Facile synthesis of ordered large-pore mesoporous silica thin film with Im3m symmetry using n-butanol as the cosurfactant

A facile synthesis route to ordered large-pore (10.7 nm) mesoporous silica film with the cubic Im3m mesostructure is reported in a TEOS–F127–BuOH–HCl–H₂O system through dip-coating method. Characterization by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen sorption reveals that the obtain mesoporous silica material possessed high surface area and large pore diameter. A relative comparison between the mesoporous silica films synthesized with and without BuOH is also presented. A reasonable formation mechanism of the large-pore mesoporous silica film is depicted in this work.     

Synthesis of bulky mesoporous silica (FSM) by hydrothermal hot-pressing method

In this study, we successfully synthesized the bulk of dense mesoporous silica (FSM) bodies by a short-term hydrothermal hot-pressing (HHP) method. It was thought that these dense bodies were achieved by solution/precipitation mechanism during HHP. Bulk pieces with the dimension in the range of centimeters in diameter possessed a high surface area of over 1000 m²/g and sharp distribution of mesopores with an average diameter of approximately 2.4 nm. This successful synthesis of bulky mesoporous silica will expand the capabilities of application to various fields, for example, gas separation (CO₂ and H₂ etc.) and catalysis.     

In situ studies of order–disorder phenomena in the synthesis of mesoporous silica

The initial hydrolysis of a silicon alkoxide in the presence of a suitable structural directing agent (template) so as to form a mesoporous silica powder exhibiting long-range hexagonal ordering was monitored using in situ XRD (X-ray diffraction), SAXS (small angle X-ray scattering) and SANS (small angle neutron scattering). The non-ionic triblock copolymer P123 (EO₂₀PO₆₉EO₂₀) was employed as the organic templating agent and tetramethoxysilane (TMOS) was used as the silica source in the presence of a water/acid catalyst. The synthesis method described herein is based around a high volume concentration ratio of surfactant to TMOS. The formation of a long-range mesoscopically ordered organic–inorganic hybrid that could be subsequently calcined to form a hexagonally structured mesoporous oxide material was monitored over 6 days using the characteristic (1 0 0) reflection. It was seen that during this ‘maturation’ period the reaction is not progressive and SANS and SAXS data together with XRD experiments show that there is an initial kinetically rapid organic ordering process which provides a template for the formation of an ordered metastable organic–inorganic oxide phase which then becomes progressively more disordered before a final kinetically slow stable long-range ordered phase is formed. Discussions of the origin of the unexpected order–disorder phenomena are made.     

Crystallization of amorphous Al2O3–SiO2 precursors doped with nickel

The crystallization of amorphous diphasic Al₂O₃–SiO₂ precursors doped with nickel has been studied by differential scanning calorimetry (DSC), XRD diffraction (XRD) and scanning and transmission electron microscopy (SEM, TEM) equipped with energy dispersive X-ray spectroscopy (EDS). Diphasic gels with constant atomic ratio (Al + Ni)/Si = 3:1, where 0, 1, 2 and 3 at.% of aluminum were replaced by nickel, have been prepared by hydrolyzing of TEOS in aqueous solution of aluminum nitrate. Crystallization of Ni-containing γ-Al₂O₃ preceded the crystallization of Al–Si spinel. Activation energy of 603 ± 16 kJ mol⁻¹ for crystallization of Ni-containing γ-Al₂O₃ was obtained in non-isothermal conditions. Ni-incorporated γ-Al₂O₃ transforms gradually with the temperature increase into Ni aluminate spinel, while Al–Si spinel reacts with amorphous silica forming mullite at about 1200 °C. Rietveld structure refinement of phases present in the samples annealed at 1600 °C and SEM-EDS and TEM-EDS analyses of related phases have shown that nickel predominantly crystallizes as NiAl₂O₄, but small amount of nickel is incorporated in mullite structure, as well as, dissolved in the glassy phase of the system.     

