Silicate Condensation Research Articles

Morphology-controlled functional colloids by heterocoagulation of zein and nanoparticles

A general and reproducible heterocoagulation method is presented to prepare sub-micron sized zein protein particles, loaded with negatively charged nanoparticles. These composite carrier particles can be obtained in three different morphologies, and each morphology can be prepared using nanoparticles of various size, shape and composition. An important feature of the zein composites is their long-term stability in water even in conditions where free nanoparticles often aggregate within days. Additionally, we modify the composite particles by coating them with a thin layer of silica via condensation of sodium silicate, opening possibilities for highly specific, functionalized carrier particles. Finally, the formation of hollow silica shells containing negatively charged nanoparticles is demonstrated, using the zein composites as a template.

Short time interval for condensation of high-temperature silicates in the solar accretion disk

Chondritic meteorites are made of primitive components that record the first steps of formation of solids in our Solar System. Chondrules are the major component of chondrites, yet little is known about their formation mechanisms and history within the solar protoplanetary disk (SPD). We use the reconstructed concentrations of short-lived (26)Al in chondrules to constrain the timing of formation of their precursors in the SPD. High-precision bulk magnesium isotopic measurements of 14 chondrules from the Allende chondrite define a (26)Al isochron with (26)Al/(27)Al = 1.2(±0.2) × 10(-5) for this subset of Allende chondrules. This can be considered to be the minimum bulk chondrule (26)Al isochron because all chondrules analyzed so far with high precision (∼50 chondrules from CV and ordinary chondrites) have an inferred minimum bulk initial ((26)Al/(27)Al) ≥ 1.2 × 10(-5). In addition, mineral (26)Al isochrons determined on the same chondrules show that their formation (i.e., fusion of their precursors by energetic events) took place from 0 Myr to ∼2 Myr after the formation of their precursors, thus showing in some cases a clear decoupling in time between the two events. The finding of a minimum bulk chondrule (26)Al isochron is used to constrain the astrophysical settings for chondrule formation. Either the temperature of the condensation zone dropped below the condensation temperature of chondrule precursors at ∼1.5 My after the start of the Solar System or the transport of precursors from the condensation zone to potential storage sites stopped after 1.5 My, possibly due to a drop in the disk accretion rate.

Parallel optimization of a reactive force field for polycondensation of alkoxysilanes.

We have optimized a reactive force field (ReaxFF) in order to model the gelation of alkoxysilanes in bulk precursor solutions. The force field parameter set was refined using a parallelized local search algorithm. Using this approach, each processor is assigned a small list of parameters. At the end of every iteration, all parameters are updated simultaneously after being independently evaluated. In comparison to the serial evaluation of parameters, this results in faster parametrization of ReaxFF, as well as helps to prevent entrapment in local minima. The resulting model is found to reproduce hydrolysis and condensation reaction energies well. By applying the model to the condensation of silicic acid monomers at several temperatures, the activation energy of silane condensation is determined. The expected behavior, a gradual depletion of hydrolyzed silicon and growth of condensed silica clusters is observed over timescales of a few nanoseconds. The new model is also verified by modeling the early stages of clusterization in an alkoxysilane precursor solution. Both hydrolysis and condensation reactions are observed in a system containing a mixture of tetramethoxysilane, methanol, and water.

Synthesis, Characterization and Textural Analysis of Functionalized Mesoporous Silica Using Sodium Silicate as Precursor and Silicone Surfactant as Template

Three mesoporous silica with different functional group were prepared by one-step synthesis based on the simultaneous hydrolysis and condensation of sodium silicate with organo - silane in the presence of template surfactant polydimethylsiloxane - polyethyleneoxide (PDMS - PEO). The prepared materials were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), atomic force microscopy (AFM) and nitrogen adsorption/desorption experiments. The results indicate that the preparation of methyl and phenyl functionalized silica were successful and the mass of methyl and phenyl groups bonded to the silica structure are 15, 38 mmol per gram silica. The average diameter of the silica particles are 103.51, 167.25 , and 86.41 nm while the average pore diameter are 6.7, 16.4, and 2.7 nm for unfunctionalized, methyl, and phenyl functionalized silica respectively.

Synthesis, Characterization and Textural Analysis of Functionalized Mesoporous Silica Using Sodium Silicate as Precursor and Silicone Surfactant as Template

Three mesoporous silica with different functional group were prepared by one-step synthesis based on the simultaneous hydrolysis and condensation of sodium silicate with organo - silane in the presence of template surfactant polydimethylsiloxane - polyethyleneoxide (PDMS - PEO). The prepared materials were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), atomic force microscopy (AFM) and nitrogen adsorption/desorption experiments. The results indicate that the preparation of methyl and phenyl functionalized silica were successful and the mass of methyl and phenyl groups bonded to the silica structure are 15, 38 mmol per gram silica. The average diameter of the silica particles are 103.51, 167.25 , and 86.41 nm while the average pore diameter are 6.7, 16.4, and 2.7 nm for unfunctionalized, methyl, and phenyl functionalized silica respectively.

