Hydrolysis Of Tetraethyl Orthosilicate Research Articles

Formation Mechanism of Silica Particles with Dendritic Structure

AbstractThe silica particles having a dendritic structure (kcc‐1) synthesized by the biphase method are a novel porous material. In this work, the effect of the disturbance state at the oil‐water biphase interface on the reaction was investigated. The experimental results showed that when the oil‐water biphase interface was in an absolute state of quiescence, no silica particles could be obtained regardless of the temperature of 70 °C or 140 °C were used for reaction. However, when there was a disturbance in the oil‐water biphase interface, whether the disturbance was a very slight disturbance caused by convection or a severe disturbance due to agitation, porous silica particles with kcc‐1 structure could be prepared. Based on the above experimental results, we propose that the formation mechanism of kcc‐1 particles mainly includes the following three steps: (1) interface disturbance induces deformation of surfactant molecules to form micelles; (2) deformation of micelles leads to hydrolysis of tetraethyl orthosilicate; (3) the micelles modified with silica form a porous silica particle having a kcc‐1 structure through cooperative interaction.

Optical Transparent and Hydrophobic Properties of TEOS/OTES Hybrid Materials by Sol-Gel Processing

The objective of this project was to develop the hydrophobic film for self-cleaning glasses. The effects of octyltriethoxysilane (OTES) additions to hydrolysis of tetraethylorthosilicate (TEOS) on hydrophobic and optically transparent properties were studied. The film was prepared by sol-gel method from the precursors namely, TESO, OTES, isopropanol alcohol (IPA), and deionized water (DI). The sols for coating were obtained with TEOS/OTES ratio of 50:50 to 99:1. The sols were deposited on a commercial glass and dried at 60oC for an hour. After drying, the film properties were characterized by fourier transform infrared spectroscopy (FTIR), UV-VIS Spectrophotometer, x-Ray Diffractometer (XRD), atomic force microscope (AFM), optical microscopy and contact angle meter. It was found that contact angles of the hybrid films increased with the OTES addition, reaching a maximum at 10 wt.%, and the contact angle values were the same as for further addition. The light transmittance was rather stable with increasing amounts of OTES. For the optimized condition, the water contact angle of 108o and light transmittance of 91%, was obtained with TEOS/OTES ratio of 90:10.

Encapsulated Cadmium Sulfide in Silicon Dioxide Porous Shells for Enhanced Photocatalytic Sustainability and Commendable Protection of Organic Carriers

AbstractThe purpose of this study is to provide a solution to two troublesome problems on photocorrosion of cadmium sulfide (CdS) and photocatalysis damage to organic carrier. An encapsulation system of CdS in silicon dioxide (SiO2) porous shell can be constructed by following strategies: polyporrole (PPy) layer is deposited on the surface of CdS nanoparticles via chemical redox polymerization; then the resulting PPy@CdS is covered by metasilicic acid (H2SiO3) with polyethylene glycol by sol–gel process, which originates from hydrolysis of tetraethyl orthosilicate; after removing PPy interlayers by calcination, CdS@void@SiO2 yolk–porous‐shell nanospheres (YSNs) are fabricated. As expected, YSN nanoarchitecture is verified by transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) analysis. The tailored void can be tuned by the sacrificed layers of PPy. CdS@void@SiO2 YSNs exhibit excellent photostability with a considerably low level of Cd2+ concentration at <30 ppm, which is dropped down 18 times less than ≈520 ppm of CdS. CdS@void@SiO2 YSNs show good dye removal efficiency up to 99.5%, and commendable hydrogen evolution of 126.8 µmol g−1 h−1. More interestingly, the transparent and porous SiO2 shell in the YSNs has an impressive shielding to organic carrier. Our versatile YSNs have great potential to translate CdS photocatalyst to industrial‐scale application because of its stability and nondestructivity.

