SiOH Groups Research Articles

Preparation of core/shell structured silicate composite filler and its reinforcing property

Core/shell structured composite particles have been frequently reported to enhance the performance of products. In this work, core/shell structured calcium silicate composite filler was prepared to mitigate the negative effect of calcium silicate filler on paper strength and allow for increasing filler content in paper. Calcium silicate as the core which was used as silica source, and reacted with hydrochloric acid to form SiO2 as shell. Results from XRD, FT-IR, SEM and BET specific surface area analysis indicated that nano-SiO2 particles were formed on the surface of calcium silicate. The active SiOH group on the surface of the composite filler enhanced the bondability between fillers and fibers. Physical testing of handsheets showed notable improvement in mechanical properties (tensile index increased 33.0%, tear index increased 18.1%). In addition, the SiOH group also helped to flocculate of composite filler to larger particles, which was also beneficial to the paper strength.

Salinity-dependent adhesion of model molecules of crude oil at quartz surface with different wettability

The adhesion forces between model chemical moieties of oil molecules (CH3–, C6H5–, COOH–, and NH2–) and quartz surfaces with different wettability were investigated by the aid of chemical force microscopy at low and high salinity (10 mM and 100 mM). Our results showed that the adhesion force on hydrophilic surfaces decreased as in the order: –NH2 > –COOH > –C6H5 ≈ –CH3, due to the contribution of hydrogen bonding interactions between polar groups of functionalized tips and Si-OH groups of quartz surfaces. By comparison, the adhesion force decreased almost in an opposite order: –CH3 > –C6H5 > –COOH ≈ –NH2, in the case of hydrophobic surfaces, attributed to the strong trend of hydrophobic interactions between nonpolar oil groups and hydrophobic surface (modified with alkyl chains). A high potential of low salinity effect on improving oil recovery can be found in polar oil system in the presence of hydrophilic surfaces, as well as in nonpolar oil system in the presence of hydrophobic surfaces, because of the significantly reduced adhesion forces from high to low salinity environment. Thus it can be concluded that for hydrophilic reservoirs, the low salinity effect may be remarkable in the case of crude oil containing more polar components. And for hydrophobic reservoirs, crude oil with more nonpolar components would exhibit a significant low salinity effect. All these provide a better understanding in the molecular level for low salinity water flooding applications.

Preparation and Characterization of Organic-Inorganic Hybrid Macrocyclic Compounds: Cyclic Ladder-like Polyphenylsilsesquioxanes.

Organic-inorganic hybrid macrocyclic compounds, cyclic polyphenylsilsesquioxanes (cyc-PSQs), have been synthesized through hydrolysis and condensation reactions of phenyltrichlorosilane. Structural characterization has revealed that cyc-PSQs consist of a closed-ring double-chain siloxane inorganic backbone bearing organic phenyl groups. The cyc-PSQ molecules have been simulated and structurally optimized using the Forcite tool as implemented in Materials Studio. Structurally optimized cyc-PSQs are highly symmetrical and regular with high stereoregularity, consistent with the dimensions of their experimentally derived structures. Thermogravimetric analysis showed that these macrocyclic compounds have excellent thermal stability. In addition to these perfectly structured compounds, macrocyclic compounds with the same ring ladder structure but bearing an additional Si-OH group, cyc-PSQs-OH, have also been synthesized. A possible mechanism for the formation of the closed-ring molecular structures of cyc-PSQs and cyc-PSQs-OH is proposed.

Synthesis of incompletely caged silsesquioxane (T7-POSS) compounds via a versatile three-step approach