Synthesis of hybrid mesoporous spheres using the chitosan as template

Hybrid mesoporous spheres of Al and Si oxides were synthesized for the mixture of organic material (chitosan) with inorganic material (aluminum and silicon hydroxide). It was observed that chitosan with larger polymerization degree, resulted in a larger mechanical resistance of the spheres. The oxides were characterized by the following: Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), differential scanning calorimetry (DSC), as well as, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and adsorption isotherms of N₂ (BET). Highly uniform oxide sphere diameters were obtained (average of 1.0 mm). The results of the adsorption isotherms indicated that the material is mesoporous. The surface area of the materials ranged between 620 and 245 m²/g, and the pore volume varied between 0.82 and 0.28 cm³/g, depending on the molar ratio of the organic and inorganic materials.     

Preparation and characterization of nickel based catalysts on silica,alumina and titania obtained by sol–gel method

This work reports the investigation of the characteristics of catalysts produced by the sol gel process. Our analysis focuses on the properties related to heterogeneous catalysis, such as methane steam reforming, dry reforming, hydrogenation of organic compositions. Alumina, silica and titania based materials doped with Ni were synthesized. The characterization techniques used were: temperature programmed reduction, thermogravimetric analysis, specific surface area and X-ray powder diffraction. The specific surface area values obey the following sequence: Ni–SiO₂ > Ni–Al₂O₃ > Ni–TiO₂. The temperature programmed reduction indicated that in the Ni–SiO₂ sample, the nickel oxide is present in two different forms on the surface; the Ni–Al₂O₃ material presented one peak at high temperature, suggesting the presence of a nickel aluminate form. However, Ni–TiO₂ did not present reduction peaks. The thermogravimetric analysis, which was performed under inert atmosphere, showed the decomposition of the organic residues adsorbed on surface. The X-ray powder diffraction patterns of calcined materials showed two crystalline forms for TiO₂ in Ni–TiO₂ rutile and anatase. In Ni–Al₂O₃, crystalline areas composed of α-Al₂O₃, γ-Al₂O₃ and NiO were observed and finally for Ni–SiO₂, amorphous areas and NiO were found.     

Polymer nano-encapsulation of templated mesoporous silica monoliths with improved mechanical properties

Macroporous (1–5 μm) monolithic silica aerogels consisting of both random but also ordered mesoporous walls have been synthesized via an acid-catalyzed sol–gel process from tetramethoxysilane (TMOS) using a triblock co-polymer (Pluronic P123) as a structure-directing agent and 1,3,5-trimethylbenzene (TMB) as a micelle-swelling reagent. Pluronic P123 was removed by Soxhlet extraction, and materials in monolithic form were obtained by extracting the pore filling solvent with liquid CO₂, which eventually was taken out supercritically. Although these monoliths are more robust than base-catalyzed silica aerogels of similar density, nevertheless, the mechanical properties can be improved dramatically by letting an aliphatic di-isocyanate (Desmodur N3200) react with the silanols on the macro- and mesoporous surfaces. As it turns out, the polymer fills the mesopores and coats conformally the macropores of templated samples, so that BET surface areas decrease dramatically, from 550–620 m² g^?1 to <5 m² g^?1. By comparison, polymer nano-encapsulation of non-templated acid-catalyzed aerogels preserves a large fraction of their mesoporous surface area, and BET values decrease from 714 m² g^?1 to 109 m² g^?1. Finally, since polymer nano-encapsulation preserves the macroscopic physical dimensions of the monoliths before drying, comparative analysis of the physical dimensions against XRD data of native versus polymer nano-encapsulated samples provides evidence that upon drying macropores (micron size regime) shrink less than mesopores (nanometer size regime).     

Synthesis of Pt-containing mesoporous silica using Pt precursor as a pore-forming agent

We synthesized Pt nanoparticle-containing mesoporous silica in a one-pot process using tetraammineplatinum(II) hydroxide (TPH) precursor as a pore-forming agent and silica nanospheres as a silica source. The TPH precursor was added into as-prepared colloidal silica sol with silica nanospheres (SN) of about 8 nm in particle diameter, to obtain the SN–TPH sol. During drying process of the SN–TPH sol, an amorphous SN–TPH nanocomposite was formed via hydrogen-bonding interaction between silanol groups and amine groups of the TPH precursor. The hydrogen-bonding interaction was confirmed by thermal gravimetry and differential thermal analysis (TG–DTA) profiles and Fourier transform infrared (FTIR) spectra. Using the TPH precursor as a pore-forming agent, incorporation of the Pt nanoparticles into the mesoporous silica can be simultaneously achieved with the synthesis of the mesoporous silica in a one-pot process. In addition, Pt nanoparticle size and pore diameter of the mesoporous Pt/silica were simultaneously controlled by simply varying the concentration of the TPH precursor. The pore diameter of the mesoporous silica was easily controlled from 3.2 nm to 6.5 nm with an increase in the TPH concentration.     

