Polymerization Of Tetraethylorthosilicate Research Articles

Synthesis of iron oxide nanocubes and their incorporation with luminescent lanthanide (Ln = Tb/ Eu)-Terephthalate complex in silica nanospheres using a reverse microemulsion method

Luminescent magnetic nanocomposites are of interest because of their promising applications in the biomedical field. This article reports the preparation of silica-coated lanthanide terephthalate complexes, Ln-TA (Ln = Tb and Eu) containing luminescent magnetic nanocomposites. Cubic-shaped iron oxide nanoparticles were synthesized through the thermal decomposition of the iron-oleate complex. Then, polymerization of tetraethyl ortho silicate in a water-in-oil reverse microemulsion in the presence of previously prepared iron oxide nanocubes and a terbium (Tb3+)/europium (Eu3+)-terephthalate (TA) complex was performed to obtain luminescent magnetic Fe3O4@Ln-TA (Ln = Tb, Eu)/SiO2 nanocomposites. The size (8.9 nm) and cubic shape of magnetic core were determined via transmission electron microscopy and the superparamagnetic behavior using a vibrating sample magnetometer. Energy dispersive X-ray analysis and inductively coupled plasma optical emission spectroscopy found that the luminescent Tb-TA and Eu-TA complexes were incorporated in the magnetic silica nanocomposites. The nanocomposites, Fe3O4@Ln-TA/SiO2, exhibited distinct luminescent green and red emission peaks and showed promise as a T1 contrast agent for magnetic resonance imaging.

Selective and Rapid Optical Detection of Citalopram Using a Fluorescent Probe Based on Carbon Quantum Dots Embedded in Silica Molecularly Imprinted Polymer.

In this study, a citalopram optical nano-sensor was developed. Citalopram is a well-known antidepressant drug that reduces the reuptake of serotonin in neurons as a result, serotonin neurotransmission, the primary response to antidepressant treatments, increases in many parts of the brain. This study introduces a carbon quantum dots (CQDs)-based optical nanosensor for rapid detection of citalopram. This fluorescent nanosensor was made through the polymerization of tetraethyl orthosilicate in the presence of CQDs as the fluorescent materials and citalopram as the template molecule. Following the polymerization, the templated molecules were washed and removed from the structure, and the matrix of the polymer was left with some cavities that resembled citalopram in terms of size and shape. The final structure which is used as a chemical nanosensor, is named carbon quantum dots embedded silica molecularly imprinted polymer (CQDs-SMIP). The materials used in designing nano-sensors were characterized using FTIR, UV/Vis, and fluorescence spectroscopy, as well as high-resolution transmission electron microscopy (HR-TEM), and field emission scanning electron microscopy (FESEM). CQDs-SMIP showed a strong fluorescence emission at 420nm in the absence of the template molecule. The fluorescence intensity of the nanosensor decreased in the presence of citalopram. The correlation between the extent of the fluorescence quenching and the concentration of citalopram provided the nano-sensor signal. The nano-sensor was used to measure citalopram in complex matrices such as human plasma and urine samples with remarkable selectivity and sensitivity. The detection limit of 10.3µg.L-1 over a linear range of 100 to 700µg.L-1, and RSD of 3.15% was obtained. This nano-sensor was applied to analyze of citalopram in plasma and human urine samples with remarkable results.

Effect of polystyrene and silica compositions on formation of raspberry-like hollow nanoparticles: synthesis strategy and morphological study