New underfill material based on copper nanoparticles coated with silica for high thermally conductive and electrically insulating epoxy composites

With the microelectronics technology going toward its physical limits and the emergence of three-dimensional chip stack architectures, now more than ever there are both needs and opportunities for novel materials to help address some of these pressing thermal management challenges. In this paper, a high-thermal-conductivity insulative SiO2-coated nano-Cu particle is prepared for new-type underfill materials of high-performance microelectronics packaging. It was found that nano-Cu can be successfully coated with SiO2 by using the surface modification between cetyltrimethyl ammonium bromide and silane coupling agent although nano-Cu particles have silicon-disordered property during the coating process of tetraethyl orthosilicate hydrolysis. Moreover, the thermal conductivity of epoxy mixed with nano-Cu@SiO2 as the packaging underfill is dramatically increased from 0.15 W/m K of the pure-EP and 0.60 W/m K of the EP/SiO2 to 2.9 W/m K due to electronic heat transfer, heat network and fast heat transfer center. It effectively releases the heat generated by the IC device, and the service life of the device is significantly improved from 63 min of pure-EP and 350 min of the EP/nano-SiO2 to 1039 min. The new material creates a challenging environment for keeping modern electronic devices cool, a critical factor in determining their speed, efficiency and reliability.

Regulation of the Charge and Hydrodynamic Diameter of Silica Nanoparticles in AOT Microemulsions

Stable SiO2 organosols have been obtained by hydrolyzing tetraethyl orthosilicate in water-in-oil microemulsions of sodium bis(2-ethylhexyl) sulfosuccinate (Aerosol OT, AOT) in n-decane. Phase analysis light scattering and photon-correlation spectroscopy have been employed to study the electrophoretic mobility and hydrodynamic diameter of silica nanoparticles as depending on the concentrations of water (0–10 vol %), chloroform in n-decane–chloroform mixtures (0–40 vol %), and an oxyethylated surfactant (Tergitol NP-4, 0–0.125 M), as well as temperature (0–60°C). The electrophoretic mobility of the nanoparticles has been found to increase by three to four times upon the addition of water and chloroform. Nanoparticles with a hydrodynamic diameter of 20 nm are negatively charged in the absence of water, while the surface charge reversal takes place at water and chloroform concentrations of higher than 0.1 and 17 vol %, respectively.

Nitrogen-Doped Hollow Mesoporous Carbon Tube for Supercapacitors Application

Hollow mesoporous carbon tube with high specific surface area are widely used in supercapacitors due to their length-diameter ratio, unique tubular structures, low density, fast ionic diffusion and good electrical conductivity. Herein, N-doped hollow mesoporous carbon tube (HMCT) were prepared via electrostatic assembly approach by using MnO2 rods as the templates, resorcinol/formaldehyde (RF) as the carbon precursor, tetraethyl orthosilicate (TEOS) as pore-forming agents, ethylenediamine (EDA) as the base catalyst and nitrogen precursor. The obtained N-doped HMCT replicates the morphology of MnO2 and has a uniform hollow tubular structure. The addition of TEOS creates rich mesoporous on the shell which greatly improves the surface area. In addition, EDA is not only a catalyst for resin polymerization and TEOS hydrolysis, but also a nitrogen precursor that leads to in situ N-doping in the HMCT framework. An electrode made of this material exhibits a specific capacitance of 307 F g−1 at 1 A g−1 and excellent rate performance (78.2% retention ratio at 20 A g−1). Furthermore, N-doped HMCT based two-electrode system possesses energy density of 72.4 Wh kg−1 at a power density of 3.2 KW kg−1 in the wide voltage range of 1.6 V, exhibiting its potential for electrode materials with high performance.

