Highly porous titania network: fabrication,characterization and photocatalytic activity

Highly porous titania network (CPTN) has been prepared using the protein entrapped cellulose gel as structural template via a template-assisted sol–gel process. The key point toward highly porous titania network lies in the entrapped proteins with template. To elucidate this, the effect of protein loading of template on the structure of final material was investigated. It reveals that high protein loading in cellulose gel gives rise to both large macroporosity and large surface area of final titania network. Specially, highly porous titania network is possessed of bimodal pore system and withstands high compressive pressure over 19 MPa. The highly porous titania network is found to have higher catalytic activity for the photodegradation of methylene blue than its counterpart of commercial P25 and microporous titania one (CTN) that derived from the pure cellulose gel. As a result, the macropores of titania network serve as the leading role in improving the photocatalytic activity. The proposed method might be applied to fabricate other inorganic network with desired macropore structure.     

The influence of nanodisperse iron(III) oxide on the morphology of microsized alumina fibers

The influence of fine-disperse iron oxide particles on the structure of alumina fibers prepared via the template synthesis has been studied. The template (fibers of bleached cotton cellulose) has been impregnated with mixed aqueous dispersions of aluminum and iron(III) hydroxides prepared via the sol–gel route. Thermal treatment of the precursor has afforded alumina ceramic fibers with average diameter of 3–10 µm containing uniformly distributed iron(III) oxide nanoparticles at the surface. Increase of the iron(III) oxide nanoparticles concentration has deteriorated the texture properties of the product.     

Deposition of silver nanoparticles into porous system of sol–gel silica monoliths and properties of silver/porous silica composites

Porous monolithic gels based on silica with pore size from 16 nm to 3–5 μm have been synthesized using sol–gel technology. Parameters of porous structure are determined by the components molar ratio in the reaction mixture. The reduction processes of silver ions by formamide in the synthesized porous gel were studied. It has been shown that at the initial stage of the reaction, silver particles with size up to 10 nm are formed in the absence of any stabilizers. The composites Ag/SiO₂ were synthesized by means of the threefold impregnation of porous monoliths using the solution of silver nitrate in the mixture of methanol and formamide. Their catalytic activity in the CO oxidation was studied. It was discovered that after activation in oxygen and hydrogen the samples display a low temperature activity, which depends on the number of Si–O-nonbridging oxygen groups on the surface of silica porous monoliths.     

Template-free sol–gel synthesis of high surface area mesoporous silica based catalysts for esterification of di-carboxylic acids

High surface area mesoporous silica based catalysts have been prepared by a simple hydrolysis/sol–gel process without using any organic template and hydrothermal treatment. A controlled hydrolysis of ethyl silicate-40, an industrial bulk chemical, as a silica precursor, resulted in the formation of very high surface area (719 m²/g) mesoporous (pore size 67 Å and pore volume 1.19 cc/g) silica. The formation of mesoporous silica has been correlated with the polymeric nature of the ethyl silicate-40 silica precursor which on hydrolysis and further condensation forms long chain silica species which hinders the formation of a close condensed structure thus creating larger pores resulting in the formation of high surface mesoporous silica. Ethyl silicate-40 was used further for preparing a solid acid catalyst by supporting molybdenum oxide nanoparticles on mesoporous silica by a simple hydrolysis sol–gel synthesis procedure. The catalysts showed very high acidity as determined by NH₃-TPD with the presence of Lewis as well as Brønsted acidity. These catalysts showed very high catalytic activity for esterification; a typical acid catalyzed organic transformation of various mono- and di-carboxylic acids with a range of alcohols. The in situ formed silicomolybdic acid heteropoly-anion species during the catalytic reactions were found to be catalytically active species for these reactions. Ethyl silicate-40, an industrial bulk silica precursor, has shown a good potential for its use as a silica precursor for the preparation of mesoporous silica based heterogeneous catalysts on a larger scale at a lower cost.     

