Silicic Acid Molecules Research Articles

Pivotal role of pH value in the preparation of mesoporous silica with high surface area for toluene adsorption

Porous silica samples were prepared by a non-template approach using silicate and HCl at different pH values. Macroporous silica with a low surface area of 72.0 m2/g was obtained at pH = 7. Surprisingly, mesoporous silica with very high surface area of 806.0 m2/g was obtained at pH = 3. This was due to the formation of protonated silicic acid molecules under acidic condition which had enough time for the polymerization and assembly to mesoporous structure, and the rapid polymerization and assembly of silicic molecules under neutral condition to silica nanoparticles among which macropores were formed. The mesoporous silica showed a saturation toluene adsorption capacity of 79.1 mg g−1, 9 times higher than that of the macroporous silica.

Study on the mechanism of PAMAM(DETA as the core) against silica scale.

Molecular simulation was performed to study the interaction between PAMAM(DETA as the core) with different generations and silicic acid molecules, and discussed the inhibition effect mechanism against silica scale through gyration radius and radial distribution function et al. The results showed that adsorption interactions between silicic acid molecules and the PAMAM with -NH2 terminated groups molecule (G1.0 and G2.0) were stronger than those and the PAMAM with -COOH terminated groups molecule (G0.5 and G1.5). The adsorption interactions were primarily divided into electrostatic interactions, vdW interactions as well as H-bond interactions, where electrostatic interaction was dominant. Molecular simulation results were consistent with our experimental results.

A chrome-free combination tanning strategy: based on silicic acid and plant tannin

Silicic acid, commonly derived from cheap and easily available sodium silicate, has recently received great attention for application in leather industry to produce ecological leather with a cleaner approach. However, leather tanned with silicic acid alone is poor in storage stability, which limits its practical application in leather production. In this work, a new environment-friendly combination tannage based on silicic acid and plant tannin was developed to address this issue along with improving the comprehensive performances of leather. The obtained leather was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and so on. The results showed that compared with leather tanned with silicic acid alone, the leather tanned with this combination method possessed improved thermal stability, enhanced mechanical properties, acceptable softness, appropriate hydrophilicity, and especially enhanced storage stability. More importantly, the combination tanned leather with 1:1 of the mass ratio of silicic acid to vegetable tannin (composed of valonea extract and mimosa extract with the same weight) had more prominent comprehensive performances. In addition, the results demonstrated that hydrogen bonding played an important role in the combination tanning process. Furthermore, the hydrogen bonds generated between phenolic hydroxyl groups of polyphenols with silicon hydroxyl groups of silicic acid molecules inhibited the excessive condensation of Si-OH groups between themselves. Subsequently, the assessment of environmental impact revealed the value of BOD5/COD of the wastewater produced in this combination tanning process is more than 0.3, indicating the chrome-free combination tannage based on silicic acid and plant tannin was an environment-friendly tanning technology. These findings therefore indicated that a new chrome-free tanning method with silicon and biomass materials as main tanning agents has potential practical application prospect in leather production.Graphical abstract

A novel high-toughness, organic/inorganic double-network fire-retardant gel for coal-seam with high ground temperature

In order to address the issue of spontaneous combustion of coal, this paper proposes a high-toughness hydrogel (P(AA-co-AM)/WG gel) for fire prevention and extinction, which is suitable for the conditions of coal-seam with high ground temperatures. In the initial stage, the silicic acid molecules in the material system react under the action of the coagulant to form the first network structure. Simultaneously, the superabsorbent monomers in the material system use the geothermal energy in the mines to polymerize and form the second network structure. The first and second network cross each other, forming P(AA-co-AM)/WG gel with interpenetrating network structure and high toughness. The differences in WG gel, P(AA-co-AM), and P(AA-co-AM)/WG gels were analyzed via testing of their in-situ infrared, and viscoelasticity. The results indicate that P(AA-co-AM)/WG gel had the best water retention, elasticity, inhibitory performance, compression resistance and lowest cost among the studied gels. In addition, the fire extinction experiments of comparison with other fire extinction materials indicated that P(AA-co-AM)/WG gel could uniformly cover the surface of the burning coal body forming a dense enwrapping on the coal and densely filling the cracks. Moreover, the fire extinction effect of the proposed gel is stable as there was no re-ignition phenomenon.