CTAB-functionalized C@SiO2 double-shelled hollow microspheres with enhanced and selective adsorption performance for Cr(VI)

A novel cetyltrimethylammonium bromide (CTAB)-functionalized C@SiO2 with structure of double-shelled hollow microspheres (F-C@SiO2) was successfully synthesized by hydrolysis of tetraethyl orthosilicate (TEOS) on the carbonaceous hollow sphere (C). The as-prepared F-C@SiO2, C@SiO2 resulting from extracting CTAB from F-C@SiO2, and C were characterized comparatively by XRD, TGA-DSC, SEM, TEM, N2 adsorption-desorption and zeta potential. Batch adsorption experiments show that the F-C@SiO2 with CTAB functionalization presents the fastest adsorption kinetics and the highest adsorption capacity of 202.02 mg g−1 towards Cr(VI) among the samples (161.81 mg g−1 for C@SiO2 and 33.16 mg g−1 for C, respectively). The adsorption mechanisms involving the electrostatic attraction and reduction reaction were also discussed. In addition, coexistence of the ion interference experiments show that the F-C@SiO2 has a highly selective adsorption capacity of 91.11 mg g−1 towards Cr(VI) under a multiple system of Cr(VI), Cu2+, Cd2+, Zn2+, and Ni2+ with the concentration of 100 mg L−1, respectively. The successful decoration of the CTAB and the SiO2 onto the external surface of the hollow C spheres provides an effective method to develop promising composite for Cr(VI) removal from wastewater.

Effect of various amount of ammonium hydroxide on morphology of silica nanoparticles grown by sol-gel

Silica nanoparticles have drawn significant intentions for their potential in solar cell coating applications. These products occupy a noticeable position in a scientific research because of their easy preparation and wide uses for different technological applications. The quality of silica nanoparticles are highly dependent on the size. This study reports the synthesis of monodisperse silica nanoparticles by hydrolysis of tetraethyl orthosilicate (TEOS) in a mixture of ethanol and DI water as a solvent and ammonium hydroxide solution (NH4OH) as a catalyst. The solutions are stirred overnight and dried in a low-pressure furnace under 100 mbar for 3 hours at 60°C. Various-sized silica nanoparticles in the range 80 nm – 250 nm were examined under field emission scanning electron microscopy (FESEM). With the increasing volume of ammonia solution, an increase in the size of silica nanoparticles were observed.

Yolk-porous shell nanospheres from siliver-decorated titanium dioxide and silicon dioxide as an enhanced visible-light photocatalyst with guaranteed shielding for organic carrier

A nagging problem for the decompostion of photocatalyst organic carrier can be expected to be resolved by shielding effect from our yolk-porous shell nanospheres. The nanospheres were synthesized by a facile strategy: polyporrole (PPy) and silver were deposited together on TiO2 by chemical oxidative polymerization; then PPy/Ag-coated TiO2 nanoparticles were encapsulated in silicon dioxide (SiO2) shell with polyethylene glycol (PEG) as a pore-forming agent via sol-gel method based on hydrolysis of tetraethyl orthosilicate (TEOS). After removing intermediary PPy between yolk and shell by calcination and washing off PEG in shell, yolk-porous shell (SiO2@void@Ag/TiO2) nanospheres were formed. The voids in SiO2@void@Ag/TiO2 can serve as photocatalytic reactors. The channels in porous shell at outer layer provide passages for light transmission, dye molecule accessing and degradants out. More importantly, the euphotic and porous shell exhibited an impressive protection to organic carrier, lest unfavorable decomposition occurred. Yolk-porous shell nanospheres showed commendable performance with >99.5% of dye removal efficiency under 3 h visible light irradiation, higher than pristine TiO2 and Ag/TiO2 nanoparticles, due to the synergy effect of robust adsorption capacity and photocatalysis. Our work could provide a good strategy for developing novel carrier-based photocatalysts for environmental remediation application, which can be readily extended to the combination of other nanophotocatalysts and organic carriers for enhancing sustainable photocatalytic performance.

Engineered Silica Nanoparticles and silica nanoparticles containing Controlled Release Fertilizer for drought and saline areas.

