Hydrolysis-condensation processes of the tetra-alkoxysilanes TPOS, TEOS and TMOS in some alcoholic solvents

Bernards, T.N.M.; Bommel, M.J. van; Boonstra, A.H.

doi:10.1016/0022-3093(91)90005-q

Cited by 114 publications

(87 citation statements)

References 18 publications

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“…[5][6][7] Crucial parameters of the silica sol-gel processes are the water:alkoxide molar hydrolysis ratio or r-value, the pH, and the nature of the alkoxide. 5,[8][9][10][11][12][13][14][15][16][17] In general terms, homogeneous acid catalysts direct silica polymerization toward linear polymers and materials having low fractal dimension, while basic catalysts generally favor formation of tridimensional highly branched silicate networks. 8,15 Raman spectroscopy and 29 Si NMR are frequently used for investigation of silica polymerization.…”

Section: ' Introductionmentioning

confidence: 99%

²⁹Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

et al. 2011

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ABSTRACT:The initial molecular steps of the acid-catalyzed silica sol-gel process departing from tetraethylorthosilicate (TEOS) were investigated by in situ 29 Si NMR and UV-Raman spectroscopy. The use of a substoichiometric H 2 O:TEOS molar ratio (rvalue 0.2-1.2) slowed the silicate oligomerization reaction and allowed unraveling the initial steps of silica condensation. Molecular modeling confirmed Raman signal and 29 Si NMR shift assignment. A comprehensive listing of all Raman and 29 Si NMR assignments is provided, including unique Raman assignments of cyclosilicates and the linear tetramer. The combination of experiment and modeling allowed an analysis of the reaction kinetics. The derived kinetic model and the experimental observation both revealed that the H 2 O: TEOS molar ratio had a strong influence on the reaction kinetics but not on the reaction pathways. The multianalytical approach led to development of an oligomerization scheme. As dominant oligomerizations, chain growth, cyclodimerization, and branching were identified. Under the investigated conditions, chains did not grow longer than pentamer, and ring sizes were limited to 6-rings. Chains of 4 Si atoms and 4-rings were abundant species. Branched rings and chains were formed by attachment of dimers and trimers. Gelation proceeded from branched 4-rings and branched chains with limited hydroxyl functionalities.

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Section: ' Introductionmentioning

confidence: 99%

²⁹Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

et al. 2011

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“…The results show that, for template-free synthesis (E1-E3 samples), E2 titania consists of the highest content of anatase and the largest anatase and rutile crystallites. Based on previous work 18,21 , the rate of hydrolysis reaction increases with increasing water content, and as a result, the fast hydrolysis reaction in E1 samples would produce fine particles. However, these particles are likely to agglomerate into larger particles.…”

Section: Resultsmentioning

confidence: 88%

“…The average crystallite sizes of anatase and rutile were estimated by employing Debye-Scherrer equation. The fraction of anatase phase is 18 (1+I R /0.8I A ) −1 , where I A and I R are the intensity of strongest diffraction line of anatase (101) and rutile (110) phase, respectively. N 2 adsorption and desorption experiments were conducted using Autosorb-1 instrument (Quantachrome, USA).…”

Section: Characterizationmentioning

confidence: 99%

Sol-gel template synthesis and photocatalytic behaviour of anatase titania nanoparticles

Loryuenyong¹,

Angamnuaysiri²,

Sukcharoenpong³

et al. 2012

ScienceAsia

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In this study, titania nanoparticles were successfully prepared by a sol-gel template method, employing cetyltrimethylammonium bromide (CTAB) and CaCO3 nanoparticles as templates. Titanium(IV) tetraisopropoxide and ethanol were used as a titanium precursor and alcoholic solvent, respectively. The obtained nanosized-titania was characterized by X-ray diffraction, transmission-electron microscopy, and N2 adsorption and desorption methods. The photocatalytic activity of titania was investigated from the photodegradation of methylene blue solution under UVC irradiation. The results indicated that the amount of anatase crystallites and pore characteristics were important factors influencing the degree of photocatalysis of titania nanoparticles. Highly crystalline anatase titania could be obtained through the controlled hydrolysis reaction rate and the formation of loose-packed titania nanoparticles, while high specific surface area could be achieved with a template method.

