Carbon Silica Composites Research Articles

Functionalization of mesostructured silica–carbon composites

A strategy for synthesizing highly functionalized porous silica–carbon composites made up of a sulphur- or nitrogen-doped carbon layer coating the pores of two mesostructured silica samples (i.e. SBA-15 and KIT-6) is presented. The synthesis scheme involves several steps: a) infiltration of the silica pores by sulphur-rich (thiophene) or nitrogen-rich (pyrrole) monomers, b) in situ polymerization of these precursors to form polythiophene or polypyrrole, and c) carbonization of the polymers. The resulting silica–carbon composites contain ∼25 wt % of carbonaceous matter and a large number of nitrogen and sulphur functional groups attached to the deposited carbon (up to 4.2 wt % of nitrogen and 6.1 wt % of sulphur). The structural characteristics of the parent silica are retained in the composite materials, which exhibit high surface area, large pore volume and a well-ordered porosity made up of uniform mesopores.

Synthesis of texturally biphasic mesoporous carbon-silica composites and carbons

We report a new synthesis of texturally biphasic carbon-silica composites and carbons that exhibit high surface areas (up to 1500m2g−1), pore volumes (up to 1.9cm3g−1) and mesopores (4.6–6.9nm). The composite materials have ordered mesoporous carbon domains embedded in a disordered mesoporous composite carbon-silica phase. This biphasic texture is preserved for the carbons obtained after silica etching. The synthesis involves the addition of tetraethoxysilane (TEOS) into an alkaline triblock copolymer (PEO140PPO39PEO140) aqueous solution, followed by addition of phenol and formaldehyde. The resol-silica composites, obtained after several days under stirring and heating, are pyrolyzed at 500°C or 800°C. TEOS and resin monomers effects on the copolymer self-assembly to form micelles and vesicles were studied by dynamic light scattering (DLS) before flocculation. We propose a formation mechanism, where siliceous species, are localized mainly in micelles outside the vesicles and in the vesicles bilayers, modifying their properties. The hydrophilic resol monomers are absorbed by micelles outside the vesicles as well as by those inside the vesicles core. After flocculation, biphasic materials, with a resol containing phase embedded in a resol–silica composite phase, are obtained. The in-situ formation of silica reduces the mesopores shrinking occasioned by pyrolysis in both the hybrid carbon-silica and carbon domains although causes disorder in the pores of the hybrid domain.

Sulfonated mesoporous silica–carbon composites and their use as solid acid catalysts

The synthesis of highly functionalized porous silica–carbon composites made up of sulfonic groups attached to a carbon layer coating the pores of three types of mesostructured silica (i.e. SBA-15, KIT-6 and mesocellular silica) is presented. The synthesis procedure involves the following steps: (a) removal of the surfactant, (b) impregnation of the silica pores with a carbon precursor, (c) carbonization and (d) sulfonation. The resulting silica–carbon composites contain ∼30wt % of carbonaceous matter with a high density of acidic groups attached to the deposited carbon (i.e.SO3H, COOH and OH). The structural characteristics of the parent silica are retained in the composite materials, which exhibit a high surface area, a large pore volume and a well-ordered porosity made up uniform mesopores. The high density of the sulfonic groups in combination with the mesoporous structure of the composites ensures that a large number of active sites are easily accessible to reactants. These sulfonated silica–carbon composites behave as eco-friendly, active, selective, water tolerant and recyclable solid acids. In this study we demonstrate the usefulness of these composites as solid acid catalysts for the esterification of maleic anhydride, succinic acid and oleic acid with ethanol. These composites exhibit a superior intrinsic catalytic activity to other commercial solid acids such as Amberlyst-15.

Carbon silica composites for sulfur dioxide and ammonia adsorption

This work focuses on creating nanoporous carbon silica composites from MCM-41 and two carbon sources, sucrose and furfuryl alcohol. The carbon silica composite with sucrose as the carbon phase was synthesized using a novel low temperature procedure. These novel, biphasic materials were tested for their ability to adsorb two distinct types of gases: sulfur dioxide, an acidic gas, and ammonia, a basic gas. The materials are characterized by XRD, nitrogen adsorption isotherms, high resolution TEM, and TGA. The characterization techniques show that impregnation with the carbon phases does not disrupt the hexagonal mesoporous silica structure. Equilibrium breakthrough results show that the presence of the carbon phase enhances both ammonia and sulfur dioxide adsorption capacities compared to the parent MCM-41 and BPL activated carbon.

