Reaction Of Tetraethylorthosilicate Research Articles

Enantioselective recognition of esomeprazole with a molecularly imprinted sol-gel-based electrochemical sensor.

A simple, selective, and accurate electrochemical chiral sensor based on molecularly imprinted polymer (MIP) has beendevelopedfor sensitive and selective detection of esomeprazole (ESOM). For this purpose, the porous MIP sensor was prepared using tetraethyl orthosilicate (TEOS) and cetyltrimethylammonium bromide (CTAB) in the presence of β-cyclodextrin (β-CD) as a chiral recognizing element on aglassy carbon electrode (GCE). The changes in the MIP-layer related to removal and rebinding of the target ESOM were performed via differential pulse voltammetry (DPV) and cyclic voltammetry (CV) by using [Fe(CN)6]3-/4- as the redox probe. The structures of the developed sensor surface were characterized by using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Electrochemical impedance spectroscopy (EIS) was also utilized for a complementary electrochemical characterization. The calibration curve was obtained in the range 1.0 × 10-14-2.0 × 10-13M with alimit of detection (LOD) of 1.9 × 10-15M. The developed method has improved the accessibility of binding sites by producing the porous material via hydrolysis/condensation reaction of TEOS in presence of CTAB. The selectivity tests of the developed SiO2-β-CD@MIP/GCE sensor indicated a high specificity towards ESOM compared with structurally related competitor molecules such as R-omeprazole (R-OM), R-lansoprazole, and S-lansoprazole. The developed sensor was successfully used to determine ESOM in tablets and commercial human serum samples with satisfactory recoveries (100.25 to 100.60%) and precision (RSD 0.46 to 0.66%).

The effect of core-shell BaTiO3@SiO2 on the mechanical and dielectric properties of PVDF composites

ABSTRACT In this study, polymer composite films were prepared by the solution casting method using ceramic filler barium titanate (BT) to enhance the mechanical and dielectric properties of polyvinylidene fluoride (PVDF). A silicon dioxide (SiO2) shell was coated on BT surface by hydrolysis reaction of tetraethyl orthosilicate (TEOS) at different concentrations in order to provide a strong interface between PVDF and BT. The influence of SiO2 coating on morphology, structure, thermal, tensile and dielectric properties of composites were investigated compared to neat PVDF. The results of analyses show that SiO2 is successfully coated on BT and that the ceramic filler enhances the tensile and dielectric properties of the composites. At low BT concentrations (5 and 10 vol.%) the tensile strength and Young modulus are improved compared to neat PVDF. For films having a high content of SiO2, in particular, coated BT high values, such as 24.8 at 102 Hz are found for the dielectric constant, which is greatly improved by almost 2.3 times compared to neat PVDF. Properties, such as flexibility and thermal stability, are well retained in the prepared composites.

Nanoscale silica coating of porous stainless steel and its impact on water wettability

The water wettability of porous stainless steel specimens was enhanced via a nanoscaled silica coating for application to passive two-phase heat transfer devices. A combination of porous stainless steel and water has attracted attention in the area of the heat transfer devices. However, the water wettability of stainless steel is poor, limiting the performance of the devices. In the present study, the silica coating of the specimens was conducted via a reaction of tetraethyl orthosilicate (TEOS) after pretreatment using NaOH aq. or HCl aq. Energy-dispersive X-ray spectrometry revealed that the amount of silica deposited on the surface was dependent on the pretreatment conditions and the composition of the silica-coating solutions. Measurement of porous properties indicated that the silica coating did not affect pore diameter and gas permeability since the coating was in nanoscale. Microscale contact angles were directly evaluated using an environmental SEM. The specimens showed excellent water wettability when they were covered with numerous tiny silica bumps. When the specimen was pretreated with 2 M NaOH aq. and coated in weak alkaline TEOS solution, the contact angle of the porous stainless steel decreased from 87° to 54° after silica coating. The excellent water wettability originated from the relatively smooth surface and a sufficient coverage ratio, which resulted from the moderate strength of chemical etching of the NaOH aq. and the mild silica-coating condition in the weak alkaline solution.