Functionalized Bentonite clay-sPEEK based composite membranes for direct methanol fuel cells

Composite membranes comprising functionalized Bentonite (HSO3-BEN)-sulfonated poly(ether ether ketone) (sPEEK) is fabricated as an alternative polymer electrolyte membrane (PEM) for direct methanol fuel cells (DMFCs). K+-Bentonite is functionalized through silane condensation to introduce organo sulfonic acid groups. Ion-exchange capacity, sorption and proton conductivity for the composite membranes have been investigated. These composite membranes are also characterised for their mechanical and thermal properties. DMFCs employing sPEEK-HSO3-BEN composite membrane delivered peak power density of 140 mW cm−2, while peak power density of 71 mW cm−2 is obtained for the DMFC employing pristine sPEEK membrane at 70°C. The results show that these composite membranes exhibits lower methanol permeability in comparison to pristine sPEEK membrane.

Effects of alkaline media on the controlled large mesopore size distribution of bimodal porous silicas via sol-gel methods

A series of bimodal mesoporous silicas (BMMs) have been synthesized under different aqueous alkaline conditions, including sodium hydroxide (NaOH), ethylenediamine (EDA) as well as dipotassium phosphate (DKP). Their morphologies and textural properties were fully characterized by X-ray diffraction (XRD), scanning and transmission electron microscope (SEM/TEM), N2 adsorption/desorption isotherms, and Fourier transform infrared (FT-IR) spectroscopy. The results showed that a weak alkaline system was beneficial to obtain a low order degree of the mesopore structure with uniform spherical morphology, whereas a strong alkaline medium was favorable to achieve a high order degree of the mesopore structure with relatively larger but irregular nanoparticles. During the sol–gel process with combination of the template synthesis technique, the use of a strong base may accelerate the silicate condensation with irregular morphologies as a result. Also, it may accelerate the growth of the micellar (cetyltrimethyl ammonium bromide) phase with ordered arrangement. Therefore, the effects of different alkaline media on the mesopores and morphologies of these BMMs were remarkable. To account for the observation, a possible mechanism was proposed.

Bioinspired Approach to Multienzyme Cascade System Construction for Efficient Carbon Dioxide Reduction

An efficient multienzyme cascade system based on ultrathin, hybrid microcapsules was constructed for converting CO2 to methanol by combining the unique functions of catechol and gelatin. Gelatin was modified with catechol groups (GelC) via well-defined EDC/NHS chemistry, thus endowed with the ability to covalently attach enzyme molecules. Next, the first enzyme (FateDH)-containing CaCO3 templates were synthesized via coprecipitation and coated with a GelC layer. Afterward, GelC was covalently attached with the second enzyme (FaldDH) via Michael addition and Schiff base reactions. Then, GelC induced the hydrolysis and condensation of silicate, and the third enzyme (YADH) was entrapped accompanying the formation of silica particles. After removal of CaCO3 templates, the GelCSi-based multienzyme system was obtained, in which the three enzymes were appropriately positioned in different places of the GelCSi microcapsules, and the amount of individual enzyme was regulated according to enzyme activity. The syste...

Amorphous silica in ultra-high performance concrete: First hour of hydration

Amorphous silica in the sub-micrometer size range is widely used to accelerate cement hydration. Investigations including properties of silica which differ from the specific surface area are rare. In this study, the reactivity of varying types of silica was evaluated based on their specific surface area, surface silanol group density, content of silanol groups and solubility in an alkaline suspension. Pyrogenic silica, silica fume and silica synthesized by hydrolysis and condensation of alkoxy silanes, so-called Stoeber particles, were employed. Influences of the silica within the first hour were further examined in pastes with water/cement ratios of 0.23 using in-situ X-ray diffraction, cryo scanning electron microscopy and pore solution analysis. It was shown that Stoeber particles change the composition of the pore solution. Na+, K+, Ca2+ and silicate ions seem to react to oligomers. The extent of this reaction might be highest for Stoeber particles due to their high reactivity.