Silicon supplementation was explored to increase salinity tolerance in plants, in the beginning of this cenutury, therefore silica nanoparticles (SiO2 Nps ) can also be used as a trial to improve salinity tolerance in plants. In this study SiO2 Nps have been synthesyzied by some modification in the conventional method of Stober by thermal hydrolysis of Tetraethylorthosilicate. A compound Controlled Release Fertilizer (CRF) was synthesized that carried NPK and SiO2 Nps inside the core and Chitosan as the first semi-permeable coating and Sodium Alginate and Kaolin as an outer most superabsorbent coating. The synthesized SiO2 Nps were characterized by TEM and XRD. The water absorbency of CRF beads showed that they can absorb large amounts of water and double their weight. The Nutrient released rate from CRF beads was very slow and sustained for six months at room temperature. The SiO2 Nps containing superabsorbent CRF was capable of releasing the nutrients slowly, withhold large amounts of water therefore can help plants control salinity and survive better in drought and saline conditions without harming the environment. The synthesized compound fertilizer is biocompatible, biodegradable and nontoxic so ideal for growing plants in drought and salt effected areas.

Synthesis of superhydrophobic fluoro-containing silica sol coatings for cotton textile by one-step sol–gel process

Superhydrophobic coatings were successfully fabricated on cotton textiles through a simple one-step sol–gel process. A fluorinated copolymer (PHFA-MPS), as a precursor in the sol–gel reaction, was prepared by copolymerization of hexafluorobutyl methacrylate (HFA) and 3-methacryloxypropyltrimethoxysilane (MPS) as monomers. Then, the fluoro-containing silica sols were formed by alkaline hydrolysis of tetraethylorthosilicate (TEOS) and PHFA-MPS solution in an ethanol solution, which was used to impart the cotton textiles with excellent superhydrophobicity via a facile dip-coating method. The effects of ammonium hydroxide solution (NH4OH) and PHFA-MPS concentration on the structure of the fluoro-containing silica sols, as well as the wetting behavior, surface morphology, and surface composition of the as-prepared cotton textiles were characterized. The results show that the resultant cotton textiles exhibited excellent superhydrophobicity with a WCA of 153.4° and satisfied stability, which offers a simple procedure to generate the superhydrophobicity on cotton textiles for use in a wide range of fields.

Luminescent properties of a hybrid SiO2-PMMA matrix doped with terbium

Using the sol-gel technique a SiO2-PMMA hybrid matrix was synthesized by the simultaneous hydrolysis of tetraethyl orthosilicate (TEOS) and the polymerization of methyl methacrylate (MMA). The hybrid material was doped with terbium ions for it's luminescent properties for applications in thin film devices, sensors and as an active laser media. The optical properties of the material were characterized by UV–vis and photoluminescence spectroscopy. Surface morphology of the material properties were observed using atomic force microscopy and the material's composition was studied using Raman spectroscopy. Distribution of the dopant inside matrix was analyzed by confocal microscopy. Measurements indicate that a homogeneous, non-porous composite was obtained with the terbium ions retaining their luminescent properties with good optical transmission across all the visible spectra.

Facile sonication‐assisted synthesis and characterisations of silica decorated graphene nanocomposites

This work demonstrates the fabrication of a composite nanomaterial consisting of spherical silica nanoparticles decorated onto the graphene sheets which has been prepared by the sonication-assisted method. Graphene/silica nanocomposites were fabricated by the hydrolysis of tetraethyl orthosilicate in the presence of graphene oxide which has been obtained by modified Hummer's method. The obtained nanostructures were characterised by the X-ray diffraction (XRD), Raman spectroscopy, Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD analysis depicts the coexistence of silica and graphene in the composite material. The morphology of synthesised silica–graphene nanocomposites was characterised by SEM and TEM. All images have been observed in the presence of SiO2 nanoparticles of similar sizes which were grafted on the surface of graphene effectively. More significantly, the BET analysis revealed that the silica decorated graphene nanocomposites exhibit enhanced surface area than bare silica and graphene.

