Original Silica Research Articles

Chemical and spatial promotional effects of bimodal pore catalysts for methane dry reforming

SiO 2, ZrO 2 and Al 2O 3 bimodal pore supports were prepared by incipient-wetness impregnation of silica gel, with SiO 2, ZrO 2 and Al 2O 3 sol respectively. The obtained bimodal pore supports showed two different kinds of pores, new mesopores and original macropores, simultaneously. The increased BET surface areas and the decreased pore volumes of bimodal pore supports, compared to those of the original silica gel, proved that the nano particles of precursor sols indeed entered into the macrospores of silica gel and aggregated to form mesopores by self-organization at the calcination step. Platinum supported onto these supports were applied in carbon dioxide reforming of methane (dry reforming). It was found that SiO 2 bimodal catalyst was better than unimodal ones due to high metal dispersion and fast intra-pellet diffusion of reactants as well as products. Among all bimodal catalysts, ZrO 2 and Al 2O 3 bimodal catalysts exhibited higher activity and stability contributed by both the spatial promotional effect of bimodal pore structure and intrinsical chemical effect of ZrO 2 and Al 2O 3, at the same time.

Synthesis of Ordered Mesoporous Manganese Oxides by Double Replication for Use as an Electrode Material

Periodically ordered mesoporous manganese oxides were synthesized in a single and double replication procedure. Mesoporous SBA-15 and -16 silica and their reverse replica carbons were successively used as hard templates. The silica and carbon pore systems were infiltrated with or , which was then converted to at 873 K; the silica and carbon matrix were finally removed by NaOH solution or calcinations in air. The structure of the mesoporous , using a carbon template, corresponds to that of the original SBA-15 and SBA-16 silica. The products consist of hexagonally arranged cylindrical mesopores with crystalline pore walls or cubic mesoporous pores. The structure of replica has been confirmed by XRD, TEM analysis, and its electrochemical properties were tested with cyclic voltammetry. Formation of inside the mesoporous carbon pore system showed much improved electrical properties.

Wider Pore Superficially Porous Particles for Peptide Separations by HPLC

Fused-core superficially porous particles have recently created considerable interest for high-performance liquid chromatography separations because of their unusual high column efficiency and much lower back pressure when compared to sub-2-microm particles. With superficially porous particles, larger solutes can move rapidly in and out of a thin porous shell, resulting in reduced band broadening at higher mobile phase velocities for greater separation speeds. The original silica fused-core particles were 2.7 microm in diameter with a 0.5-microm thick shell of 90 A pores designed for the fast separation of small molecules with molecular weights of less than approximately 5000. This manuscript describes new fused-core particles with similar physical characteristics except with a porous shell of 160 A pores designed specifically for rapidly separating peptides (and some small proteins) with molecular weights up to approximately 15,000 Daltons. Because of the larger pore size, restricted diffusion of these larger molecules is not seen since ready access to the entire porous shell is featured. Data are given to define sample loading qualities for columns of these new particles. Column stability studies indicate that these particles bonded with a sterically protected C(18) stationary phase can be used at low pH and higher temperatures with excellent results. The wider-pore particles of this study are shown to be particularly useful with a mass spectrometer detector for the rapid gradient separation of peptides using both volatile trifluoroacetic acid and formic acid containing mobile phases. Examples are provided for the separation of complex peptide mixtures to illustrate the capabilities for columns of these new wider-pore, fused-core particles.

