Precursor Tetraethyl Orthosilicate Research Articles

Sol–gel network silica/modified montmorillonite clay hybrid nanocomposites for hydrophobic surface coatings

Sol–gel silica/nanoclay composites were prepared through sol–gel polymerization technique using tetraethylorthosilicate precursor and montmorillonite (MMT) clay in aqueous media. In this study, both montmorillonite-K + and organically modified MMT (OMMT) clays were used. The prepared composites were coated on glass substrate by making 1 wt% solution in ethyltrichlorosilane. The incorporation of nanoclay does not alter the intensity of characteristic Si–O–Si peak of silica network. Thermogravimetric studies show that increasing clay content increased the degradation temperature of the composites. Differential scanning calorimetry (DSC) results of organically modified MMT nanoclay incorporated composite show a shift in the melting behavior up to 38 °C. From DSC thermograms, we observed that the Δ H value decreased with increasing clay loading. X-ray diffraction patterns prove the presence of nanoclay in the composite and increase in the concentration of organically modified nanoclay from 3 to 5 wt% increases the intensity of the peak at 2 θ = 8° corresponds to OMMT. Morphology of the control silica gel composite was greatly influenced by the incorporation of OMMT. The presence of nanoclay changed the surface of control silica gel composite into cleaved surface with brittle in nature. Contact angle measurements were done for the coatings to study their surface behavior. These hybrid coatings on glass substrate may have applications for hydrophobic coatings on leather substrate.

Corrosion behavior of organically modified silicates coatings

PurposeThe purpose of this paper is to develop hybrid organic‐inorganic silica‐based nanocomposite films, by sol‐gel method, for corrosion protection of AA2024 alloy. Also, cerium nitrate corrosion inhibitor is introduced into the optimized coating in the next step of the investigations in order to study the improvement in the corrosion protection properties of the organically modified silicate (Ormosil) films.Design/methodology/approachThe sol‐gel films have been synthesized from 3‐glycidoxypropyltrimethoxysilane and tetraethylorthosilicate precursors. In order to investigate the effective factors on the properties of Ormosils films, different coatings with different organic and hydrolysis water content were developed. Then, cerium nitrate corrosion inhibitor was added to the coatings. The structure of the hybrid sol‐gel films was studied by scanning electron microscopy. The corrosion protection properties of the films were studied by potentiodynamic scanning, and electrochemical impedance spectroscopy, respectively.FindingsThe results indicate that the hybrid films provided exceptional barrier and corrosion protection in comparison with untreated aluminium alloy substrate. Moreover, improvement of the protection properties of the films containing cerium nitrate corrosion inhibitor occurred with immersion time. This would imply that cerium ions could reach the defects, and reduce the corrosion rate.Originality/valueThis paper provides the development of Ormosils coating, which exceptionally improves the corrosion protection of 2024 aluminium alloy.

Counter-ions diffusion properties of silica embedded poly(perfluorosulfonic) acid membrane

To study the possibility of modifying diffusional-transport properties of the poly(perfluorosulfonic) acid (Nafion-117) membrane, the silica particles were incorporated in its matrix by in situ sol–gel method. The amount of silica incorporated in the membrane samples was varied by controlling the equilibrating time of the membrane sample in solution containing fixed proportion of precursor tetraethylorthosilicate (TEOS), methanol and water. The silica contents in the membrane samples were characterized by gravimetry, energy dispersive X-ray analysis (EDXRF) and transmission electron microscopy (TEM). Differential scanning calorimetry (DSC) studies showed that there were no significant difference in transition peak temperatures of both samples (Nafion-117 and Nafion/SiO 2) in same ionic form except that enthalpies were increased in Nafion/SiO 2 samples in all the ionic forms. The increase in enthalpy was due to higher water content in Nafion/SiO 2 as compared to Nafion-117 in given ionic form as enthalpies normalized with water content of the respective membrane were comparable. The ion-exchange capacity, water uptake capacity and ion-exchange isotherms of the Na + + Cs + and Na + + Ba 2+ binary systems in silica embedded membrane samples were experimentally measured using appropriate radiotracers, and compared with that of pristine Nafion-117 membrane. The specific conductivities of the membrane samples with and without silica were studied in Na +, Cs + and Ba 2+ ionic forms by electrochemical impedance spectroscopy (EIS). The self-diffusion coefficients of Na +, Cs + and Ba 2+ ions in the Nafion/SiO 2 were measured by the radiotracer method. It was observed from the experimentally measured specific conductivities and self-diffusion coefficients data that diffusion mobility of Cs + and Ba 2+ counter-ions were enhanced significantly after incorporation of SiO 2 in the Nafion-117 matrix. Contrary to this, diffusion mobility of Na + counter-ion decreased in Nafion/SiO 2 sample. The selectivity of Cs + and Ba 2+ counter-ions was reduced in Nafion/SiO 2 sample with respect to pristine Nafion-117.