Design and Application of an Optical pH Sensor Based on Thionine Doped Modified Sol–Gel Film

An optical chemical sensor was constructed by incorporating the thionine (TN) dye molecules into a sol–gel silica matrix and it was used for determination the pH of the aqueous solutions. Entrapment of TN dye into the silica matrix was made via an acid-catalyzed sol–gel reaction of tetraethyl orthosilicate (TEOS) and the thionine molecules. The thionine molecules in the immobilized form, showed a different spectral behavior than its solution form. After optimizing the experimental conditions, the fabricated optical sensor showed a fast response to pH changes in the range of 11–13 with a response time about one minute. Also, the obtained results indicate that the proposed pH sensor, has a good reproducibility, reversibility, stability and low leaching and a long lifetime of over 7 months.

Surface modification of Kevlar fiber by nanoSiO2 deposition in supercritical fluid

ABSTRACTIn this work, we modified Kevlar fiber first by depositing nano SiO2 on its surface from sol-gel reaction of tetraethylorthosilicate (TEOS) and formic acid using supercritical carbon dioxide (scCO2) as the solvent. The results showed that the Kevlar fiber surface can be successfully deposited with nano SiO2 in this manner while its properties were hardly affected by the supercritical carbon dioxide environment. However, special attention needs to be given to an optimal scCO2 pressure for the purpose of enhancing the interfacial adhesion and shear strength between Kevlar fiber and epoxy resin as too low or too high pressures result in certain morphologies of deposited nano SiO2 particles that give rise to insufficient penetration of the resin into the fiber surface. Plasma treatment was found to provide a significant surface etching effect that is more effective than nano SiO2 deposition alone. Moreover, it has such a synergistic effect with nano SiO2 deposition that when they were employed sequentially, the interface between the Kevlar fiber and the epoxy resin has the strongest adhesion and shear strength, which are 83.6% higher than those in the original composite with no surface treatment.

Mechanically durable superamphiphobic surfaces via synergistic hydrophobization and fluorination

Superhydrophobic poly(ethylene terephthalate) (PET) fabrics were firstly fabricated by one-pot in situ Stöber reaction of tetraethylorthosilicate (TEOS) and dodecyltrimethoxysilane (DTMS), in which the as-formed silica particles roughened the fiber surfaces and the hydrolyzed dodecyltrimethoxysilane hydrophobized the fabrics. Then the superhydrophobic fabrics were turned superamphiphobic after modification with perfluorodecyltrichlorosilane (PFDTS), with water and oil contact angles higher than 150°. The synergistic hydrophobization of DTMS, PFDTS and PDMS made the roughened fabrics easy to be superamphiphobic using very low concentration of PFDTS. Meanwhile, the as-obtained superamphiphobic fabric showed excellent chemical robustness even after exposure to different chemicals, such as acid, base, and salt. Importantly, the fabrics were durable to 100 cycles of laundries, 1000 cycles of mechanical abrasion as well as long time exposure to UV irradiation without apparently changing the amphiphobicity. Also, the surface of the superamphiphobic fabrics showed excellent blood stain resistance properties.

Preliminary Study on Tensile Properties of Electrospun Silica Fibers/Polypropylene Composites

Composites based on silica and glass fibers conventionally contain fibers with dimension in the range of a few micrometers to millimeters. Electrospinning technique allows fabrication of fibers in the submicron length scale. With smaller dimension, these fibers when applied as reinforcement in composites may yield interesting composite properties. In this paper, silica fibers fabricated via electrospinning were utilized as reinforcement in polypropylene-matrixed composites. The silica precursor was prepared by sol-gel reaction of tetraethyl orthosilicate, ethyl alcohol, de-ionized water and hydrochloric acid. Viscous silica precursor was made into fibers by electrospinning with electric field of 1 kV/cm. Electrospun non-woven fiber mats were stabilized at 200°C and calcined at 800°C to remove remaining organic residues. The fiber diameter average was 279±40 nm. In the process of making composites, the silica fiber mats were sandwiched between polypropylene sheets, and the layers were compression-molded together. The composite samples with varied silica fiber contents up to 2 wt% were mechanically tested. Tensile tests demonstrate slight increases in tensile modulus, tensile strength with increasing silica fiber content. However, silica fiber content within the experimental range does not have prominent effects on yield strength and strain at break.