Raspberry-like hollow hybrid nanoparticles were facilely prepared via simultaneous miniemulsion sol–gel reaction/free radical polymerization of tetraethyl orthosilicate, 3-methacryloxypropyl trimethoxysilane (MEMO) and styrene (ST). MEMO played an important role in controlling their morphologies from dense silica nanoparticles to raspberry-like and raspberry-like hollow hybrid nanoparticles. The hybrid nanoparticles were obtained from the miniemulsion reaction technique with 2 wt% MEMO with or without ST exhibit raspberry-like hollow nanoparticles. The corresponding number-average diameter of hybrid nanoparticles increased from 112 to 126 nm as the ST concentration increased from 0 to 5 wt%. The (raspberry-like hollow) porous silica particle sizes after calcination are 47, 76, 78 and 85 nm for the runs with 0, 1, 2 and 5 wt% ST, respectively. Moreover, for constant level of MEMO at 2 wt%, the highest specific surface area (800 m2 g–1) was achieved for the runs with the ST concentration = 0–1 wt%. Then, it steadily decreased from ca. 710 to 510 m2 g–1 when the ST concentration increased from 1.5 to 20 wt%. As for constant level of ST at 0.5 wt%, the specific surface area is ca. 626, 797 and 580 m2 g–1 for the runs with 1, 2 and 3 wt% of MEMO, respectively.

Atomic-Scale Structure of Mesoporous Silica-Encapsulated Pt and PtSn Nanoparticles Revealed by Dynamic Nuclear Polarization- Enhanced 29Si MAS NMR Spectroscopy.

Mesoporous silica encapsulated Pt (Pt@mSiO2) and PtSn (PtSn@mSiO2) nanoparticles (NPs) are representatives of a novel class of heterogeneous catalysts with uniform particle size, enhanced catalytic properties, and superior thermal stability. In the ship-in-a-bottle synthesis, PtSn@mSiO2 intermetallic NPs are derived from Pt@mSiO2 seeds where the mSiO2 shell is formed by polymerization of tetraethyl orthosilicate around a tetradecyltrimethylammonium bromide template, a surfactant used to template MCM-41. Incorporation of Sn into the Pt@mSiO2 seeds is accommodated by chemical etching of the mSiO2 shell. The effect of this etching on the atomic-scale structure of the mSiO2 has not been previously examined, nor has the extent of the structural similarity to MCM-41. Here, the quaternary Q2, Q3 and Q4 sites corresponding to formulas Si(O1/2)2(OH)2, Si(O1/2)3(OH)1 and Si(O1/2)4, in MCM-41 and the mesoporous silica of Pt@mSiO2 and PtSn@mSiO2 NPs were identified and quantified by conventional and dynamic nuclear polarization enhanced Si-29 Magic Angle Spinning Nuclear Magnetic Resonance (DNP MAS NMR). The connectivity of the -Si-O-Si-network was revealed by DNP enhanced two-dimensional 29Si-29Si correlation spectroscopy.

Synthesis and Gas Transport Properties of Poly(2,6-dimethyl-1,4-phenylene oxide)⁻Silica Nanocomposite Membranes.

The emulsion polymerized mixed matrix (EPMM) method is a new approach to prepare nanocomposite membranes, in which inorganic nanoparticles are synthesized in situ at the interface of a dispersed aqueous phase in a continuous phase of polymer solution. In this paper, we report the synthesis and characterization of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)-based EPMM membranes, in which silica nanoparticles are synthesized by the polymerization of tetraethylorthosilicate (TEOS) in the presence of two different co-solvents, ethanol and acetone, which are soluble in both the aqueous phase and the polymer solution. The EPPM membranes prepared in the presence of acetone show greater conversions of TEOS and a different structure of the synthesized silica nanoparticles compared to the EPMM membranes prepared in the presence of ethanol. The former membranes are both more permeable and more selective for O2/N2 and CO2/CH4. Both types of EPMM membranes are more permeable than the reference PPO membranes. However, while their O2/N2 selectivity is practically unchanged, their CO2/CH4 selectivity is decreased compared to the reference PPO membranes.

Enhancement of the stability of green-emitting Ba2SiO4:Eu2+ phosphor by hydrophobic modification

This paper proposes a simple and feasible surface modification method to suppress the moisture-induced degradation of the green-emitting phosphor Ba2SiO4:Eu2+ (BSO:Eu2+), which hits its reliability very hard and restricts its wide commercialization in WLEDs. A hydrophobic surface layer was formed on the surface of this phosphor via hydrolysis and polymerization of tetraethylorthosilicate (TEOS) and polydimethylsiloxane (PDMS). The produced surface layer consisted of an amorphous silicon dioxide with a thickness of ∼2nm along with the presence of −CH3 groups on the surface. The modified phosphor featured superior stability in high-pressure water steam conditions at 150°C.

