Rapid reduction in gelation time and impregnation of hydrophobic property in the tetraethoxysilane (TEOS) based silica aerogels using NH4F catalyzed single step sol–gel process

Nadargi, Digambar Y.; Kalesh, Ravindra R.; Rao, A. Venkateswara

doi:10.1016/j.jallcom.2009.02.027

Cited by 42 publications

(20 citation statements)

References 27 publications

(19 reference statements)

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“…44 In the absence of a catalyst and H 2 O, the gelation time of TEOS-based gels is very high. 45 In this work, TEOS was deposited on a substrate surface under ambient conditions. Although no catalyst was used, humidity was expected to play a role in initiating the gelation processes.…”

Section: Resultsmentioning

confidence: 99%

Quantum Cascade Laser Based Photoacoustic Spectroscopy for Depth Profiling Investigations of Condensed-Phase Materials

2012

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We report on the development of a photoacoustic device for the detection of condensed-phase materials. A mid-infrared quantum cascade laser (QCL) was used for depth-profiling studies to distinguish among glycerol films and tetraethoxysilane (TEOS) films deposited on photoresist-coated silicon wafers. The QCL was continuously tunable from 1015 cm−1 to 1240 cm−1, allowing for collection of photoacoustic vibrational spectra for these materials. Variation of the laser pulse repetition rate allowed for identification and molecular discrimination of glycerol, TEOS, and photoresist based solely on photoacoustic spectra collected at different film depths.

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Section: Resultsmentioning

confidence: 99%

Quantum Cascade Laser Based Photoacoustic Spectroscopy for Depth Profiling Investigations of Condensed-Phase Materials

2012

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“…It is well known that fluoride ions act as a nucleophilic catalyst and accelerates the hydrolysis and condensation rates of TEOS [116][117][118][119][120]. The increased hydrolysis comes from a nucleophilic attack, where the fluoride ion assists with the removal of an alcohol chain.…”

Section: The Effect Of Fluoride Ionsmentioning

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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“…Sol-gel precursors are mainly alkoxysilanes which can be obtained in a high degree of purity [1,2]. Tetraethoxysilane (TEOS) has been widely used as a cheaper and less toxic precursor; it has very poor reactivity in the sol-gel reaction [3]. So that sol-gel process involves the reaction of liquid alkoxide precursor such as tetraethoxysilane (TEOS) with water in the presence of acid or base catalyst.…”

Section: Introductionmentioning

confidence: 99%

“…Wave number , Cm -1 Chemical Bond References 3433 O-H stretching [3] , [11] 1634 O-H deformation [12] 1082…”

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confidence: 99%

Mechanistic Investigation of Sol–Gel Reactions Using Alkoxysilane Precursor

Yousif

Eltoum

2020

CSIJ

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The present study has been carried out to investigate the mechanisms of sol–gel reactions using TEOS as precursor in the presence of acid or base catalyst. The gels were prepared by hydrolysis of TEOS using hydrochloride acid or ammonium hydroxide catalyst. The obtained gels were also characterized by FTIR spectroscopy. The results of FTIR spectroscopy indicated the existence of silanol and siloxane bonds; due to the formation of hydrolyzed species as reactive intermediate compounds in initial stage converted by condensation reactions to gels as ultimate products. Accordingly, appropriate mechanisms have been proposed for sol – gel reaction using TEOS as precursor in the presence of acid or base catalyst. These mechanisms involve three-steps SN2 mechanisms for base catalyzed hydrolysis reaction of TEOS and SN1 mechanisms for acid catalyzed hydrolysis reaction of TEOS. Three mechanisms have been also proposed for condensation reaction as second stage in sol-gel process. These mechanisms include alcoxolation, oxolation and oltaion.

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Rapid reduction in gelation time and impregnation of hydrophobic property in the tetraethoxysilane (TEOS) based silica aerogels using NH4F catalyzed single step sol–gel process

Cited by 42 publications

References 27 publications

Quantum Cascade Laser Based Photoacoustic Spectroscopy for Depth Profiling Investigations of Condensed-Phase Materials

Quantum Cascade Laser Based Photoacoustic Spectroscopy for Depth Profiling Investigations of Condensed-Phase Materials

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

Mechanistic Investigation of Sol–Gel Reactions Using Alkoxysilane Precursor

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