Nouveaux Matériaux hybrides organiques–inorganiques obtenus par action du tétraethoxysilane avec des molécules hétérocycliques bi-fonctionnelles

GRAPHICAL ABSTRACT

Hybrid silica bearing different organosilanes produced by the modified Stöber method

The Stöber method was used to prepare a variety of functionalized silica through the reaction of tetraethyl orthosilicate (TEOS) and several organosilanes. The organosilanes differed in the number of carbons in the alkyl chain as well as in the functional groups. The TEOS:organosilane ratio employed was 90:10M. The resulting materials were characterized by nitrogen adsorption-desorption porosimetry, small angle X-ray scattering, scanning electron microscopy, transmission electron microscopy, contact angle measurements and Fourier transform infrared spectroscopy. Spherical functionalized silica microparticles approximately 0.5μm in size with increased hydrophobicity were obtained. The adsorption-desorption isotherms were independent of the nature of the organosilane employed and can be classified as type II, typical of nonporous solids. The contact angle was between 0 and 153°. The presence of organic moieties on the silica can modify the morphology and the hydrophilicity of the materials produced by the Stöber method.

Sol–gel derived silica thin films immobilized with 1,10-phenanthroline and their binding activity toward iron(II)

Transparent sol–gel thin films immobilized with 1,10-phenanthroline were prepared via the acid-catalyzed sol–gel reaction of tetraethylorthosilicate (TEOS) in the presence of phen. Three surfactants that include cationic cetyl trimethyl ammonium bromide (CTAB), anionic sodium dodecyl sulfate (SDS) and non-ionic Triton X-100 (TX-100) were tested for the improvement of the host material mesostructure, increasing its porosity and good accommodation of the phen within the silica matrix. The immobilized phen thin films showed similar behavior as their free counterpart in aqueous solution. The immobilized phen complex retained its activity toward Fe2+ metal ions by immobilization and produced a stable complex without any shift in the wavelength of Vis absorption spectra comparing with its free counterpart. Different parameters including concentrations of phen, Fe2+ and surfactant, type of surfactant, lifetime and number of measurements were investigated. The phen thin film sensor showed high sensitivity, chemical stability, good reproducibility and long lifetime behavior. The immobilized phen thin films were used for quantification of iron(II) in versatile aqueous samples. The polarized light microscopy indicated that the phen molecules were distributed uniformly within the host silica network.

Effects of in situ and ex situ formations of silica nanoparticles on polyethersulfone membranes

This study deals with the observed changes in the structure and performance of polyethersulfone (PES) membranes due to in situ formation and ex situ addition of silica particles (SiO2). Hydrolysis and condensation of tetraethyl orthosilicate (TEOS) inside the PES polymer matrix and the reaction of TEOS with ammonium hydroxide were chosen to form in situ and ex situ SiO2 formations, respectively. The resultant structure confirmed by X-ray diffraction for the composite PES membranes showed the retention of the amorphous nature even after the addition of SiO2. The FTIR study revealed the functional groups corresponding to silica networks with enhanced OH signatures on the surface of the composite membranes. Field emission scanning electron microscopic images showed the variation in the surface and cross-sectional structures for the pure and composite membranes. Considerable reduction in the thickness of the skin, difference in the pore structure and ‘finger-like’ cross-sectional morphology with the presence of SiO2 was observed in PES membranes. Both SiO2/PES composite membranes were showed a minor change in their glass transition temperature (Tg). The ex situ methodically formed composite membrane displayed an increase in the pure water flux and decrease in bovine serum albumin rejection as compared to in situ and pure PES membranes. These kinds of composite membranes can be utilized for water treatment applications demanding higher water flux.

Modulating Release of Metoprolol Tartrate with Nanostructured Silica Particles

To develop a kind of gastrointestinal timed-release preparation for Metoprolol Tartrate, nanostructured silica particles were chose for the purpose. Briefly, MCM-41 type mesoporous silica nanospheres with a size of 100-200 nm were synthesized through the reaction of tetraethyl orthosilicate (TEOS) in the water medium at 353 K, with introducing some cetyltrimethyl ammonium bromide (CTAB) as porogens. Various analytical methods, including FT-IR, XRD, TEM, N2 physisorption and thermal analysis, were applied to characterize the final products. Metoprolol Tartrate was then loaded into the mesoporous silica nanospheres by soaking. Results of the release of the drug in simulated gastric juice indicated that the drug can release up to 24 h and its maximum released amount was 4.5%. In the simulated intestinal juice the maximum cumulative released amount of metorprolol was 10.8%.In vitro release behavior revealed that the mesoporous silica were appropriate used as drug delivery system.

