Hydrolysis and Solvolysis of Methyltriethoxysilane Catalyzed with HCl or Trifluoroacetic Acid: IR Spectroscopic and Surface Energy Studies (original) (raw)
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Hybrid Xerogels: Study of the Sol-Gel Process and Local Structure by Vibrational Spectroscopy
2021
The properties of hybrid silica xerogels obtained by the sol-gel method are highly dependent on the precursor and the synthesis conditions. This study examines the influence of organic substituents of the precursor on the sol-gel process and determines the structure of the final materials in xerogels containing tetraethyl orthosilicate (TEOS) and alkyltriethoxysilane or chloroalkyltriethoxysilane at different molar percentages (RTEOS and ClRTEOS, R = methyl [M], ethyl [E], or propyl [P]). The intermolecular forces exerted by the organic moiety and the chlorine atom of the precursors were elucidated by comparing the sol-gel process between alkyl and chloroalkyl series. The microstructure of the resulting xerogels was explored in a structural theoretical study using Fourier transformed infrared spectroscopy and deconvolution methods, revealing the distribution of (SiO)4 and (SiO)6 rings in the silicon matrix of the hybrid xerogels. The results demonstrate that the alkyl chain and the ...
Adsorption, 2011
The mild synthetic conditions provided by the sol-gel process and the versatility of the colloidal state allow for the mixing of inorganic and organic components at the nanometre scale in virtually any ratio for the preparation of hybrid materials. Our interest in hybrid xerogels focuses on combining their porosity with other properties to prepare optic-fibre sensors. The specific aim of this paper is to synthesise hybrid xerogels in acid media using methyltriethoxysilane (MTEOS) and tetraethoxysilane (TEOS) as silica precursors and to investigate the effect of the MTEOS molar ratio on the structure and porous texture of xerogels. Gelation time exponentially increased as the MTEOS molar ratio increased. Increasing the MTEOS molar ratio yielded xerogels with lower density and lower particle size. The incorporation of MTEOS resulted in new FTIR bands at 1276 and 791 cm −1 , which was attributed to vibrational modes of methyl group. The band around 1092 cm −1 associated with siloxane bonds shifted to lower wavenumbers and split into two bands. The 29 Si spectra only showed the Q n (n = 2, 3, 4) signal in xerogels with 0% MTEOS and the T n (n = 2, 3) signal in xerogels with 100% MTEOS; hybrid xerogels showed both Q and T signals. From XRD peaks at 2θ around 9°, we inferred that xerogels (>70% MTEOS) consisted of nanocrystalline CH 3 -SiO 3/2 species. Increasing the MTEOS molar ratio produced xerogels with lower pore volumes and lower average pore size. The integration of methyl groups on the surface decreased the surface polarity and, in turn, the characteristic energy.
Porous xerogels with a bifunctional surface layer of the composition ≡Si(CH2)3SH/≡Si(CH2)2H3
Russian Journal of Physical Chemistry A, 2007
The sol-gel method with ethanol as a solvent and fluoride ion as a catalyst was used to prepare polysiloxane xerogels containing both 3-mercaptopropyl and n -propyl groups in the surface layer. An increase in the relative amount of n -propyltriethoxysilane in the initial reaction solution was found to result in the formation of xerogels with developed porous structures, which was accompanied by an increase in the specific surface area from 370 to 550 m 2 /g; simultaneously, other porous structure parameters such as sorption volume and pore size exhibited a tendency to increase. Atomic-force microscopy was used to show that the xerogels synthesized comprised aggregates of mean size 30 nm. An analysis of the IR and 13 C cross-polarization magic angle spinning NMR data led us to conclude that the surface layer of bifunctional xerogels contained not only 3-mercaptopropyl and n -propyl groups but also silanol groups, part of nonhydrolyzed alkoxy groups, and H-bonded water molecules. The 29 Si cross-polarization magic angle spinning NMR spectra revealed the presence of structural units of the compositions í 1 [( ≡ SiO ) Si ( OR ') 2 ( CH 2 CH 2 CH 3 ) and/or ( ≡ SiO ) Si ( OR ') 2 ( CH 2 ) 3 SH, R' = H, OCH 3 , or OC 2 H 5 ], T 2 [( ≡ SiO ) 2 Si ( OR ')( CH 2 CH 2 CH 3 ) and ( ≡ SiO ) 2 Si ( OR ')( CH 2 ) 3 SH], and í 3 [( ≡ SiO ) 3 SiCH 2 CH 2 CH 3 and ( ≡ SiO ) 3 Si ( CH 2 ) 3 SH] in the xerogels synthesized.
Journal of Non-crystalline Solids, 2006
Silica xerogels were prepared from sonohydrolysis of tetraethoxysilane and exchange of the liquid phase of the wet gel by acetone. Monolithic xerogels were obtained by slow evaporation of acetone. The structural characteristics of the xerogels were studied as a function of temperature up to 1100°C by means of bulk and skeletal density measurements, linear shrinkage measurements and thermal analyses (DTA, TG and DL). The results were correlated with the evolution in the UV-Vis absorption. Particularly, the initial pore structure of the dried acetone-exchanged xerogel was studied by small-angle X-ray scattering and nitrogen adsorption. The acetone-exchanged xerogels exhibit greater porosity in the mesopore region presenting greater mean pore size ($4 nm) when compared to non-exchanged xerogels. The porosity of the xerogels is practically stable in the temperature range between 200°C and 800°C. Evolution in the structure of the solid particles (silica network) is the predominant process upon heating up to about 400°C and pore elimination is the predominant process above 900°C. At 1000°C the xerogels are still monolithic and retain about 5 vol.% pores. The xerogels exhibited foaming phenomenon after hold for 10 h at 1100°C. This temperature is even higher than that found for foaming of non-exchanged xerogels.