Tunable distributed feedback lasing from leaky waveguides based on gel-glass dispersed liquid crystal thin films

Different amount of nematic liquid crystal (LC) 4-Cyano-4′-pentylbiphenyl(5CB) was encapsulated in sol–gel derived organically modified silica(ORMOSIL) matrices to fabricate dye doped gel-glass dispersed liquid crystal (GDLC) thin films by co-hydrolyzation/condensation of ethyl triethoxisilane (ETES) and tetraethyl orthosilicate (TEOS) precursors. Distributed feedback (DFB) leaky waveguide lasers from GDLC thin films using a dynamic grating were demonstrated. Tunable laser action from 558 to 570 nm was obtained in the sample with lowest LC concentration of 0.375 mol%. The DFB laser performance of GDLC thin films with various LC concentrations was investigated using the same pumping geometry, and it was shown that the encapsulation of 5CB also led to the red shift of lasing peak.

Preparation and Properties of Hydrophobic Silica Aerogels by Ambient Pressure Drying Method

Silica alcogels were prepared by hydrolysis with hydrochloric acid and condensation with NH4OH of ethanol diluted tetraethylorthosilicate (TEOS) precursor and trimethylchlorosilane and hexane as surface modifying agent. The physical properties such as density, appearance, hydrophobicity, surface area, pore size distribution and thermal stability were measured. It was found that the physical and hydrophobic properties of the silica aerogels depend on the TMCS/hexane (V) volume ratio. The density decreased with increase ofV, and the aerogels are more hydrophobic asV=3%. The aerogels were thermally stable up to a temperature of 350 °C, and the aerogel prepared has a high surface area and large pore volume.

The Use of Highly Ordered Vesicle Gels as Template for the Formation of Silica Gels

A spontaneously forming gel of unilamellar vesicles based on sodium oleate (Na oleate) and 1-octanol as amphiphiles has been employed as a template in the formation of a silica gel formed by the hydrolysis of the inorganic precursor tetraethyl orthosilicate (TEOS). Up to about 10 wt % TEOS can be incorporated into this vesicle gel without phase separation and in a fully homogeneous formation process by simple mixing of the components. The process itself relies solely upon the self-organizing properties of this amphiphilic template system. The formation process was followed by means of time-resolved turbidity, rheology, and small-angle neutron scattering (SANS) experiments. It can be concluded that the presence of the precursor TEOS affects the kinetics of the process but the original vesicle gel structure is retained even up to highest TEOS content. The kinetic studies confirm that under the chosen conditions the vesicle formation proceeds much faster than the hydrolysis of TEOS and the subsequent formation of the silica gel. SANS displays in the low q-range an additional scattering due to the silica gel network, i.e., a hybrid material of an amphiphilic vesicle gel and an inorganic oxide gel is formed. Thus, this method is a very facile novel route of forming a highly ordered silica/vesicle gel by employing a self-organizing amphiphilic system as template and the formation of the silica network proceeds in a fully homogeneous fashion under kinetic control.

