Hydrolysis Of Tetraethoxysilane Research Articles

Protocrystallinity of Monodispersed Ultra-Small Templated Mesoporous Silica Nanoparticles.

Monodisperse and semi-faceted ultra-small templated mesoporous silica nanoparticles (US-MSNs) of 20-25 nm were synthesized using short-time hydrolysis of tetraethoxysilane (TEOS) at room temperature, followed by a dilution for nucleation quenching. According to dynamic light scattering (DLS), a two-step pH adjustment was necessary for growth termination and colloidal stabilization. The pore size was controlled by cetyltrimethylammonium bromide (CTAB), and a tiny amount of neutral surfactant F127 was added to minimize the coalescence between US-MSNs and to favor the transition towards internal ordering. Flocculation eventually occurred, allowing us to harvest a powder by centrifugation (~60% silica yield after one month). Scanning transmission electron microscopy (STEM) and 3D high-resolution transmission electron microscopy (3D HR-TEM) images revealed that the US-MSNs are partially ordered. The 2D FT transform images provide evidence for the coexistence of four-, five-, and sixfold patterns characterizing an "on-the-edge" crystallization step between amorphous raspberry and hexagonal pore array morphologies, typical of a protocrystalline state. Calcination preserved this state and yielded a powder characterized by packing, developing a hierarchical porosity centered at 3.9 ± 0.2 (internal pores) and 68 ± 7 nm (packing voids) of high potential for support for separation and catalysis.

Diffusion and chemical kinetics of methylene blue dye adsorption on silica doped with iron (III) ions

Silica are widely used in catalysis, adsorption, and chromatography. In the last decade, they have been increasingly used in medicine, however, to ensure their biocompatibility, silica need to be modified and the simplest way of such a modification is doping them with iron cations. The article presents a study of the sorption characteristics of silica doped with iron cations. The purpose of the study was to assess the effect of doping silica with iron ions on the kinetics of their adsorption of model sorbate of methylene blue dye. Doped silica were synthesised by the alkoxide sol-gel method at pH=1.5 and pH=5.0 with the introduction of iron cations into the reaction mixture during the hydrolysis of tetraethoxysilane. The iron content in the samples was 1.5, 2.3, and 3.8 at. %. According to the results of X-ray phase analysis, all samples were X-ray amorphous. According to the shape of the isotherms of low-temperature nitrogen adsorption, all samples were classified as microporous. The specific surface area of the samples and the total pore volume decreased slightly with an increase in the iron content in the samples. The adsorption of methylene blue dye was carried out at temperatures of 25, 30, and 35 °C. The kinetic adsorption curves were analysed using the following diffusion kinetics models: Boyd model (external diffusion process) and Weber-Morris model (internal diffusion process). Also, the kinetic data were analysed using kinetic models of pseudo first-order (Lagergren model) and pseudo second-order (Ho and McKay's model). It was established that all samples were characterised by a mixed-diffusion regime of the sorption process. Adsorption kinetics was adequately described by the model of pseudo-second-order.

Detection of tetanus toxoid with iron magnetic nanobioprobe

Diagnosis of diseases with low facilities, speed, accuracy and sensitivity is an important matter in treatment. Bioprobes based on iron oxide nanoparticles are a good candidate for early detection of deadly and infectious diseases such as tetanus due to their high reactivity, biocompatibility, low production cost and sample separation under a magnetic field. In this study, silane groups were coated on surface of iron oxide nanoparticles using tetraethoxysilane (TEOS) hydrolysis. Also, NH2 groups were generated on the surface of silanized nanoparticles using 3-aminopropyl triethoxy silane (APTES). Antibody was immobilized on the surface of silanized nanoparticles using TCT trichlorothriazine as activator. Silanization and stabilized antibody were investigated by using of FT-IR, EDX, VSM, SRB technique. UV/vis spectroscopy, fluorescence, agglutination test and ELISA were used for biosensor performance and specificity. The results of FT-IR spectroscopy showed that Si–O–Si and Si-O-Fe bonds and TCT chlorine and amine groups of tetanus anti-toxoid antibodies were formed on the surface of iron oxide nanoparticles. The presence of Si, N and C elements in EDX analysis confirms the silanization of iron oxide nanoparticles. VSM results showed that the amount of magnetic nanoparticles after conjugation is sufficient for biological applications. Antibody stabilization on nanoparticles increased the adsorption intensity in the uv/vis spectrometer. The fluorescence intensity of nano bioprobe increased in the presence of 10 ng ml−1. Nanobio probes were observed as agglomerates in the presence of tetanus toxoid antigen. The presence of tetanus antigen caused the formation of antigen-nanobioprobe antigen complex. Identification of this complex by HRP-bound antibody confirmed the specificity of nanobioprobe. Tetanus magnetic nanobioprobe with a diagnostic limit of 10 ng ml−1 of tetanus antigen in a short time can be a good tool in LOC devices and microfluidic chips.