Changes in wetting properties of silica surface treated with DPPC in the presence of phospholipase A 2 enzyme

Wetting properties of silica plates contacted with dipalmitoylphosphatidylcholine (DPPC) or DPPC/enzyme (phospholipase PLA 2) in NaCl solution were determined by thin layer wicking and with a help of Washburn equation. The wicking experiments were performed both for bare plates and the silica plates precontacted overnight with the probe liquid saturated vapors the silica plates, as well as untreated and DPPC (or DPPC/enzyme) treated. Adsorption of DPPC on original silica plates increases a bit hydrophobic character of silica surface in such a way that hydrocarbon chains are directed outwards and the polar part towards the silica surface. However, after the enzyme action the products of DPPC hydrolysis by PLA 2 (palmitic acid and lysophosphatidylcholine) increase again hydrophilic character of silica surface (an increase in acid–base interactions, γ s A B ). The changes of silica surface wettability are evidently dependent on the time of enzyme contacting with DPPC in NaCl solution. Although, the changes of total surface free energy of silica after treatment with DPPC/enzyme solution are minor about 2–6 mJ/m 2, the changes of the electron-donor ( γ s − ) and Lifshitz–van der Waals ( γ s L W ) component of the surface free energy are noticeable. Despite, these results are somehow preliminary, it seems that thin layer wicking method is an interesting tool for investigation of the effect of adsorbed DPPC on hydrophobicity/hydrophilicity of silica surface and influence of enzyme PLA 2 action.

Soft-Chemical Approach of Noble Metal Nanowires Templated from Mesoporous Silica (SBA-15) through Vapor Infiltration of a Reducing Agent

Noble metal (Pt, Ag, and Au) nanowires are synthesized by using mesoporous silica (SBA-15) powders as templates through vapor infiltration of a reducing agent (dimethylamine borane, DMAB) under the same reduction conditions. Because SBA-15 has micropores connecting mesochannels, Pt nanowires are connected and periodically packed, reflecting the micropores and the mesochannel arrangements in the original mesoporous silica. On the other hand, other metal (Ag and Au) nanowires are mainly unconnected. Such a difference is attributed to the relatively faster deposition rate of Ag and Au than Pt. Therefore, Ag and Au tend to grow rapidly along the mesochannels, and the metal deposition in micropores is insufficient to occur. The length of the metal nanowires is controlled by the reduction time. As a typical case, the surface plasmon resonance spectra of the Au nanowires embedded in SBA-15 change depending on the length of the nanowires. The present reduction is a soft-chemical, straightforward, and general approach, which has advantages for the synthesis of metal nanowires in large amounts.

Development of platinum-based bimodal pore catalyst for CO 2 reforming of CH 4

The synthesis and preparation conditions for bimodal pore catalyst support were studied. SiO 2–SiO 2, ZrO 2–SiO 2, or Al 2O 3–SiO 2 bimodal pore support could be optimally prepared by incipient-wetness impregnation (IWI) of silica Q-50 pellet with silica, zirconia or alumina sol, respectively. Pore size measurement results suggested that the obtained bimodal pore supports showed two kinds of pores, mesopores and original macropores, simultaneously. The newly formed mesopores contributed to the increased BET surface area of bimodal pore support, compared with that of the original silica Q-50. Pt catalysts supported on these kinds of supports were tested in CO 2 reforming of CH 4. The performances of Pt/ZrO 2–SiO 2 and Pt/Al 2O 3–SiO 2 bimodal pore catalysts were better. Furthermore, it was found that Pt/Al 2O 3–SiO 2 bimodal catalyst showed better reforming performance than Pt/ZrO 2–SiO 2 bimodal catalyst. And furthermore, CeO 2 modified Pt/Al 2O 3–SiO 2 bimodal pore catalyst exhibited highest activity and stability under the present study conditions.

