Bis(triethoxysilyl)ethane Research Articles

Mesoporous organosilicas with ultra-large pores: Mesophase transformation and bioadsorption properties

Large pore ordered mesoporous organosilicas (OMOs) with distinct mesophase structure was synthesized under low temperatures by the co-condensation of 1,2bis(triethoxysilyl)ethane (BTESE) and tetraethyl orthosilicate (TEOS) in acidic solution, using triblock copolymer F127 as a template and 1,3,5-trimethylbenzene (TMB) as a swelling agent. With the decrease of temperature, a mesophase transformation from 2D hexagonal structure (p6mm) via mesostructured cellular foam to a highly ordered 3D cubic structure (Fm3m) was evidenced by small angle X-ray diffraction (SAXS), transmission electron microscopy (TEM) and N 2 sorption. It reveals that the lower synthesis temperatures may influence the hydrolysis and condensation of silica species and the hydrophilic–hydrophobic property of F127, as well as the swelling capacity of F127 micelles with TMB, which resulting in a formation of large pores ordered mesoporous organosilicas with various mesostructures materials. Finally, the enzyme adsorption properties of the OMOs were investigated and the results showed that the OMOs with a 3D large pore structure and regular morphology is much more qualified for enzyme adsorption.

Organic–inorganic hybrid silica membranes with controlled silica network size: Preparation and gas permeation characteristics

Bis(triethoxysilyl) ethane (BTESE), which consists of Si–C–C–Si bonds, was used as a silica precursor to prepare organic–inorganic hybrid silica membranes with loose amorphous networks. Single-gas permeation and binary-component gas separation characteristics for hybrid silica membranes were examined to discuss the effect of silica precursors on amorphous networks. The pore size distribution, as determined by single-gas permeation, suggested BTESE-derived silica membranes have loose amorphous structures compared to TEOS-derived silica membranes due to the differences in the minimum units of silica networks. For example, BTESE-derived silica membranes showed a high hydrogen permeance (0.2–1 × 10 −5 mol m −2 s −1 Pa −1) with a high selectivity of H 2 to SF 6 (H 2/SF 6 permselectivity: 1000–25,500) and a low H 2 to N 2 permselectivity (∼20). The binary-component gas separation of He and SF 6 for a BTESE-derived silica membrane revealed that the swelling effect (adsorption-induced expansion of the zeolite crystals) by SF 6 molecules, which has been suggested for zeolite membranes, was not observed in amorphous silica networks. In the present study, BTESE-derived silica membranes had high hydrothermal stability due to the presence of Si–C–C–Si bonds in the amorphous silica network.

Periodic Mesoporous Organosilica in Confined Environments

Periodic mesoporous organosilica (PMO) mesophases based on bis(triethoxysilyl)ethane (BTSE) were synthesized within the confined tubular environment of anodic alumina membrane (AAM) channels. The resulting mesophases were investigated by transmission small angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR), nitrogen sorption, and transmission electron microscopy (TEM). Two different surfactants--nonionic Brij 56 and ionic cetyltrimethylammonium bromide (CTAB)--were used in an acid-catalyzed evaporation-induced self-assembly (EISA) process. Brij 56 as the structure-directing agent (SDA) resulted in the formation of either the hexagonal circular or the cubic mesophase. While the hexagonal circular mesophase is common for such kinds of composites, the cubic mesophase has never been reported before. The template could be removed from the mesophases by template extraction and calcination after annealing the samples. When using CTAB as the SDA during EISA, the only mesophase observed was the hexagonal circular structure. This is in contrast to previous experiments and reports on pure silica mesophases, where the only mesophase formed with CTAB is hexagonal columnar.

Design of Silica Networks for Development of Highly Permeable Hydrogen Separation Membranes with Hydrothermal Stability

A sol-gel method was applied for the development of highly permeable hydrogen separation membranes using bis(triethoxysilyl)ethane (BTESE) as a silica precursor. Hybrid silica membranes showed quite high hydrogen permeance (1 x 10(-5) mol m(-2) s(-1) Pa(-1)) with a high H(2)-to-SF(6) selectivity of 1000 because of loose organic-inorganic silica networks. Hybrid silica membranes were found to show high hydrothermal stability due to the presence of Si-C-C-Si bonds in silica networks.

Influence of cerium (IV) ions on the mechanism of organosilane polymerization and on the improvement of its barrier properties

In this work, the effect of cerium (IV) ammonium nitrate (CAN) addition on the polymerization of bis-[triethoxysilyl]ethane (BTSE) film applied on carbon steel was studied. The electrochemical characterization of the films was carried out in 0.1 mol L −1 NaCl solution by open-circuit potential measurements, anodic and cathodic polarization curves and electrochemical impedance spectroscopy (EIS). Morphological and chemical characterization were performed by atomic force microscopy (AFM), contact angle measurements, infrared-spectroscopy, nuclear magnetic resonance and thermogravimetric analysis. The results have clearly shown the improvement on the protective properties of the Ce 4+ modified film as a consequence of the formation of a more uniform and densely reticulated silane film. A mechanism is proposed to explain the accelerating role of Ce 4+ ions on the cross-linking of the silane layer.