Stable Formamidinium‐Based Perovskite Solar Cells via In Situ Grain Encapsulation

AbstractFormamidinium (FA)‐based lead iodide perovskites have emerged as the most promising light‐absorber materials in the prevailing perovskite solar cells (PSCs). However, they suffer from the phase‐instability issue in the ambient atmosphere, which is holding back the realization of the full potential of FA‐based PSCs in the context of high efficiency and stability. Herein, the tetraethylorthosilicate hydrolysis process is integrated with the solution crystallization of FA‐based perovskites, forming a new film structure with individual perovskite grains encapsulated by amorphous silica layers that are in situ formed at the nanoscale. The silica not only protects perovskite grains from the degradation but also enhances the charge‐carrier dynamics of perovskite films. The underlying mechanism is discussed using a joint experiment‐theory approach. Through this in situ grain encapsulation method, PSCs show an efficiency close to 20% with an impressive 97% retention after 1000‐h storage under ambient conditions.

Synthesis of Hydrophobic Filler for Polymer Composites

Silica (SiO2) particles are increasingly more used for the productions of polymer composites. But introduction of silica in polymer disturbs the natural structure uniformity also this technique is difficult with the aid of the high propensity of silica to agglomeration. So to create polymer composites it is better to use fillers with a hydrophobic surface. In this study, it was investigated the possibility of surface amendment of Silica particles for their hydrophobization. Silica particles had been organized by way of the tetraethyl orthosilicate hydrolysis reaction at high temperature and pressure. The morphology and shape of the silica were studied by way of X-ray powder diffraction, approach of particle measurement analysis by using laser diffraction, and electron micrograph. For floor amendment of silica particles was use hydroalcoholic answer of sodium methylsiliconate. The bought results of the contact perspective measurements show that the floor of initial particles of silica is hydrophilic (contact perspective – 74°). The surface of Silica particles after the change are strongly hydrophobic (contact angle – 92-126°). The most suitable is the introduction of a modifier in an amount of 2%..

Microwave-Assisted Synthesis of C/SiO2 Composite with Controllable Silica Nanoparticle Size.

A C/SiO2 composite was produced from 3-aminophenol and tetraethyl orthosilicate (TEOS) by a synthesis protocol that involved microwave irradiation. This protocol featured simultaneous 3-aminophenol polymerization and TEOS hydrolysis and condensation, which were achieved rapidly in a microwave reactor. The SiO2 component was formed from low-concentration TEOS confined in cetyltrimethylammonium bromide micelles. We demonstrated a control of the SiO2 particle size, ranging from 20 to 90 nm, by varying the 3-aminophenol concentration. The carbon component provided a microporous structure that greatly contributed to the high specific surface area, 375 m2/g, and served as a host for the nitrogen functional groups with a content of 5.34%, 74% of which were pyridinic type. The composite formation mechanism was clarified from time-series scanning electron microscopy images and dynamic light scattering analysis. An understanding of the composite formation mechanism in this protocol will enable the design of composite morphologies for specific applications.

Deep Insights into the Processes Occurring during Early Stages of the Formation and Room-Temperature Evolution of the Core (Amorphous SiO2)@Shell (Organocations) Nanoparticles

Following the assumption that the crucial processes governing the formation, properties, and evolution of the core (amorphous silica)@shell (organocations) nanoparticles (NPs) take place during short-time, room-temperature (rt) stirring/aging of the homogeneous reaction mixtures (HmRMs) formed by hydrolysis of tetraethyl orthosilicate (TEOS) in solutions of Org(OH)n, we investigated these processes by various experimental methods (pH, ionic conductivity, 29Si NMR, dynamic light scattering, and atomic force microscopy). The analysis of the data obtained by detailed and careful investigation of the “model” HmRMs having the starting chemical composition, xTEOS/0.25TPAOH/20H2O (TPAOH = tetrapropylammonium hydroxide; x = 0.05–1), offer some new elements for the understanding of the mechanisms of the formation and rt evolution of the core@shell silica NPs: (1) There is a resolute evidence of the formation of the stable, about 1.2 nm-sized core (amorphous SiO2)@shell (TPA+ ions) NPs below the critical aggregatio...

