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

2011 ◽  
Vol 115 (9) ◽  
pp. 3562-3571 ◽  
Author(s):  
Anouschka Depla ◽  
David Lesthaeghe ◽  
Titus S. van Erp ◽  
Alexander Aerts ◽  
Kristof Houthoofd ◽  
...  
Keyword(s):  
Sol Gel ◽  
Silica Sol ◽  
Reaction Pathways ◽  
29Si Nmr ◽  
Uv Raman ◽  
Acid Catalyzed ◽  
Oligomerization Reaction

scholarly journals Cross-Condensation Reactions in an Organically Modified Silica Sol-Gel

1994 ◽  
Vol 346 ◽  
Author(s):  
S. Prabakar ◽  
R. A. Assink ◽  
N. K. Raman ◽  
C. J. Brinker
Keyword(s):  
Experimental Error ◽  
Molecular Level ◽  
Sol Gel ◽  
Resonance Assignments ◽  
Silica Sol ◽  
Modified Silica ◽  
Organically Modified ◽  
Organically Modified Silica ◽  
Acid Catalyzed ◽  
Hydrolysis Of

ABSTRACTHigh resolution 29Si NMR has been used to study the extent of cross condensation taking place in a hybrid organic/inorganic sol-gel system. Tetraethoxysilane (TEOS) and methyltriethoxysilane (MTEOS) sol-gels were chosen for this purpose. The sols were prepared by acid catalyzed hydrolysis of TEOS and MTEOS with a H2O/Si ratio of 0.3. 29Si NMR shows signals due to both self-condensation and cross-condensation between TEOS and MTEOS. Resonance assignments were made by comparing the positions and intensities of peaks in the spectra of single and multicomponent systems. It was found that, within experimental error, the self- and cross-condensation rates are equal and that extensive molecular level mixing takes place during the early stages of the reaction.

29Si NMR Study of Distribution of Oligomers in Polycondensation of Tetraethoxysilane

1996 ◽  
Vol 61 (5) ◽  
pp. 691-703 ◽  
Author(s):  
Jiří Brus ◽  
Jiří Karhan ◽  
Petr Kotlík
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Sol Gel ◽  
29Si Nmr ◽  
Nmr Study ◽  
Nmr Spectrometry ◽  
Concentration Changes ◽  
Acid Catalyzed ◽  
The Moment

29Si NMR spectrometry has been used to determine the number molecular weight distribution of polymerization degrees of a system of oligomers formed in the sol-gel polycondensation of tetraethoxysilane (TEOS). On the basis of identification of the oligomers, monitoring of the concentration changes during the initial phase of the sol-gel polycondensation, and from the deviations observed between the experimentally determined number molecular weight distribution of polymerization degrees and the Flory-Stockmayer model it has been proved that cyclization represents a significant process in the acid-catalyzed polycondensation with substoichiometric amount of water (ratio of amounts TEOS/H2O = 1 : 1). The cyclization becomes important at the moment when the reaction mixture contains increased amounts of the linear tetramer and pentamer. The cyclization products form a basis for formation of polycyclic, highly condensed building units whose gradual aggregation produces the gel.

Sol-Gel Kinetics: 29Si NMR and a Statistical Reaction Model

1988 ◽  
Vol 121 ◽  
Author(s):  
Roger A. Assitik ◽  
Bruce D. Kay
Keyword(s):  
Chemical Speciation ◽  
Functional Group ◽  
Sol Gel ◽  
Early Time ◽  
Reaction Model ◽  
29Si Nmr ◽  
Mathematical Framework ◽  
Time Behavior ◽  
Acid Catalyzed ◽  
Group Distribution

ABSTRACTThe early time behavior of an acid catalyzed Si(OCH3),4 (TMOS) sol-gel was studied by high resolution 29Si nuclear magnetic resonance (NMR). Both the water producing and the alcohol producing condensation reactions were found to contribute significantly to the overall condensation rate. A general theoretical kinetic formalism which specifically treats the temporal evolution of the various chemical function groups about a specific silicon atom was developed. The experimentally observed functional group distribution was in agreement with the distribution predicted by a simplified statistical reaction model. The mathematical framework for the study of chemical speciation at the next-to-nearest functional group level was developed. This framework was used to assign several fine structure resonances, and to show that the formation of various dimeric species is also largely statistical in nature.