Template synthesis of ordered mesoporous organic polymeric materials using hydrophobic silylated KIT-6 mesoporous silica

Porous organic materials can be synthesized via free-radical polymerization of crosslinkable olefinic monomers within the interstices of porous templates. The synthesis process has been employed to generate ordered mesoporous structures through use of a mesoporous silica template, KIT-6. The mesoporous silica features a bicontinuously mesoporous structure belonging to the cubic Iad space group. Pore diameters of the silica could be varied over the range 3.6–7.3 nm by varying the synthesis conditions, while maintaining a constant pore wall thickness of 3.7 nm. The polymerization reaction proceeded with heating at 150 °C after initiation with α,α′-azobisisobutyronitrile. The resultant polymeric materials were characterized after template extraction using hydrofluoric acid. Characterization results demonstrated that the polymeric materials retained a cubic Iad mesoporous structure only when the template pore diameters exceeded 5 nm, even if highly crosslinkable monomers, such as divinylbenzene, ethylene glycol dimethacrylate, and trimethylolpropane trimethacrylate, were incorporated. The polymeric structure collapsed unless the template pore diameters were sufficiently larger than the distance between crosslinking points. In addition, structural integrity was maintained only if the mesopore walls were hydrophobically functionalized via silylation. Under optimal replication conditions, the ordered mesoporous polymeric materials exhibited a very narrow pore size distribution and a high specific surface area (619 m2 g−1) that reflected the qualities of the original silica template. Such mesoporous polymeric materials could be functionalized via copolymerization with other functional monomers or via organic reactions. The functionalized mesoporous polymers are suitable for catalytic and adsorption applications because the porous structures feature a high surface area and excellent functional group density.

Design and Determination of New Bimodal Pore Catalyst Structure with Hetero Atom Combination by Inside-Pore Organization of Nano-Particles from Sol

A catalyst support with spatially-connected small pores and large pores, as a distinct bimodal pore structure, has been developed, which has excellent advantages in solid-catalysis reactions because the large pores provide pathways for rapid molecular transportation and the small pores serve a large area of active surface. The obtained ZrO2-SiO2 bimodal support loaded with cobalt was applied in slurry-phase Fischer-Tropsch synthesis (FTS). The bimodal catalyst presented the best reaction performance in slurry-phase FTS as higher reaction rate and lower methane selectivity, because the spatially promotional effect of bimodal structure and the chemically promotional effect of the porous zirconia were available at the same time inside the large pores of original silica gel.

Silica supported single‐walled carbon nanotubes as a modifier in polyethylene composites

AbstractComposites have been made from single‐wall carbon nanotubes in a polyethylene (PE) matrix, in which different methods of preparation were used to disperse the nanotubes. The study includes using either the refined pure nanotubes (P‐NT) as the source, or the original silica supported nanotubes (SS‐NT). SS‐NT contained nanotubes still incorporated in and around the silica as originally grown. Composites were then made by (1) coprecipitation from a suspension of P‐NT or SS‐NT in a PE solution, or (2) by forming a polymerization catalyst from the SS‐NT, and using it to polymerize ethylene, which ruptures and expands the silica as polymer builds up in the pores. Extrusion was also studied as a method of additional dispersion. Nanotubes were found to have a powerful effect on the melt rheology, increasing the low shear viscosity dramatically. Increasing the nanotube concentration also increased the flexural and tensile moduli, decreased the elongation, and increased the electrical conductivity. Consistent trends were observed from all of these diverse properties: SS‐NT had a stronger effect than P‐NT, and within the SS‐NT group the choice of silica type also had a major effect. Polymerization was generally preferred as the method of dispersing the nanotubes. The conductivity, which in some cases was quite high, was found to be pressure sensitive. Conductive NT/PE composites could be molded into films or extruded into other shapes, or comolded with other PE. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Nascent morphology of syndiotactic polystyrene synthesized over silica-supported metallocene catalyst

The nascent morphology of semi-crystalline syndiotactic polystyrene (sPS) polymerized over silica-supported pentamethyl cyclopentadienyl titanium trimethoxide (Cp∗Ti(OCH3)3) catalyst in a liquid slurry polymerization has been investigated under various reaction conditions. The scanning electron microscopic analysis of nascent polymers reveals that sPS molecules grow as long nanofibrils of 30–50nm diameter and X-ray diffraction analysis shows the co-crystalline phases including both sPS and low molecular weight guest molecules of monomer and diluent. The energy dispersive X-ray spectroscopy also shows that the disintegration of silica primary particles occurs during the polymerization as evidenced by the uniform dispersion of silicon and aluminum in a polymer particle. The fibrous growth of the polymer inside a polymer particle leads to the shape replication of the original silica particles.

