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

Comments

Originally published at http://doi.org/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.

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VCU Chemistry Publications

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Mesopore etching under supercritical conditions ‒ a shortcut to hierarchically porous silica monoliths

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