Synthesis and characterization of organic-inorganic hybrid mesoporous silica materials with new templates

1-Hexadecane-3-methylimidazolium bromide and 1-hexadecane-2,3-dimethylimidazolium bromide were used as new templates for the syntheses of periodic mesoporous organosilica (PMO) materials; using these new templates, ethane-bridged PMO materials were successfully synthesized and characterized under basic conditions.     

Imide-siloxane block copolymer/silica hybrid membranes: preparation, characterization and gas separation properties

Imide-siloxane block copolymer/silica hybrid membranes with covalent bonds were prepared via sol–gel reaction. The structural informations of these hybrid membranes were obtained by using Fourier transform-infrared spectrometry (FT-IR), ²⁹Si nuclear magnetic resonance (²⁹Si NMR), XPS and thermogravimetric analysis (TGA). The gas separation properties of the hybrid membranes were also investigated in terms of organosiloxane (PDMS) or silica content at various temperatures. In the hybrids, the addition of PDMS phase increased the permeabilities of gases such as He, CO₂, O₂, and N₂, indicating that the gas transport occurred mainly through rubbery organic matrix. Meanwhile, the PDMS phase contributed the decreased gas selectivities to nitrogen but the reduction in selectivities was very small in comparison with other siloxane containing polymeric membranes. This might be due to the restriction of chain mobility by the existence of inorganic component such as silica network in the hybrids. Additionally, the increase of silica content in these hybrid membranes considerably retarded the falling-off of gas selectivity at elevated temperature. The increase of silica content in hybrid membranes resulted in well-formed silica networks and hence these inorganic components restricted the plasticization of organic matrix by the thermal segmental motion of organic components, leading to preventing the large decrease of the gas selectivity.     

Synthesis, characterization and thermal properties of novel PMDA-PAPD/silica hybrid network polymers

Novel PMDA-PAPD/silica hybrid polymers were synthesized by the sol-gel process. Fourier transform infrared spectroscopy and ²⁹Si nuclear magnetic resonance spectroscopy were used to characterize the structure of the hybrids, (condensed siloxane bonds designated as Q¹, Q², Q³, Q⁴, wth 3-aminopropyltriethoxysilane having mono-, di-, tri-, tetra-substituted siloxane bonds is designated as T¹, T² and T³). The results revealed that Q³, Q⁴ and T³ are the major microstructure elements in forming a network structure. The surface morphology, particle size, crystallinity and the thermal stability of the hybrids were investigated using Scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), Thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC). SEM and TEM revealed that the hybrids were nanocomposites. The XRD indicated that covalent bonding (Si-O-Si) between the organic and inorganic components enhanced miscibility. DSC and TGA results showed that these hybrid materials had excellent thermal stability. The heat capacities of some materials were reported for the temperature range 273 K and 363 K as no thermal anomaly was found in this temperature range.     

Structural characterization of silica modified polyimide membranes

Polyimide and hybrid polyimide‐siloxane were synthesized by polycondensation, imidization, and sol‐gel reaction. The polyimides were prepared from pyromellitic dianhydride (PMDA) and 4,4‐oxydianiline (ODA) in N‐methyl‐2‐pyrollidone (NMP). Trimethoxyvinyl silane (TMVS) was used as a source of silica. Their surface morphologies, structures and thermal performances were determined using scanning electron microscopy (SEM), infrared spectroscopy (IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that the silica particles were finely and rather homogeneously dispersed in polymers. The glass transition temperature (T_g) of hybrid membrane materials increased with the increasing silica content. TGA analysis showed that polyimides were thermally stable with silica. Modified polyimide‐siloxane films, thermal characteristics were found to be better than the polyimide films without silica. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis and rapid characterization of amine-functionalized silica