Effects of manganese oxide–mixed abrasive slurry on the tetraethyl orthosilicate oxide chemical mechanical polishing for planarization of interlayer dielectric film in the multilevel interconnection

In this article, the authors have studied the chemical mechanical polishing (CMP) characteristics of mixed abrasive slurry (MAS) retreated by adding of manganese oxide (MnO2) abrasives within 1:10 diluted silica slurry. The slurry designed for optimal performance should produce reasonable removal rates, acceptable polishing selectivity with respect to the underlying layer, low surface defects after polishing, and good slurry stability. The modified abrasives in MAS are evaluated with respect to their particle size distribution, surface morphology, and CMP performances such as removal rate and nonuniformity. As an experimental result, the authors obtained the comparable slurry characteristics compared to original silica slurry in the viewpoint of high removal rate and low nonuniformity.

Preparation of ordered mesoporous crystalline alumina replicated by mesoporous carbon

Ordered mesoporous alumina with crystalline framework walls has been fabricated using a repeated nanocasting strategy. Mesoporous silica and mesoporous carbon were successively employed as the exotemplates. Constrained by the rigid carbon template structure, the alumina precursor in the channels of the carbon template could be well crystallized by elevating the temperature in an inert atmosphere, yielding γ-Al 2O 3 with ordered mesoporous structure upon the carbon template removal. The resulting alumina sample displays a faithfully negative replication both in the pore arrangement and particle morphology of the carbon template, thus a positive replication of the original silica template. The mean pore sizes of the alumina replicas can be tuned from 4.8 nm to 6.2 nm through choosing mesoporous silicas with different pore sizes as the templates. The ordered structure maintained stable until 750 °C, above which it was significantly destroyed due to the overgrowth of the alumina nanocrystallites and the phase transformation-associated constraint. Besides the hexagonally ordering, a 3D cubic ordered mesoporous alumina with γ-alumina framework walls has also been prepared using cubic CMK-8 as the template.

Preparation of a variety of fluoroalkyl end‐capped N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide oligomer/silica nanocomposites possessing no weight loss characteristic at 800°C

AbstractA variety of fluoroalkyl end‐capped N‐(1,1‐dimethyl‐3‐oxobutyl)acrylamide oligomer [RF‐(DOBAA)n‐ RF]/silica nanocomposites, in which the oligomer contents are 18–96%, were prepared by reactions of the corresponding fluorinated oligomer with tetraethoxysilane and silica nanoparticles under alkaline conditions. Each fluorinated oligomer/silica composite thus obtained is nanometer size‐controlled very fine particles (22–68 nm) possessing a good dispersibility and stability in a variety of solvents including water. Interestingly, the weight loss of RF‐(DOBAA)n‐RF/silica nanocomposites, in which the oligomer contents are 18–72%, were not observed at all even at 800°C, as well as the original silica nanoparticles, although the corresponding sub‐micrometer size‐controlled RF‐ (DOBAA)n‐RF/silica composites (particle size: 359 nm) decomposed completely at 800°C to afford the weight loss in proportion to the content of RF‐(DOBAA)n‐RF oligomer in composites. On the other hand, a slight weight loss of RF‐(DOBAA)n‐RF/silica nanocomposites, in which the oligomer contents are 75–94%, was observed at 800°C compared to that of the original silica nanoparticles. Copyright © 2008 John Wiley & Sons, Ltd.