Kinetic Regularities of the Synthesis of Silica Nanoparticles by Heterogeneous Hydrolysis of Tetraethoxysilane Using L-Arginine as a Catalyst

Abstract The kinetics of the synthesis of silica nanoparticles (<50 nm) has been studied under the conditions of heterogeneous hydrolysis of tetraethoxysilane (TEOS) using L-arginine as an alkaline catalyst. The rates of silica formation have been determined in a temperature range of 10–95°C at catalyst concentrations of 6–150 mM. It has been shown that the activation energy of the process depends on catalyst concentration and varies in a range of 21.5–13.9 kJ/mol, while decreasing linearly with increasing concentration of L-arginine in the system. The criterion of maintaining the monodispersity has been estimated for SiO2 particles being grown “onto seeds.” The density of submicron-sized silica particles has been experimentally determined as depending on the annealing temperature. Within a temperature range of 200–1000°C, the particle density varies from 2.04 to 2.20 g/cm3.

Gold-silica plasmonic nanobones with tunable size and optical bimodality for bioimaging

Silica-coated gold nanotags were developed for multimodal Raman and fluorescent imaging. These nanotags, shaped like bones, offer significant absorption at 700 nm, aligning with the first window of tissue transparency. Gold nanobones were modified with cyanine 5.5 and 7 dyes and a silica shell for stability and biocompatibility via a modified Stober method involving tetraethoxysilane hydrolysis. Folic acid was attached on outer surface of nanotags to serve as a model delivery vector. The nanotags were characterized by dynamic light scattering, transmission electron microscopy, and spectroscopy. These methods showed that a thickness of the silica shell can be precisely controlled via a concentration of tetraethoxysilane. Surface-enhanced Raman scattering and emission spectra were registered and demonstrated the intensity dependent on the distance between the dye and core. Raman mapping of cell samples highlighted the nanotags bioimaging potential and revealed the partial nanotags agglomeration post-cell uptake accompanied by formation of optical hot-spots. Cell viability assays with HeLa and HEP 2 G cell lines suggested the nanotags safety below 0.2 mg/L concentration. These findings highlight the benefits of silica-coated gold nanotags and open the doors in advanced medical imaging.

Hierarchically porous silica particles: One-pot synthesis, tunable hydrophilic/hydrophobic properties, prospects for selective oil adsorption

Submicron spherical silica particles were synthesized via base hydrolysis of tetraethoxysilane (TEOS) and phenyltriethoxysilane (PTEOS) in a presence of cetyltrimethylammonium bromide. It was shown that the replacement of a part of TEOS with PTEOS in the reaction mixture led to formation of particles containing hierarchical micro-mesoporous structure with specific surface area of up to ∼ 1170 m2 g−1. The amount of PTEOS leads to the increase of water contact angle of the particles from 10° to 155° which causes a gradual change in their surface properties from hydrophilic to superhydrophobic. The static adsorption capacity of the particles was measured for water, toluene and methyl isobutyl ketone and was found to be affected by both the amount of OH- or C6H5-groups on the surface and the characteristics of porosity. In particular, the adsorption capacity for non-polar volatile organics increases with the increase of the hydrophobicity of particles. It was found that synthesized superhydrophobic silica particles efficiently and quickly absorb oil from water surface and then can be easily removed mechanically.