Arsenic removal from water/wastewater using nanoparticle-assisted hollow fiber solid-phase microextraction combined with hydride generation–atomic fluorescence spectroscopy

In the present work, hollow fiber solid-phase microextraction coupled with hydride generation–atomic fluorescence spectroscopy was employed in the extraction and determination of Arsenic(III), in water samples including acid mine drainage, gold mine wastewater and spring water of Iran. In this technique, an innovative solid sorbent containing mixture of nano TiO2 and a composite microporous compound was developed by the sol–gel method via the reaction of tetraethylorthosilicate and methyltrimethoxysilane. Sol–gel processing was done under acidic catalyst condition. The stated sol was held in the lumen of a porous polypropylene hollow fiber segment for in situ gelation procedure. The experimental setup is very simple and highly affordable. The hollow fiber is disposable, so single use of the fiber reduces the risk of cross-contamination and carry-over problems. The main factors influencing the pre-concentration and extraction of As(III) have been examined in detail. The optimized conditions were obtained and the relationship between the atomic fluorescence signal versus As(III) concentration was linear over the range of 0.01–30 μg L−1 for As(III). The limits of detection and quantification were 0.003 and 0.01 μg L−1, respectively. Under the adjusted conditions, the enrichment factor was 501.4.

VOCs physisorption on micro–mesoporous solids: Application for dichloroethylene, trichloroethylene, and tetrachloroethylene on SiO2 and Ag/SiO2

An experimental physisorption study on the adsorption of chloroalkenes (CXHYClZ), such as dichloroethylene, trichloroethylene and tetrachloroethylene, on SiO2 and Ag-doped SiO2 micro–mesoporous solids is performed. The existence of the adsorbed phase is assessed by observing the position of the incumbent FTIR chloroalkene vibration bands. The SiO2 substrates are prepared from the reaction of tetraethyl orthosilicate and water in the presence of ethanol. Adsorption of CXHYClZ compounds on the pristine and Ag-doped SiO2 samples is measured in the temperature range 408–523K by a chromatographic method. The uptake degree of the chlorinated compounds results to be temperature dependent, and the Freundlich adsorption model is found to fit the CXHYClZ adsorption data. The degree of interaction between these molecules and the SiO2 samples is analyzed through evaluation of the isosteric heat of adsorption of C2H2Cl2 at different sorption loadings on the SiO2 and Ag/SiO2 substrates. This heat is found to fulfill the following decreasing order: SiO2>Ag/SiO2 (2wt.% Ag)>Ag/SiO2 (10wt.% Ag)>Ag/SiO2 (5wt.% Ag).

Alcohol Interchange Synthesis of a Novel Titanium Glycolate

A much simpler and more straightforward method, alcohol interchange for the synthesis of titanium glycolate has been suggested. The method implied the reaction of tetraethyl orthosilicate with ethylene glycol on heating in air. The thermal property of titanium glycolate was characterized by thermal gravimetric (TG) and Differencial Thermal Analysis (DTA) analysis. X-ray diffraction (XRD) was used to confirm the conversion of crystalline phase of titanium glycolate from anatase to rutile. The characterization of titanium glycolate and products of its pyrolysis was conducted using scanning electron microscopes.

Synthesis and Characterization of Sn Doped SiO<sub>2</sub> by Reverse Micelle and Sol-Gel Process

Sn doped SiO2nanoparticles have been synthesized using a reverse micelle technique combined with metal alkoxide hydrolysis and condensation. The size of the particles and the thickness of the coating can be controlled by manipulating the relative rates of the hydrolysis and condensation reactions of tetraethyl orthosilicate (TEOS) within the micro-emulsion. The properties of the Sn doped SiO2nanoparticles were studied as a function of various processing parameters such as R and H value. The average size of synthesized Sn doped SiO2nanoparticles was about in the size range of 20-40 nm and core particle (Sn) 1-5 nm. The Sn doped SiO2nanoparticles were characterized by X-ray diffraction (XRD) and Transmission electron microscopy (TEM).

Synthesis of Au–silica core–shell particles by sol–gel process

This paper describes an amine free sol–gel method for silica coating of Au nanoparticles and shows an X-ray image of a colloid solution of the silica coated Au (Au–SiO2) particles. The Au nanoparticles that had a size of 16·9±1·2 nm were prepared through a conventional citrate reduction method. The silica coating was performed with a sol–gel reaction of tetraethylorthosilicate (TEOS) catalysed with NaOH in the presence of Au nanoparticles. The silica shell thickness was varied from 37 to 68 nm for TEOS concentrations of 1×10−3–20×10−3M at 4·3×10−5M of Au, 10·7M of H2O and 1·0×10−3M of NaOH. The optical properties of the Au–SiO2 particle colloid solution were related to the refractive index around the Au particles and the intensity of scattering from silica shells. The as prepared colloid solution could be concentrated up to an Au concentration of 4·3×10−2M with salting out. The concentrated colloid solution showed a high contrast X-ray image.