A study on the chemical mechanical polishing of oxide film using a zirconia (ZrO 2)-mixed abrasive slurry (MAS)

We have studied the chemical mechanical polishing (CMP) characteristics of mixed abrasive slurry (MAS) retreated by adding of zirconium oxide (ZrO 2) abrasives within 1:10 diluted silica slurry. These mixed abrasives in the MAS are evaluated with respect to their particle size distribution, surface morphology, and CMP performance such as removal rate and non-uniformity. As an experimental result, the comparable slurry characteristics when compared to the original silica slurry were obtained from the viewpoint of high removal rate and low non-uniformity for excellent CMP performance. Therefore, our proposed ZrO 2-MAS can be useful to save on the high cost of slurry consumption since we used a 1:10 diluted silica slurry.

Corrugated and nanoporous silica microspheres: synthesis by controlled etching, and improving their chemical adsorption and application in biosensing

Corrugated and nanoporous silica microspheres were synthesized by simple controlled etching of smooth spherical silica microspheres of various sizes with aqueous KCN or KOH solution. The smooth silica microspheres were prepared by the Stober method. The structure and morphology of the etched microspheres were controlled by varying the type and concentration (pH value) of the etchants and the etching time. Upon etching the original silica microspheres with a higher concentration of etchant for a longer time, highly corrugated and hollow silica microspheres were obtained. Shorter etching time and a lower concentration of etchant have resulted in only moderately corrugated microspheres. Comparative studies revealed that the etching with KCN solution proceeds more slowly due to the milder concentration of OH− ions it generates compared to a similar concentration of KOH solution. By optimizing the etching process, silica microspheres with increased adsorption capacity for chemicals such as rhodamine 6G can be obtained. By encapsulating gold nanoparticles and horseradish peroxidase into the etched microspheres having optimized corrugated structures and then casting the resulting nanocomposite materials on a glassy carbon electrode, sensitive electrochemical biosensors for the detection of micromolar concentrations of H2O2 were fabricated. The correlations between the microspheres' size, the etchant's concentration and the etching time with the structures and shapes of the etched microspheres, their adsorption properties to chemicals, and their potential in biosensing application were established. The synthetic method also proved to be applicable in producing corrugated/hollow titania microspheres. This controlled etching synthetic method to produce corrugated metal oxide microspheres is versatile and is useful for controlling nanomaterials' structure and morphology, enhancing their surface area and adsorption capacity of chemicals and drug molecules, as well as making sensitive electrochemical biosensors.

In situ Grafting onto Silica Surface with Epoxidized Natural Rubber via Solid State Method

An in situ solid state grafting reaction between epoxidized natural rubber (ENR) and silica was performed in a Haake internal mixer. Resulting ENR‐grafted silica was characterized by Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) measurements. Based on these results, it was concluded the silanol groups (Si‐OH) of silica caused the ring opening of ENR oxirane rings so that ENR was grafted onto the silica surface. Transmission electron microscopy (TEM) photographs showed ENR‐grafted silica had better dispersibility and smaller aggregates compared with the original silica. Dynamical mechanical analysis (DMA) of vulcanized rubber compounds contained ENR‐grafted silica showed the glass transition temperature (T g) of grafted ENR molecules shifted to higher temperature, from −3°C to 20°C, indicating the mobility of ENR was greatly restricted. As a result, the compounds containing ENR‐grafted silica have higher hysteresis, and can be applied in a much wider field, such as damping materials, tires of racing cars, and so on.

Silicon life forms

A simple chemical reduction process has been used to replicate intricate natural networks of silica at a relatively low temperature. The equally elaborate product is made of silicon — electronics' golden boy. A low-temperature method of reducing silica (SiO2) to silicon (Si) could open up a multitude of new applications for micro-scale structures previously available only as the insulating oxide, such as diatom microshells and self-assembled structures made to order. The method converts silica to silicon at 650 °C — compared with the 2,000 °C or so needed for approaches involving molten silicon — at the same time retaining the original silica architecture. Silicon replicas, like the 14 µm-long example pictured, could find applications as sensors, and in the worlds of electronics, optics and biomedicine.