Silane grafting of TiO2 nanoparticles: dispersibility and photoactivity in aqueous solutions

AbstractTitania nano‐sized particles were treated by various amounts of tetraethyl orthosilicate precursor. The extent of grafting was characterized using Fourier transform infrared (FTIR) and ultraviolet‐visible (UV‐Vis) spectroscopy techniques, thermal gravimetric analysis, X‐ray fluorescence and zeta potential measurements. Sedimentation behaviour of titanium dioxide (TiO2) nanoparticles in aqueous solutions was evaluated visually and using a separation analyser. Photocatalytic activity of nanoparticles was studied by photo‐activated degradation reaction of Rhodamine B dyestuff in aqueous solutions. The results showed that grafted particles had acquired enhanced dispersion stability and lower photocatalytic activity in aqueous solutions. Untreated TiO2 dispersions settled rapidly and sedimentation completed within 24 h through the coagulation mechanism, whereas that of the silica‐treated nanoparticles, depending on the silica content, showed different degrees of stability by flocculation mechanism. Photodebleaching of Rhodamine B in the presence of treated nanoparticles is evident by weaker intensity of UV absorption peak of 554 nm due to lowering concentration of Rhodamine B accompanied with the blue shift in UV absorption peaks. However, untreated TiO2 nanoparticles showed only weaker intensity of UV absorption peak. Copyright © 2011 John Wiley & Sons, Ltd.

Comparative study of the initial stage sintering behaviour of micro- and nano-size dense spherical silica particles

The initial stage sintering behaviour of dense spherical silica particles as a function of particle size in the range of 100–370 nm has been studied. Three powders of dense spherical silica particles (average size 370, 150 and 100 nm) with a sharp size distribution were synthesised by controlled hydrolysis of a tetraethylorthosilicate precursor. Sintering was performed in a conventional electrical furnace and the initial compact was not put under any forming mechanical pressure. The shrinkage was monitored indirectly by measuring the specific surface area of the samples using nitrogen adsorption at 77 K. As the size approaches 100 nm, the activation energy decreases ca. one order of magnitude (125–140 kcal mol−1 for d≥150 nm and 11–13 kcal mol−1 for d≃100 nm). The authors propose that a densifying sintering mechanism, lattice diffusion from grain boundary or/and grain boundary diffusion, prevails throughout the particle size range under investigation.

Synthesis of mesoporous metal complex-silica materials and their use as solvent-free catalysts

Incorporation of various Pd(II) complexes into the framework of MSU-X mesoporous silica has been achieved by co-condensation using a facile solvent-free one-pot synthesis. The use of ligands with triethoxysilyl terminal groups permitted the synthesis of three different metallosilanes precursors (metal complexes with ligands containing trialkoxysilane terminal groups), which allow for the homogeneous in situ incorporation of metal complexes covalently bonded to the porous support. Inorganic precursor tetraethylorthosilicate was used both as silica source and as solvent for the synthesis of the complexes, avoiding the use of other organic co-solvents, making the synthesis environmentally benign. The gentle synthesis conditions used such as neutral pH, room temperature and mild ethanol extraction of the surfactant, allowed a cleaner route for the immobilization of homogeneous Pd(II) catalysts in mesoporous silica, while protecting the structural and chemical integrity of the metal complexes. For comparison purposes, monomer complexes [trans-PdCl2L2] (L = NH2(CH2)3Si(OEt)3, 4-C5H4N–(CH2)2Si(OEt3), PPh2(CH2)2Si(OEt)3) were synthesized using the same aerobic reaction conditions to those use for the co-condensation processes and fully characterized before their incorporation in the mesoporous silica. The catalytic performance of these materials was tested for the Suzuki-Miyaura reaction under solvent-free conditions. Efficient mixing of all the components was accomplished by applying either magnetic stirring or ball milling. The good yields obtained, even at room temperature, confirmed the catalytic activity of the metal complexes once incorporated into the mesoporous silica framework. The possibility to work under solvent-free conditions even with solid starting reactants, is a significant step forward in the Suzuki-Miyaura coupling reaction because its benefits in terms of cost and impact of the environment.

