Fabrication of mesoporous polymer/silica hybrid using surfactant-mediated sol–gel method

A mesoporous polymer/silica hybrid was fabricated by a surfactant-mediated sol–gel method. Under our experimental conditions, acrylonitrile (AN) monomer was located at the exterior of micelles and the sol–gel reaction of tetraethoxyorthosilicate (TEOS) proceeded concurrently with the polymerization reaction of the AN monomer. In other words, the micelle/polyacrylonitrile/silica precursor was synthesized through the radical polymerization accompanied with a hydrolysis/condensation single reaction in a reaction system. This is a unique characteristic of our methodology, which embraces the concept of ‘micelle templating’. The pore diameter of the mesoporous polymer/silica hybrid could be tuned by varying the spacer length and concentration of surfactants. Furthermore, compared with conventional mesoporous carbons, the carbonized mesoporous polymer/silica hybrids displayed an enhanced electrical performance favorable for use as a supercapacitor.     

Textural characterization of high temperature silica aerogels

Silica alcogels were synthetized by the sol–gel polymerization of tetraethylorthosilicate in acid media. Conventional and supercritical drying was performed in order to obtain xerogels and aerogels. Different process parameters of the supercritical drying were altered in order to control the texture of the resulting gel. The texture and the structural evolution of xero- and aerogels were studied by thermogravimetric-differential thermal analysis, Fourier-transform infrared spectroscopy, transmission electron microscopy and N₂ physisorption at 77 K. ²⁹Si magic angle spinning nuclear magnetic resonance experiments on silica samples were used to resolve various silicon local environments. Hydrophilic microporous xerogels and hydrophobic micro- or mesoporous silica aerogels were obtained, whose microscopic structure is very similar. However, the samples obtained by different drying procedures exhibit a different structural evolution with temperature.     

New route for producing crack-free xerogels: Obtaining uniform pore size

We propose an innovative strategy to obtain crack-free gels by using a surfactant as a template for the silica pores. We use a neutral surfactant – n-octylamine – which weakly interacts by hydrogen bonding with the silica precursor. This allows it to be removed by simple drying in ambient air. We investigate the effect of the surfactant in simple inorganic silica obtained from tetraethoxysilane (TEOS) and an organic–inorganic hybrid xerogel, containing TEOS and polydimethylsiloxane (PDMS), as precursors. Although both the syntheses promote the formation of a crack-free uniform mesoporous silica gel, the hybrid gel network exhibits a larger pore size than the gel containing exclusively the silica from TEOS.     

Synthesis and characterization of high nickel-containing mesoporous silica via a modified direct synthesis method

A method by modifying tetraethyl orthosilicate (TEOS) with nickel species has been developed for the synthesis of mesoporous silica with high nickel content (up to 14.7 wt% of Ni). Using the method, nickel-containing mesoporous materials were obtained with high BET surface area and pore volume. The materials were characterized by means of X-ray powder diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, N₂ adsorption, Fourier transform infrared. Nickel species were incorporated into the silica frameworks. Formation of nickel phyllosilicates was also confirmed. After activation, mesostructures are still intact. Small nickel clusters embedded in the silica walls were found.     

Immobilization of 5-amino-1,3,4-thiadiazole-thiol onto silica gel surface by heterogeneous and homogeneous routes

The compound 5-amino-1,3,4-thiadiazole-thiol (ATT) was anchored onto silica gel surfaces by homogeneous and heterogeneous routes. Both silica modification methodologies resulted in similar products, named SiCTT and SiATT, respectively. These materials were characterized by infrared and Raman spectroscopies, superficial area and elemental analysis as well as ¹³C and ²⁹Si NMR spectroscopy. Elemental analysis proved that the material SiCTT presented a higher ATT immobilization than SiATT, with values of 0.73 and 0.65 mmol g⁻¹, respectively. NMR, Raman and infrared spectroscopy corroborate to confirm the immobilization of ATT on both surfaces. Raman spectroscopy showed that the reaction of the ATT with silylant agent or pre-modified silica occurred by the thiol group, resulting in a surface with two sulfur groups and one free amine group able to complex soft and hard acids.     