Positron annihilation study of pore size in ordered SBA-15

Ordered mesoporous materials such as SBA-15 possess a network of channels and pores with a well-defined size in the nanoscale range (2–50 nm). This particular pore architecture makes them suitable candidates for a variety of applications. Different techniques have been used to measure pore diameters. PALS (positron annihilation lifetime spectroscopy) nanoprobe has been used to investigate free volume in several materials, including mesoporous silica. PALS can be used to find out if the micropore and mesopore structures of samples prepared under different experimental conditions are different. Indeed, considering that the pores present a cylindrical shape, an equation was developed that uses specific pore volumes, theoretical density, and specific surface measurements to evaluate structural connectivity. Our goal is to determine the influence of aging temperature on the porous structure of SBA-15 samples. The structural evolution was studied by PALS, small-angle X-ray (SAXS), N₂ adsorption desorption isotherms and computational modeling to evaluate connectivity. The variation of aging temperature changes the pore structure, indicating the presence of micropores and connections between mesopores. Materials aged at high temperatures present the lowest microporosity.     

Influence of synthesis temperature on the structural characteristics of mesoporous silica

The characteristics of mesoporous silica prepared at different temperatures and the behavior of this system relating to the microencapsulation of a model drug were investigated. The preparation of mesoporous materials was initiated with the dissolution of a surfactant in distilled water and strong acid medium. After this, tetraethyl orthosilicate was added under agitation. The mixture was heated for 24 h at the synthesis temperature (60 °C, 80 °C, 100 °C and 130 °C) under static conditions. The surfactant was removed by calcination, which was carried out by increasing the temperature to 550 °C for 5 h. Atenolol was used as a model drug to study the kinetics of drug delivery. It could be observed that aging materials at higher temperatures presents no microporosity, and this influences the control of the release of the model drug.     

Synthesis and characterization of mesoporous,tungsten-containing molecular sieve composites

Mesoporous, tungsten-containing molecular sieve (W-SBA-15) composites were successfully synthesized via one-step hydrothermal processing using tetraethyl orthosilicate (TEOS) as the silica precursor, sodium tungstate as the tungsten precursor, and pluronic P123 triblock polymer (EO₂₀PO₇₀EO₂₀, M_av = 5800) as a structure-directing reagent. The influence of various synthesis factors, such as TEOS/sodium tungstate (Si/W) molar ratios, stirring solution temperatures, TEOS pre-hydrolysis time, and crystallization temperatures, on the structure of the W-SBA-15 composite were investigated. The prepared materials were characterized by using X-ray diffraction (XRD), infrared spectroscopy (IR), diffuse reflectance ultraviolet–visible spectroscopy (DR UV–vis), scanning electron microscopy (SEM), and nitrogen adsorption–desorption measurements. The results showed that all the W-SBA-15 composite materials retained the mesopore structure of SBA-15 and the tungsten oxide species successfully substituted silica in the framework.     

Preparation of mesoporous silicas using food grade emulsifiers and its application for enzyme supports

A novel mesoporous silica (TMPS) was synthesized via self-assembly using a myristic acid ester of pentaglycerol. The ester is obtained from catalytic esterification and it is commercially available as a food grade emulsifier. TMPS material was employed for preparation of a biocatalyst in order to examine the ability as an enzyme support in comparison with the other mesoporous silica materials having a channel or a cage-like pore system. The used TMPS materials possessed the interconnected channel-like pore system with the pore sizes of 9.2, 12, and 16 nm. The materials successfully entrapped lipase into their mesopores with the high loadings. The resultant lipase/TMPS conjugates functioned as the biocatalyst for hydrolysis of p-nitrophenyl propionate (p-NPP), having the higher activity than those of the used mesoporous silica conjugates. The high activities were ascribed to the textural properties such as the small particle length, large pore size and the three-dimensional pore connectivity that permit the accessibility of p-NPP to the immobilized lipases during the reactions. Consequently, we concluded that TMPS materials are of the suitable mesoporous support for the enzymes.     