Synthesis and microwave absorbing properties of FeNi alloy incorporated ordered mesoporous carbon–silica nanocomposite

Ordered mesoporous carbon–silica/FeNi nanocomposite were prepared by a sol–gel method and following sintering process. The electromagnetic parameters were measured in the 0.5–18GHz range. Compared with ordered mesoporous carbon–silica composite, the permittivity of ordered mesoporous carbon–silica/FeNi nanocomposite decreases, while the permeability almost remains unchanged. The optimal reflection loss of ordered mesoporous carbon–silica/FeNi nanocomposite can reach −45.6dB at 11.1GHz for a layer thickness of 3.0mm. The enhanced microwave absorption of the mesoporous carbon–silica/FeNi nanocomposite is due to better balance between the complex permittivity and permeability, geometrical effect, as well as multiple reflections by the ordered mesoporous structure.

Uniformly dispersed pt nanoparticles as fuel-cell catalyst supported onto ordered mesoporous carbon–silica composites

Ordered mesoporous carbon–silica composites, were synthesized via direct-templating method using soluble phenolic resins as carbon sources, tetrabutyl orthosilicate as SiO2 precursors and triblock copolymer F127 as the structure-directing agent. The structure and the corresponding electrocatalytic activity of carbon–silica composites with various silica contents are systematically investigated. Textual characterization results show that the ordered mesoporous structure of carbon–silica composite with trace SiO2 is well preserved. The electrochemical properties of the supported catalysts were studied by cyclic voltammogram, revealing that ordered mesoporous carbon–silica composites as the support possess excellent electrochemical performance for hydrogen oxidation. The electrochemical active surface area of carbon–silica supported Pt nanoparticles can achieve 63.8m2/g, which is about 7-fold that of non-silica supported Pt catalyst.

Fabrication of Ordered Mesoporous Silica-Carbon Nanotubes Composites as Catalyst Supports for Loading with Pt Nanoparticles and Their Electrocatalytic Performance

Ordered mesoporous silica-carbon nanotubes composites have been obtained using tetraethyl- orthosilicate as silicon source and cetyltrimethylammonium bromide as templating agent and subsequentlyl were used as supports for loading with platinum nanoparticles by a microwave-irradiated polyol process. X-ray diffraction (XRD) and transmission electron microscope (TEM) show that carbon nanotubes is highly dispersed into silicon oxidation substrate. Electrocatalysis tests reveal that Pt-C/Si catalysts show excellent catalytic performance, which could be due to the doped of the high electrical conductivity carbon nanotubes (CNTs) and the ordered mesoporous structure that is beneficial to electron transfers. When 40 milligram of carbon nanotubes was added to the composites, the electrochemical active surface area (EASA) of this elec- trocatalyst is 120.9 m 2 •g -1

ChemInform Abstract: Amorphous Carbon—Silica Composites Bearing Sulfonic Acid as Solid Acid Catalysts for the Chemoselective Protection of Aldehydes as 1,1‐Diacetates and for N‐, O‐ and S‐Acylations.

AbstractIn the title reaction a highly active, selective, stable and recyclable catalyst is used.

SOLID SULFONIC ACID CATALYSTS BASED ON POROUS CARBONS AND CARBON–SILICA COMPOSITES

Mesoporous carbons prepared using a templating method under different carbonization temperatures are sulfonated with concentrated H2SO4 . Without the moving of silica template carbon–silica composites were prepared, which can maintain the pore structure well during sulfonation reaction process. The resultant samples are characterized using nitrogen adsorption, transmission electron microscope, field-emission scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, and elemental analysis techniques. The catalytic performances of the sulfonated carbons and composites are evaluated by esterification reaction of methanol with acetic acid. The results show that a low-temperature carbonization process is favorable for improving the reaction conversion of acetic acid. In addition, the sulfonated carbon–silica composites show a higher acetic acid conversion than the sulfonated mesoporous carbons.