Highly Stable Red‐Emitting Sr2Si5N8:Eu2+ Phosphor with a Hydrophobic Surface

One of the biggest problems in white light‐emitting diodes (WLEDs) is the moisture‐induced degradation of phosphors. This paper proposes a simple and feasible surface modification method to solve it, whereby a hydrophobic surface layer is developed on the surface of the phosphors. The particular case of orange‐red‐emitting Sr2Si5N8:Eu2+ (SSN) phosphor was investigated. The mechanism to develop the hydrophobic layer involves hydrolysis and polymerization of tetraethylorthosilicate (TEOS) and polydimethylsiloxane (PDMS). The experimental results showed that the surface layer of SSN phosphor was successfully modified to a hydrophobic nanolayer (8 nm) of amorphous silicon dioxide that contains CH3 groups in the surface. This hydrophobic surface layer gives the modified phosphor superior stability in high‐pressure water steam conditions at 150°C.

Synthesis of hollow α-Fe2O3–silica composites templated by poly(acrylic acid) colloidal aggregates

The synthesis of inorganic hollow nanoparticles has attracted more and more attention in recent research. In this article, hollow α-Fe2O3–silica composites were synthesized by a modified Stober method. Tetraethyl orthosilicate (TEOS) formed oil drops, and ammonia solution facilitated the hydrolysis polymerization of TEOS. In the hydrolysis process of TEOS, we used cetyltrimethylammonium bromide and poly(acrylic acid) colloidal aggregates as the surfactant and template, respectively. The diameters of the composites we obtained are about 20 and 180 nm, respectively, which are smaller than that of pure silica spheres (200 nm). Moreover, Brunauer–Emmett–Teller surface areas of hollow α-Fe2O3–silica composites were determined to be in the range of 377–498 m2/g, and their pore sizes are around 2 nm as were determined by BJH method. The mesoporous silica was successfully coated around the α-Fe2O3. The synthesis process of the composites is a simple, one-step route, which exhibits the potential need for a great amount of synthesis for future research.

One-pot synthesis and characterization of rhodamine derivative-loaded magnetic core–shell nanoparticles

A new method to produce elaborate nanostructure with magnetic and fluorescent properties in one entity is reported in this article. Magnetite (Fe3O4) coated with fluorescent silica (SiO2) shell was produced through the one-pot reaction, in which one reactor was utilized to realize the synthesis of superparamagnetic core of Fe3O4, the formation of SiO2 coating through the condensation and polymerization of tetraethylorthosilicate (TEOS), and the encapsulation of tetramethyl rhodamine isothiocyanate-dextran (TRITC-dextran) within silica shell. Transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, and X-ray diffraction (XRD) were carried out to investigate the core–shell structure. The magnetic core of the core–shell nanoparticles is 60 ± 10 nm in diameter. The thickness of the fluorescent SiO2 shell is estimated at 15 ± 5 nm. In addition, the fluorescent signal of the SiO2 shell has been detected by the laser confocal scanning microscopy (LCSM) with emission wavelength (λem) at 566 nm. In addition, the magnetic properties of TRITC-dextran loaded silica-coating iron oxide nanoparticles (Fe3O4@SiO2 NPs) were studied. The hysteresis loop of the core–shell NPs measured at room temperature shows that the saturation magnetization (Ms) is not reached even at the field of 70 kOe (7T). Meanwhile, the very low coercivity (Hc) and remanent magnetization (Mr) are 0.375 kOe and 6.6 emu/g, respectively, at room temperature. It indicates that the core–shell particles have the superparamagnetic properties. The measured blocking temperature (TB) of the TRITC-dextran loaded Fe3O4@SiO2 NPs is about 122.5 K. It is expected that the multifunctional core–shell nanoparticles can be used in bio-imaging.