Three kinds of incompletely condensed polyhedral oligomeric silsesquioxanes (T7-POSS) with three Si–OH groups: (i-C4H9)7Si7O9(OH)3, (i-C8H17)7Si7O9(OH)3 and (C6H5)7Si7O9(OH)3 were prepared by a versatile three-step approach (hydrolysis, condensation, and neutralization) from i-C4H9Si(OEt)3, i-C8H17Si(OEt)3, and C6H5Si(OEt)3, respectively, with the LiOH·H2O as catalyst. The structures of the three T7-POSS were characterized by FTIR, 1H NMR, 13C NMR, 29Si NMR, MALDI-TOF MS and XRD. The accurate incompletely caged structure of the three T7-POSS indicated that the built-up three-step approach is a versatile and effective way to synthesize T7-POSS with high yield. The best reaction conditions to synthesize the isobutyl-T7, isooctyl-T7 and phenyl-T7 POSS have been suggested, involving acetone and a co-solvent, the molar ratio of the RSi(OEt)3: LiOH·H2O: H2O and the reaction temperature. The thermal stability of the three T7-POSS were characterized by TGA, showing different degradation behaviors. The thermal stability of phenyl-T7 POSS was the highest among the three T7-POSS.

Structure of water in hybrid cellulose acetate-silica ultrafiltration membranes and permeation properties

Hybrid cellulose acetate (CA) silica (SiO2) (CA/SiO2) membranes were synthesized by promoting the in situ condensation between silanols from the SiO2 precursor and the COH or acetate groups from the CA polymer.For all the CA/SiO2 membranes, the ATR-FTIR peak assigned to (SiOC) proves the hybrid condensation reaction and confirms the synthesis of monophasic hybrid membranes.ATR-FTIR shows the presence of uncondensed highly reactive SiOH species, in membranes with silica contents higher than 20 mol%. Together with RMN studies, results show molecular water strongly hydrogen-bonded with SiOH groups, yielding a drastic decrease in the membrane hydraulic permeability, from 57 to 10 kg/h/m2/bar.The incorporation of 5 and 10 mol% of silica increased the hydraulic permeability from 32 to 82 kg/h/m2/bar when compared to the CA membrane.

Bacterial cell killing properties of silver-loaded polysiloxane microspheres

Cross-linked polysiloxane microspheres containing a large number of SiOH groups were modified by introduction of organic thiol groups, which were further used for the functionalization of the microspheres with silver thiolate groups. The microspheres were characterized by 29Si MAS NMR, 13C MAS NMR, SEM, XPS and elemental analysis. They were tested as biocides against selected Gram-positive and Gram-negative bacteria strains and exhibited high bactericidal activity. Separately, linear polysiloxane polymers equipped with organothiol groups and loaded with silver were synthesized. Their antibacterial activity was compared with that of silver thiolate-functionalized microspheres. Different shape of particles and a different form of silver explained somewhat lower activity of polymers.

Introduction of Boron Functionalities into Silsesquioxanes: Novel Independent Methodologies.

Owing to their versatile application possibilities, silsesquioxanes (SQs) are of considerable interest for creating hybrid inorganic-organic materials. In this report, two novel and independent strategies for the direct attachment of boron functionalities to silsesquioxanes are presented. Encouraged by our previous work concerning the synthesis of borasiloxanes through the catalyst-free dehydrogenative coupling of silanols and boranes, we decided to apply our method to a synthesis of various boron-functionalized silsesquioxanes. During our tests, we also investigated the activity of scandium(III) triflate, which we have previously used as an excellent catalyst for the obtaining of Si-O-Si and Si-O-Ge moieties. As a result, we also discovered a novel approach for the O-borylation of Si-OH groups in silsesquioxanes with allylborane. Both routes are highly chemoselective and efficiently lead to the obtaining of Si-O-B moiety under air atmosphere and at room temperature.

Enhanced Stability of MFI Zeolite Membranes for Separation of Ethanol/Water by Eliminating Surface Si-OH Groups.

The practical application of pure-silica MFI zeolite membranes for ethanol/water separation by pervaporation is limited by its poor stability. Herein, we present the Si-OH eliminated MFI membranes by a simple dopamine modification, which can effectively prevent the chemical reaction between Si-OH groups and components, endowing the long-term pervaporation stability.

