Mesopore etching under supercritical conditions – A shortcut to hierarchically porous silica monoliths
| Autor: | Martin von der Lehr, Massimo F. Bertino, Ulrich Tallarek, Kristof Hormann, Arved E. Reising, Bernd M. Smarsly, Lauren S. White, Alexandra Höltzel |
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| Rok vydání: | 2017 |
| Předmět: |
Materials science
Nanotechnology 02 engineering and technology 010402 general chemistry 01 natural sciences law.invention chemistry.chemical_compound Adsorption law General Materials Science Calcination Monolith Porosity geography geography.geographical_feature_category Silica gel Supercritical drying General Chemistry 021001 nanoscience & nanotechnology Condensed Matter Physics Supercritical fluid 0104 chemical sciences Chemical engineering chemistry Mechanics of Materials 0210 nano-technology Mesoporous material |
| Zdroj: | Microporous and Mesoporous Materials. 243:247-253 |
| ISSN: | 1387-1811 |
| DOI: | 10.1016/j.micromeso.2017.02.036 |
| Popis: | Hierarchically porous silica monoliths are obtained in the two-step Nakanishi process, where formation of a macro–microporous silica gel is followed by widening micropores to mesopores through surface etching. The latter step is carried out through hydrothermal treatment of the gel in alkaline solution and necessitates a lengthy solvent exchange of the aqueous pore fluid before the ripened gel can be dried and calcined into a mechanically stable macro–mesoporous monolith. We show that using an ethanol–water (95.6/4.4, v/v) azeotrope as supercritical fluid for mesopore etching eliminates the solvent exchange, ripening, and drying steps of the classic route and delivers silica monoliths that can withstand fast heating rates for calcination. The proposed shortcut decreases the overall preparation time from ca. one week to ca. one day. Porosity data show that the alkaline conditions for mesopore etching are crucial to obtain crack-free samples with a narrow mesopore size distribution. Physical reconstruction of selected samples by confocal laser scanning microscopy and subsequent morphological analysis confirms that monoliths prepared via the proposed shortcut possess the high homogeneity of silica skeleton and macropore space that is desirable in adsorbents for flow-through applications. |
| Databáze: | OpenAIRE |
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