Sol-Gel-Derived Functional Coatings for Pre-Sowing Seed Treatment

The superatomic structure of film-forming sols obtained by the acid hydrolysis of tetraethoxysilane (TEOS) in an aqueous medium (free of organic solvents) was studied using the SAXS method. The formation of nanoparticles (NPs) was confirmed in alcohol-free silica sols with both a low (1 vol. %) content of TEOS and a high (10 vol. %) content of TEOS, hydrolyzed in an aqueous-alcoholic medium. A trimodal size distribution was revealed for the resulting NPs, with radii ranging from less than 1 nm to ~11 nm. The volume fraction of NPs tends to grow with increases in TEOS concentration, as well as with the introduction of magnetic NPs of iron oxides into silica sols. The synthesized silica sols and suspensions based on silica sols with FexOy NPs were used for the pre-sowing treatment of white and cauliflower cabbage seeds in order to provide a functional coating on their surfaces, thereby improving seed germination, stimulating their growth in the early stages of development, and suppressing the effect of phytopathogens. The effect of the pre-sowing seed treatment in sol-gel compositions on seed germination and the growth characteristics of plant seedlings is analyzed, including the influence of iron-oxide magnetic NPs’ compositions and concentrations in silica sols.

Core-shell deAlY@SiO2 composite: A superior adsorbent for toluene capture under humidity condition

Y zeolite has been regarded as an effective adsorbent in removal of volatile organic compounds (VOCs). However, the low Si/Al ratio causes Y zeolite to preferentially adsorb water when dealing with wet VOCs, which limits its practical application. In present work, Y zeolite was first dealuminated treated by steaming and acid etching, and then the obtained deAlY was used as cores to prepare deAlY@nSiO2 core–shell composites. The shell layer thickness in the as-prepared core–shell composites was adjusted by controlling the hydrolysis of tetraethoxysilane (TEOS). The Si-species yielded from the hydrolysis of TEOS not only fabricated the mesopore shell directed by CTA+, but also entered the zeolite framework by polycondensation with the adjacent hydroxyl (silicon hydroxyl of (SiO)3Si(OH) species or aluminum hydroxyl of penta-coordinated aluminum caused by steaming and acid etching) in the defect sites of the core deAlY. During the adsorption of dry toluene, the as-synthesized composite displayed an adsorption capacity superior to mesopore SiO2 while inferior to deAlY. When toluene and water molecules competed for the adsorption sites, the core–shell composite preferred to adsorb the former because of the greatly reduced sensitivity to the presence of water vapor. Under 55 % and 83 % relative humidity, the core–shell deAlY@nSiO2 (n < 1.5) respectively had 4.2 and 9.0 times higher toluene adsorption than the deAlY. The mesopores in the SiO2 shell was conducive to a fast mass transfer, the high hydrophobic surfaces (internal and external) resulted from reduced hydroxyl content, elevated framework Si/Al ratio and constructed SiO2 shell, contributed to shielding water, which promoted toluene in the wet VOCs to be adsorbed efficiently by the deAlY zeolite core.

Synthesis of silicon dioxide xerogels and their sorption- desorption properties with respect to nicotine and glycols

Composites based on silicon dioxide xerogels containing glycerol and nicotine were prepared by hydrolysis of tetraethoxysilane by a single-stage synthesis and two-stage sorption method with a single-stage glycerol sorption in relation to the sorbent reaches 3: 1 by weight. The kinetics of release (desorption) of nicotine from an aerosol mixture with glycols has been studied. The synthesized sorbent is promising for use in aerosol generating systems, as well as carriers and delivery systems for biologically active substances and medicines.

Подготовка тетраэтоксисилана для получения сферических частиц кремнезема. Часть 2. Примеси и их влияние на размеры формирующихся глобул

Monodisperse spherical silica particles, as a basis for creating supramolecular 3D matrices, are currently of increasing interest due to the prospects for their wide application in the synthesis of new nanocomposite materials. At the same time, one of main problems of their large-scale synthesis is associated with the unstable behavior of tetraethoxysilane (TEOS) during hydrolysis, which leads both to the deviation of the particles from a given size and their shape from a spherical one. In this paper, on the basis of the study of tetraethoxysilane from various manufacturers, we continued to work on determining factors that can influence the process of hydrolysis of tetraethoxysilane and, as a result, the monodispersity and size of the formed particles, and also other factors. To solve this task, all TEOS samples were studied by various physicochemical methods of analysis, including Fourier IR and Raman spectroscopy, gas chromatography-mass spectrometry. As a result of the studies, we showed that the presence of di- and trisiloxanes in the system did not significantly affect the size of the formed silica particles, while significantly accelerating the rate of formation of silica spheres. Moreover, the presence of methoxyl groups in the initial silane, and an insignificant content of ethanol in the system did not affect the size stability of the formed particles. At the same time, the replacement of part of the ethoxy groups in the initial TEOS by methyl or ethyl groups, as they are not capable of participating in the hydrolysis reaction, largely contribute to the deviation of sizes of the formed silica particles from each other. The results obtained on the effect of impurities on the size of the formed silica globules are important, among other things, for understanding the processes of formation of natural supramolecular structures of silica.