Vapor assisted “in situ” transformation of mesoporous carbon–silica composite for hierarchically porous zeolites

Ordered mesoporous carbon–silica composite was “in situ” transformed into hierarchically porous zeolites ZSM-5 (H-ZSM-5) under water vapor, which synthesized from evaporation induced “tri-constituent” co-assembly of resin, silica and surfactant. The vapor assisted transformation was realized within 2-D hexagonally mesochannels of carbon–silica composite infused with tetrapropylammonium hydroxide at 130 °C for 72 h. The calcined H-ZSM-5-570 possesses a mesostructure with mean pore sizes of 0.6 and 9.0 nm, BET surface area of 409 cm 2/g, and pore volume of 0.54 cm 3/g. High-resolution TEM images of H-ZSM-5-570 display that mesoporous walls consisted of zeolite nanocrystals of about 6 nm in the same domain. Weak acidity of H-ZSM-5-570 has also been concluded from ammonia desorption measurements.

Carbon–silica composites prepared by the precipitation method. Effect of the synthesis parameters on textural characteristics and toluene dynamic adsorption

Three synthesis routes are presented here that leads to carbon–silica composites. These were characterized by nitrogen physisorption, by thermogravimetric analysis and by dynamic toluene adsorption test similar to Ashrae standard I45.1. The carbon–silica composites possess high microporosity and mesoporosity as well as large surface areas. Furthermore, the control of the microporosity as well as pore size distribution is possible because they depend on the amount of carbon used and of the synthesis route. Following routes I and III a wide micro-mesoporous pore size (1–32 nm) was obtained where as by route II narrow micro-mesoporous pore size (1–4 nm) was observed. In addition, pore diameters center in the range of 1.13–1.17 nm was observed when carbon content was 32 or 45 wt%. The dynamic adsorption of toluene was evaluated for carbon–silica composites obtained by three preparation routes at two different carbon contents, 32 and 45 wt% The results showed that a composite with 45 wt% carbon content and obtained via preparation route I gave the highest toluene adsorption capacity (27.6 wt% relative to carbon content). The large uptake capacity of this composite was attributed to the presence of high microporosity volume and a wide (1–32 nm) bimodal pore system consisting of extensive mesopore channels (2–32 nm) as well as large surface area. These capacity values of carbon–silica composites are by weight relative to carbon content and are competitive to, results obtained for commercial coconut activated carbon (31.1 wt%) and significantly better than a commercial alumina-carbon composite (9.5 wt%) at 0% efficiency.

Facile Synthesis of Transparent Mesostructured Composites and Corresponding Crack-free Mesoporous Carbon/Silica Monoliths

Transparent ordered mesostructured resin-silica composite monoliths with uniform rectangular shape which fully copies the inner-shape of vessels and size (5 × 3 × 0.3 cm3) are prepared via a facile approach of evaporation induced self-assembly (EISA) without adding any protecting agent by using triblock copolymer Pluronic F127 as a template. Ordered mesoporous carbon-silica composite monoliths can be obtained in a wide range of silica content (34–82 wt %) after calcination in N2. Monolithic shape can be maintained with shrinkage (∼20%) in sizes. Furthermore, each component of the composites can be easily removed after the simple post treatments. After etching silica, mesoporous carbon monoliths retain the same in shape and sizes, but show much larger pore volume (∼2.65 cm3/g) and higher surface area (∼1800 m2/g) than the carbon–silica composites. Besides, mesoporous silica monoliths with large pore size (∼14.6 nm) show an integral and uniform shape after air combustion. The obtained mesoporous carbon monoliths show high capacitance (186 F/g) and high cycling stability (8% capacitance loss after 1000 cycles), exhibiting an excellent potential in capacitor applications.

Amorphous carbon-silica composites bearing sulfonic acid as solid acid catalysts for the chemoselective protection of aldehydes as 1,1-diacetates and for N-, O- and S-acylations

Amorphous carbon-silica composites bearing sulfonic acid derived from inexpensive natural organic compounds (glucose, maltose, cellulose, chitosan and starch) were prepared by partial carbonization followed by sulfonation and their catalytic activity was evaluated for the protection of aldehydes as 1,1-diacetates and for N-, O- and S-acylations under solvent-free conditions. Different biomaterials have been chosen, with a view to select the most active solid acid catalyst. Carbon-silica composites were characterized by FTIR, XRD and elemental analysis. Sulfonated carbon-silica composite derived from starch was found to be the most active and could be recycled for several runs without loss of significant activity. It was also characterized by TGA, SEM and TEM.