High-performance hybrid pervaporation membranes with superior hydrothermal and acid stability

A new organic–inorganic hybrid membrane has been prepared with exceptional performance in dewatering applications. The only precursor used in the sol–gel synthesis of the selective layer was organically linked 1,2- bis(triethoxysilyl)ethane (BTESE). The microporous structure of this layer enables selective molecular sieving of small molecules from larger ones. In the dehydration of n-butanol with 5% of water, the membrane shows a high separation factor of over 4000 and ultra-fast water transport at a rate of more than 20 kg m −2 h −1 at 150 °C. This can be related to the high adsorption capacity of the material and the sub-micron thickness of the selective layer. The selectivity has now remained constant over almost one and a half years under continuous process testing conditions. Apart from the hydrothermal stability, the membrane exhibits a high tolerance for acid contamination. A slow performance decline in flux and separation factor is only observed at a pH lower than 2. The high stability and effective separation indicate a broad industrial application potential of the hybrid membrane material.

Structure of hybrid organic–inorganic sols for the preparation of hydrothermally stable membranes

A procedure for the preparation of hybrid sols for the synthesis of organic–inorganic microporous materials and thin film membranes is reported. We describe silane reactivity and sol structure for acid-catalysed colloidal sols from mixtures of either tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES), or bis(triethoxysilyl)ethane (BTESE) and MTES. Early-stage hydrolysis and condensation rates of the individual silane precursors were followed with 29Si liquid NMR and structural characteristics of more developed sols were studied with Dynamic Light Scattering. Condensation was found to proceed at more or less similar rates for the different precursors. Homogeneously mixed hybrid colloids can therefore be formed from precursor mixtures. The conditions of preparation under which clear sols with low viscosity could be formed from BTESE/MTES were determined. These sols were synthesised at moderate water/silane and acid/silane ratios and could be applied for the coating of defect-free microporous membranes for molecular separations under hydrothermal conditions.

Synthesis of poly(ethylene glycol) (PEG)-grafted colloidal silica particles with improved stability in aqueous solvents

The known grafting procedures of colloidal silica particles with poly(ethylene glycol) (PEG) lead to grafting layers that detach from the silica surface and dissolve in water within a few days. We present a new grafting procedure of PEG onto silica with a significant improvement of the stability of the grafting layers in aqueous solvents. Moreover, the procedure avoids any dry states or other circumstances leading to strong aggregation of the particles. To achieve the improved water stability, Stöber silica particles are first pre-coated with a silane coupling agent (3-aminopropyl)triethoxysilane (APS) to incorporate active amine groups. The water solubility of the pre-coating layer was minimized using a combination of APS with bis-(trimethoxysilylpropyl)amine (BTMOSPA) or bis-(triethoxysilyl)ethane (BTEOSE). These pre-coated particles were then reacted with N-succinimidyl ester of mono-methoxy poly(ethylene glycol) carboxylic acid to form PEG-grafted silica particles. The particles form stable dispersions in aqueous solutions as well as several organic solvents.

Disilazane functionalization of large-pore hybrid periodic mesoporous organosilicas

Ordered inorganic–organic hybrid periodic mesoporous organosilicas (HPMOs) with hexagonal symmetry were synthesized under acidic conditions by using triblock copolymer Pluronic P123 as a structure-directing agent and mixtures of tetraethylorthosilicate (TEOS) and bis(triethoxysilyl)ethane (BTEE) as the silica source. All mesoporous materials were characterized by powder X-ray diffraction, N2 physisorption, and 13C CP MAS NMR and 29Si MAS NMR spectroscopy. High TEOS : BTEE molar ratios improved the long-range ordering of the HPMOs remarkably, and increased the pore diameter, while the pore wall thickness gradually decreased. Addition of the organic expander molecule mesitylene to the synthesis gel also enlarged the pore diameter and improved the long-range ordering of the materials. Surface silylation with the bissilylamine reagents tetramethyldisilazane (HN(SiHMe2)2), hexamethyldisilazane (HN(SiMe3)2) and diphenyltetramethyldisilazane (HN(SiMe2Ph)2) revealed that the silylation efficiency decreased according to the steric bulk of the silyl groups affording surface silanol populations in the range 0.76–2.19 OH nm−2.

A new extra large pore organic–inorganic hybrid silicoaluminophosphate

A new extra large pore organic–inorganic hybrid silicoaluminophosphate (HSAPO-1) has been synthesized hydrothermally at 443 K by using 4,4′-trimethylene-dipiperidine (TMDP) as the single molecule template and bis(triethoxysilyl)ethane (BTEE) as the hybrid silicon precursor at almost neutral pH. The use of the organic-free silica precursor tetraethyl orthosilicate (TEOS) instead of BTEE in an otherwise identical synthesis gel also leads to the formation of a novel microporous silicoaluminophosphate (SAPO-L). Powder XRD, TEM-EDS, N2 sorption, TGA, CHN and ICP-AES chemical analysis, 13C, 29Si, 27Al and 31P MAS NMR and FTIR spectroscopic tools were employed to characterize these novel materials.