Effect of mixing sequences of γ-piperazine propylmethyl dimethoxysilane on the tracking and erosion resistance of silicone rubber

γ-Piperazin propylmethyl dimethoxysilane (HD-110) was introduced into silicone rubber containing platinum catalyst to enhance the tracking and erosion resistance by two mixing sequences:adding HD-110 in the preparation of silicone rubber masterbatch (SR-1) or silicone compound (SR-2). The effects of HD-110 and its mixing sequence on the thermal stability, tracking and erosion resistance, and mechanical properties of silicone rubber were investigated by rubber process analyzer (RPA), transmission electron microscopy (TEM), extraction resistance test, thermogravimetric analysis (TGA) and inclined plane (IP) test. It was indicated that HD-110 could significantly improve the thermal stability and tracking and erosion resistance of silicone rubber. Especially, SR-1 could pass the IP test at 4.5 kV with a eroded mass ratio of 0.35 wt%, which was much less than the 5.34 wt% of SR-2. SR-1 also had better mechanical properties. RPA, TEM and extraction resistance test revealed that HD-110 in SR-1 could easily condense with the Si-OH groups of silica to make HD-110 stable in the silicone rubber matrix and improve the interfacial interaction between silica and silicone rubber. Therefore, under the continuous elution of conductive solution and the heat stress generated by dry-band arcing, HD-110 was stable enough to enhance the tracking and erosion resistance of silicone rubber.

FTIR spektroskopsko istraživanje alkalno aktiviranog pepela

Fly ash is byproduct of thermal power plants. Millions tons of fly ash is produced globally. Fly ash is disposed partly in landfills but it could also be released into the atmosphere in the past. Fly ash is composed of silica, alumina, iron oxide, magnesia and activated carbon. Due to large surface area, fly ash is very suitable for catalysis application. It is well known and well reported that fly ash can be converted into efficient adsorptive material such as zeolites. In the present work, the transformation of fly ash into zeolite was carried out by alkali activation process of aluminosilicates material. The alkali solution releases silicon and aluminum ion into solution, which form afterwards Si-OH and Al-OH groups. FTIR spectroscopy was applied to characterize fly ash chemical activation, in order to conduct a study making intensive use of infrared spectroscopy and further to provide information on chemical bond vibrations in the molecular units of fly ash. The FTIR spectrum of solid base fly ash (SBFA) after chemical activation shows a significant increase in peak intensity of the band for -OH group.

Understanding the deformation mechanism and mechanical characteristics of cementitious mineral analogues from first principles and reactive force field molecular dynamics.

In this paper, first principles and reactive force field molecular dynamics were utilized to study the mechanical properties of tobermorite 9 Å, tobermorite 11 Å and jennite. These are essential minerals in cement chemistry. The mechanical properties calculated by the first-principle method match well with previous experimental results, pointing to the introduction of vdW dispersion-type forces as able to improve the precision. The calculated elastic constants of the three minerals confirm anisotropic mechanical behavior of the layered structures. The crystals jennite and tobermorite 9 demonstrate stronger mechanical behavior in the ab plane than the interlayer direction due to the presence of stable covalent "dreierketten" silicate chains. For tobermorite 11 Å, the Q3 silicate tetrahedrons bridging the neighboring calcium silicate sheets heal the weak interlayer structure and enhance the c-direction stiffness and cohesive strength. Furthermore, analysis of uniaxial tension by reactive force MD elucidated the chemical and mechanical responses of the atomic structures in loading resistance. The stress-strain relation of the layered mineral tensioned along b direction, showing the "strain hardening" region, where stress continues to increase past the yield stage. The strain hardening and ductility enhancement for the minerals is largely due to the ability of the silicate chains to first de-polymerize into short chains or separate tetrahedrons before the broken Q species re-polymerize to form branched networks and ring structures which are able to resist loading. For all three minerals, protons transfer to oxygen and water, resulting in the formation of Si-OH and Ca-OH groups during the strain hardening stage as Si-O-Si or Si-O-Ca bonds start to break and the calcium atoms and silicate morphology is rearranged. Hydrolysis therefore accelerates structural damage and contributes to weakening of mechanical properties in the interlayer direction. Increased tensile stress level in the tobermorite 11 Å can contribute to a greater extent of water damage.