Colloid silica in hydrothermal heat carrier: characteristics, technology of extraction, industrial applications

Hydrothermal solution as one of new mineral source for silica production. We have developed methods for silica extraction from hydrothermal solution. Ultrafiltration membrane concentration was used to obtain silica sols. Ultrafiltration membranes have selectivity on colloid silica particles about 1.0 and low selectivity on silicic acid molecules and ions. Thus, ultrafiltration provides with a low content of impurities and stability of water sols up to the highest SiO2 content (up to 62.5 %). Cryochemical vaccum sublimation of silica sols was used for production nanopowders with specific surface of particles up to 500 m2/g. Cryochemical vacuum sublimation of sols gave the possibility to reduce particles aggregation when silica was extracted from liquid phase. By extraction of silica purification of heat carrier can be achived and the problem of solid scales formation in heat equipment of GeoPPs can be decided. Perspective ways of industrial applications for sols and nanopowders obtained from hydrothermal heat carrier such as building industry and agriculture were dicussed.

Synthesis and formation mechanism of amorphous silica particles via sol–gel process with tetraethylorthosilicate

Silica microspheres with narrow particle size distribution and average diameter of 80–200 nm were prepared by hydrolysis and condensation of tetraethylorthosilicate (TEOS) in ethanol solution. Effects of TEOS, ammonia, water concentration, and temperature on particle size and morphology were investigated by laser particle size analysis and field emission scanning electron microscopy (FESEM), in conjunction with energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) spectroscopy. Monomer addition model was employed to analyze the stability of intermediate, as well as the direction in which the reaction of silica particles proceeds. The analysis was carried out by Materials Studio. Results demonstrated that particle size of Nano-silica increases with increasing concentrations of H2O, NH3·H2O, and TEOS in ethanol, whereas the size decreases with increasing temperature. In addition, when proper amount of H2O was added into NH3·H2O at suitable temperature, silicic acid can act as a nucleus for amorphous Nano-silica particles, forming microspheres with round and smooth surfaces. By contrast, when TEOS was used, resultant nanoparticles have poor surfaces. During nucleation process of Nano-silica, silicic acid can also acts as nucleating agent providing a platform for the growth of nanoparticles with symmetric structure. Findings further indicated that the reaction proceeds by first silicic acid participates in the reaction, and the dimer and trimer molecules then react with the surface of silicic acid molecules; the same products could be produced by different reactions.

Study on the Mechanism of the Interactions Between the Dendritic Macromolecule PAMAM and Silicic Acids in Neutral Solution

In this work, a molecular modeling method was used to investigate the interactions between PAMAM with different generations and silica acid molecules in neutral solution. The calculated results show that adsorption interactions of silicic acid molecules with the generation 2.0 PAMAM molecule are stronger than those with the generation 1.5 PAMAM molecule. The adsorption interactions are dominated by electrostatic interactions, vdW interactions as well as O⋯H-O and C-H⋯O H- bond interactions. We qualitatively discuss the effect of PAMAM molecules on the silica polymerization in neutral solution, where the inhibition effect of generation 2.0 is better than that of generation 1.5. The theoretical discussion is in reasonable agreement with experiment results.

A theoretical study of the inhibition effect of PAMAM molecule on silica scale.

In this work, the molecular modeling method was performed to study adsorption interaction between PAMAM molecules of different generations and silicic acid molecules, and the inhibition effect on silica scale were discussed. The results show that adsorption energies of PAMAM molecule of generation 1.0 with amine-terminated groups are stronger than those of generation 1.5 with terminated carboxyl group. The composition of adsorption interactions are the dominating electrostatic interactions and van de Waals interactions as well as H-bond interactions. It is qualitatively discussed that the inhibition effect of generation 1.0 on silica scale is stronger than that of generation 1.5 in the neutral solution.

Highly transparent silica aerogel thick films with hierarchical porosity from water glass via ambient pressure drying

Highly transparent silica aerogel films of 2–3.6 μm thick and with the hierarchical porosity were deposited on fluorine doped tin oxide (FTO) conductive glass substrate via the sol–gel and ambient drying processes, by using water glass as the silicic source. An innovative aging process was developed by immersing the hydrogel film in large volume of tetraethoxysilane (TEOS)–ethanol solution. Obtained aerogel films possessed both the mesopores and the submicron pores, with the average pore size of 19.1 nm, the specific surface area of 530 m2 g−1, and the pore volume of 2.96 cm3 g−1. The leaching of silicic acid molecules from the hydrogel film into the bulk aging solution was responsible for the formation of submicron pores. The aging of the hydrogel film in TEOS–ethanol solution could greatly enhance the silica skeleton and resist the film shrinkage during the ambient drying process, and an aging time longer than 8 h was appropriate to obtain thick aerogel films without obvious structure collapse. The SiO2 content in the precursor should be kept at medium level, to avoid nonuniform film thickness or lower surface area. In addition, the aerogel film synthesized at optimal condition possessed good hydrophobicity (contact angle: 132°), high transparency (70–82% in 400–1200 nm band), and low dielectric constant (k = 1.42). The work demonstrates a facile and low-cost route toward transparent silica aerogel films with hierarchical pore structures, which can be used as the intermetal dielectrics or the template to synthesize novel functional materials requiring high transmittance, high surface area and effective mass transport.