A fluoroalkyl end-capped N-(1,1-dimethyl-3-oxobutyl)acrylamide oligomer/silica gel nanocomposite with no weight loss even at 800 °C equal to an original silica gel

Fluoroalkyl end-capped N-(1,1-dimethyl-3-oxobutyl)acrylamide oligomer [RF-(DOBAA)n-RF]/silica gel nanocomposite, which was prepared by reaction of the corresponding fluorinated oligomer with tetraethoxysilane and silica gel nanoparticles under alkaline conditions, exhibited no weight loss even at 800 °C equal to the original silica gel, although the corresponding parent RF-(DOBAA)n-RF oligomer was completely degraded at 600 °C. Thermogravimetric analyses/mass spectra of fluorinated nanocomposite showed that this nanocomposite decomposed around 280 °C to afford CO2 and H2O as the major evolved gaseous products including some minor fluoro- and hydrocarbons. X-ray photoelectron spectroscopy analyses also showed that the contents of C, F, and Si atoms in RF-(DOBAA)n-RF/SiO2 nanocomposite after the calcination at 800 °C were similar to those before the calcination. These findings suggest that the evolved gaseous products should be encapsulated quantitatively into nanometer-size-controlled silica matrices to give the fluorinated silica gel nanocomposite with no weight loss even at 800 °C equal to the original silica gel.

TiO 2 coating on silica particles by deposition of sol-gel-derived nanoparticles

TiO 2 was coated on nonporous transparent silica particles of 3.2 μm diameter by deposition of sol-gel-derived TiO 2 nanoparticles. Effects of water concentration, feed rate of titanium tetraisopropoxide (TTIP) solution and amount of supplied TTIP solution on the amount of TiO 2 coated on the silica particles were examined. Scanning electron microscopy observation confirmed that TiO 2 was coated on the silica particles in the form of ‘nanoparticles’ by using this method. Because of that, even though the TiO 2 surface area decreased due to sintering after calcination at high temperature to change the crystalline phase of TiO 2 to the anatase phase, the final surface area was still much larger than that of the original silica particles. The results also showed that as the water concentration increased, the amount of coated TiO 2 decreased. On the other hand, when the amount of supplied TTIP solution increased, the amount of coated TiO 2 increased. It was also confirmed that the feed rate of TTIP solution had little effect on the amount of coated TiO 2. The photocatalytic activities of the resulting TiO 2-coated silica particles were also evaluated by the photocatalytic decomposition of 2,4-dinitrophenol as a model substance. The results showed that the photocatalytic activity of the particles is not a function of the total surface area, but of the surface area in which anatase phase TiO 2 is exposed to the reaction space. The sedimentation velocity of the TiO 2-coated silica particles becomes about 5 orders of magnitude faster than that of the primary particles of the TiO 2. This indicates that the handling of the TiO 2 was also improved considerably by coating on the silica particles.

Synthesis of Mesoporous Magnesium Oxide by CMK-3 Carbon Structure Replication

Periodically ordered mesoporous magnesium oxide was synthesized in a double replication procedure. Mesoporous SBA-15 silica and CMK-3 carbon were successively used as hard structure matrixes. The carbon pore system was infiltrated with Mg(NO3)2, which was then converted to MgO at 573 K; the carbon matrix was finally removed by thermal combustion. The structure of the mesoporous MgO corresponds to that of the original SBA-15 silica. The products consist of hexagonally arranged cylindrical mesopores and crystalline pore walls. The efficiency of the replication series was studied by variation of the infiltration method and comprehensive pore size analysis of all involved mesoporous materials. The in situ formation of MgO inside the CMK-3 carbon pore system was monitored by thermal analysis. Postsynthetic treatment of the products at 823 K in a vacuum prior to removal of the carbon matrix was found to improve the crystallinity but to diminish the periodic order of the pore system.