Document Type
Article
Original Publication Date
2017
Journal/Book/Conference Title
MICROPOROUS AND MESOPOROUS MATERIALS
Volume
243
First Page
247
Last Page
253
DOI of Original Publication
10.1016/j.micromeso.2017.02.036
Date of Submission
June 2017
Abstract
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.
Rights
(C) 2017 Elsevier Inc. All rights reserved.
Is Part Of
VCU Chemistry Publications
Mesopore etching under supercritical conditions ‒ a shortcut to hierarchically porous silica monoliths
Comments
Originally published at http://doi.org/10.1016/j.micromeso.2017.02.036