Non-porous and porous materials prepared by cross-linking of polyhydromethylsiloxane with silazane compounds

In the work, polyhydromethylsiloxane (PHMS) was cross-linked with two vinylsilazanes: 1,1,3,3-tetramethyl-1,3-divinyldisilazane (ViSiNSiVi) or 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasilazane ((ViSiN)4) in the presence of Karstedt’s catalyst. When the reactions were carried out in solvent-free conditions non-porous polysiloxane-silazane networks were obtained. The processes conducted in high internal phase emulsion (HIPE) resulted in macroporous materials. Their non-porous or porous morphology was established by SEM studies. They were also analyzed by elemental analysis, swelling measurements, FTIR and 29Si MAS-NMR spectroscopies and thermogravimetry coupled with mass spectrometry (TG/MS). Results showed that the non-porous networks contained high amounts of silazane moieties and were fairly hydrolytically stable. In contrast, contents of silazane units in most porous materials were low. Moreover, hydrolysis of SiH groups of PHMS followed by condensation of the resulting SiOH groups took place in HIPE conditions. This led to additional cross-linking of PHMS by siloxane bonds. During preparation of porous systems using ViSiNSiVi, hydrolysis of silazane bonds (SiN) also occurred. All the materials studied in the work contained reactive SiH groups and therefore exhibit a great potential for various applications. Presence of nitrogen atoms in their structure as well as porosity may be additional advantages.

FT-IR study of the hydrolysis and condensation of 3-(2-amino-ethylamino)propyl-trimethoxy silane

The hydrolysis and self-condensation reactions of 3-(2-amino-ethylamino)propyl-trimethoxy silane have been studied by means FT-IR spectroscopy for different water and ethanol concentrations. The hydrolysis of 3-(2-amino-ethylamino)propyl-trimethoxy silane occurs at a high rate and depends if the water concentration is lower or higher than the stoichiometric one for hydrolysing all the hydrolysable groups. The presence of ethanol delays the hydrolysis reaction. The hydrolysis of 3-(2-amino-ethylamino)propyl-trimethoxy silane gives hydroxyl groups (Si–OH) that self-condense to form Si–O–Si bonds in linear and cyclic structures. For high water and low ethanol concentrations not all Si–OH groups self-condense, whereas for low water or high ethanol concentrations the major part of the Si–OH groups self-condense and tends to disappear in the gel state.

IR and NMR studies of hierarchical material obtained by the treatment of zeolite Y by ammonia solution

Ammonia treatment of ultrastable zeolite Y has a great impact on its features. XRD showed a partial loss of crystallinity coupled with a loss of long-distance zeolite ordering. However, a typical short-range zeolite ordering, in the light of 29Si NMR studies, was largely preserved. 27Al MAS NMR spectra evidenced that most of Al was located in zeolitic tetrahedral positions, but some of them adopted a distorted configuration. Evolution of zeolites acidity was followed quantitatively by using IR. In particular, such studies revealed the presence of strongly acidic SiOHAl groups. IR studies suggest also heterogeneity of these OH groups. The heterogeneity of SiOHAl groups was a consequence of the less ordered structure of zeolites treated with ammonia solutions. It was also found that the treatment with ammonia solutions yields hierarchical material. The samples revealed promising catalytic properties in the liquid phase isomerization of α-pinene. Zeolites desilicated with ammonia may constitute an inexpensive route yielding viable hierarchical catalysts.

Acidity enhanced [Al]MCM-41 via ultrasonic irradiation for the Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam

Using solid acid catalysts to replace liquid acids in the liquid-phase Beckmann rearrangement of cyclohexanone oxime (CHO) into ɛ-caprolactam (CPL) is crucial for the environmentally friendly production of synthetic fibers, such as Nylon-6. In this work, we prepared aluminum-containing MCM-41 catalysts under ultrasonic irradiation with various Si/Al ratios for this purpose. Quantitative 1H MAS NMR investigations show that ultrasonic irradiation significantly promotes the formation of active Brønsted acid sites (BAS) on the [Al]MCM-41 catalysts up to 8 times higher than those prepared at the same conditions without ultrasonic irradiation, and up to 12 times higher BAS density than those reported in the literatures. The catalytic performance of [Al]MCM-41 catalysts can be strongly improved with increasing the BAS density, particularly to the ratio of BAS/(weakly acidic SiOH groups). Moreover, [Al]MCM-41 catalysts dehydrated at 393 K obtained two time higher CHO conversion and CPL yield than that dehydrated at 473 K. Hydrogen-bonded water molecules retained at low dehydration temperature may block surface SiOH groups and promote the reaction process. With higher BAS density resulting from ultrasonic irradiation, [Al]MCM-41 catalyst (Si/Al = 10) in this work obtained the highest CPL yield among all [Al]MCM-41 materials reported for liquid-phase Beckmann rearrangement up to now. Finally, the reusability of [Al]MCM-41 catalyst was tested and no significant activity loss can be observed after five reaction cycles.

Fluorine-induced microporous silica membranes: Dramatic improvement in hydrothermal stability and pore size controllability for highly permeable propylene/propane separation

A molecular sieving membrane was fabricated using triethoxyfluorosilane (TEFS), which contains Si–F bonds and is categorized as a pendant-type alkoxysilane. The hydrothermal stability and hydrocarbon (C3H6, C3H8) permeation properties were evaluated for TEFS membranes. When a fluorine-induced silica membrane had a Si–F bond in the amorphous structure, the reaction of steam and Si-F groups during steam treatment formed Si-OH groups, which slightly decreased the gas permeance. Even though gas permeance slightly decreased under a steam atmosphere, a TEFS membrane calcined at 350°C had networks that were looser and more uniform than those of a conventional SiO2. In addition, the formation of adsorption sites (Si-OH groups) under steam treatment enhanced both interactions with the π-bonds (C=C double bond) of C3H6 and the C3H6/C3H8 permeation properties (C3H6 permeance: 2.2 × 10−7molm−2s−1Pa−1, C3H6/C3H8 permeance ratio: 42 at 35°C). The hydrothermal stability was dramatically enhanced by calcination temperatures as high as 750°C due to the presence of fewer Si-OH and Si–F bonds in the amorphous structure, although the network pore size of a TEFS membrane was the same whether it was calcined at 750°C or at 350°C.

Well-Defined Silanols in the Structure of the Calcined High-Silica Zeolite SSZ-70: New Understanding of a Successful Catalytic Material.

The structure of the calcined form of the high-silica zeolite SSZ-70 has been elucidated by combining synchrotron X-ray powder diffraction (XRPD), high-resolution transmission electron microscopy (HRTEM), and two-dimensional (2D) dynamic nuclear polarization (DNP)-enhanced NMR techniques. The framework structure of SSZ-70 is a polytype of MWW and can be viewed as a disordered ABC-type stacking of MWW-layers. HRTEM and XRPD simulations show that the stacking sequence is almost random, with each layer being shifted by ±1/3 along the ⟨110⟩ direction with respect to the previous one. However, a small preponderance of ABAB stacking could be discerned. DNP-enhanced 2D 29Si{29Si} J-mediated NMR analyses of calcined Si-SSZ-70 at natural 29Si isotopic abundance (4.7%) establish the through-covalent-bond 29Si-O-29Si connectivities of distinct Si sites in the framework. The DNP-NMR results corroborate the presence of MWW layers and, more importantly, identify two distinct types of Q3 silanol species at the surfaces of the interlayer regions. In the first, an isolated silanol group protrudes into the interlayer space pointing toward the pocket in the adjacent layer. In the second, the surrounding topology is the same, but the isolated -SiOH group is missing, leaving a nest of three Si-O-H groups in place of the three Si-O-Si linkages. The analyses clarify the structure of this complicated material, including features that do not exhibit long-range order. With these insights, the novel catalytic behavior of SSZ-70 can be better understood and opportunities for enhancement recognized.