Synthesis and Characterization of Stable Monodisperse Silica Nanoparticle Sols for in Vitro Cytotoxicity Testing

For the investigation of the interaction of nanoparticles with biomolecules, cells, organs, and animal models there is a need for well-characterized nanoparticle suspensions. In this paper we report the preparation of monodisperse dense amorphous silica nanoparticles (SNP) suspended in physiological media that are sterile and sufficiently stable against aggregation. SNP sols with various particle sizes (2-335 nm) were prepared via base-catalyzed hydrolysis and polymerization of tetraethyl orthosilicate under sterile conditions using either ammonia (Stober process (1) ) or lysine catalyst (Lys-Sil process (2) ). The series was complemented with commercial silica sols (Ludox). Silica nanoparticle suspensions were purified by dialysis and dispersed without using any dispersing agent into cell culture media (Dulbecco's Modified Eagle's medium) containing antibiotics. Particle sizes were determined by dynamic light scattering. SNP morphology, surface area, and porosity were characterized using electron microscopy and nitrogen adsorption. The SNP sols in cell culture medium were stable for several days. The catalytic activity of the SNP in the conversion of hydrogen peroxide into hydroxyl radicals was investigated using electron paramagnetic resonance. The catalytic activity per square meter of exposed silica surface area was found to be independent of particle size and preparation method. Using this unique series of nanoparticle suspensions, the relationship between cytotoxicity and particle size was investigated using human endothelial and mouse monocyte-macrophage cells. The cytotoxicity of the SNP was strongly dependent on particle size and cell type. This unique methodology and the collection of well-characterized SNP will be useful for further in vitro studies exploring the physicochemical determinants of nanoparticle toxicity.

FT‐IR Study of the Hydrolysis and Polymerization of Tetraethyl Orthosilicate and Polydimethyl Siloxane in the Presence of Tetrabutyl Orthotitanate

In this work, we have used FT‐IR spectroscopy to study the hydrolysis and polymerization reactions of tetraethyl orthosilicate (TEOS) and polydimethyl‐siloxane (PDMS) in the presence of tetrabutyl orthotitanate (TBOT). These reactions are used for obtaining SiO2–PDMS–TiO2 organically modified silicates (Ormosils). In order to obtain semi‐quantitative information about such reactions, a deconvolution procedure of the FT‐IR spectra has been done by use of a computer program. Hydrolysis reactions have been characterized by Me–O–C (Me = Si, Ti) bonds, and polymerization reactions by Me–O–Me bonds. Instantaneous hydrolysis of TEOS has been observed, together with condensation reactions between Si–OH groups, which give crosslinked and linear Si–O–Si structures. The TBOT is also hydrolyzed, but the high acid concentration inhibits condensation reactions between Ti–OH groups. The PDMS also condenses mainly with Si–OH groups and probably with Ti–OH, finally forming Me–O–PDMS bonds. The formation of Si–O–Si crosslinked structures and also Me–O–PDMS structures continues until the end of reaction. The gelling time is dependent on TBOT concentration in the reaction medium and, therefore, polycondensation reactions are dependent on TBOT concentration.

Seed polymerization of tetraethyl ortho-silicate in the presence of rod-like colloidal particles of anionic palygorskite and cationic ?-FeO(OH)

Kinetic analyses were made of the seed polymerization of tetraethyl ortho-silicate (TEOS) in the presence of rod-like colloidal particles of palygorskite and cationic β-FeO(OH) by turbidity and dynamic light-scattering measurements. Transmission electron microscopic measurements supported the formation of core-shell particles. The seed polymerization of TEOS took place exclusively on the surfaces of palygorskite. The main cause of the observation is due to the fact that the main component of palygorskite is SiO2 and the affinity between palygorskite and TEOS is high, though the electrostatic repulsion between them is not favorable for shell formation. The shell formation of silica on a β-FeO(OH) particle also proceeded. The electrostatic attraction forces between the anionic polar TEOS monomers and cationic β-FeO(OH) particles played an important role in shell formation. These results are consistent with a polymerization mechanism consisting of the formation of small preliminary particles followed by their coalescence on the surfaces of the seeds to give the final large particles coated with silica layers.