SYNTHESIS AND CHARACTERIZATIONOF ORGANIC FUNCTIONALIZED MESOPOROUS SILICA AND EVALUATE THEIR ADSORPTIVE BEHAVIOR FOR REMOVAL OF METHYLENE BLUE FROM AQUEOUS SOLUTION

Three Mesoporous Silica (MPS) with different functional groups were prepared by one-step synthesis based on the simultaneous hydrolysis and condensation of tetraethoxy silane with organo-silane in the presence of template surfactant Polydimethylsiloxane-Polyethyleneoxide (PDMS-PEO). The prepared materials were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA) and nitrogen adsorption-desorption experiments. The results indicate that the preparation of methyl and phenyl functionalized silica were successful. The adsorption behavior of methylene blue from aqueous systems onto these mesoporous silica has been studied. Batch experiments were carried out to measure the adsorption as a function of contact time, initial concentration (2.5-20 mg L-1) and temperature (288, 298, 308 and 318 K). The equilibrium of the process was achieved within (30-60) min. The adsorption of methylene blue on the mesoporous silica increases with increasing temperature which indicating an endothermic process. Adsorption isotherms were fitted with the Langmuir, Freundlich models. The kinetic data were analyzed using pseudo-first- order and pseudo-second-order models and intraparticle diffusion. The adsorption kinetics of methylene blue on mesoporous silica matched well with pseudo-second order kinetic model.

Silane surface modification of boron carbide in epoxy composites

Boron carbide (BC) is a boron-rich ceramic material used as a radiation absorber for shielding parts in the nuclear industry and for particle physics experimentation. BC parts are generally manufactured using the sintering process, which tends to limit the size and shape of components and imparts high cost. Low temperature and lower pressure moulding using a BC polymer matrix composites (PMC) provides an alternative process for developing lower cost parts whilst accommodating increased complexity of geometry and size. However, a lack of adhesion exhibited between BC and the resin led to a composite with limited mechanical strength and durability. In this study a silane coupling agent was used to improve the adhesion between the epoxy resin and BC. An improvement in mechanical strength was observed in the treated composite by means of three-point bending, Iosipescu and double v-notch tests. Initial investigation of the surface chemistry also showed the presence of hydroxyl groups and B–O bonds, which may promote improved adhesion through silane condensation and the formation of covalent bonds.

Surface Modification of Cured Cement Pastes by Silane Coupling Agents

X-ray photoelectron spectroscopy (XPS) and static contact angle measurements were used to study the interaction between silane coupling agents and cured cement paste. Three different silane coupling agents were investigated: aminopropyltriethoxy silane (APTES), 3-glycidyloxypropyltrimethoxy silane (GPTMS), and methoxy-terminated polydimethxyl siloxane (PDMS). These silanes have different end groups, so the change in surface energy after undergoing a successful reaction between the silane and hydroxyls on the surface of the cement paste was demonstrated by a change in contact angle. Relative to untreated samples, APTES samples decreased the contact angle, PDMS samples increased the contact angle, and GPTMS did not show a significant change in contact angle. Samples with a water-to-cement ratio (w/c) of 0.5 showed a larger change in contact angle than 0.4 w/c ratio samples, because of a greater number of hydroxyl groups at the surface. Deconvolution of the O 1s and Si 2p XPS peaks were performed to determine contributions from bridging and nonbridging atoms. An increase in bridging silicon and oxygen atoms relative to untreated samples indicated successful silane condensation and that a covalent bond was formed between the cement paste and silanes.

Polymerization of Silicate on Hematite Surfaces and Its Influence on Arsenic Sorption

Iron oxides and oxyhydroxides are important sorbents for arsenic in soils, sediments, and water treatment systems, but their long-term potential for arsenic retention may be diminished by the formation of polymeric silicate on their surfaces. To study these interactions, we first investigated the sorption of silicate to colloidal hematite (α-Fe(2)O(3)) in short-term (48 h) and long-term (210 days) batch experiments. The polymerization of silicate on the hematite surface was monitored by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The pH dependence of silicate sorption exhibited a maximum between pH 9.0 and 9.5. The condensation of silicate on hematite surfaces adsorbed from monomeric silicate solutions steadily continued over the 210 day period, whereby surface polymerization was slower at pH 3 than at pH 6. The effect of silicate surface polymerization on arsenate and arsenite sorption was studied by use of hematite pre-equilibrated with silicate for different time periods of up to 210 days. The competitive effect of silicate on arsenate and arsenite sorption increased with increasing silicate pre-equilibration time. Only under strongly acidic conditions (pH 3), where silicate sorption was weakest and surface polymerization was slowest, was arsenate and arsenite sorption not affected by the presence of silicate. We conclude that the long-term exposure to dissolved silicate can decrease the potential of natural iron (oxyhydr)oxides for adsorbing inorganic arsenic.