Measurement of Si―OH content in fused silica with extended dynamic range by Fourier transform infrared spectroscopy

Fourier transform infrared (FTIR) spectroscopy Si―OH group is widely used in Si―OH content measurement of fused silica optics. However, the measurement accuracy is influenced by water molecular absorption bands in low Si―OH content samples and absorption saturation in high Si―OH content samples, leading to limited measurement range. FTIR spectroscopy is employed to measure 2500 cm-1 ~5000 cm-1 transmittance spectra of fused silica samples with different OH contents and thicknesses. The interference of water molecular absorption band to 3673 cm-1 is eliminated. Then Si―OH contents, corresponding measurement errors and limits of detection at 3673 cm-1 and 4522 cm-1 bands are calculated. Based on the experimental results and Beer’s law, a model to correlate Si―OH content, sample thickness, measurement error of transmittance, and measurement error of Si―OH content is established. From this model, by using 3673 cm-1 band for fused silica samples with Si―OH content less than 8.17×10-4 and 4522 cm-1 band for samples with Si―OH content more than 8.17×10-4 to measure the Si―OH content, a dynamic range from 0.4×10-6 to10-2 Si―OH can be achieved with optimized accuracy for fused silica samples with 2 mm thickness.

Silica aerogels formed from soluble silicates and methyl trimethoxysilane (MTMS) using CO2 gas as a gelation agent

Silica aerogel has been formed using CO2 gas as the gelation agent through the low-cost ambient pressure drying technique. With water wash and the following solvent exchange process for Na+ removal, this synthesis route has no ion exchange resin used and becomes more straightforward. In order to reduce the silica particle and pore sizes, different hydrolysis-condensation rate control agents including dimethylformamide (DMF), methyltriethoxysilane (TMES), Glycerol and methyltrimethoxylsilane (MTMS) have been applied to modify the structural groups of silica network. Results show that MTMS is the most effective control agent and the optimized MTMS/silica sol volume ratio has been found at 1% by testing the specific surface area of the aerogel. In addition, the effects of chlorotrimethylsilane (TMCS) amount and the calcining temperature on the physicochemical properties of the aerogel have been also investigated. When the TMCS/silica sol volume ratio is 0.4, Thermogravimetric and Differential Scanning Calorimetry analysis (TG/DSC) measurement shows that there is an apprent exothermic peak at calcining temperture of 420°C, caused by the transformation of Si-CH3 group to Si-OH group. X-ray photoelectric spectroscopy (XPS) results show that the percentages of Si-C(-H) bonds with binding energy of 102.4eV have decreased from 25.5% to 7.2% after 420°C calcining. The contact angle of the as-dried aerogel is as high as 154° and dramatically decreases to ca. 109° after calcining at 450°C. The pore volume and BET specific surface area both increase first and then decrease with the increase of calcining temperature, and the pore volume reaches the maxmium of 1.45cm3/g at 400°C and it confirms Si-CH3 group release. This study offers a new facile route to the synthesis of silica aerogel and presents a promising way of the cost-effective large-scale manufacturing.

Effects of AC and DC corona on the surface properties of silicone rubber: Characterization by contact angle measurements and XPS high resolution scan

This study utilized a multi-needle corona electrode system to investigate the influence of AC and DC coronas on the surface properties of high temperature vulcanized (HTV) silicone rubber. Contact angle measurements and X-ray photoelectron spectroscopy (XPS) analysis were performed to characterize the chemical structure and hydrophobicity changes in state of the silicone rubber surface after corona exposure. The results indicated that the effects of AC corona were greater than that of DC corona, and the effects of negative DC corona were slightly greater than that of positive DC corona. XPS results showed that the C elemental content on the silicone rubber surface decreased, whereas the O elemental content increased. High-resolution scan on Si 2p XPS spectra proved that surface oxidation occurred during corona exposure and caused the high binding energies of Si atoms and silica-like layer. High-resolution C 1s XPS spectra showed that corona exposure destroyed the Si-CH3 groups on the surface. Some C-O and C=O bonds appeared following the corona exposure. High-resolution O 1s XPS spectra confirmed the formation of Si-OH groups and chemically absorbed water, which was ignored in the past research. Chemically absorbed water was detected as one of the essential factors that caused the loss of hydrophobicity of silicone rubber after corona exposure, together with Si-OH groups and silica-like layer.