Preparation of Silica Abrasives from Water Glass and Application in Silicon Wafer Polishing

Chemical mechanical polishing technique is more frequently adopted for planarization in integrated circuit fabrication. The silica abrasives in colloidal state are fabricated with the sodium silicate solution as raw materials through the polymerization reaction among silicic acid molecules. By continuous injection of silicic acid into the preexisting silica solution, the diameter of silica nanoparticles increases. The different sized silica nanoparticles are imaged by scanning electron microscopy, and the dried silica are characterized by X-ray diffraction and thermal analysis. The polishing test on silicon wafer with as-fabricated silica abrasives shows that the surface flatness reaches 1.1 nm roughness, however, micro scratches are still present in the surface.

Computational model for protein-mediated biomineralization of the diatom frustule

The mechanism of silicification from which the intricate cell walls of diatoms emerge, as well as the stereochemical relationship between the wall's organic casing and the siliceous materials within, continue to elude current technology. The present study further develops Hecky et al.'s standing model of the organicinorganic interface with semi-empirical computer simulations of a biosilicification pathway. Polycondensation reactions between silicic acid molecules and a hydroxyl-rich β-sheet protein template results in a stereochemically-compatible chemisorbed tetrasiloxane ring. The 24-stage reaction pathway has an activation barrier of +15.4 kcal mol-1 and results in a net stabilization of-28.0 kcal mol-1. Spatial matching and favorable thermodynamics support the theory of protein-mediated biomineralization of the diatom.

Molecular Dynamics Study of Silica−Alumina Interfaces

Computer simulations of silica−alumina interface formation by a sol-gel process were performed using the molecular dynamics method. The polymerization reaction of silicic acid molecules was simulated for 1 ns (10 000 000 time steps). A complete transformation from liquid silicic acid to dense silica was observed due to removal of water from the sample. The reaction kinetics was characterized using the degree of polymerization of polysiloxane chains and relative concentrations of silicon Q species. Hydroxyl groups originally present on the alumina surface played a crucial role in formation of an ordered atomic structure in the interface region.

In-situ infrared characterization of a chemically oxidized silicon surface dissolving in aqueous hydrofluoric acid

An in-situ infrared observation of silicon surfaces immersed in aqueous hydrofluoric acid using a multireflection internal-reflection technique with a spectrochemical cell has been carried out. Hydrogen termination and its revolution, associated with the dissolution of silicon oxides in hydrofluoric acid, were observed on the surface. In the liquid phase attaching to the silicon surface, the creation of silicic acid molecules associated with hydrogen-bonded water molecules and their polymerization were assigned based on the vibrational characteristics on changing the flow speed of the acid. The time evolution of the observed absorption peaks were consistent with the assignment.

Bond stretching force constants and compressibilities of nitride, oxide, and sulfide coordination polyhedra in molecules and crystals

Molecular quadratic stretching force constants are calculated for a variety of MX bonds (X = N, O, S) in coordinated polyhedra containing row 1 and 2 metal atoms, M, using SCF molecular orbital methods and 6-31G* basis sets. The resulting data scatter along three distinct trends, depending on whether the bonds involve row 1 atoms, row 1 and row 2 atoms, or row 2 atoms. When compared with spectroscopically determined force constants, the calculated force constants are found to be ∼ 20% larger. A single trend seems to obtain when the calculated force constants are plotted as a function of the effective nuclear charges of the bonded atoms and their interatomic separations. Scaled force constants calculated for the SiO bond are in rough agreement with values provided by spectroscopic measurements for silicic acid molecules and silicate crystals. Polyhedral compressibilities for nitride-, oxide-, and sulfide-coordinated polyhedra are inversely related with force constants calculated for their MX bonds. The close similarity of these compressibilities and those recorded for chemically similar crystals suggests that force constant-compressibility relationships in chemically similar molecular and crystalline systems are not significantly different.

Sol-gel polymerization: analysis of molecular mechanisms and the effect of hydrogen

Abstract The polymerization of silicic acid molecules (H4SiO4) was simulated using classical molecular dynamics with multibody potentials. The mechanisms involved in the condensation process were analyzed. Although a condensation mechanism was observed in the simulations which corresponds to the mechanism commonly assumed, additional mechanisms not previously presented were also observed. The advancement of polymerization was found to depend on the non-bridging oxygens' coordination with hydrogen, the number of bridging oxygens around five-coordinated silicons and atomic momentum. The results show consistency with the chemistry described for the acid catalyzed sol-gel process where hydrogen acts as the catalyst and chains form before rings.