Studies of the pumping effect on the nanoporous microstructure of disordered mesoporous silica materials prepared by calcinations of PMMA-silica hybrids

We present the first comparative studies of pumping effect (i.e., exhaustive vacuum evacuation) on the as-prepared nanoporous microstructure silica to elucidate the effect of different preparative procedure on a series of obtained disordered mesoporous silica materials. The as-prepared hybrid materials (PMMA-silica) through the pumping treatment exhibited higher thermal decomposition temperature (T_d) and density (D) than these system without pumping treatment based on the studies of thermogravimetric analysis and density measurements and compared with the nanoporous materials by calcinations of PMMA-silica materials was found to exhibit a significant higher value of surface area (A_BET) based on N₂ adsorption–desorption isotherm. Furthermore, a marked decrease in A_BET and V_BJH of as-prepared mesoporous silica are observed as the feeding content of TEOS is increased. The morphological images of as-prepared hybrid sol–gel glasses and their corresponding disordered mesoporous silica materials were also studied by scanning electron microscopy and transmission electron microscopy.     

Silica encapsulated hemoglobin and myoglobin powders prepared by an aqueous fast-freezing technique

Hemoglobin and myoglobin were encapsulated in silica gels and powders. Protein encapsulated powders were fabricated via the condensation of silicic acid around the protein, followed by a fast freezing with liquid nitrogen, and subsequent thawing. The fast-freezing technique led to high surface area stable silica encapsulated protein powders. Transmission UV-vis spectroscopy techniques were used to verify that neither protein was damaged during gelling or freezing processes. Both hemoglobin and myoglobin gels and powders retained their biological activity and were able to bind cyano ligands while in the oxidized Fe³⁺ state and carbon monoxy ligands while in the reduced Fe²⁺ state. Kinetics experiments showed that the rates of binding of CO and CN⁻ to the proteins in the silica gel versus a buffer solution are decreased by 30-45%. This result was likely due to mass transfer effects associated with diffusion through the gel network. Hemoglobin/silica powders were successfully stabilized in the Fe²⁺ oxidation state by addition of the amino acid l-cysteine.     

Preparation and characterization of ordered mesoporous silica membrane

Hexagonal mesoporous silica (MCM-41) membranes were prepared at air-water interface by means of an interfacial silica-surfactant self-assembly process. The free-standing and oriented mesoporous silica membranes with pore size ≈2.9-3.8 nm were synthesized at room temperature in acidic media and were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) observations. Small-angle X-ray diffraction (SAXRD) patterns of membranes clearly indicated that as-synthesized membranes were typical of MCM-41 materials with a periodic hexagonal structure with the channels parallel to the surface. SEM images showed that the as-synthesized membrane was continuous and crack-free. In this paper, some novel findings are reported.     

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.     

Synthesis of cubic mesoporous silica and carbon using fly ash

A supernatant solution of silicate species extracted from coal fly ash in a power plant by alkali fusion was used under acidic conditions to prepare a mesoporous silica, SBA-16. SBA-16 was used as a template for the synthesis of a mesoporous carbon using sucrose as a carbon source. These mesoporous silica and carbon materials were characterized by XRD, N₂ adsorption-desorption, SEM, and TEM. Textural properties of the silica and carbon samples prepared using fly ash were found to be comparable to those prepared by pure chemicals, successfully demonstrating the feasibility of recycling fly ash for the synthesis of high quality porous materials.     

Micron scale and nanoscale structure of mesoporous silica thin films

Ordered mesoporous silica thin films have been prepared on silicon substrates by spin-coating technique using poly(alkaline oxide) triblock copolymers EO₂₀PO₇₀EO₂₀ (P123) as structure-directing agent. The X-ray diffraction and transmission electron microscopy investigations show that the obtained mesoporous silica thin films have an ordered pore array structure in nanoscale. The atomic force microscopy analysis reveals that the obtained mesoporous silica thin films exhibit a tile arrangement structure in micron scale.     

Sorption properties of silica gel with adsorbed copolymers of 4-vinylpyridine and styrene with respect to Cu(II), Pb(II) and Fe(III) ions

Abstract

A number of new organo-mineral composites in different mass ratios of organic and inorganic components were obtained by adsorption on the silica gel surface of 4-vinylpyridine–styrene copolymer. The fact of the copolymer immobilization on the silica gel surface was confirmed by Fourier transform infrared spectroscopy (FTIR) spectroscopy and thermogravimetry combined with mass-spectrometry analysis. Thermogravimetric analysis was employed for estimation of copolymers mass content in the composite obtained. It has been established that all the synthesized composites exhibit sorption activity toward traces of Cu (II), Pb (II) and Fe (III) ions in neutral aqueous medium.     