Nanoporous Organosilicas: Periodic Materials Synthesized with Surfactant Templates in Acidic Media

Nanoporous organosilicas have been synthesized by the acid-catalyzed hydrolysis and condensation of bis(triethoxysilyl)ethane (BTSE) using a hydrothermal approach. Cetyltrimethylammonium chloride (CTAC), polyoxyethylene(10) cetyl ether (Brij 56), and polyoxythylene(10) stearyl ether (Brij 76) were employed as structure directors using the surfactant template method. The surfactants were extracted from the nanoscopic composite precipitates with acidified ethanol. The resulting nanoporous organosilicas have been characterized by nitrogen gas sorption, powder X-ray diffraction, and high-resolution thermogravimetric analysis. While the organosilicas synthesized with CTAC exhibit large surface areas (1000 m2/g) and pore volumes (1.0 cm3/g), they form relatively disordered matrixes as evidenced by broad pore size distributions and X-ray diffraction patterns. Brij 56 gives periodic nanoporous organosilicas with pore diameters 36−39 Å. The use of brij 76 as the structure director gave better quality organosilicas, with large surface areas, sharp pore size distributions, and pore diameters of 43−45 Å. X-ray diffraction patterns exhibit three well-defined peaks typical of hexagonal (p6mm) mesoporous materials. The effects of initial HCl concentrations on the chemical and structural properties of the final products are examined.

Probing the Structure of Organosilane Films by Solvent Swelling and Neutron and X-ray Reflection

Thin films of organosilanes have great technological importance for adhesion promotion, durability, and corrosion resistance. Although the cross-link density profile within such films is likely to strongly affect their performance, no reliable assay has been available to characterize this distribution. In this work we use solvent swelling combined with neutron and X-ray reflection to study the cross-link density distribution within ultrathin films (50−100 Å) of (3-glycidoxypropyl)trimethoxysilane (GPS) and bis(triethoxysilyl)ethane (BTSE) on silicon. The films are swelled with vapors of the good solvent nitrobenzene (NB). For GPS films, the solvent concentration profile has a strong maximum in the central region of the film. We conclude from this that the GPS films possess a high cross-link density near the silicon surface and a much lower cross-link density in the bulk of the film. The decreased solvent concentration at the air surface is more difficult to interpret. It appears to also indicate an elevated cross-link density, but may also involve contributions from other effects such as the difference in surface tension between GPS and NB. The degree of swelling reaches ∼50−60% in the bulk of the films. Good reproducibility is obtained for several swelling/deswelling cycles, indicating that swelling with d-NB does not irreversibly change the structure of the network. In contrast to GPS, highly cross-linked films of BTSE do not swell when exposed to d-NB, even though NB is also a good solvent for the BTSE monomers.

Direct Synthesis of Periodic Mesoporous Organosilicas: Functional Incorporation by Co-condensation with Organosilanes

Mesoscopic organosilicas were synthesized with bis(triethoxysilyl)ethane (BTSE) and cetyltrimethylammonium chloride (CTAC) under basic conditions. Further functionalization was achieved by co-condensation with trialkoxyorganosilanes. Surfactant extraction produced periodic mesoporous organosilicas (PMO's) functionalized with the respective organosilane pendent groups. Organosilanes used in this study include: 3-aminopropyltrimethoxysilane, n-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 2-(trimethoxysilylethyl)pyridine, n-(3−triethoxysilylpropyl)-4,5-dihydroimidazole, phenethyltrimethoxysilane, and benzyltriethoxysilane. These materials have been characterized by nitrogen gas adsorption, powder X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), elemental analysis (EA), and high-resolution thermogravimetric analysis (TGA). The effect of organosilane incorporation on the porous structure of these materials is examined.

Mesoporous Sieves with Unified Hybrid Inorganic/Organic Frameworks

Mesoporous materials have been synthesized that are composed of hybrid frameworks in which inorganic and organic components have a fixed stoichiometry and are covalently bonded. The creation of UOFMN (unified organically functionalized mesoporous networks) materials incorporates concepts employed in the synthesis of MCM-41 mesoporous silicates, making use of a quaternary ammonium cationic surfactant and a double trialkoxysilyl precursor such as bis(triethoxysilyl)ethane (BTSE) or bis(triethoxysilyl)ethylene (BTSEY). The cetyltrimethylammonium (CTA+) surfactant is removed by extraction with acid, resulting in a high surface area porous organosilicate framework in which Si atoms are bridged by ethane (from BTSE) or ethylene (BTSEY) groups. The channels are wormlike and uniform in diameter. UOFMN materials are more hydrothermally stable than MCM-41 prepared under similar conditions and have thicker pore walls. Ethylene groups in products made with BTSEY can be brominated, the brominated product itself being reactive as a bromide source. The UOFMN products were characterized by XRD, N2 adsorption, solid-state 29Si and 13C NMR, and TEM.