Molecular Simulations of the Polymerization of Silicic Acid Molecules and Network Formation

Polymerization of 216 silicic acid molecules, H 4 SiO 4 , has been studied using the molecular dynamics computer simulation technique. Multibody potentials which reproduce bulk and surface structures of silica and silicate glasses, as well as molecular configurations containing Si, O, and H ions, were used in the simulations. Results of the simulations are consistent with experimental data of sol-gel systems. Chains form at the early stages of polymerization, followed by ring formation, consistent with interpretations of NMR data and semiempirical molecular orbital quantum calculations. The activation energy for formation of branching Q n species is 12 kcal/mol, consistent with the experimental data of 12 kcal/mol for gelation. The relative time evolution of the various Q n species is consistent with experimental NMR data

Kinetics of reaction between silicic acid and amorphous silica surfaces in NaCl solutions

The condensation polymerization between silicic acid and silica surfaces has been studied in the absence of nucleation, by seeding silicic acid solutions with colloidal amorphous silica particles of known surface area. Experiments were performed at 25–50°C, 0–1 M NaCl, and 4 ≦ pH ≦ 8 in unbuffered solutions. The reaction falls into two kinetic regimes, limited at high silicic acid concentration by polymerization-dissolution events, but at lower concentration by a process whereby deposited silicic acid condenses further to silica. The overall rates of both events appear directly proportional to the silica surface area A s . Polymerization is first-order in both silicic acid concentration, C, and in the surface concentration of ionized hydroxyl groups (the surface charge) on amorphous silica, [SiO −]. Thus, −dc dt ∝ k 0A s [ SiO −]C . Solution pH influences silica surface charge but not the rate constant, while salt concentration influences both. The salt-free polymerization rate constant is k 0 = 1.03 ± 0.12 M −1 s −1 at at 25°C, and exhibits an Arrhenius temperature dependence with an apparent activation energy of 13.1 ± 0.9 kcal/mole in the range 25–100°C, based upon analysis of the present data combined with two studies from the literature. Polymerization is not diffusionally limited under these conditions. Freshly deposited silica exhibits an enhanced solubility roughly twice the equilibrium level; this means that polymerization approaches this pseudoequilibrium point rather than approaching amorphous silica solubility. This also means that silica dissolution rates vary with the surface concentration of freshly deposited silicic acid molecules; thus, the overall kinetics of silicic acid concentration decline are determined by both surface and solution concentrations of silicic acid. A rate law is proposed which reproduces these and other recent literature data; this model appears applicable to silica dissolution data as well. Conflicting reports of both the reaction stoichiometry and the effect of silica surface charge have been resolved.

Matrix reactions of silane and oxygen atoms. Infrared spectroscopic evidence for the silanol, silanone, and silanoic and silicic acid molecules

Par photolyse, obtention de composes comportant la double liaison SiO: H 2 SiO, H(HO)SiO et (HO) 2 SiO. HSiOH est egalement prepare avec un bon rendement par decharge hyperfrequence de O 2 dans un exces d'argon. Pour les deux techniques SiH 3 OH est propose comme produit de reaction primaire par insertion d'atomes O dans une liaison SiH de SiH 4

Infrared spectroscopic evidence for silicon-oxygen double bonds: silanone and the silanoic and silicic acid molecules

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInfrared spectroscopic evidence for silicon-oxygen double bonds: silanone and the silanoic and silicic acid moleculesRobert Withnall and Lester AndrewsCite this: J. Am. Chem. Soc. 1985, 107, 8, 2567–2568Publication Date (Print):April 1, 1985Publication History Published online1 May 2002Published inissue 1 April 1985https://doi.org/10.1021/ja00294a070RIGHTS & PERMISSIONSArticle Views547Altmetric-Citations75LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (287 KB) Get e-Alerts Get e-Alerts

ケイ酸塩のケイ酸重合形態の解析方法としてのトリメチルシリレーション法とケイモリブデン酸法の比較研究

The polymeric forms of silicic acid in various silicate antacids were studied by the trimethylsilyation and silicomolybdate methods. Composition and distribution were markedly influenced by the kind of silicates. The low molecular weight silicic acids determined by the silicomolybdate method were estimated to include silicic acid molecules such as H4SiO4, H6Si2O7, H8Si3O10, H3Si4O12, and some linear polymer, and the forms of colloidal silicic acids were estimated to have H2n+4Si2nO5n+2. The trimethylsilylation method is excellent for the silicate structure analysis. It is possible to learn of a measure of the gastrointestinal absorption of silicic acid by the silicomolybdate method.