Hydrolysis and condensation behavior of tetraethoxysilane, hexaethoxydisiloxane, and octaethoxytrisiloxane

In the initial stage of the hydrolysis–condensation of tetraethoxysilane (TEOS), hexaethoxydisiloxane (HEDS) and octaethoxytrisiloxane (OETS) are formed. However, little is known about the hydrolysis–condensation of HEDS and OETS. In this study, the hydrolysis–condensation of TEOS, HEDS, and OETS was investigated. HEDS and OETS were synthesized from diethoxy(diisocyanato)silane, a raw material with controllable functionality. The hydrolysis of TEOS, HEDS, and OETS was analyzed by mass spectroscopy, gel permeation chromatography, and nuclear magnetic resonance. The hydrolysis–condensation product of TEOS was a three-dimensional network-type polysiloxane. The hydrolysis–condensation product of HEDS consisted mainly of four-membered cyclic siloxane. The hydrolysis–condensation product of OETS consisted mainly of various membered cyclic siloxanes.Graphical

A kinetic approach to the mechanism of formation of mesoporous silica nanoparticles

The synthesis of mesoporous silica nanoparticles (MSNs), widely investigated for application in nanomedicine, depends on many experimental factors and lacks reproducibility. Furthermore, its mechanism is not fully understood, in particular for the chemistry of the hydrolysis and condensation of tetraethoxysilane (TEOS). We coupled simple pH measurements with light diffusion monitoring directly within the reaction vessel in order to understand the early stages of the synthesis until the formation of nanoparticles. We found that two regimes of hydrolysis can be detected before the nanoparticles are formed. At the turning point, only 28% of the TEOS molecules are singly hydrolyzed and the condensation reaction only starts after the aggregation of the silicate-surfactant micelles. Experimental factors such as stirring strength or presence of carbonates of sodium hydroxide exert a strong influence on the kinetics of MSNs formation and on their size, and must be carefully controlled for reproducibility. Based on all our experimental evidence and on previous literature reports, a formation mechanism was proposed in order to highlight the importance of the interplay between chemical and physicochemical processes in such a complex system.

Formation of stable microporous core-shell V2O5/SiO2 colloidal particles potential for heterogeneous catalysis

An approach for the synthesis of stable core-shell V2O5/SiO2 colloidal particles has been proposed. First, ammonium vanadate particles ∼ 300 nm in size, which act as a precursor for vanadium pentoxide synthesis, are obtained from NH4VO3 saturated solution. To prevent possible changes in morphology of the obtained particles during the synthesis of V2O5 they are coated with silica shell via hydrolysis of tetraethoxysilane. The formed SiO2 shell possesses microporous structure with an average size of pores ∼ 1.5 nm and specific surface area 170 m2/g. It is shown that the presence of pores makes it possible to provide efficient removal of decomposition products during conversion of NH4VO3 to V2O5 during annealing at 550 °C and preserve the shape and size of the core-shell particles. The obtained V2O5/SiO2 particles are of ∼ 700 nm in size have an almond-like shape and form a stable aqueous suspension. It is found that they exhibit intense broadband room-temperature photoluminescence with maximum intensity at 660 nm. The shell retains its porous structure after annealing and gives access to the core of particles – V2O5, which allows complete conversion of V2O5 to, for example, V2O3 and makes the core-shell particles promising for use in heterogeneous catalysis.

