Addition Of Tetraethyl Orthosilicate Research Articles

Effect of Tetraethyl Orthosilicate on the Structural, Thermal, and Morphological Properties of a Cellulose Acetate Membrane

The present investigation deals with the preparation of a new organic–inorganic hybrid membrane based on cellulose acetate (CA)/tetraethyl orthosilicate (TEOS) by the sol–gel and phase-inversion process. This paper also investigates the effect of TEOS content on the mechanical, thermal, and ultrafiltration (UF) performance of the newly prepared membranes. These newly prepared membranes were characterised by Fourier transform infrared spectroscopy (FTIR), thermogravimetry analysis (TGA) and scanning electron microscopy (SEM). The ultrafiltration performance of the membranes was examined by water content (%), compaction, and pure water flux. Results showed that the addition of TEOS increased the thermal and mechanical properties. SEM results showed that the pore size decreased but the number of pores increased on the addition of TEOS. Moreover, the hydrophilicity and permeability increased with increase in TEOS content from 0 to 2 wt%. Thus, it can be concluded that these hybrid membranes may be suitable for use in the UF separation process.

Synthesis and characterization of nanosilica/waterborne polyurethane end‐capped by alkoxysilane via a sol‐gel process

AbstractA novel method was used to synthesis nanosilica/waterborne polyurethane (WPU) hybrids by in situ hydrolysis and condensation of tetraethyl orthosilicate (TEOS) and/or 3‐aminopropyltriethoxylsilane bonding at the end of the WPU molecular chain. The hybrid was characterized by scanning electron microscopy, energy dispersive spectroscopy (EDS), transmission electron microscopy, Fourier transform infrared spectroscopy (FTIR), and X‐ray photoelectron spectroscopy (XPS). The results showed that the nanosilica/WPU hybrids with well‐dispersed nanosilica particles were synthesized, in which the particles had typical diameters of about 50 nm. In addition, XPS and FTIR analyses demonstrated that chemical interaction occurred between WPU and silica. The effects of TEOS on surface wettability, water resistance, mechanical strength, and thermal properties of the hybrid were also evaluated by contact angle measurements, water absorption tests, mechanical tests, and differential scanning calorimetry, respectively. An increase in advancing contact angles, water resistance, and tensile strength, as well as decrease in elongation at break and glass transition temperature, were obtained with the addition of TEOS. Water absorption decreased from 17.3 to 5.5%. The tensile strength increased to a maximum of 29.7 MPa, an increase of about 34%. Elongations at break of the hybrids decreased 191%. These results were attributed to the effects of the nanosilica and the chemical interaction between WPU and silica. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The influence of tetraethylorthosilicate and polyethyleneimine on the performance of polyethersulfone membranes

The effect of inorganic and organic additives in polyethersulfone (PES) membranes was investigated for the possible enhancement in ultrafiltration performances. Tetraethylorthosilicate (TEOS) and polyethyleneimine (PEI) were chosen as inorganic respective silica precursor and organic additive based on their potential to promote hydrophilicity in PES membranes. With the addition of TEOS and PEI in PES casting solution, the viscosity and hydrophilicity were increased.In addition of TEOS in PES, the SiO2 particles were homogeneously dispersed in PES matrix, a large amount of OH groups on the SiO2 particles generated, and led to an improvement in the hydrophilic property. Characterizations of membranes by FTIR and X-ray Diffraction (XRD) confirmed that the PES suffered a transform from various functional groups due to the addition of TEOS. The 40% of water permeability was found by 5% addition ion of TEOS and PEI repressively. The top surface and cross-section morphology of PES membranes changed from dense-like structure to finger-like macrovoids structure with increasing TEOS and PEI content. Protein solution separation was investigated using lysozyme and bovine serum albumin (BSA) with the concentration of 1000ppm. The observed sieving coefficient of protein decreased exponentially with increasing contents of TEOS and PEI in PES membranes.

Silica encapsulation of highly luminescent hydrophobic quantum dots by two-step microemulsion method