Sol–gel synthesis of porous inorganic materials using “core–shell” latex particles as templates

Here we report on the sol–gel synthesis of porous inorganic materials based on manganese, molybdenum, and tungsten compounds using the “core–shell” siloxane-acrylate latex as a template. The chemical composition and structural characteristics of the materials obtained have been investigated. It was shown that temperature conditions and gaseous media composition during the template destruction controlled the composition and structure of porous materials. To obtain porous inorganic materials for catalytic applications, the “core–shell” latex template was preliminarily functionalized by gold and palladium nanoparticles obtained by thermal reduction of noble metal ions-precursors in a polycarboxylic “shell”. Upon the template removal, noble metals nanoparticles of a size of dozens of nanometers were homogeneously distributed in the material porous structure. The evaluation of the catalytic activity of macroporous manganese, tungsten, and molybdenum oxides under the conditions of liquid phase catalytic oxidation of organic dyes has been performed. The prospects of employing macroporous oxide systems with immobilized nanoparticles of noble metals in the processes of hydrothermal oxidation of radionuclide organic complexes in radioactive waste decontamination have been demonstrated.     

Sol–gel synthesis of silica containers using a corrosion inhibitor,catamine AB,as a templating agent

It has been shown that silica container particles containing a large amount (~1 g/g of SiO₂) of a corrosion inhibitor, catamine AB, can be obtained, with the inhibitor being loaded at the stage of the sol–gel synthesis of the particles by using catamine micelles as a template. Being introduced into an H₂S-containing aggressive aqueous medium, such containers protect rather efficiently carbon steel from hydrogen-sulfide corrosion and hydrogenation. The protection effect seems to be realized via not only the release (desorption) of catamine AB molecules from the containers, but also the adsorption of the products of gradual dissolution of silica matrix on the surface of metal being protected.     

Fabrication of hierarchically porous silica nanospheres through sol–gel process and pseudomorphic transformation

Hierarchically porous silica nanospheres with well-defined morphology and uniform particle size had been synthesized through a multistep sol–gel method combined with pseudomorphic transformation in the presence of polyvinylpyrrolidone (PVP) and cetyltrimethylammoium bromide (CTAB) as dual template. The prepared materials were characterized by small-angle X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and nitrogen physical adsorption techniques. The preparation process and the origin of hierarchical structure were also investigated. It had been shown that the hierarchical structure of synthesized materials comprises wormlike framework mesopores with diameters of about 3 nm and bubble-like pores with diameters of 20–30 nm. CTAB and PVP behave as dual-template and are responsible for the formation of the mesopores and big pores, respectively. Not only the porous structure, but also the morphology and particle size of hierarchical materials can be adjusted by controlling the addition of PVP. In addition, the formation process of hierarchically porous silica was investigated by transmission electron microscopy, FT-IR spectra and thermo-gravimetric curves and a possible synthetic mechanism had been proposed.     

Sol–gel synthesis of mesostructured SiO<Subscript>2</Subscript> containers using vesicles of hydrolyzable bioactive gemini surfactant as a template

Peculiarities of the sol–gel synthesis of SiO₂ container particles using vesicles of a hydrolyzable bactericidal gemini surfactant, decamethoxin, as a template have been studied.     

Hierarchical meso–macroporous bioglass for bone tissue engineering

A novel meso–macroporous bioglass has been synthesized based on a sol–gel technique. This method used mushroom stalk as macroporous template and EO₂₀PO₇₀EO₂₀ as the mesoporous template. The final sample has copied the macroporous structure of the plant template, precisely. Ibuprofen was used as the model drug, and the drug loading and release test indicated the loading amount of the sample could reach 33.59 wt% and the releasing amount closed 75 wt% after 48 h. The excellent biomineralization and bioactive are also confirmed in vitro tests. It takes only 4 h to induce the formation of hydroxyapatite. Notably, the biocompatibility assessment confirmed that the obtained materials presented good biocompatibility and the enhanced adherence of HeLa cells. The exquisite mesoporous structure of the sample would be propitious to storage and transport guest molecule, making the hierarchical porous materials have more distinctive performance and application on bone tissue regeneration and drug delivery, etc.     

Morphological,mechanical, and in vitro cytocompatibility analysis of poly(vinyl alcohol)–silica glass hybrid scaffolds reinforced with cellulose nanocrystals

Cellulose nanocrystal-reinforced poly(vinyl alcohol)/silica glass hybrid scaffolds were fabricated using the freeze-drying method. In this study, we develop molecular-level-based hybrid scaffolds with possible bioactivity behavior by adding silica sol–gel. The results showed a highly porous structure and a significant improvement in mechanical performance (stiffness) of hybrid scaffolds with an increased content of cellulose nanocrystals followed by the addition of silica-based bioactive glass. In vitro cell study with MC3T3-E1 cells on hybrid scaffolds for 1 and 3 days revealed good cell adhesion and growth. Thus, the obtained hybrid scaffold may be a competitive candidate for bone tissue engineering applications.     

