens to hundreds of micrometers, feature a zigzag arrangement ofperiodically twinned segments with a rather uniform thickness along the entire growthlength. Computer simulation has been used to generate three-dimensional atomicstructures of the zigzag columnar twin structure by the stacking of hexagonal discs of{111} planes of SiC. A minimum surface energy and strain energy argument isproposed to explain the formation of periodic twins in the SiC nanowires. Thethickness of the periodic twinned segments is found to be linearly proportional to thenanowire diameter, and a constant volume model is proposed to explain the relation.

Formation Mechanism of Si3N4 Nanowires via Carbothermal Reduction of Carbonaceous Silica Xerogels

Si3N4 nanowires prepared from the carbothermal reduction of carbonaceous silica xerogels with metal salt additives usually contain a small amount of nanotubes. This paper is devoted to the investigation of the formation mechanism of the Si3N4 nanowires. As-prepared samples heated at 1300 degrees C for different reaction times (1, 5, 10, and 30 h) were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results showed that all the samples mainly consisted of nanowires, while their crystalline phases changed with the heating time. Nitrogen-doped silicon oxide nanowires were first produced via the vapor-liquid-solid process and then underwent a stepwise surface nitrogenization to silicon nitride. The suggested mechanism can easily explain the existence of nanotubes in the Si3N4 nanowires.

Beaded silicon carbide nanochains via carbothermal reduction of carbonaceous silicaxerogel

Novel silicon carbide nanostructures, beaded nanochains, are prepared from thecarbothermal reduction of a carbonaceous silica xerogel with cetyltrimethylammoniumbromide and lanthanum nitrate as additives. The nanochains consist of a stemwith a diameter of about 50 nm and uniform beads with diameters of 100–200 nm.It is demonstrated that the tensile strength of an epoxy composite filled withthe SiC nanochains improves significantly due to the unusual morphology of thenanochains.

Sol–gel synthesis of Si 3N 4 nanowires and nanotubes

Silicon nitride nanowires and nanotudes were synthesized from a binary sol–gel route, in which tetraethoxysilane (TEOS) and phenolic resin were used to prepare a carbonaceous silica xerogel and ferric nitrate was employed as additive. Raw Si 3N 4 product was obtained by heating the xerogel at 1300 °C for 10 h in nitrogen flow (200 ml/min). The Si 3N 4 sample after purification was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersion X-ray (EDX) spectrum and selected area electron diffraction (SEAD). The results showed that the sample mainly consisted of α-Si 3N 4 nanowires with a few of nanotubes. Both the nanowires and nanotubes have a diameter of 30–100 nm and a length of hundreds microns. Liquid droplets were also found at the tip of the nanowires, and this indicated that the growth of the nanowires and nanotubes followed the vapor–liquid–solid (VLS) mechanism.

Synthesis of nanometre silicon carbide whiskers from binary carbonaceous silica aerogels

A novel synthesis process, based on a carbothermal reduction reaction of binary carbonaceous silica aerogels, has been developed for producing nanometre silicon carbide whiskers. The process uses binary carbonaceous silica aerogels as precursors. The precursors, which are derived from carbonaceous sol and silica sol, are prepared by sol–gel supercritical fluid drying and provide a high contact area of reactants. The homogeneous distribution of silica within carbon and their loose structure result in the formation of purer nanometre silicon carbide whiskers. The precursors and their carbothermal reduction products are investigated by TEM, EDX and XRD analyses. The effect of heat-treatment temperature on the production of SiC whiskers is discussed.