Deposited Thin SiO2 for Gate Oxide on n-Type and p-Type GaN

Here, we report on a comparison of two different methods to achieve thin deposited layers for gate oxide on n- and p-type GaN by using plasma-enhanced chemical vapor deposition with silane and tetraethyl orthosilicate precursors. An annealing was performed at for 2 min in ambient as an attempt to improve electrical characteristics. Before and after annealing, capacitors were electrical/physically analyzed by capacitance–voltage (C-V), conductance–voltage, current–voltage, optical microscope, scanning electron microscope, atomic force microscope, and secondary-ion mass spectrometry. Globally, the p-type samples presented higher interface state density and rougher surfaces, and in some C-V measurements, it is possible to observe inversion-like characteristics. The surface roughness also increases after annealing. The interfacial trap density for the different interfaces has been determined. Silane samples exhibit lower than TEOS samples. For n-type, annealed from silane has been found as the sample with the lowest . The annealing on the from silane samples is not so efficient for the p-type with the actually increasing. A discussion on the different diffusion mechanisms in correlation with the electrical results is performed in the last section of this paper.

Properties of Ionic Liquid Confined in Porous Silica Matrix

Porous silica matrices of different pore sizes with confined ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) [BMIM] [PF(6)] were prepared by sol-gel technique using a tetraethyl orthosilicate (TEOS) precursor with an aim to study the changes in physico-chemical properties of ionic liquid on confinement. It is found that on confinement 1) melting point decreases, 2) fluorescence spectra shows a red shift and 3) the vibrational bands are affected particularly those of imadazolium ring, which interacts more with the walls of the silica matrix. Preliminary theoretical calculations suggest that SiO(2) matrix interact more with the heterocyclic group of [BMIM] cation than the tail alkyl chain end group resulting in significant changes in the aromatic vibrations.

Atmospheric pressure plasma enhanced synthesis of flame retardant cellulosic materials

AbstractFlame retardant cellulosic materials have been produced using a silicon dioxide (SiO2) network coating. SiO2 network armor was prepared through hydrolysis and condensation of the precursor tetraethyl orthosilicate (TEOS), prior coating the substrates, and was cross linked on the surface of the substrates using atmospheric pressure plasma (APP) technique. Because of protection effects of the SiO2 network armor, the cellulosic based fibers exhibit enhanced thermal properties (characterized by TGA and DSC) and improved flame retardant (proven by ASTM D1230‐99). Furthermore, the surface analysis (XPS and SEM) confirmed the presence of the SiO2 network attached to the substrates even after intense ultrasound washes. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

In vitro and In vivo Optical Imaging Using Water-Dispersible, Noncytotoxic, Luminescent, Silica-Coated Quantum Rods

A facile method for synthesis of monodisperse, biocompatible, silica coated CdSe/CdS/ZnS quantum rods (QRs) and their use as probes for in vitro and in vivo optical bioimaging is presented. The silica coating procedure involves condensation-polymerization of the precursor tetraethylorthosilicate (TEOS) over QRs encapsulated within the reverse micellar core of Igepal CO-520/cyclohexane microemulsion. The silica-coated QRs have been characterized by TEM, DLS, and photoluminescence spectroscopy. The silica shell thickness has also been shown to be tuned by varying the ratio of TEOS and QRs. Confocal bioimaging of different cell lines (Panc 1 and RAW), treated with silica coated QRs, has shown a robust uptake of the nanoparticles, without the need of specific targeting molecules. To evaluate the cytotoxicity of the nanoparticles, MTS assay has been carried out over a period of 48 h. In vivo imaging of subcutaneously xenografted tumor-bearing mice, following direct intratumoral injection of the nanoparticles, ...