Dependence of SBA-15 formation on the block copolymer concentration in the course of synthesis with precursor containing ethylene glycol residues

The formation of silica is governed by two parallel processes triggered by the addition of a precursor to a solution of P123 block copolymer. One process is sol–gel synthesis, while the other is the transformation of an initial micellar phase consisting of spherical micelles of P123 into a hexagonal mesophase, which serves as a template. The gelation of the reaction mixture terminates all transformations, thus making it possible to examine the phase state of the block copolymer at the moment of the sol–gel transition. The systematic study of systems with different P123 concentrations has shown that the structure, morphology, and porosity of the material is determined by the ratio between the rates of the aforementioned processes. A material with the structure of SBA-15 containing hexagonally packed cylindrical mesopores is formed at a block copolymer content of 10 wt %. As the P123 concentration is reduced, the rate of the transformations of its structures decreases relative to the rate of the sol–gel process. Analysis of electron micrographs has revealed that the material being formed contains, initially, irregular short rodlike mesopores rather than cylindrical ones; then, as the P123 concentration is further decreased, amorphous silica arises in the material. The role of their templates is played by intermediate structures formed during the transformation of the P123 micellar phase into the hexagonal mesophase. Advantages of the SBA-15 synthesis with the precurosr containing ethylene glycol residues are the good reproducibility, one-pot procedure, no addition of acid and organic solvent or heating, and the formation of bimodal monolithic material containing both meso- and macropores.     

Syntheses of ordered mesoporous silica by new hybrid template

Ordered mesoporous silica with macroscopic shape has been prepared with a hybrid template of gel and poly(ethylene oxide)₁₀₆–poly(propylene oxide)₇₀–poly(ethylene oxide)₁₀₆ (pluronic F127) surfactant, where both water-soluble agar gel and pluronic F127 significantly affect the mesoporous structure and morphology of silica. The thermal analysis revealed the noticeable interaction between agar and F127, which contributes to the formation of homogenous hybrid template. In the hybrid template, agar gel contributed to the maintenance of morphology structure, while F127 was responsible for the formation of ordered porous structure in silica solids.     

Correlation between gelation time, structure and texture of low-doped silica gels

It is shown how the properties of a porous silica xerogel prepared using a classical sol-gel synthesis can be fine-tuned by a minor modification of the composition. The addition of a doping cation (Cu(2+), Ca(2+), Na(+)) in trace quantities in the silica sol was found to exert a dramatic effect at all stages of material preparation. An investigation of both liquid and solid phases is presented, making it possible to highlight strong correlations. The time-resolved speciation of Si-containing moieties in the sol was found to be an indication of the structuration of the gel, which was reflected by the porosity and by the molecular structure of the resulting porous material. Based on a careful comparison of several slightly doped silica gels, a model is proposed which makes it possible to predict the structure and the texture of a silica gel from data recorded early in the liquid phase.     

Evaluation of a novel silica-supported sol–gel sorbent prepared by a surface molecular imprinting technique for the selective separation of estazolam from human plasma

A molecular imprinting polymer (MIP) based on surface modification of silica gel was prepared via the sol–gel process with 3-aminopropyltriethoxysilane and phenyltrimethoxysilane as functional monomers, and estazolam as the template. The imprinted silica sorbent was characterized by Fourier Transform Infrared Spectroscopy, surface elemental analysis, and scanning electron microscopy (SEM). An MIP of agglomerated nano-particles with multi-pores was grafted onto the surface of the silica gel after hydrolytic condensation of the siloxane. The imprinted silica sorbent was used for solid phase extraction (SPE). Using water as loading solvent, the extraction efficiency for estazolam was higher compared to the use of an organic solvent. The imprinted silica sorbent was selective not only for the template, but also for the analogue. Compared to C₁₈-SPE and liquid–liquid extraction, the MIP-SPE was the most feasible technique for extraction of estazolam from human plasma; up to 98.7?±?1.2% recovery was achieved.     