Seed polymerization of tetraethyl orthosilicate in the presence of anionic and cationic polystyrene colloidal spheres

Kinetic analyses are made for the seed polymerization of tetraethyl orthosilicate (TEOS) in the presence of anionic and cationic polystyrene colloidal sphere seeds by turbidity and dynamic light-scattering measurements. Transmission-electron microscopy pictures of the spheres formed are also used. The seed polymerization of TEOS is difficult to take place on the surface of anionic polystyrene spheres (44–212 nm in diameter). On the other hand, the reaction proceeds easily on the cationic polystyrene spheres. Hairy and soft surfaces of polystyrene spheres will disturb the seed polymerization. Furthermore, the electrostatic attraction between the anionic hydrolytic products of TEOS molecules and cationic polystyrene spheres plays an important role for the seed polymerization.

Effect of sol‐gel polymerization of tetraethylorthosilicate on internal aggregate structure in zinc‐neutralized ethylene‐methacrylic acid ionomers

Effect of sol‐gel polymerization of tetraethylorthosilicate on internal aggregate structure in zinc‐neutralized ethylene‐methacrylic acid ionomers

Characterization and acidic properties of silica pillared titanates

Reaction of alkylammonium titanates with tetraethylorthosilicate (TEOS) resulted in the intercalation and polymerization of TEOS between the titanate sheets. After heating to 500 °C, the basal spacing of pillared silica titanates increased with increasing length of the alkylamine chains and the amount of silicon intercalated. Although the layers of pillared titanates were expanded by the silica species, and the specific surface area increased, only negligible micropores were formed, suggesting that the interlayer region was “stuffed” with the pillaring species. The adsorption of pyridine indicated the formation of strong Brönsted acid sites up to 300 °C. In addition some basic Lewis sites were detected on silica pillared titanates.

The Effect of Copolymerization of Tetraethylorthosilicate and Aluminum Hydroxonitrates

Polymerization of tetraethylorthosilicate (TEOS) in the presence of aqueous solutions of aluminum hydroxonitrates (Al(OH)x(NO3)3−x (0<x<2.5) was investigated by means of optical spectrophotometry and 27Al NMR. It was shown that gelation rate increases drastically in the system with x>2. The effect is due to copolycondensation of aluminum hydroxocomplexes and TEOS. Aluminum species entering copolymerization reaction have proved to contain tetrahedrally coordinated aluminum. The effect discovered might be useful for the preparation of certain metal oxide–silica composites or silicate materials, such as mullite.

Structure and formation process of silica microparticles and monolithic gels prepared by the sol-gel method

Silica microparticies and monolithic gels were prepared via the hydrolysis and polymerization of tetraethylortho silicate (TEOS) with NH 3 as the catalyst. The scanning electron microscope (SEM) observations revealed that the microparticles were formed through the aggregation of smaller particles. In the small angle X-ray scattering (SAXS) measurements, an abrupt change in the power dependence of the scattered intensity on the wave number was observed, which suggests that both the microparticles and monolithic gels were formed via multi-staged aggregation. Elementary silica particles first assemble into a fractal precursory aggregate, and a further aggregation of the precursory aggregates leads to the resultant structure. The fractal dimensionality of those precursory aggregate was estimated as approximately 1.5, in common both for the formation of the silica dispersed microparticies and monolithic gels.

Raman analysis of the initial stages of the hydrolysis and polymerization of tetraethylorthosilicate

Raman spectroscopy has been employed to study the time evolution of the beginning of the hydrolysis and condensation reaction of tetraethylorthosilicate (TEOS) in ethanol. Symmetric stretch SiO4 vibrational frequencies for the non-OH substituted di-, tri-and tetramer of TEOS are observed at 600, 576 and around 545 cm−1, respectively, in sequence below the characteristic frequency of TEOS at 654 cm−1. Some OH-substituted products are detected in the spectra around 702 and 725 cm−1 as well. Identification of the various oligomers of TEOS is achieved by synthesizing these compounds separately, and comparing the Raman spectra with corresponding 29Si-NMR analyses.