Effect of a Tetraethoxysilane Hydrolysis Reaction Catalyst on the Precipitation of Hydrolysis Products in the Pores of a Polyimide Track Membrane

This paper presents the results of obtaining a composite film based on polyimide track membranes filled with a silica filler, although the issue of the deposition of this filler in the pores of the given membranes remained unexplored. The filler was obtained by hydrolysis of tetraethoxysilane using an alkaline and acid catalyst. This paper presents the results of the effect of the tetraethoxysilane hydrolysis reaction catalyst on the precipitation of hydrolysis products in the pores of the polyimide track membrane. The factors influencing the formation of silicon oxide nanofibers within the matrix template (polyimide track membrane) are determined. It was found that the use of an acid catalyst provides the highest rates of filling, while when using an alkaline catalyst, the filling is practically not observed, and only single pores are filled. The properties of the composite film obtained were investigated. SEM images of the surface and chip of the composite while using alkaline and acid catalyst are presented. The spatial structure of composite films based on track membranes was investigated by FTIR spectroscopy. The hydrolysis of tetraethoxysilane in an acid medium significantly decreases the optical density index of the membranes and simultaneously increases their light transmission index. The greatest changes are observed in the range of 500–1000 nm, and there are no detectable changes in the range of 340–500 nm. When using an alkaline catalyst, there is not the same significant decrease in the relative optical density index D.

Synthesis of Hydrophobic Nanosized Silicon Dioxide with a Spherical Particle Shape and Its Application in Fire-Extinguishing Powder Compositions Based on Struvite.

Textural and morphological features of hydrophobic silicon dioxide, obtained by the hydrolysis of tetraethoxysilane in an ammonia medium followed by modification of a spherical SiO2 particles surface with a hydrophobic polymethylhydrosiloxane, were studied in this work. The size of silicon dioxide particles was controlled during preparation based on the Stöber process by variation of the amount of water (mol) in relation to other components. The ratio of components, synthesis time and amount of the hydrophobizing agent were determined to obtain superhydrophobic monodisperse silicon dioxide with a spherical particle size of 50-400 nm and a contact angle of more than 150°. In the case of the struvite example, it was demonstrated that the application of spherical- shaped hydrophobic silicon dioxide particles in powder compounds significantly improves the flowability of crystalline hydrates. The functional additive based on the developed silicon dioxide particles makes it possible to implement the use of crystalline hydrates in fire-extinguishing powders, preventing agglomeration and caking processes. The high fire-extinguishing efficiency of the powder composition based on struvite and the developed functional additive has been proven by using thermal analysis methods (TGA/DSC).

Study on the Hydrophobicity and Antibacterial Activity of Silica Sol-Chitosan-HDTMS Treated Cotton Fabric Dipped in an Aquas Media

A hydrophobic surface with an antibacterial property has numerous uses, including self-cleaning, anti-sticking, anti-contamination, sports apparel, and wound healing/implant materials. The durability of the coating in an aquas media (pH 7.4) is a vital requirement for use in technical textile sectors, particularly in medical applications. In this study, we used silica sol, chitosan and hexadecyltrimethoxysilane (HDTMS) to create exceptionally hydrophobic surfaces with antibacterial properties on cotton fabrics. First, cotton fabric was treated with silica sol, which was produced by the hydrolysis and condensation of tetraethoxysilane (TEOS) in an alkaline environment. After that, chitosan was applied on the silica sol-treated fabric to add an antibacterial characteristic. The silica sol-chitosan-treated fabric was then given a hydrolysed HDTMS treatment to give a highly hydrophobic property. The hydrophobicity was assessed by measuring the water contact angle, while the AATCC-147 test protocol was used to assess the antibacterial property. The developed fabric exhibited a strong hydrophobic property. The fabric samples were immersed in an aquas media for 30 days to assess the coating durability by observing changes in hydrophobicity and anti-bacterial activity in terms of the zone of inhibition (ZOI). After 30 days of immersion in the aquas media, it was observed that the contact angle decreased from 151.7° to 129.5°, and the ZOI increased from 1 mm to 5 mm, which indicates an increase in anti-bacterial activity in relation to time of immersion. The wicking characteristics of coated and uncoated fabrics were also measured to determine how coating affects the wicking behaviour of fabric. EDS was performed to observe the coating stability for coated-dipped fabric samples after 30 days. SEM analysis was performed to examine the surface morphology, while FTIR was used to determine the surface functional groups after coating and changes after dipping in the aquas media. The developed hydrophobic cotton fabrics with anti-bacterial properties may help in the fabrication of natural biomaterials and other technical textile products.