A method has been developed to incorporate multiple hydrophobic CdSe/Cd x Zn 1− x S QDs into SiO 2 beads by a two-step microemulsion process and retain the high photoluminescence (PL) efficiencies of the QDs. In step 1, the QDs were silanized by using partially hydrolyzed tetraethyl orthosilicate (TEOS) via replacing oleic acid (OA) on the surface of QDs. In step 2, these silanized QDs were transferred into aqueous phase in the reverse micelle solution by adding a small amount of water and stirring for a few hours. Then these silanized QDs assembled and subsequently encapsulated in a SiO 2 shell by a reverse micelle synthesis. The initial silanization plays an important role for the QDs to be coated within a homogeneous SiO 2 shell and retain a high PL efficiency in water. Single QDs were coated into silica beads by this two-step microemulsion process without water addition before ammonia and TEOS addition and pre-stirring for a certain time. The number of QDs incorporated into the silica beads can be controlled by adjusting the stirring time. More QDs can be incorporated into silica spheres by partially hydrolyzed 3-mercaptopropyl trimethoxysiliane (MPS) or 3-aminopropyltrimethoxysilane (APS) functionalization at step 1. An improvement in the PL efficiency (up to 35%) of silica spheres was obtained after APS functionalization of QDs. The silica coating shows a bit blueshift for the PL peak wavelength of the QDs. The full width at half maximum (FWHM) of PL spectra was decreased 4 nm after silica coating of the QDs.

Ordered dispersion of ZnO quantum dots in SiO2 matrix and its strong emission properties

ZnO nanoparticles in the form of quantum dots (QDs) have been dispersed in SiO(2) matrix using StÖber method to form ZnO QDs-SiO(2) nanocomposites. Addition of tetraethyl orthosilicate (TEOS) to an ethanolic solution of ZnO nanoparticles produces random dispersion. On the other hand, addition of ZnO nanoparticles to an already hydrolyzed ethanolic TEOS solution results in a chain-like ordered dispersion. The photoluminescence spectra of the as-grown nanocomposites show strong emission in the ultraviolet region. When annealed at higher temperature, depending on the sample type, these show strong red or white emission. Interestingly, when the excitation is removed, the orderly dispersed ZnO QDs-SiO(2) composite shows a very bright blue fluorescence visible by naked eyes for few seconds indicating their promise for display applications. The emission property has been explained in the light of structure-property relationship.

Control of spacing between aminoalkyl functions by mesostructural transition in a polysilsesquioxane lamellar assembly

We synthesized lamellar solids by co-condensation of 3-(2-aminoethylamino)propyltriethoxysilane (AeAPTES) and tetraethyl orthosilicate (TEOS) in the presence of hexadecylsuccinic acid (C16SA) and hexadecanol (C16OH) producing a composition in the gel such that AeAPTES : C16SA was kept constant at 1 : 1, as is the ratio of TEOS : C16OH, while the ratio AeAPTES : TEOS was varied from 10 : 0 to 1 : 9. Since a good lamellar solid is obtained only from AeAPTES and C16SA, TEOS and C16OH were expected to be dilutants of AeAPTES and C16SA, respectively, in order to increase the inter-spacings of 3-(2-aminoethylamino)propyl (AeAP) functions in the polysilsesquioxane layer (NH2C2H4NHC3H6SiO1.5)n. All XRD patterns are attributed to lamellar structures with the interlayer distance d = 4.10 ± 0.06 and 2.86 ± 0.10 nm, for the solids 10–0 to 4–6 and the solids 3–7 to 1–9, respectively, where m–n denotes after mixing ratio m : n of AeAPTES : TEOS. Assemblies of alkyl chains in all-trans conformation were revealed by infrared spectroscopy for all of these lamellar solids. The ionization state of –COOH also changed between 4–6 and 3–7, while the amount of nitrogen in the solid continuously decreased with addition of TEOS into the sol. In the sorption of Cu2+ by the lamellar solids and the structural analysis of sorbate by ESR and XAFS, we show that, at the XRD pattern change, the local structure of Cu2+ changes also from [Cu(AeAP)2]2+ to [Cu(AeAP)(H2O)2]2+, which is accompanied by a sudden change in the uptake of Cu2+ as measured by Cu : N ratio, from Cu/N = 0.23 ± 0.03 to Cu/N = 0.43. Since the structure [Cu(AeAP)2]2+ is possible only with short mutual distances of AeAP, these discontinuous changes imply that the enlargement of the spacing between AeAP functions is induced by contraction of the lamellar structure. We further investigated the chemical bond between Cr in chromate and Cu2+ in the above structures by Cr K-edge XANES and EXAFS and demonstrate that the bond is stronger with [Cu(AeAP)2] than with [Cu(AeAP)(H2O)2]. From this result regarding the reactivity of Cu2+, the enlargement of the spacings in the support matrix by a mesostructural transition may become a key concept to provide highly active adsorbents and catalysts with a hierarchical structure.