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“…TMOS has a faster hydrolysis rate than TEOS [112]. The hydrolysis of TEOS needs an acidic or basic catalyst to occur, and the hydrolysis rate is in general directly proportional to the concentration of acid or base, except for when only small amounts of acids are present [113,114].…”

Section: Hydrolysis and Condensationmentioning

confidence: 99%

Mesoporous Building Blocks: Synthesis and Characterization of Mesoporous Silica Particles and Films

Björk¹

2013

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On the cover, the structure of SBA-15 is illustrated. Inside the pores SEM micrographs have been inserted showing (clockwise from the top): rods, fibers, a film consisting of rods grown on a substrate, a film consisting of platelets grafted on a substrate, short rods, and platelets. In the center the sheet morphology is presented.© Emma Björk, unless otherwise stated.ISBN: 978-91-7519-516-2 ISSN: 0345-7524 Printed by LiU-tryck, Linköping, Sweden, 2013 Research is formalized curiosity. It is poking and prying with a purposeZora Neale Hurston (1903Hurston ( -1960 i ABSTRACTCatalyst supports, drug delivery systems, hosts for nanoparticles, and solar cells are just some examples of the wide range of exciting applications for mesoporous silica. In order to optimize the performance of a specific application, controlling the material's morphology and pore size is crucial. For example, short and separated particles are beneficial for drug delivery systems, while for molecular sieves, the pore size is the key parameter.In this thesis, mesoporous silica building blocks, crystallites, with hexagonally ordered cylindrical pores were synthesized, with the aim to understand how the synthesis parameters affect the particle morphology and pore size. The synthesis of the particles is performed using a sol-gel process, and in order to increase the pore size, a combination of low temperature, and additions of heptane and NH 4 F was used. By variations in the amounts of reagents, as well as other synthesis conditions, the particle morphology and pore size could be altered. Separated particles were also grown on or attached to substrates to form films. Also, a material with spherical pore structure was synthesized, for the first time using this method.It was found that a variation in the heptane concentration, in combination with a long stirring time, yields a transition between fiber and sheet morphologies. Both morphologies consist of crystallites, which for the fibers are joined end to end, while for the sheets they are attached side by side such that the pores are accessible from the sheet surface. The crystallites can be separated to a rod morphology by decreasing the stirring time and tuning the HCl concentration, and it was seen that these rods are formed within 5 min of static time, even though the pore size and unit cell parameters were evolving for another 30 min. Further studies of the effects of heptane showed that the shape and mesoscopic parameters of the rods are affected by the heptane concentration, up to a value where the micelles are fully saturated with heptane. It was also observed that the particle width increases with decreasing NH 4 F concentration, independent of heptane amount, and a platelet morphology can be formed. The formation time of the particles decrease with decreasing NH 4 F, and the growth mechanism for platelets was further studied. The pore sizes for various morphologies were altered by e.g. variations in the hydrothermal treatment conditions, or the method for removing the surfactants.ii T...

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Hydrolysis-condensation processes of the tetra-alkoxysilanes TPOS, TEOS and TMOS in some alcoholic solvents

Cited by 114 publications

References 18 publications

²⁹Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

²⁹Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

Sol-gel template synthesis and photocatalytic behaviour of anatase titania nanoparticles

Mesoporous Building Blocks: Synthesis and Characterization of Mesoporous Silica Particles and Films

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Hydrolysis-condensation processes of the tetra-alkoxysilanes TPOS, TEOS and TMOS in some alcoholic solvents

Cited by 114 publications

References 18 publications

29Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

29Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

Sol-gel template synthesis and photocatalytic behaviour of anatase titania nanoparticles

Mesoporous Building Blocks: Synthesis and Characterization of Mesoporous Silica Particles and Films

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²⁹Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry

²⁹Si NMR and UV−Raman Investigation of Initial Oligomerization Reaction Pathways in Acid-Catalyzed Silica Sol−Gel Chemistry