Ionic liquid mediated sol–gel sorbents for hollow fiber solid-phase microextraction of pesticide residues in water and hair samples

An ionic liquid mediated sol–gel sorbents for hollow fiber solid-phase microextraction (HF-SPME) was developed for extraction of the pesticides: diazinon, fenitrothion, malathion, fenvalerate, phosalone and tridemorph from human hair and water samples. The analytes were subsequently analyzed with high performance liquid chromatography and diode array detection (HPLC–DAD). Preliminary experiments were carried out in order to study experimental conditions for pesticides’ extraction from spiked hair and water samples with HF-SPME using hollow fiber-supported ionic liquid mediated sol–gel sorbent. The sol–gel nanocomposites were reinforced with nanoparticles such as carboxylic functionalized multi-walled carbon nanotubes (COOH-MWCNTs), amino functionalized multi-walled carbon nanotubes (NH 2-MWCNTs), nano SiO 2, nano TiO 2 and nano MgO comparatively to promote extraction efficiency. In this device, the innovative solid sorbents were developed by the sol–gel method via the reaction of tetraethylorthosilicate (TEOS) with 2-amino-2-hydroxymethyl-propane-1,3-diol (TRIS). In the basic condition (pH 10–11), the gel growth process in the presence of ionic liquid and nanoparticles was initiated. Then, the sol was injected into a polypropylene hollow fiber segment for in situ gelation process. Parameters affecting the efficiency of HF-SPME were thoroughly investigated. Linearity was observed over a range of 0.01–25,000 ng/mL with detection limits between 0.004 and 0.095 ng/mL for the pesticides in the aqueous matrices and 0.003–0.080 ng/mL in the hair matrices. The relative recoveries in the real samples ranged from 82.0% to 94.0% for the pesticides store seller's hair and the work researchers’ hair. Results are showing the great possibilities of HF-SPME–HPLC-PDA for analysis of pesticides in biological and environmental samples.

The Research of Silica-Coated Chromium Oxide Green Pigment Prepared by Liquid Phase Method

This paper is researched on SiO2-coated Cr2O3 for the hydrolysis reaction of tetraethyl orthosilicate. The influences of precursors, solid contents of suspension and Si ratio of water on coated particle surface are investigated. The products are characterized and the conclusion shows that the experimental method is feasible.

Simultaneous extraction and determination of lead, cadmium and copper in rice samples by a new pre-concentration technique: Hollow fiber solid phase microextraction combined with differential pulse anodic stripping voltammetry

In the present work, a novel solid phase microextraction (SPME) technique using a hollow fiber-supported sol–gel combined with multi-walled carbon nanotubes, coupled with differential pulse anodic stripping voltammetry (DPASV) was employed in the simultaneous extraction and determination of lead, cadmium and copper in rice. In this technique, an innovative solid sorbent containing mixture of carbon nanotube and a composite microporous compound was developed by the sol–gel method via the reaction of tetraethylorthosilicate (TEOS) with 2-amino-2-hydroxymethyl-propane-1,3-diol (TRIS). The growth process was initiated in basic condition (pH 10–11). Afterward this sol was injected into a polypropylene hollow fiber segment for in situ gelation process. The main factors influencing the pre-concentration and extraction of the metal ions; pH of the aqueous feed solution, extraction time, aqueous feed volume, agitation speed, the role of carbon nanotube reinforcement (as-grown and functionalized MWCNT) and salting effect have been examined in detail. Under the optimized conditions, linear calibration curves were established for the concentration of Cd(II), Pb(II) and Cu(II) in the range of 0.05–500, 0.05–500 and 0.01–100 ng mL −1, respectively. Detection limits obtained in this way are, 0.01, 0.025 and 0.0073 ng mL −1 for Cd(II), Pb(II) and Cu(II), respectively. The relative standard deviations (RSDs) were found to be less than 5% ( n = 5, conc.: 1.0 ng mL −1).