In situ synthesis and characterization of sulfonic acid functionalized hierarchical silica monoliths
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ORIGINAL PAPER: FUNDAMENTALS OF SOL–GEL AND HYBRID MATERIALS P R O CE S S I N G
In situ synthesis and characterization of sulfonic acid functionalized hierarchical silica monoliths Richard Kohns1,2 Ralf Meyer2 Marianne Wenzel3 Jörg Matysik3 Dirk Enke2 Ulrich Tallarek ●
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Abstract Surface functionalization of porous materials with sulfonic acid (SO3H) groups is of particular interest in applications involving ion exchange, acidic catalysis and proton conduction. Macro-mesoporous silica monoliths are ideal support structures for these applications, as they combine advection-dominated mass transport in the macropores with short diffusion lengths and a large surface area (available for functionalization) in their mesoporous skeleton. Here, we report on SO3H functionalized sol–gel silica monoliths with bimodal pore systems exhibiting macro- and mesoporosity, prepared according to a simple, efficient in situ synthesis protocol. Based on the co-condensation approach, thiol groups were introduced homogeneously into the pore structure, followed by their oxidation to SO3H groups and the simultaneous removal of the template. The macropore size, specific surface area, and coverage with SO3H groups are easily adjusted in this synthesis route. Importantly, the hybrid monoliths have a substantially narrower mesopore size distribution (relative standard deviation ~25%) than conventional sol–gel materials (>40%) and can be engineered crack-free in a robust column design (suitable for high-pressure flow-through operation) with mean mesopore size down to ~7 nm. They are characterized by IR spectroscopy, thermogravimetry, and elemental analysis as well as 13C and 29Si solid state NMR to corroborate the simple, efficient combination of sol–gel-based material synthesis, surface functionalization, and template removal (i.e., polymer extraction). Complementary, inverse gas chromatography is presented as a new approach to characterize the incorporated SO3H groups via surface energy analysis and particularly resolve changes in the Lewis acid–base characteristics engendered by that functionalization. Graphical Abstract Combined oxidaon & extracon step
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Received: 16 April 2020 / Accepted: 30 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
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Supplementary information The online version of this article (https:// doi.org/10.1007/s10971-020-05383-z) contains supplementary material, which is available to authorized users. * Ulrich Tallarek [email protected] 1
Department of Chemistry, Philipps-Universität Marburg, HansMeerwein-Strasse 4, 35032 Marburg, Germany
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Institute of Chemical Technology, Universität Leipzig, Linnéstrasse 3, 04103 Leipzig, Germany
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Institute of Analytical Chemistry, Universität Leipzig, Linnéstrasse 3, 04103 Leipzig, Germany
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