UV-Raman and 29Si NMR Spectroscopy Investigation of the Nature of Silicate Oligomers Formed by Acid Catalyzed Hydrolysis and Polycondensation of Tetramethylorthosilicate

2011 ◽  
Vol 115 (22) ◽  
pp. 11077-11088 ◽  
Author(s):  
Anouschka Depla ◽  
Elke Verheyen ◽  
An Veyfeyken ◽  
Marc Van Houteghem ◽  
Kristof Houthoofd ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
29Si Nmr ◽  
Uv Raman ◽  
Acid Catalyzed ◽  
Hydrolysis And Polycondensation ◽  
29Si Nmr Spectroscopy

scholarly journals A simple approach to prepare fluorescent molecularly imprinted nanoparticles

RSC Advances ◽  
2021 ◽  
Vol 11 (13) ◽  
pp. 7732-7737
Author(s):  
Fenying Wang ◽  
Dan Wang ◽  
Tingting Wang ◽  
Yu Jin ◽  
Baoping Ling ◽  
...  
Keyword(s):  
High Performance ◽  
Low Cost ◽  
Sol Gel ◽  
Silica Sol ◽  
Simple Approach ◽  
Imprinted Polymer ◽  
Molecularly Imprinted ◽  
Low Toxicity ◽  
Good Biocompatibility ◽  
Molecularly Imprinted Nanoparticles

Fluorescent molecularly imprinted polymer (FMIP) gains great attention in many fields due to their low cost, good biocompatibility and low toxicity. Here, a high-performance FMIP was prepared based on the autocatalytic silica sol–gel reaction.

Silica Sol-Gel Supported Nickel Nano-Catalyst for Hydrogen Production Using Microreactors

2005 ◽  
Vol 885 ◽  
Author(s):  
Krithi Shetty ◽  
Shihuai Zhao ◽  
Wei Cao ◽  
Naidu V. Seetala ◽  
Debasish Kuila
Keyword(s):  
Steam Reforming ◽  
Average Pore Size ◽  
Sol Gel ◽  
Supported Catalyst ◽  
Silica Sol ◽  
Average Pore ◽  
Steam Reforming Of Methanol ◽  
Nano Catalyst ◽  
Before And After ◽  
Reforming Reactions

ABSTRACTThe goal of this research is to investigate the activities of a non-noble nano-catalyst (Ni/SiO2) using Si-microreactors for steam reforming of methanol to produce hydrogen for fuel cells. The supported catalyst was synthesized by sol-gel method using Ni (II) salts and Si(C2H5O)4 as starting materials. EDX results indicate that the actual loading of Ni (5-6%) is lower than the intended loading of 12 %. The specific surface area of the silica sol-gel encapsulated Ni nano-catalyst is 452 m2/g with an average pore size of ∼ 3 nm. Steam reforming reactions have been carried out in a microreactor with 50 µm channels in the temperature range of 180-240 °C and atmospheric pressure. Results show 53% conversion of methanol with a selectivity of 74 % to hydrogen at 5 l/min and 200 °C. The magnetic properties of the catalysts were performed using a Vibrating Sample Magnetometer (VSM) to study the activity of the catalysts before and after the steam reforming reactions. The VSM results indicate much higher activity in the microreactor compared to macro-reactor and Ni forms non-ferromagnetic species faster in the microreactor.

Characterization of the Effect of Formamide Additive on the Silica Sol-Gel-Glass Forming Process by1H NMR*

1987 ◽  
Vol 153 (Part_1_2) ◽  
pp. 27-36 ◽  
Author(s):  
H. Rosenberger ◽  
H. Bürger ◽  
H. Schütz ◽  
G. Scheler ◽  
G. Maenz
Keyword(s):  
Sol Gel ◽  
Silica Sol ◽  
Forming Process ◽  
Glass Forming
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