Effectiveness of nanoparticles-based ultrahydrophobic coating for concrete materials

Moisture interaction and extreme weather may complicate the service life and increase the maintenance cost of various building materials. This paper investigates the performance of protective surface coatings applied to the most common building material, concrete. A novel synthesis route for producing ultrahydrophobic surface coatings is demonstrated to enhance the impermeability of concrete. The concrete specimens were chemically modified with silica sol, which was synthesized by hydrolysis of tetraethoxysilane (TEOS) under alkaline conditions, followed by treatment with hexadecyltrimethoxysilane (HDTMS) solution. The concrete specimens coated with proposed micro-composite coating were tested for hydrophobicity and self-cleaning characteristics in terms of contact angle and sliding angle at various water exposure conditions and periods of exposure. The permanency and efficiency of proposed coatings was further tested after exposure to alternate wet-dry cycles and highly saline environment. The modified specimens exhibited a contact angle of 121° – 135° and a sliding angle of 9° – 22° at various exposure conditions, depicting superior hydrophobicity. The overall findings of this study could aid in maintaining the intended longevity and performance of various concrete materials.

Композитные магнитовосприимчивые фотокатали-заторы на основе оксидов Fe3O4/SiO2/TiO2

In the present study the composite materials based on the Fe3O4/SiO2/TiO2 oxides, synthe-sized by the sol-gel method, were investigated. At the first stage, magnetite nanoparticles were precipitated by sodium hydroxide from a mixture of aqueous solutions of iron(II) and iron(III) sulfates under continuous ultrasonic treatment, after which they were washed with distilled water and dried under vacuum. At the second stage, the resulting magnetite particles were coated with silicon oxide according to the Stober method by dispersing them under the ultrasonic treatment in a solution of tetraethoxysilane in n-propanol, followed by hydrolysis of tetraethoxysilane in the presence of aqueous ammonia, washing and drying the obtained materials under vacuum. At the third stage, photocatalytically active particles based on titanium oxide were introduced into the composite by the solvent replacement procedure via dispersing the samples in an aqueous solution of peroxotitanic acid and adding n-propanol, stirring vigorously, followed by activation based on boiling in the water/ethanol (1:1) mixture, washing and drying under vacuum. The properties of samples influenced by the citrate stabilization and separation of magnetite particles at the stage of their synthesis into “light” and “heavy” magnetic fractions, as well as calcination of samples at 450 °C, were studied. The photocatalytic properties of the synthesized samples were studied during photodegradation of methyl orange, as well as their magnetic extraction from the suspension. The physicochemical characterization of the samples was performed using a high-resolution scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray powder diffraction, thermal analysis (TG–DSC), combined with mass spectrometry of gaseous thermolysis products. It has been found that the composites based on the mixed titanium-silicon oxide have a higher photocatalytic activity than the composites based on the pure titanium dioxide obtained via a similar procedure. The resulting photocatalysts can be used to purify water from dyes, followed by their extraction using a magnet.

Gas-Chromatographic Identification of Unusual Unstable Products of the Partial Hydrolysis of Tetraethoxysilane

Gas-Chromatographic Identification of Unusual Unstable Products of the Partial Hydrolysis of Tetraethoxysilane

Подготовка тетраэтоксисилана для получения сферических частиц кремнезема. Часть 1. Ультрафильтрация

The paper considers the problem of instability of tetraethoxysilane hydrolysis in an ethanol medium in the presence of ammonia as a catalyst to obtain monodisperse spherical silica particles of a given size. This problem is associated with the presence of various impurities affecting rate of particle formation and, as a consequence, their size, monodispersity and shape. To solve this problem, we present novel studies of possible application of ultrafiltration for hydrolysis of initial tetraethoxysilane and ethanol through hydrophobic filters with a pore size of 50 nm. In both cases, we noted a decreasing intensity of light scattering after filtration. The elemental analysis of filtered impurities showed a significant content of SiO2 solid phases in tetraethoxysilane, and a number of impurities in ethanol. The experiments on the synthesis of silica particles from pre-filtered components showed that the resulting silica particles had a greater degree of monodispersity, and their sizes were much more reproducible, regardless of the used tetraethoxysilane. Thus, according to the obtained data, ultrafiltration is one of the effective ways to solve the problem of instability in the synthesis of monodisperse spherical silica particles.