Design and synthesis of large-pore p6mm mesoporus zirconia thin films templated by a novel block copolymer

A novel poly(butadiene-b-ethylene oxide) (PB-PEO) block copolymer was employed as the structure-directing agent for the preparation of large-pore, mesoporous for zirconia with two-dimensional (2D) hexagonal (p6mm) mesostructure through evaporation-induced self-assembly (EISA) approach. The presented materials, calcined at 400 °C and 500 °C, were characterized in detail by X-ray diffraction, transmission electron microscopy, and nitrogen sorption. The results showed that the mesoporous zirconia possesses a large-pore diameter, high BET surface area, and large-porosity. A probable formation mechanism was also presented in this work.     

Preparation and characterization of amorphous silica nanowires from natural chrysotile

By chemical dispersing and acid leaching, silica nanowires have been prepared from the natural mineral, chrysotile. X-ray fluorescence analysis (XRF), thermogravimetric analysis and differential thermogravimetric analysis (TGA–DTA), powder X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize the silica nanowires. The results indicate that the chemical composition of the silica nanowires is SiO_1.8 · 0.6H₂O, and although the silica is amorphous, its structure is regular to some extent. The structural unit of the silica nanowires is the [SiO₄] tetrahedron and six-member silicon–oxygen ring with the tetrahedral positioned alternately up and down in the six-member ring. The silica nanowires are well-dispersed and have cylindrical morphology and smooth surface, with lengths over 10 μm and diameters of 30–60 nm.     

An alumina mat with a nano microstructure prepared by centrifugal spinning method

Ceramic fiber products specially alumina mat because of low thermal conductivity and high melting point are used as high temperature insulating materials. Alumina has so high melting point (T_m > 2040 °C) that its mat can be produced through sol–gel method. In this research alumina mat has been manufactured by sol–gel spinning method using our laboratory-designed centrifugal spinneret. The desired viscosity of sol for spinning is 150 P. Phase transformation of the product begins at 600 °C and there is not any amorphous phase at 800 °C and theta alumina (θ-Al₂O₃) is the main phase. In this work, transformation of transitional phase to alpha alumina (α-Al₂O₃) takes place from 1000 °C to 1200 °C. The optimum percent of silica in alumina mat is 4 wt%. Fibers constitute network structure that their average diameter is about 10 μm and contains very fine grains (100 nm). The silica percent concerning the limits of this study (<10 wt%) does not effect on fiber diameter, but grain size decreases from about 200 nm to less than 100 nm while increasing silica percent.     

Preparation of nickel oxide– and nickel–silica nanocomposites by spray pyrolysis

Nickel oxide–silica and nickel–silica nanocomposites were prepared by spray pyrolysis of aqueous sols of silica nanoparticles containing nickel nitrate hexahydrate, without and with ethanol, respectively. During pyrolysis, the silica nanoparticles were restructured, losing their identities, while the nickel oxide or nickel particles in the composites grew by coalescence and sintering. Compactness of the composites, higher in nickel–silica composites than their counterpart nickel oxide, increased with the temperature of preparation and the concentration of nickel nitrate. Nickel always formed larger crystallites than its counterpart nickel oxide, due to its higher sintering rate. At 500 °C, the crystallite growths of nickel oxide and nickel were inhibited by the low sintering rate and the formation of nickel intermediates, respectively, while at 1000 °C their phase-pure crystallites continuously grew with the increase in the nitrate concentration.     

Stabilization of dopamine in nanosilica sol–gel matrix to be used as a controlled drug delivery system

Sol–gel silica reservoirs were synthesized using tetraethoxysilane and functionalized with OH groups to stabilize dopamine into a ceramic matrix. The synthesis was made in air and N₂ atmosphere. The dopamine–silica reservoirs were analyzed by FTIR spectroscopy, DTA–TGA and BET techniques. Nanostructured materials with a high specific surface area (500 m²/g) and a mean pore size between 40 and 152 Å were obtained. It was found that dopamine is entrapped and stabilized into the SiO₂–OH matrix when the reservoirs are synthesized in N₂ atmosphere.     