Hydrous layer silicates as precursors for zeolites obtained through topotactic condensation: a review

In the search for new synthesis routes of zeolites, the topotactic condensation of hydrous layer silicates shows promising results in generating novel zeolite materials with distinct framework types which might have new, interesting properties as, e.g ., molecular sieves or form-selective catalysts. In order to manipulate and optimise the condensation process detailed knowledge of the crystal structures is essential. The layer silicates considered here are of a special type and can be designated as high-silica hydrous layer silicates , HLSs. The structures consist of a tetrahedral layer of interconnected [SiO4]-units containing equal numbers of terminal silanol/siloxy groups on either side of the layer and of an inter-layer region where cations of low charge density (predominantly organic cations) and water molecules are located. A topotactic condensation of the layers performed at temperatures of around 500°C with simultaneous expulsion of the inter-layer constituents is able to form fully condensed, uninterrupted framework silicates. The topotactic conversion has so far been described rarely in comparison to the classical hydrothermal synthesis of zeolites. Nevertheless, several hydrous layer silicates with different layer topologies were successfully converted into zeolites of different framework types using this synthesis route: CAS (type material: EU-20, EU-20b), CDO (type material: CDS-1), FER (type material: siliceous ferrierite), MWW (type material: MCM-22), NSI (type material: NU-6(2)), RRO (type material: RUB-41), RWR (type material: RUB-24), SOD (type material: guest-free silica sodalite). Thereby, four new zeolite framework types were obtained which have not been synthesized, so far, by direct hydrothermal synthesis (CDO, NSI, RRO, RWR). This review gives an overview on the hydrous layer silicates being structurally characterized in detail, on the condensation process and on some properties of the resulting zeolite materials.

Dissolution from inside: a unique degradation behaviour of core–shell magnetic mesoporous silica nanoparticles and the effect of polyethyleneimine coating

The degradation of composite mesoporous silica nanoparticles is quite important for the in vivo use of this delivery carrier. We investigated the dynamic silica degradation of core–shell structured magnetic mesoporous silica nanoparticles (M-MSNs) and its counterpart with polyethyleneimine coating (M-MSN@PEI) in PBS. It is confirmed for the first time that M-MSNs unexpectedly experienced a preferential dissolution from the inside part of the mesoporous shell, leading to a rattle-type degradation structure. Additionally, the presence of polyethylenimine (PEI) can maintain this transition state of rattle-type structure for more than 50 h of immersion in PBS, whereas the same structure was disintegrated after 2 h for bare M-MSNs. We then tried to put forward a possible degradation mechanism for this type of core–shell M-MSNs by studying and comparing with the dissolution behaviour of pristine mesoporous silica nanoparticles (MSNs). It is discovered that two pivotal factors governed this unique process: (a) the unique shell structure with lower interior pore order and (b) the role of PEI chains in affecting silicate condensation. There is no doubt that the present study will provide guidance for the design and in vivo bio-applications of an M-MSN-based delivery system.

Deposition of hybrid 3-GPTMS's film on AA2024-T3: Dependence of film morphology and protectiveness performance on coating conditions

This paper describes the elaboration of 3-glycidoxypropyltrimethoxysilane (3-GPTMS) films onto AA2024-T3 aluminum alloy for corrosion protection.The dependence of sol–gel morphology on both precipitation under cathodic polarization and nitrate incorporation was investigated via scanning electron microscopy (SEM).Once added into silanization solution, sodium nitrate promoted the reaction of silane condensation and enhanced the film compactness.Electrochemical impedance spectroscopy results (EIS) indicated that doping silane film with NaNO3 ameliorated its barrier property and protectiveness. Silane films applied onto AA2024-T3 surface by using potentiostatic method, exhibited obviously higher corrosion resistance than those obtained by conventional “dip-coating” method. The resistance of coating is accentuated when not very negative potential was applied.

Decorative, hydrophobic sol–gel coatings densified using near-infrared radiation

Decorative, hydrophobic coatings were generated using sols synthesized from hydrolysis and condensation of methyltriethoxy silane, tetraethoxy silane and 1H,1H,2H,2H-perfluorooctyltriethoxysilane, in combination with nanosized and submicron-sized inorganic black pigment particles. Coatings were densified at 250 °C using near-infrared radiation as well as by a conventional curing method. The densified coatings were characterized for their thickness, roughness, contact angles and adhesion. The properties of the near-infrared radiation cured pigmented coatings were found to be comparable with those of the conventionally cured coatings. The pigmented coatings generated using nanosized pigments, whether near-infrared radiation cured or conventionally cured were seen to exhibit improved hydrophobicity with contact angles ranging from 130 to 145° when compared to their transparent unpigmented counterparts, that showed water contact angles from 93 to 97°. The improved hydrophobicity was explained on the basis of presence of a possible double length scale roughness of the coatings.