Thermodynamics of Silica Nanoparticle Self-Assembly in Basic Solutions of Monovalent Cations

Silica nanoparticle formation is studied using microcalorimetry to measure the heats of reaction evolved from the addition of tetraethylorthosilicate (TEOS) to basic aqueous solutions of monovalent cations. This approach tracks a series of reactions, beginning with the formation of soluble species (i.e., monomers/oligomers), followed by the self-assembly of nanoparticles at a critical silica concentration (CAC). Contributions to the net enthalpy arise from three primary reactions: TEOS hydrolysis, silanol dissociation, and silica condensation. Analyses are performed in the presence of tetrapropylammonium (TPA) ion, which serves as a structure-directing agent (SDA) in hydrothermal syntheses of the all-silica zeolite, silicalite-1. Plots of enthalpy versus TEOS concentration exhibit sigmoidal behavior with a 18 ± 3 kJ/mol reduction in the magnitude of enthalpy, which is related to the CAC and is independent of solution alkalinity, but dependent on the identity of the cation. Solutions of Na+ and various tetraalkylammonium (TAA) cations display similar sigmoidal curves with much lower changes in the magnitude of enthalpy at the CAC (∼5 kJ/mol SiO2). Nanoparticle formation may involve endothermic reactions, derived from protonation of negatively charged silica to form neutral species, which participate in condensation, thereby providing an explanation for the previously observed exothermic−endothermic crossover as a function of time during silicalite-1 syntheses.

A new method to prepare organic–inorganic hybrid membranes

In this paper we present a new method to prepare organic–inorganic hybrid PVDF/Si membranes by adding tetraethyl orthosilicate (TEOS) into the polyvinylidene fluoride (PVDF) casting solution. During the membrane coagulation in acid bath (pH = 1), the TEOS was hydrolyzed and polymerized, and silicon–oxygen polymers were formed. The silicon–oxygen polymers may entangle or interpenetrate with PVDF chains, which is beneficial to the mechanical performances of hybrid membranes. Element analysis showed Si existed on the surface and bottom of hybrid membrane when TEOS was added to the casting solution. The effects of TEOS on the performances of hybrid membranes were investigated. The results showed that the pure water flux increased firstly and then decreased and the BSA retention decreased with TEOS content increasing. When TEOS content was about 12 wt.%, the pure water flux of hybrid membrane was similar to that of PVDF membrane without TEOS addition, but the tensile strength and elastic modulus of hybrid membrane was almost twice.

Physicochemical Characterization of Novel Chitosan-Soy Protein/ TEOS Porous Hybrids for Tissue Engineering Applications

In this paper we report a new type of cross-linked porous structure based on a chitosansoy protein blend system developed by means of combining a sol-gel process with the freeze-drying technique. The final structure was investigated by Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR), contact angle measurements and the morphology by scanning electron microscopy (SEM). The water uptake capability and the weight loss were measured up to 14 days and their mechanical properties were assessed with compression tests. Results showed that the addition of tetraethyl orthosilicate (TEOS) to the chitosan-soy protein blend system provide specific interactions at the interface between the two polymers allowing to tailor the size and distribution as well as the degradation rate of the hybrids. Finally, TEOS incorporation induces an increase of the surface energy that influences the final physicochemical properties of the materials.

Controlled Growth of Pt-Containing SiO2 Nanotubes with High Aspect Ratios

Rectangular prisms of [Pt(NH3)4](HCO3)2 were grown from its aqueous solution by solvent modification with ethanol. The polydispersity of the prisms, being influenced by temperature, the rate of ethanol addition, and the Pt concentration in the aqueous solution, actually results from the iso-oriented aggregation of primary nanofibers into bundles. The employment of prehydrolyzed tetraethyl orthosilicate (TEOS) as a capping agent can effectively stabilize the primary nanofibers. With this stabilized nanofiber as a structure-directing agent, about 100−200 nm thick and up to 40 μm long SiO2 nanotubes, which contain up to 40 wt % of Pt, could be synthesized by further addition of TEOS. The capping mechanism of hydrolyzed TEOS can be reasonably explained through the selective adsorption of silanol species on specific surfaces of primary nanofibers. In our method, the ingenious employment of TEOS as the reactant for the nanotube formation and also as a capping agent avoids the introduction of additional substanc...

Direct coating of gold nanoparticles with silica by a seeded polymerization technique

Gold nanoparticles prepared through a conventional citrate-reduction method were directly coated with silica by means of a seeded polymerization technique based on the Stöber method. The method required no surface modification. The addition of tetraethylorthosilicate and water prior to ammonia was found to be critical to obtain a proper coating. The silica shell thickness was varied from 30 to 90 nm for TEOS concentrations of 0.0005–0.02 M at 10.9 M of water and 0.4 M of ammonia. The optical spectra of the core–shell gold–silica composite particles agreed with predictions of Mie theory.