10.1007/s11490-008-1011-4

In view of laser-assisted medical applications, the construction of silica-based sol-gel fiberoptic sensors based on photolon (Ph) and protoporphyrin IX (PP IX) is discussed. Electron microscopy and AFM were used to characterize the silica sol-gel coatings. AFM measurements indicate a change in the surface porosity. The PP IX-based sensors were constructed as a one-layer optode as well as a multilayered structure. An additional hybrid sensor made up of alternate layers of PP IX-and Ph-doped sol-gel was also constructed and examined. Sol-gel matrices were prepared from silicate precursor tetraethylorthosilicate (TEOS) mixed with ethanol in acid-catalyzed hydrolysis. The carrier matrices of photosensitive dyes were produced with factor R = 20, where R denotes the ratio of solvent moles (ethanol) to the number of TEOS moles. A multilayered coating was built up using the reverse-dipping technique. The overall coating thickness was determined by electron microscopy. Doped sol-gels with different PP IX concentrations were used to produce fiberoptic coatings. The film optodes with a different number of layers were examined by fluorescence spectroscopy. It was found that photolon and protoporphyrin IX entrapped in sol-gel preserve their chemical reactivity and have contact with the external environment. The hybrid sensor demonstrated clear fluorescence and a reversible behavior in gaseous environments.

In situ generated silica nanoparticles as pore-forming agent for enhanced permeability of cellulose acetate membranes

Due to its rigid and tunable structure, inorganic pore-forming agent may exhibit the great potential in fabricating membranes with high flux. In this study, in situ generation of silica (SiO 2) nanoparticles was coupled with polymer phase separation process for preparing cellulose acetate (CA) membranes with enhanced permeation property. The pH values of coagulation bath were adjusted with acid and basic solutions to perform the hydrolysis and polycondensation reaction of tetraethyl orthosilicate (TEOS) precursor at moderate rate. The pore-forming mechanism of the generated SiO 2 nanoparticles was tentatively proposed. Majority of SiO 2 nanoparticles were instantly extracted into the coagulation bath during the phase inversion process and the spaces they once occupied turned into the pores of membranes, ensuring the great improved permeability of the CA membranes. The remained nanoparticles were mostly enriched and homogenously distributed on the membrane surface without lowering the hydrophilicity of CA membranes. Ultrafiltration experiments showed that the as-fabricated CA membranes exhibited higher permeability and kept superior antifouling properties compared with the control CA membrane in oil/water emulsion separation.

Effect of precursor types on the characteristics of the Pb-based glass powders prepared by spray pyrolysis

Lead (Pb)-based glass powders with a spherical shape and submicron size were directly prepared by spray pyrolysis using spray solutions with various types of Pb and silicon (Si) components. The glass powders formed by the spray solution with Pb chloride and tetraethyl orthosilicate (TEOS) precursors had a broad X-ray diffraction (XRD) peak at around 28° with small crystalline peaks. The powders had an impurity peak caused by chlorine in the EDX spectrum. However, the glass powder formed from the spray solutions that contained Pb nitrate and Pb acetate precursors had an amorphous phase, irrespective of the type of Si precursor. The dielectric layers formed from the glass powders obtained from the spray solutions with Pb nitrate and Pb acetate had a dense structure and high transmittance above 85%, irrespective of the type of Si precursor components. In contrast, the dielectric layer formed from the glass powders prepared from the spray solution with Pb chloride and TEOS had large voids in the layer and had low transmittance below 50% under the visible range.