Biomorphic SiC Prepared from Carbonized Millet by Sol-Gel and Carbothermal Reduction Processing

Biomorphic silicon carbide (bioSiC) was prepared by high temperature pyrolysis and sol-gel and carbothermal reduction processing at 1600 oC. The morphology and microstructure of carbon-silica composites and purified bioSiC samples were characterized by scanning electron microscopy. The phase composition of the resulting sample was analyzed by X-ray diffraction. The results suggest that the bioSiC mainly consists of cubic ß-SiC, and principally replicates the shape and microstructure of the carbon template.

Spatially and Size Selective Synthesis of Fe-Based Nanoparticles on Ordered Mesoporous Supports as Highly Active and Stable Catalysts for Ammonia Decomposition

Uniform and highly dispersed γ-Fe(2)O(3) nanoparticles with a diameter of ∼6 nm supported on CMK-5 carbons and C/SBA-15 composites were prepared via simple impregnation and thermal treatment. The nanostructures of these materials were characterized by XRD, Mössbauer spectroscopy, XPS, SEM, TEM, and nitrogen sorption. Due to the confinement effect of the mesoporous ordered matrices, γ-Fe(2)O(3) nanoparticles were fully immobilized within the channels of the supports. Even at high Fe-loadings (up to about 12 wt %) on CMK-5 carbon no iron species were detected on the external surface of the carbon support by XPS analysis and electron microscopy. Fe(2)O(3)/CMK-5 showed the highest ammonia decomposition activity of all previously described Fe-based catalysts in this reaction. Complete ammonia decomposition was achieved at 700 °C and space velocities as high as 60,000 cm(3) g(cat)(-1) h(-1). At a space velocity of 7500 cm(3) g(cat)(-1) h(-1), complete ammonia conversion was maintained at 600 °C for 20 h. After the reaction, the immobilized γ-Fe(2)O(3) nanoparticles were found to be converted to much smaller nanoparticles (γ-Fe(2)O(3) and a small fraction of nitride), which were still embedded within the carbon matrix. The Fe(2)O(3)/CMK-5 catalyst is much more active than the benchmark NiO/Al(2)O(3) catalyst at high space velocity, due to its highly developed mesoporosity. γ-Fe(2)O(3) nanoparticles supported on carbon-silica composites are structurally much more stable over extended periods of time but less active than those supported on carbon. TEM observation reveals that iron-based nanoparticles penetrate through the carbon layer and then are anchored on the silica walls, thus preventing them from moving and sintering. In this way, the stability of the carbon-silica catalyst is improved. Comparison with the silica supported iron oxide catalyst reveals that the presence of a thin layer of carbon is essential for increased catalytic activity.

Mesostructured silica–carbon composites synthesized by employing surfactants as carbon source

A general synthetic route for the fabrication of carbon–silica composites with a carbon layer coating the mesopores of the mesostructured silica is presented. The carbon layer is produced by carbonizing the surfactant employed as structure-directing agent in the synthesis of the mesostructured silica materials (MSM). The synthesis of this kind of composites is based on using sulphuric acid to generate a carbon residue from the surfactant molecules confined within the mesopores of the silica. The action of the sulphuric acid takes place via dehydration and sulphonation reactions, which promote the formation of aromatic structures and favour cross-linking processes. In order to illustrate this synthetic strategy we selected three mesostructured silica materials prepared with the aid of two types of surfactants: (i) oxygen-containing non-ionic triblock PEO-EO-PEO copolymer (Pluronic P-123) used for the synthesis of SBA-15 and KIT-6 and (ii) an alkyl ionic surfactant CTAB (cetyltrimethylammonium bromide) used to synthesize MCM-41. The silica–carbon composites prepared have high BET surface areas, large pore volumes and an ordered porosity made up of uniform mesopores.

