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Characterization of polar surface groups on siliceous materials by inverse gas chromatography and the enthalpy–entropy compensation effect

Surface-modified porous silica is a well-established composite material. To improve its embedding and application behavior, adsorption studies of various probe molecules have been performed using the technique of inverse gas chromatography (IGC). For this purpose, IGC experiments were carried out in...

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Autores principales: Meyer, Ralf, Mueller, Kai, Naumov, Sergej, Bauer, Frank, Enke, Dirk
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Frontiers Media S.A. 2023
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10098098/
https://www.ncbi.nlm.nih.gov/pubmed/37065825
http://dx.doi.org/10.3389/fchem.2023.1084046
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author Meyer, Ralf
Mueller, Kai
Naumov, Sergej
Bauer, Frank
Enke, Dirk
author_facet Meyer, Ralf
Mueller, Kai
Naumov, Sergej
Bauer, Frank
Enke, Dirk
author_sort Meyer, Ralf
collection PubMed
description Surface-modified porous silica is a well-established composite material. To improve its embedding and application behavior, adsorption studies of various probe molecules have been performed using the technique of inverse gas chromatography (IGC). For this purpose, IGC experiments were carried out in the infinite dilution mode on macro-porous micro glass spheres before and after surface modification with (3-mercaptopropyl)trimethoxysilane. To provide information about the polar interactions between probe molecules and the silica surface, in particular, eleven polar molecules have been injected. In summary, the free surface energy for pristine silica ( [Formula: see text] = 229 mJ/m(2)) and for (3-mercaptopropyl)trimethoxysilane-modified silica ( [Formula: see text] = 135 mJ/m(2)) indicates a reduced wettability after surface modification. This is due to the reduction of the polar component of the free surface energy ( [Formula: see text] ) from 191 mJ/m(2) to 105 mJ/m(2). Simultaneously, with the reduction of surface silanol groups caused by surface modification of silica and, therefore, the decrease in polar interactions, a substantial loss of Lewis acidity was observed by various IGC approaches. Experiments with all silica materials have been conducted at temperatures in the range from 90°C to 120°C to determine the thermodynamic parameters, such as adsorption enthalpy ( [Formula: see text] ) and adsorption entropy ( [Formula: see text] ), using the Arrhenius regression procedure evaluating the IGC data. With the help of the enthalpy–entropy compensation, two types of adsorption complexes are assumed between polar probe molecules and the silica surface because of different isokinetic temperatures. Identical adsorption complexes with an isokinetic temperature of 370°C have been assigned to alkanes and weakly interacting polar probes such as benzene, toluene, dichloromethane, and chloroform. Polar probe molecules with typical functional groups such as OH, CO, and CN, having the ability to form hydrogen bonds to the silica surface, exhibit a lower isokinetic temperature of 60°C. Quantum chemical calculations of the probe molecules on a non-hydroxylated and hydroxylated silica cluster supported the formation of hydrogen bonds in the case of a strong polar adsorption complex with a bonding distance of 1.7 nm–1.9 nm to the silica surface.
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spelling pubmed-100980982023-04-14 Characterization of polar surface groups on siliceous materials by inverse gas chromatography and the enthalpy–entropy compensation effect Meyer, Ralf Mueller, Kai Naumov, Sergej Bauer, Frank Enke, Dirk Front Chem Chemistry Surface-modified porous silica is a well-established composite material. To improve its embedding and application behavior, adsorption studies of various probe molecules have been performed using the technique of inverse gas chromatography (IGC). For this purpose, IGC experiments were carried out in the infinite dilution mode on macro-porous micro glass spheres before and after surface modification with (3-mercaptopropyl)trimethoxysilane. To provide information about the polar interactions between probe molecules and the silica surface, in particular, eleven polar molecules have been injected. In summary, the free surface energy for pristine silica ( [Formula: see text] = 229 mJ/m(2)) and for (3-mercaptopropyl)trimethoxysilane-modified silica ( [Formula: see text] = 135 mJ/m(2)) indicates a reduced wettability after surface modification. This is due to the reduction of the polar component of the free surface energy ( [Formula: see text] ) from 191 mJ/m(2) to 105 mJ/m(2). Simultaneously, with the reduction of surface silanol groups caused by surface modification of silica and, therefore, the decrease in polar interactions, a substantial loss of Lewis acidity was observed by various IGC approaches. Experiments with all silica materials have been conducted at temperatures in the range from 90°C to 120°C to determine the thermodynamic parameters, such as adsorption enthalpy ( [Formula: see text] ) and adsorption entropy ( [Formula: see text] ), using the Arrhenius regression procedure evaluating the IGC data. With the help of the enthalpy–entropy compensation, two types of adsorption complexes are assumed between polar probe molecules and the silica surface because of different isokinetic temperatures. Identical adsorption complexes with an isokinetic temperature of 370°C have been assigned to alkanes and weakly interacting polar probes such as benzene, toluene, dichloromethane, and chloroform. Polar probe molecules with typical functional groups such as OH, CO, and CN, having the ability to form hydrogen bonds to the silica surface, exhibit a lower isokinetic temperature of 60°C. Quantum chemical calculations of the probe molecules on a non-hydroxylated and hydroxylated silica cluster supported the formation of hydrogen bonds in the case of a strong polar adsorption complex with a bonding distance of 1.7 nm–1.9 nm to the silica surface. Frontiers Media S.A. 2023-03-30 /pmc/articles/PMC10098098/ /pubmed/37065825 http://dx.doi.org/10.3389/fchem.2023.1084046 Text en Copyright © 2023 Meyer, Mueller, Naumov, Bauer and Enke. https://creativecommons.org/licenses/by/4.0/This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
spellingShingle Chemistry
Meyer, Ralf
Mueller, Kai
Naumov, Sergej
Bauer, Frank
Enke, Dirk
Characterization of polar surface groups on siliceous materials by inverse gas chromatography and the enthalpy–entropy compensation effect
title Characterization of polar surface groups on siliceous materials by inverse gas chromatography and the enthalpy–entropy compensation effect
title_full Characterization of polar surface groups on siliceous materials by inverse gas chromatography and the enthalpy–entropy compensation effect
title_fullStr Characterization of polar surface groups on siliceous materials by inverse gas chromatography and the enthalpy–entropy compensation effect
title_full_unstemmed Characterization of polar surface groups on siliceous materials by inverse gas chromatography and the enthalpy–entropy compensation effect
title_short Characterization of polar surface groups on siliceous materials by inverse gas chromatography and the enthalpy–entropy compensation effect
title_sort characterization of polar surface groups on siliceous materials by inverse gas chromatography and the enthalpy–entropy compensation effect
topic Chemistry
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10098098/
https://www.ncbi.nlm.nih.gov/pubmed/37065825
http://dx.doi.org/10.3389/fchem.2023.1084046
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