Structure and thermal stability in hydrophobic Pluronic F127-modified silica aerogels

Hydrophobic ambient pressure drying (APD) aerogels were prepared from hydrolysis of tetraethylorthosilicate (TEOS) in solutions with different concentrations of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (F127). APD was carried out after silylation of wet gels with 20% by volume of hexamethyldisilazane (HMDZ) in n-hexane. The samples were analyzed by small-angle X-ray scattering (SAXS) and nitrogen adsorption. The APD aerogels obtained in this process were submitted to heat treatment at 300, 500, 700 and 900 °C to study the pores stability. The samples were characterized by nitrogen adsorption. Wet gels are formed by mass-fractal domains, with fractal dimension close to 2.1 and characteristic size (ξ) spanning from about 9 nm (for the gel prepared without the addition of F127) up to values that exceed the maximum limit of the SAXS experimental setup, with increasing the concentration of F127. Nitrogen adsorption data showed that the pore volume (Vp) and the mean pore size (lp) of the aerogels increased with increasing the concentration of F127. The drying process diminished the characteristic size ξ and increased the dimension D of the mass-fractal domains and the size (r0) of the primary particles of the aerogels with respect to the wet gels. The characteristic size ξ of the mass-fractal of the aerogels was found significantly larger with increasing the concentrations of F127. Thermally treated aerogels exhibited a similar general behavior with temperature independent of the concentration of F127. The porosity was found fairly stable up to about 500 °C. The porosity started to be eliminated at 700 °C and it was found practically collapsed at 900 °C. The silylation layer on the silica surface of the present APD aerogels was promptly eliminated at about 350 °C yielding complete loss of hydrophobicity.

Radical-Facilitated Green Synthesis of Highly Ordered Mesoporous Silica Materials.

In the hydrothermal synthesis of highly ordered mesoporous silica material SBA-15, strong acid is typically required to catalyze the hydrolysis and condensation of silica species. Meanwhile, under strongly acidic conditions, the transition metal ions, e.g., iron ions, are difficult to incorporate into SBA-15 because of the facile dissociation of Fe-O-Si bonds. Here, we demonstrate an acid-free green synthetic strategy for the synthesis of highly ordered mesoporous SBA-15 and Fe-SBA-15 with the assistance of hydroxyl free radicals that are generated by physical or chemical methods. The prepared materials exhibit a large specific surface area compared to the counterparts prepared by conventional method under acidic conditions. Moreover, Fe-SBA-15 shows high metal loading efficiency as over 50%. Density functional theory calculations suggest that the hydroxyl free radicals exhibit higher catalytic activity than H+ ions for the hydrolysis of tetraethyl orthosilicate. This radical-facilitated synthesis approach overcomes the challenge to the direct synthesis of highly ordered SBA-15 and Fe-SBA-15 without adding any acid, providing a facile and environmentally friendly route for future large-scale production of ordered mesoporous materials.

Synthesis of Hollow Doughnut Shape Mesoporous Silica Nanoparticle: A Case of Self-Assembly Composite Templates.

The new class of silica nanoparticles with unprecedented structural morphology is synthesized by hydrolysis of tetraethyl orthosilicate (TEOS) in the presence of cetyltrimethylammonium bromide (CTAB), l-arginine, and ammonium metatungstate (AMT) composite template, all in aqueous ethanol. The morphology of the synthesized mesoporous silica nanoparticles (MSNs) can be tuned from a spherical to a hollow doughnut shape through a hollow sphere by controlling the concentration of AMT in the composite template. The formation mechanism of the hollow doughnut shaped MSNs (hd-MSNs) is well-explored by means of zeta potential, high-resolution transmission electron microscopy (HRTEM) with elemental mapping analysis, and X-ray photoelectron spectroscopy. The unique structure of the hd-MSNs as well as their high thermal and mechanical stability is expected to result in their application in shape-selective catalysis, drug-delivery, and sensors.