籾殻からバインダレスで製造した炭素シリカ複合体の力学特性

A carbon/silica composite (CSC) designed for use under sliding and compressive load was fabricated from rice husk (RH), an agricultural waste material, without using any binders. A compression pressure of 100 MPa was applied to the RH powder heated from room temperature to 150°C firstly, and then that heated at 280°C for 10min secondly. The RH powder was finally heated from280 to 500°C without compression, producing the precursor of CSCs. The CSCs were produced by sintering the precursor in an electric furnace at 800, 1000, 1200, and 1400°C without compression, innitrogen gas. The CSC sintering at 800°C for 1 h in nitrogen gas provided the maximum bulk density of 1.52 g/cm3. The maximum compressive strength was measured to be 55.7 MPa at the sinteringtemperature of 1200°C. The maximum Vickers microhardness at the surface of 476 appeared on the CSC produced at the second compression pressure of 200 MPa and then sintered at 800°C . The CSC sintered at 1000 °C showed the static friction coefficient of 0.15 and the dynamic friction coefficient of 0.05 under the contact with SUS304 stainless steel.

Effective nitrosamines trap derived from the in situ carbonized mesoporous silica MCM-41

A new route to modify the mesoporous silica MCM-41 with carbon, using the inherent surfactant template in the as-synthesized sample as the carbon precursor, is reported in this article. Apart from the advantage of omitting energy and time required for removal of template, the resulting silica–carbon composites exhibit a high efficiency in adsorption and catalytic decomposition of N-nitrosopyrrolidine (NPYR), the typical carcinogenic pollutant in environment. The influence of carbonization temperature on the structure and performance of the resulting carbon–silica composite was investigated by use of XRD, N 2 adsorption–desorption, FTIR and TG-DSC techniques, and the instantaneous adsorption and the temperature-programmed surface reaction (TPSR) of NPYR as well as the reduction of nitrosamines level of cigarette smoke were also utilized to assess the actual function of these composites. The carbonization performed in the range of 773–973 K enabled the resulting composites to possess a higher activity than parent MCM-41 in eliminating volatile nitrosamines, which is beneficial for controlling carcinogenic pollutants in environment.

Preparation of sulfonated ordered mesoporous carbon and its use for the esterification of fatty acids

Mesoporous carbon, which can be replicated from mesoporous silica and whose surface is hydrophobic, can be an ideal catalyst for the esterification of fatty acids. Here we report an easy and low cost way to prepare sulfonic acid group-functionalized mesoporous carbon. A sample of calcined mesoporous silica SBA-15 was added to an aqueous sucrose solution followed by drying and calcination at different temperatures. In contrast to existing procedures, the obtained hybrid Si/C material was then first sulfonated in H 2SO 4, before the final removal of the silica template in order to stabilize the porous structure towards the liquid phase sulfonation treatment. Thus the silica–carbon composites, instead of the mesoporous carbon, were successfully sulfonated to introduce –SO 3H groups, while keeping the ordered mesoporous structure intact. The influence of carbonization temperature was investigated, suggesting an optimum temperature of 873 K. The SO 3H group-functionalized mesoporous carbon, denoted as CMK-3-873-SO 3H, was characterized by means of XRD, N 2 physisorption, SEM, FT-IR, elemental analysis and TEM. It followed that a uniform mesoporous carbon was obtained with an average pore size of 3.89 nm, a specific surface of 807 m 2/g and a –SO 3H group loading of 0.39 meq/g of dry material. Compared with other solid acid catalysts, the resulting material shows enhanced activity in the acid-catalyzed esterification of oleic acid with methanol, and can be used repeatedly. The increased catalytic performance is attributed to the hydrophobic surface and larger pore size of the new catalyst. It can effectively accommodate long chain fatty acids and reject formed water, making the active sites easily accessible.

Synthesis and properties of mesoporous carbons with high loadings of inorganic species

A series of mesoporous carbons with high loading of silica has been synthesized by acid-catalyzed polymerization of resorcinol and formaldehyde in the presence of tetraethyl orthosilicate (TEOS), colloidal silica (silica source) and poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymer (soft template) followed by carbonization. This synthesis route can be considered as a combination of soft-templating and hard templating strategies. The resulting mesoporous silica–carbon composites contained spherical silica colloids in addition to uniformly distributed silica originated from TEOS. Dissolution of silica led to high surface area carbons, which in addition to the primary mesopores formed by thermal degradation of block copolymer template possessed spherical mesopores after dissolution of silica colloids and fine pores after removal of TEOS-generated silica species. This approach can be used to incorporate other inorganic nanoparticles into mesoporous carbons with extra microporosity created after dissolving TEOS-generated silica species.