Amine-functionalized colloidal silica finds use in a variety of applications and fundamental investigations. To explore convenient methods of synthesis and characterization of research-grade materials in relatively large quantities, nearly monodisperse colloidal silica particles were prepared by base-catalyzed hydrolysis of reagent-grade tetraethyl orthosilicate (TEOS) without the traditional time- and energy-consuming distillation step. Radius was varied reliably from 30 to 125 nm by changing the water/TEOS ratio. Asymmetric flow field flow fractionation (AF4) methods with online light scattering detection proved effective in assessing the uniformity of the various preparations. Even highly uniform commercial standards were resolved by AF4. The surface of the colloidal silica was decorated with amino groups using (3-aminopropyl) trimethoxysilane and spacer methyl groups from methyl-trimethoxysilane. The surface density of amino groups was quantified spectrophotometrically after reaction with ninhydrin; the nature of this analysis avoids interference from sample turbidity. As an alternative to the ninhydrin test, an empirical relationship between surface density of amino groups and zeta potential at low pH was found. The size of the colloidal silica was predictably decreased by etching with HF; this method will be effective for some preparations, despite a modest reduction in size uniformity.     

Synthesis and characterization of amino-functionalized silica nanoparticles

Monodispersed raw silica nanoparticles (RSNPs) with the particle size of 40 nm were successfully fabricated by condensation reaction of tetraethylorthosilicate in methanol with high concentration ammonia (1.2 M). The RSNPs were treated with the coupling agent 3-aminopropyltrimethoxysilane (APTMS) for grafting amine groups on the surface to obtain the amino-functionalized silica nanoparticles (ASNPs). The chemical structure and surface morphology of RSNPs and ASNPs were characterized by Fourier-transform infrared spectra, solid-state NMR spectra and scanning electron microscopy. In addition, a method to quantify the grafted amine groups on the surface of ASNPs was developed by using the ninhydrin assay. The ninhydrin analysis showed that 60 mol % of the APTMS molecules were immobilized on the surface, that is, 4.4 amine groups per nm2 of surface area were bonded on nonporous ASNPs. The weight loss of particles obtained from thermogravimetry analysis indicated the amount of grafted amine groups and was used as a reference to compare with the value determined from ninhydrin method.     

Crosslinked organosiloxane hybrid materials prepared by condensation of silanol and modified silica: Synthesis and characterization

Hybrid materials based on polymethylphenylsiloxane (PMPS) and organic functionalized silica were synthesized via condensation reaction between silanol and alkoxysilyl groups in the presence of quaternary ammonium hydroxide. The structure of prepared materials was investigated by FTIR and NMR, which indicate that the products have incorporated modified silica into the polymer matrix. The prepared hybrid materials show a satisfactory thermal resistance because the initial decomposition of typical product occurred at nearly 100 K higher than that of the pure polymer according to the thermogravimetric analysis (TGA) results. Differential thermogravimetric analysis (DTGA) data confirm that the thermal degradation of prepared hybrid materials comprises of two steps, of which the first one could be controlled by adjusting the content of silica particles and the ratio of surface groups on the particles. The coating films obtained from hybrid products exhibit good thermal mechanical properties. Therefore, the materials are hoped to be used for the application in thermal resistant coating.     

Synthesis and characterization of stereoregular poly(methyl methacrylate)–silica hybrid utilizing stereocomplex formation

Stereoregular poly(methyl methacrylate) (PMMA)–silica nanocomposites were prepared using stereocomplex formation between i-PMMA and s-PMMA by an in situ method. The methodology adopted here is the simultaneous formation of organic gel and inorganic gel, the so-called interpenetrating polymer network (IPN) formation. The gelation of i- and s-PMMA were performed by stereocomplex formation with the associated segments forming the crosslinking points in the presence of tetramethoxysilane (TMOS). The effects of the i/s-ratio, PMMA concentration, molecular weight, and solvent nature on the hybrid materials formation were addressed. The presence of the stereocomplex in the silica matrix was confirmed by DSC and solvent extraction methods. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 785–794, 2004     