Preparation of spherical silica particles in reverse micro emulsions using silicon tetrachloride as precursor

Silica powders with spherical shape have been prepared by precipitation reaction of silicon tetrachloride with de-ionized water in the micro emulsion system. Two kinds of micro emulsion systems were used. One was cyclohexane/polyoxyethylene nonyl phenyl ether (NP-5)/de-ionized water system, and the other was heptane e/NP-5/de-ionized water. Transmission electron microscope (TEM), thermo gravimetric analysis (TG), X-ray diffraction (XRD) patterns, infrared spectrum (IR) were employed to characterize the micro structure, shape, thermal properties, phase, and molecular structure of the obtained silica. The results show that silica featuring spherical shapes and uniform characteristics was yielded by the precipitation method using silicon tetrachloride with de-ionized water in the micro emulsion system. A decreased tendency for silica particles agglomeration could be achieved by using lower mole ratio of water and SiCl₄, and the particle size was 5.74 nm when mole ratio of water and SiCl₄ was 4 in NP-5/cyclohexane/deionized water micro emulsion system. The silica prepared by these two systems was amorphous silica and thermally stable after 600 °C treatment. The structures of silica prepared from the different micro emulsion systems were similar; organic molecules can be removed completely from the silica through 600 °C treatment.     

Adjusting the porous and structural properties of mesoporous silica by the addition of organic modifiers

The effects of the organic modifiers 2-cyanoethyltriethoxysilane and 3-aminopropyltriethoxysilane on the porous properties of silicates synthesised by co-condensation with tetraethyl orthosilicate were investigated. Materials were synthesised in aqueous solutions of cetyltrimethylammonium bromide or n-dodecylamine surfactants. Preparations using cetyltrimethylammonium bromide and sodium hydroxide gave MCM-48, with an average pore diameter of 25 Å, while addition of 10 mol% (of total silica) 2-cyanoethyltriethoxysilane improved the mesoporosity characteristics; the modified preparation gave a more intense X-ray diffraction pattern confirming a more ordered structure with a greater volume of regular mesopores. Disordered materials with pores 145 Å in diameter were formed using 2-cyanoethyltriethoxysilane modifier and ammonia as base. All preparations incorporating 3-aminopropyltriethoxysilane modifier were disordered and microporous. For silicates synthesised using n-dodecylamine surfactant, mesopores with diameter 118 Å were formed using 2-cyanoethyltriethoxysilane while preparations with 3-aminopropyltriethoxysilane and in the absence of a modifier were microporous. The particle sizes of the silicates displayed a clear correlation with the pore diameters: microporous silicates were 0.5–1 μm in particle diameter, MCM-48 phase (25/27 Å) were 1–2 μm, while relatively large mesoporous materials (>100 Å) had particle dimensions 10–100 μm.     

Microstructural and photocatalytic properties of sol–gel-derived vanadium-doped mesoporous titanium dioxide nanoparticles

The vanadium (V)-doped mesoporous titanium dioxide (TiO₂) nanoparticles at low V/Ti ratios ranging from 0 to 2 wt% were prepared using hydrolytic sol–gel method in the presence of tri-block copolymer Pluronic F127. The microstructures of TiO₂ in terms of morphology, crystallization, chemical states of species, surface area, and band gap were characterized by SEM, TEM, XRPD, XPS, surface area analyzer, and UV–Vis spectrophotometer, respectively. SEM images showed that the V-doped TiO₂ nanoparticles were porous structures, and the surface areas and pore sizes ranged from 86 ± 9 to 96 ± 15 m²/g and from 12 ± 4 to 15 ± 2 nm, respectively. The XRPD patterns indicated that V-doped mesoporous TiO₂ after calcination at 500 °C was mainly anatase phase, and the crystallite sizes were in the range 14–16 nm, which are consistent with the results obtained from SEM images. XPS spectra and HRTEM images showed that vanadia was doped both on the surface and in the lattice of anatase TiO₂. A slight red-shift in wavelength absorption was observed when V/Ti ratio increased from 0 to 2 wt%. Methylene blue (MB) was further used as the target compound to examine the photocatalytic activity of V-doped mesoporous TiO₂ nanocatalysts under illumination of solar simulator or UV light. Addition of vanadium ions slightly decreased the photocatalytic activity of TiO₂ toward the decolorization of MB under the illumination of UV light at 305 nm. However, a 1.6–1.8 times increase in rate constants for MB photodegradation was observed when 0.5–1.0 wt% V-doped TiO₂ was illuminated with sunlight at AM 1.5.