Use of poly(2-acrylamido-2-methylpropane sulfonate) modified with tetraethyl orthosilicate as sensing material for measurement of humidity

A resistive-type humidity sensor was fabricated by thick film method using the poly(2-acrylamido-2-methylpropane sulfonate) (poly-AMPS) modified with tetraethyl orthosilicate (TEOS) as the sensing material without protective film or complicated chemical procedures. Parameters that may affect the humidity sensing of material, such as the effect of adding triethylamine (TEA) or diethylamine (DEA), the dosage of TEOS on the capacity resistance to high humidity atmosphere, and the thickness of film were investigates. The characteristics of humidity sensor, such as response time, response linearity, working range, hysteresis, effect of temperature and long-term stability were further studied. The humidity sensor has less hysteresis (<2%), good linearity (R2=0.9989) at the humidity working range of 30–90% RH, long-term stability (at least 31 days) and satisfactory resistance to high humidity atmosphere (95% RH) using the addition of TEOS (16.25%, w/w) and TEA (0.4ml) into poly-AMPS as the sensing material.

Poly(L-lysine) Aggregates as Templates for the Formation of Hollow Silica Spheres

A novel and facile method for the fabrication of hollow spherical silica is presented. Mixing poly(L-lysine) together with lipophilic amine additives in water results in the formation of large aggregates, which can be transcribed into their spherical silica analogues by the addition of tetraethylorthosilicate (TEOS). By varying the additives it has been established that the amino moieties of the additive, rather than those of the poly(L-lysine), play a crucial role in the transcription process.

Control of surface expression of functional groups on silica particles

The effect of the time of addition of organosilanes to silica particle formation reaction mixtures on the resulting surface availability of the added functional groups was investigated. Base catalyzed particle formation was initiated by the addition of tetraethyl orthosilicate (TEOS) to a water-in-oil microemulsion. Subsequently, amine, mono-carboxylate, ethylenediaminetriacetic acid, or dihydroimidazole-terminated organosilanes were added to the microemulsion. Continuous growth in size of monodispersed spherical particles over time was monitored by transmission electron microscopy and light-scattering measurements. Surface primary amine and carboxylate groups on the resulting particles were labeled with fluorescamine and 1-pyrenyldiazomethane (PDAM), respectively, and the effect of varying the time of organosilane addition to the microemulsion was determined by fluorescence spectroscopy. The effect of the time of organosilane addition on surface expression of dihydroimidazole groups was determined using a direct titration method. The results demonstrate that the degree of surface functionalization of the silica particles varied with the time of organosilane addition. For each type of amine terminated organosilane used, the highest surface availability of organo-functional groups was obtained when the organosilane was added 30 min after particle growth was initialized. A progressive decrease in the surface availability of primary amine groups was observed when 3-aminopropyltrimethoxysilane (APTMS) was added later than 30 min after particle formation was initiated. For each type of carboxylate-terminated organosilane used, the highest surface availability of organo-functional groups was obtained when the organosilane was added 5.5 h after particle growth was initialized.

Sol–gel preparation and characterization of spherical ZrO 2–SiO 2 particles

Spherical zirconia/silica particles of 30–40 μm average diameter, surface area of 500–700 m 2/g and a pore volume >0.5 cm 3/g were prepared in the compositional range Zr≤18 wt%, via emulsion–gelation of mixed sols. Thermal hydrolysis of zirconyl chloride followed by addition of tetraethylorthosilicate (TEOS) and hydrolysis of TEOS in the presence of zirconyl chloride solution in ethylene glycol (EG) have been compared. In the latter case, a more homogeneous morphology and composition was obtained, when the acidic sol was emulsified in decanol and gelled in a basic solution of cyclohexylamine in decanol. Thermal aging of mixed gels in alkaline mother liquor was found to strengthen the gel network during preparation. Also surface compositions, surface properties and crystallization kinetics were different. The better behavior of samples prepared in the presence of EG was attributed to the effect of EG (as complexing agent), favouring the co-precipitation of Si-containing and Zr-containing moieties.

V [sbnd]P [sbnd]O catalysts for oxidation of butane to maleic anhydride : Influence of (VO) 2H 4P 2O 9 precursor morphology on catalytic properties

The catalytic properties of (VO) 2P 2O 7 are very dependent on its method of preparation. The best catalysts have a platey morphology and are prepared topotactically via a (VO) 2H 4P 2O 9 precursor. This paper reports a systematic study on the effect of synthesis variables on the properties of (VO) 2H 4P 2O 9 and (VO) 2P 2O 7. Variables considered were P/V synthesis ratio, addition of tetraethyl orthosilicate, and various organic solvents. Catalytic properties of (VO) 2P 2O 7 are related to defects and morphology.