Materials Chemistry and Physics, 2013
Hybrid silica xerogels favourably combine the properties of organic and inorganic components in one material; consequently these materials are useful for multiple applications. The versatility and mild synthetic conditions provided by the sol-gel process are ideal for the synthesis of hybrid materials. The specific aims of this study were to synthesise hybrid xerogels in acidic media using tetraethoxysilane (TEOS) and ethyltriethoxysilane (ETEOS) as silica precursors, and to assess the role of the ethyl group as a matrix modifier and inducer of ordered domains in xerogels. All xerogels were synthesised at pH 4.5, at 60 C, with 1:4.75:5.5 TEOS:EtOH:H 2 O molar ratio. Gelation time exponentially increased with the ETEOS molar ratio. Incorporation of the ethyl groups into the structure of xerogels reduced cross-linking, increased the average siloxane bond length, and promoted the formation of ordered domains. As a result, a transition from Q n to T n signals detected in the 29 Si NMR spectra, the SieO structural band in the FTIR spectra shifted to lower wavelength, and a new peak in the XRD pattern at 2q < 10 appeared in the XRD patterns. Mass spectroscopy detected fragments with high numbers of silicon atoms and a polymeric distribution.
Synthesis and characterization of ultramicroporous silica xerogels
Journal of Non-crystalline Solids, 2010
Tailoring the porous texture of silica xerogels is of great interest in catalysis, adsorption and sensors. We report the preparation and characterization of xerogels with pore size distribution lower than 0.5 nm, synthesized by hydrolysis and condensation of tetraethylorthosilicate (TEOS) at pH 2.5. N2 (77 K) and CO2 (273 K) adsorption isotherms and immersion calorimetry into liquids with different molecular size (dichloromethane, 0.33 nm; trichloromethane, 0.40 nm; n-hexane, 0.43 nm; cyclohexane, 0.48 nm; isooctane, 0.59 nm; and carbon tetrachloride, 0.66 nm) were used to characterize ultramicroporous xerogels. All the xerogel samples adsorbed CO2 (273 K) but not N2 (77 K). Pore size distributions from immersion calorimetry showed that hydrolysis and condensation of TEOS at pH 2.5 produced silica xerogels with pore size distributions in the 0.33–0.48 nm range. Xerogels synthesized at 333 K and a 5.5:1 water:TEOS molar ratio produced xerogels with higher specific surface areas and wider pore size distributions than xerogels obtained at 293 K and at 2.5:1 water:TEOS molar ratio.
The Sol-Gel-Xerogel Transition
1993
This contract supported the development of the technology of trapping of organic molecules and enzymes in porous sol-gel matrices. Our work led to the preparation and design of a 0 0
Preparation and study properties of xerogel silica using sol-gel method
In This study synthesis of inorganic oxide material by a sol-gel technique through the formation of colloidal suspension (sol) and gelation of the sol into the gel enables incorporation of heat-sensitive active substances into the material during processing. Sol can be further processed into forms, such as monoliths(rod shape).The objectives of this study were to evaluate sol-gel derived silica gel as an implantable (monoliths). The structural properties of the prepared samples were studied ,using X-ray diffraction (XRD) and Fourier transform infrared (FTIR), UV-VIS. Spectroscopy of xerogel silica and liner shrinkage of the samples.the sample prepared by mixing TEOS,ethonal,water,and HCL ,TEOS and ethonal were mixing and stirred for 10 min at room temp.then 0.1 MHCL was gradually added to the solution until a water to TEOS molar ratio of R=2,R=5.The results shows that, silica xerogel has amorphous structure ,FTIR spectroscopy has been used to find the amount of water (OH) ,it was found that when increase in temperatures the R (R=water:TEOS molar ratio) (R=2,R=5) the decrease intensity of H2O absorbance are consistent with loss of physisorbed water. Transmission spectra shows that the final samples have good transparency and homogeneity (the reflective index about sample R=2,n=1.41and R=5,n=1.45), and the linear shrinkage for sample R=5 less about the R=2.it was found that, increase in temp. for (R=2,R=5) will decrease intensity of H2O absorbance which indent that the water will defused outside the sample.
Materials Science Forum, 2006
Organically-modified silica xerogels from 3-aminopropyltrimethoxysilane (APTES) and 3-isocyanatepropyltriethoxysilane (ICPTES) have been synthesized through carboxylic acid (formic acid, acetic acid and valeric acid) solvolysis. The resulting hybrid materials have been characterized by powder X-ray diffraction, mid-infrared spectroscopy, 29 Si and 13 C nuclear magnetic resonance, and photoluminescence spectroscopy. The results show that urea cross-links have been formed in these hybrids. The luminescence features depend on the selected carboxylic acids. For example, comparatively to the hybrids derived from formic and acetic acid solvolysis, valeric acid shows a red-shift of the emission features.
Structural analysis of poly(dimethylsiloxane) modified silica xerogels
Journal of Non-crystalline Solids, 1999
A new type of inorganic-organic hybrid material incorporating poly(dimethylsiloxane) (PDMS) in tetraethoxysilane (TEOS) based glassy gels has been produced by a sol±gel process. SAXS and SEM studies indicate that these PDMS modi®ed silica xerogels possess multiple size-scale morphologies, ranging from # Angstroms to micrometers. The multiple-level hybrid materials show improved structural integrity relative to pure sol±gel glasses (xerogels). The eect of reaction time, water content, as well as content and molecular weight of PDMS on the structure of such materials were studied. These processing variables aect the relative rates of hydrolysis and condensation reactions, and consequently change the microstructure of the ®nal product. Ó