Mesoporous silica SBA-15 sheet with perpendicular nanochannels

Free-standing thin sheet form of mesoporous silica materials with perpendicular orientation is a much desired materials for its possible applications in catalysis, mask, and separation. A three component amphiphile system of sodium dodecyl sulfate/hexadecyltrimethylammonium bromide/pluronic-123(C16TMAB/SDS/P123) was employed to template the condensation of sodium silicates for the formation of SBA(⊥), a thin sheet of SBA-15 with perpendicular nanochannels. SBA(⊥) can be synthesized at SDS/C16TMAB=1.5 and T⩾40°C and shows pH-dependent morphology. It has uniform pore size ∼9nm, homogeneous sheet thickness in the range of 60–300nm and dimension of several microns. We studied in details the structure and morphology of the SBA(⊥) with variation of three experimental parameters: the SDS/C16TMAB ratio, the temperature, and the pH condition in the synthetic gel. It is proposed that the mixed surfactants of SDS and C16TMAB form catanionic vesicle in which the P123 and silicates are condensed. The balanced interaction of P123/silicate with the narrow confinement under surfactant bi-layers of C16TMAB/SDS promoted the formation of perpendicular nanochannels. Low temperature and pH conditions favor stronger segregation of the PPO and PEO–oligosilicate segments in the SBA(⊥) structure which gives the basis of thickness control of the sheet. The control of structure and morphology are discussed with modern theory of microphase separation in block copolymers under confinement.

Evaluation of thermodynamic properties of H4SiO4 in the ideal gas state from experimental data

Thermodynamic properties of gaseous silicon hydroxides are necessary for analyzing the silicate condensation phenomena in the primordial solar nebula [Hashimoto, 1992], the silica precipitation in steam-rich geothermal systems and recent concerns with the corrosion or deposition of SiO2-containing alloys and ceramics in high-temperature moist environments. Experimental transpiration studies (i.e. studies of the partial pressures of Si over solid phases in the presence of steam) of the reaction of water vapor with cristobalite [Hashimoto, 1992; Jacobson, et al., 2005] agree that at 1100-1650 K and water pressures close to 0.1 MPa the vapor phase concentration of Si is determined by the reaction SiO2(s) + 2H2O(g) = H4SiO4(g). (1) Mass spectrometric data on the volatile species formed from SiO2(s) and water at 1473–1773 K and water vapor pressure between 0.018 and 0.094 MPa [Opila, et al., 1997] also confirm that H4SiO4 is the primary reaction product. However, the literature data on the thermodynamic properties of gaseous H4SiO4 [Allendorf, et al., 1995; Jacobson, et al., 2005; Rutz and Bockhorn, 2005] differ up to 18 kJmol and 9 JKmol in the value of enthalpy of formation and the entropy at Tr=298.15 K and the standard pressure   P 0.1 MPa. Therefore, it was decided employ all available data for the reaction (1) to determine the optimal values of ΔfG and S of H4SiO4(g) at 298.15 K and 0.1 MPa. Selection of experimental data In addition to the transpiration data we accepted data on the solubility of quartz and amorphous silica in water vapor of density below 15 kg·m. The accepted data set of data to calculate the values of equilibrium constant of reaction (1) is given in Table.

Swelling, Functionalization, and Structural Changes of the Nanoporous Layered Silicates AMH-3 and MCM-22

Nanoporous layered silicate materials contain 2D-planar sheets of nanoscopic thickness and ordered porous structure. In comparison to porous 3D-framework materials such as zeolites, they have advantages such as significantly increased surface area and decreased diffusion limitations because the layers can potentially be exfoliated or intercalated into polymers to form nanocomposite materials. These properties are particularly interesting for applications as materials for enhancing molecular selectivity and throughput in composite membranes. In this report, the swelling and surface modification chemistry of two attractive nanoporous layered silicate materials, AMH-3 and MCM-22, were studied. We first describe a method, using long-chain diamines instead of monoamines, for swelling of AMH-3 while preserving its pore structure to a greater extent during the swelling process. Then, we describe a stepwise functionalization method for functionalizing the layer surfaces of AMH-3 and MCM-22 via silane condensation reactions. The covalently attached hydrocarbon chain molecules increased the hydrophobicity of AMH-3 and MCM-22 layer surfaces and therefore allow the possibility of effectively dispersing these materials in polymer matrices for thin film/membrane applications.