A new method for loading mesoporous silica nanoparticles with drugs: Sol–gel synthesis using drug micelles as a template

It has been shown that mesoporous nanocontainers from SiO₂ may be obtained by the sol–gel synthesis using drug (Miramistin) micelles as a template. The nanocontainers resulting from the combination of the stages of their synthesis and loading are characterized by a very high content of the drug (no less than 0.9 g per 1 g of SiO₂). The kinetics of Miramistin desorption from the mesoporous particles into an aqueous medium has been studied under static and quasi-dynamic conditions. The desorption has been shown to rather strongly depend on pH. Possible mechanisms of the desorption process have been discussed.     

Synthesis,structure, and morphology of polymer–silica hybrid nanocomposites based on hydroxyethyl methacrylate

Two types of polymer–silica nanocomposites have been prepared by undergoing free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) either in the presence of HEMA-functionalized SiO₂ nanoparticles (Type 1) or during the simultaneous in situ growing of the silica phase through the acid-catalyzed sol–gel polymerization of tetraethoxysilane (TEOS) (Type 2). Relationships between synthesis conditions, chemical structure, and resulting morphology have been studied. Type 1 systems exhibit a classical particle-matrix morphology, but where particles tend to form aggregates. Type 2 systems possess a finer morphology characterized by a very open mass-fractal silicate structure, which is believed to be bicontinuous with the organic phase at a molecular level. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3172–3187, 1999     

General and Facile Syntheses of Metal Silicate Porous Hollow Nanostructures

Porous hollow nanostructures have attracted intensive interest owing to their unique structure and promising applications in various fields. A facile hydrothermal synthesis has been developed to prepare porous hollow nanostructures of silicate materials through a sacrificial‐templating process. The key factors, such as the concentration of the free metal cation and the alkalinity of the solution, are discussed. Porous hollow nanostructures of magnesium silicate, nickel silicate, and iron silicate have been successfully prepared by using SiO₂ spheres as the template, as well as a silicon source. Several yolk–shell structures have also been fabricated by a similar process that uses silica‐coated composite particles as a template. As‐prepared mesoporous magnesium silicate hollow spheres showed an excellent ability to remove Pb²⁺ ions in water treatment owing to their large specific surface and unique structures.     

Sol–Gel Synthesis of Membrane Mo<Subscript>2</Subscript>C/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalysts with Different Architectures and Their Catalytic Activity in the Reaction of Carbon Dioxide Conversion of Methane

The methods of synthesis of composite membrane catalysts based on Mо₂C and Al₂O₃ support by a sol–gel method were developed. The samples of membrane catalysts with different architectures were developed. The difference in the catalytic activity of membrane catalysts in carbon dioxide conversion of methane depending on the porous structure and morphology of the catalytic layer was studied.     

Transparent conducting Sn:ZnO films deposited from nanoparticles

Homogeneous transparent conducting Sn:ZnO films on fused silica substrates were prepared by dip-coating from nanoparticle dispersions, while the nanocrystalline Sn:ZnO particles with different dopant concentrations were synthesized by microwave-assisted non-aqueous sol–gel process using Sn(IV) tert-butoxide and Zn(II) acetate as precursors and benzyl alcohol as solvent. The dopant concentration had a great impact on the electrical properties of the films. A minimum resistivity of 20.3 Ω cm was obtained for a porous Sn:ZnO film with initial Sn concentration of 7.5 mol% after annealing in air and post-annealing in N₂ at 600 °C. The resistivity of this porous film could further be reduced to 2.6 and 0.6 Ω cm after densified in Sn:ZnO and Al:ZnO reaction solution, respectively. The average optical transmittance of a 400-nm-thick Sn:ZnO film densified with Sn:ZnO after the two annealing steps was 91%.     

Effect of Colloidal Silica on the Porous Structure Parameters of Microspheres Prepared from Urea Formaldehyde Resin and Silica Gel

The paper concerns studies of the porous structure of spherical microparticles resulting from the polycondensation of urea and formaldehyde in the presence of silica sol (UFR–SG) and silica gel microspheres prepared from the latter. It is disclosed that, when the content of colloidal silica increases, the specific surface area of UFR–SG system rises and the porous structure (pore size distribution) of the obtained silica gel microspheres becomes more uniform.