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Acid Hydrolysis of Octahedral Mg2+ Sites in 2:1 Layered Silicates: An Assessment of Edge Attack and Gallery Access Mechanisms

Published online by Cambridge University Press:  28 February 2024

Hemamali Kaviratna  and
Thomas J. Pinnavaia
Hemamali Kaviratna
Affiliation:
Department of Chemistry and Center for Fundamental Materials Research, Michigan State University, East Lansing, Michigan 48824
Thomas J. Pinnavaia
Affiliation:
Department of Chemistry and Center for Fundamental Materials Research, Michigan State University, East Lansing, Michigan 48824
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Abstract

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The acid hydrolysis products of trioctahedral fluorohectorite and phlogopite have been investigated by XRD, MAS NMR spectroscopy and nitrogen BET surface area analysis in an effort to assess the relative importance of edge attack and gallery access mechanisms. A dramatic loss of X-ray crystallinity and the formation of Q3 and Q4 SiO4 sites accompanied the depletion of Mg2+ from the octahedral sheet of both 2:1 layered structures. Depending on the extent of hydrolysis, the products derived from fluorohectorite exhibited surface areas up to 208 m2/g, whereas phlogopite hydrolysis products gave values <20 m2/g. The dramatic differences in surface areas were not related to differences in hydrolysis mechanisms. 19F MAS NMR studies indicated that the hydrolysis of fluorohectorite occurred primarily by an edge attack mechanism equivalent to the hydrolysis pathway for phlogopite. A gallery access mechanism contributed to the hydrolysis of fluorohectorite only at the later stages of octahedral Mg2+ depletion. Solvation effects appeared to be important in determining the surface areas of the reaction products derived from the swelling (fluorohectorite) and non-swelling (phlogopite) precursors.

Keywords

Acid hydrolysisFluorohectoriteMechanismPhlogopite
Type
Research Article
Information
Clays and Clay Minerals , Volume 42 , Issue 6 , December 1994 , pp. 717 - 723
Copyright
Copyright © 1994, Clay Minerals Society

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