Preparation and characterization of novel negatively charged hybrid membranes

Charged hybrid membranes with anionic‐ or cationic‐exchange groups have attracted increasing interest due to their higher thermal stabilities and structural flexibilities which are considered suitable for use in some harsh conditions, such as higher temperature and strongly oxidizing circumstances, for industrial applications. To develop new routes to synthesize the negatively charged hybrid membranes, a series of hybrid membranes were prepared via free radical polymerization of glycidylmethacrylate (GMA) and γ‐methacryloxypropyl trimethoxy silane (MPTMS) monomers, and ring‐opening of epoxide to create negatively charged ? SO₃H groups in the polymer chains. The fundamental properties of these prepared membranes were characterized through TGA, ion‐change capacity (IEC), and MALDI–TOF mass spectra. TGA showed that the thermal degradation temperature of these membranes could reach up to 300°C and the temperature of the first endothermic peak decreased with an increase in the content of ? SO₃H groups. IEC measurements showed that their IECs were within the range of 0.22–0.35 mmol g^?1. MALDI–TOF spectrometry indicated that the incorporation of GMA into the hybrid matrix could improve the structural stability of the membranes. These findings demonstrated that the ion‐exchange properties and structural stability of negatively charged hybrid membranes can be conveniently controlled by adjusting the GMA moiety in the hybrid matrix. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis, characterization, and optical properties of well-defined N-doped, hollow silica/titania hybrid microspheres

Well-defined nitrogen-doped, hollow SiO2/TiO2 hybrid spheres were successfully prepared through a two-step sol-gel synthesis combined calcination process using triethylamine as the nitrogen source. In this approach, polystyrene (PS)/silica microspheres were first synthesized. Subsequently, the amine-treated PS/SiO2/TiO2 hybrid spheres were obtained by sol-gel method. Finally, the elimination of the PS core, nitrogen-doping process, and crystallization of amorphous TiO2 were simultaneously conducted in the calcination process to acquire the final products. The as-prepared hybrid spheres were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. The results of XRD, FTIR, and XPS spectra indicated that nitrogen was really doped into the anatase TiO2 shell and confirmed that most nitrogen dopants might be present in the chemical environments of N-Ti-O and Ti-N-O. It was found that the absorption shoulder of nitrogen-doped hollow SiO2/TiO2 hybrid spheres vastly shifted to the visible region up to around 530 nm. The photoluminescence (PL) bands showed spectral lines at about 421, 472, and 529 nm, which were attributed to the self-trapped excitons, F and F+ centers. Moreover, the intensity of the PL spectra band of hollow SiO2/TiO2 hybrid spheres increased with as the amount of titanium tetrabutoxide (TBOT) precursor increased. However, the doping of nitrogen into hollow SiO2/TiO2 hybrid spheres led to the drastic quenching of photoluminescence because of the increase in the separation efficiency of the photoinduced electron and hole pairs.     

Mesoporous silica hybrid membranes for precise size-exclusive separation of silver nanoparticles

One-dimensional (1D) nanomaterials have unique applications due to their inherent physical properties. In this study, hexagonally ordered mesoporous silica hybrid anodic alumina membranes (AAM) were synthesized using template-guided synthesis with a number of nonionic n-alkyl-oligo(ethylene oxide), Brij-type (C(x)EO(y)), which are surfactants that have different molecular sizes and characteristics. The hexagonal mesoporous silicas are vertically aligned in the AAM channels with a predominantly columnar orientation. The hollow mesostructured silicas had tunable pore diameters varying from 3.7 to 5.1 nm. In this synthesis protocol, the surfactant molecular natures (corona/core features) are important for the controlled generation of ordered structures throughout AAM channels. The development of ultrafiltration membranes composed of silica mesostructures could be used effectively in separating silver nanoparticles (Ag NPs) in both aqueous and organic solution phases. This would be relevant to the production of well-defined Ag NPs with unique properties. To create a size-exclusive separation system of Ag NPs, we grafted hydrophobic trimethylsilyl (TMS) groups onto the inner pores of the mesoporous silica hybrid AAM. The immobilization of the TMS groups allowed the columnar mesoporous silica inside AAM to retain this inner pore order without distortion during the separation of solution-phase Ag NPs in organic solvents that may cause tortuous-pore membranes. Mesoporous TMS-silicas inside 1D AAM channels were applicable as a size-exclusive separation system to isolate organic solution-phase Ag NPs of uniform morphology and size.     