A fluorophore grafted 2D-hexagonal mesoporous organosilica: Excellent ion-exchanger for the removal of heavy metal ions from wastewater

Highly ordered 2D-hexagonal luminescent organic–inorganic hybrid mesoporous silica (LHMS-2) containing a fluorophore inside the pore walls has been synthesized hydrothermally by using a non-ionic triblock co-polymer surfactant F127 as template under strongly acidic synthesis condition. XRD and HR TEM image analyses suggest the formation of highly ordered 2D-hexagonal mesophase from a mixture of diimine organosilica and tetraethyl orthosilicate (TEOS) precursors. 13C CP MAS, 29Si MAS NMR, UV–visible absorption and PL spectroscopic data suggests the incorporation of bridging organic diimine fluorophore in the solid mesoporous material. N2 sorption data indicates high BET surface area together with type IV isotherm, characteristics of well-defined mesopores for this material. This fluorophore grafted mesoporous material shows very strong affinity for metal cations like Fe3+, Zn2+, Cd2+ and Hg2+, and thus can be very efficiently utilized for the removal of these heavy metal ions from wastewater.

The Influence of Process Parameters on Chemistry, Roughness and Morphology of Siloxane Films Deposited by an Atmospheric Plasma Jet System

AbstractSiloxane coatings were deposited onto Vycor™ glass and silicon substrates from a tetraethyl orthosilicate (TEOS) precursor using the PlasmaStream™ atmospheric plasma jet system. The TEOS precursor was nebulized into He/O2 plasma and the coating growth rate was controlled by the number of passes of the jet over the ceramic substrates. The system process parameters were systematically varied to study their influence on the coating properties. The chemical properties, surface roughness, and morphology of the 1–200 nm thick coatings were studied as a function of both applied plasma power and TEOS flow rate. The deposited coatings were examined using ellipsometry, contact angle measurement, optical profilometry, Fourier transform infrared spectroscopy (FT‐IR), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM).

Influence of Atmospheric Plasma Source and Gas Composition on the Properties of Deposited Siloxane Coatings

AbstractSiloxane coatings were deposited using two different atmospheric plasma systems namely a reel‐to‐reel atmospheric plasma liquid deposition system called Labline™ and an atmospheric plasma jet system called PlasmaStream™. Both systems combine an atmospheric plasma, with the use of liquid precursors. The influence of the plasma source and processing conditions on the deposited coating properties were studied. The coatings were deposited onto Vycor glass and silicon wafer substrates from a liquid tetraethyl orthosilicate (TEOS) precursor which was nebulized into both He and He/O2 plasmas. Higher film growth rates were obtained using the plasma jet system; however, the reel‐to‐reel system facilitated the larger area coating of webs. The thickness (spectroscopic ellipsometry measurements) and water contact angle profile of the films deposited using the jet system on silicon wafer substrates in static mode were investigated. Amongst the other coatings characterization techniques used to evaluate the deposited coatings were optical profilometry, XPS, SEM, and AFM. The formation of particulates due to excess gas‐phase reactions during the atmospheric plasma deposition of coatings has been widely reported. In this study, larger number of particulates were observed under the conditions of higher plasma power, with the addition of O2 into the He plasma and also at low TEOS flow rates. The introduction of N2 into the He/O2 plasma, during the deposition of siloxane coatings led to a significant reduction in the number of particulates generated for both plasma sources. Nitrogen gas flow rate was varied systematically and a correlation was obtained on the influence of the flow rate of this gas on surface roughness and particulate formation.

Corrosion protection evaluation of silica/epoxy hybrid nanocomposite coatings to AA2024

Silica-based organic–inorganic hybrid nanocomposite films have been developed by sol–gel method for corrosion protection of AA2024 alloy. The sol–gel films have been synthesized from 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethylorthosilicate (TEOS) precursors. Interlinked organic–inorganic networks can be formed because of the presence of both epoxy and silicon alkoxide functionalities in the precursor molecules. In order to investigate the effective factors on the properties of organically modified silicates films (Ormosils), different coatings with different organic and hydrolysis water content were developed. The films were prepared by dip-coating technique. The chemical composition and the structure of the hybrid sol–gel films were studied by energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM), respectively. The corrosion protection properties of the films were studied by potentiodynamic scanning (PDS) and salt spray tests. The results indicate that the hybrid films provided exceptional barrier and corrosion protection in comparison with untreated aluminium alloy substrate.