Preparation of mesoporous oxide films via block copolymer templating

Mesoporous silica films have been synthesized by a modified sol-gel method in the presence of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers as structure-directing agents. Influence of synthetic conditions on the formation of mesoporous silica films has been investigated. Porosity of samples can be controlled by block copolymer concentration and aging time of precursor solutions, while the block length of block copolymers affects mesoporous structures. Post-deposition chemical treatment using vaporized ammonia makes it possible to control and stabilize the mesoporous structures. Cooperation interaction mechanism can be considered as an acceptable model for the structural formation in the synthesis of mesoporous silica films.     

Characteristics of composites based on PMMA modified gel silica glasses

Gel silica glass prepared by the sol-gel process can be modified by incorporating an organic phase into the intrinsically porous inorganic gel matrix, which results in a composite material with much improved mechanical and optical properties. Characterisation of PMMA modified gel silica glass prepared by the in situ polymerisation method using FT-Raman spectroscopy, gel permeation chromatography and the nitrogen adsorption technique are reported. Some essential problems encountered in the preparation are discussed.     

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.     

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.     

Cost-effective synthesis of silica aerogels from fly ash via ambient pressure drying

Silica aerogels were synthesized from the industrial fly ash by ambient pressure drying method. The process consists of two stages, preparation of sodium silicate solution from fly ash by hydrothermal reaction with sodium hydroxide, and synthesis of porous silica aerogels from the obtained sodium silicate solution. Silica wet gels were formed by vitriol-catalysis or resin-exchange-alkali-catalysis of the obtained sodium silicate solution. The trimethylchlorosilane(TMCS)/ethanol(EtOH)/hexane mixed solution was used for solvent exchange/surface modification of the wet gel so as to obtain porous silica aerogels via ambient pressure drying. The results indicated that the synthesized silica aerogels were lightweight and hydrophobic. The BET specific surface area, pore volume and average pore diameter were 362.2-907.9 m² g^− 1, 0.738-4.875 cm³ g^− 1, and 7.69-24.09 nm respectively. Particularly, the synthesized silica aerogels by resin-exchange-alkali-catalysis method showed uniform mesoporous structure, and had much higher specific surface area (907.9 m² g^− 1) and pore volume (4.875 cm³ g^− 1) than that of by vitriol-catalysis process.     

Growth,spectral and thermal studies of ibuprofen crystals

RS ‐Ibuprofen was crystallized for the first time in silica gel under suitable pH conditions by reduction of solubility method. The grown crystals were characterized by single crystal X‐ray diffraction and density measurement. The functional groups present in the crystal were identified using Fourier transform infrared spectroscopy. Optical bandgap energy of ibuprofen was estimated as 3.19(3) eV from UV‐Vis spectrum. Thermogravimetric analysis revealed that ibuprofen is thermally stable upto 102.9 °C and the initial loss of mass was due to evaporation only. Morphological study showed that the growth is prominent along b‐axis and the prominent face is {100}. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of borono phenylalanine

Borono phenylalanine abbreviated as BPA is a biologically important compound which is obtained from L‐Phenylalanine (C₉H₁₁NO₂) in which a boron atom is bonded. BPA is an amino acid analogue, helpful in the treatment of glioblastoma multiforme, a highly malignant form of brain tumor is crystallized in silica gel under pH 6.0 by single diffusion method in a period of 30 minutes. The grown crystals were characterized by x‐ray powder diffraction, Fourier Transform infrared spectroscopy and visible ultraviolet spectroscopy. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of L‐phenylalanine

L‐Phenylalanine (C₉H₁₁NO₂), having the morphology of spherulitic needles, an amino acid constituent, responsible for brain nutrition is crystallized in silica gel of pH 6.0 by single diffusion method in a period of 30 minutes. The grown crystals were characterized by X‐ray powder diffraction, Fourier Transform infrared spectroscopy and Visible Ultraviolet spectroscopy. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)