Synthesis of gold functionalized poly-bisvinylethyleneurea/silica hybrid materials

Novel gold/poly-(1,3-divinyl-imidazolid-2-one)/silica [poly-bisvinylethyleneurea (poly-BVU)/silica)] hybrid particles have been produced by adsorption and spontaneously occurring in situ reduction of Au(3+) cations on the surface of poly-BVU/silica hybrid particles. The successful functionalization of the poly-BVU/silica particles with gold nanoclusters has been evidenced by UV/vis and XPS spectroscopy as well as scanning electron microscopy. The size of the resulting gold clusters, estimated by means of the Mie-Drude theory on the full peak width at half-maximum of the surface plasmon UV/vis absorbance, correlates with the polymer content of the poly-BVU/silica hybrid particles used for the modification. Therefore, it is possible to control the size of the gold clusters simply by adjusting the monomer/silica ratio in the polymerization process, which corresponds with the polymer content of the hybrids.     

Preparation and characterization of polyimide/pure silica zeolite hybrid films

In this study, amino derivative of pure silica zeolite nanocrystal (A‐PSZN) was dispersed into polyimide (PI) matrix to prepare PI/A‐PSZN hybrid films, and their thermal and mechanical properties, as well as hydrophobicity, were characterized scientifically. The test results show that PI/A‐PSZN hybrid films possess higher glass transition temperature, higher thermal stability and lower in‐plane coefficient of thermal expansion than pristine PI. The mechanical property data suggest that the incorporation of A‐PSZN results in an increase in Young's modulus and tensile strength of the hybrid films, but as its content exceeds the critical value (maybe 5 wt%), its enhancement effect on the hybrid's strength and toughness gets weaker. Furthermore, liquid dripping imaging analysis results indicate that the film's hydrophobicity is clearly improved by the introduction of A‐PSZN. As compared with PSZN, A‐PSZN exhibits better effect on enhancing the overall performance of pristine PI films. A comparison with other studies suggests that PI/A‐PSZN is a hybrid film with superior comprehensive properties. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of micrometer-sized hard silica spheres with uniform mesopore size and textural pores

Micrometer-sized silica spheres were prepared using a new pH-induced rapid colloid aggregation method in water-in-oil (W/O) emulsion separately with F127 and the mixture of Pluronic triblock copolymer (F127, P123, or P105) and PEG20000 as templates. All the mesoporous silica spheres exhibited high surface areas (657-1145 m2/g) and large pore volumes (0.46-2.16 ml/g). Through optimizing the synthetic conditions, hard silica spheres with narrow particle size distribution, uniform pore size, and textural pores were obtained. Finally, the mechanism of this synthetic route is discussed.     

Synthesis and characterization of colloidal fluorescent mesoporous silica particles

Mesoporous silica particles with narrow size distribution were obtained by a seeded growth process. Depending on the size of seeds and on the time of addition of reactants, the size of particles can be varied between 300 and 1000 nm. In a second step the dye fluorescein isothiocyanate can be embedded. The structure of these new silica particles with low density was investigated by SEM, XRD, BET, and confocal microscopy.     

Synthesis and characterization of functional chemically modified silica fillers

Elaborated methods of synthesis of chemically modified silicas with grafted silicon hydride and amino groups are analyzed. Experimental results on use of modified silicas with bonded amino groups as fillers of carboxyl-containing rubbers and epoxy resins are reported. It was shown that modified silica fillers with grafted silicon hydride groups could be applied for carrying out processes of catalytic solid-phase hydrosilylation of 2-hydroxyethylmethacrylate and some other functional olefins.     

Synthesis and characterization of hyperbranched mesoporous silica SBA-15

Branched mesoporous silica SBA-15 materials have been prepared in a simple process using non-ionic surfactant in acidic conditions in the presence of metal ions.     

Synthesis and characterization of surface-aminated polypyrrole–silica nanocomposites

 Two synthetic routes to surface-aminated polypyrrole–silica nanocomposite particles have been investigated. Route 1 involved the initial synthesis of homopolypyrrole – silica particles as described previously, followed by surface amination using 3-aminopropyltriethoxy-silane. In Route 2 aminated polypyrrole–silica particles were synthesized directly by copolymerising an N-substituted aminopyrrole comonomer with pyrrole in the presence of an ultrafine silica sol. Both types of aminated particles were characterized in terms of their particle size and morphology, long-term colloid stability and degree of amination using transmission electron microscopy, disc centrifuge photosedimentometry and zeta potential measurements, respectively. Received: 19 May 1998 Accepted: 15 June 1998