Invited reviewSynthetic organo- and polymer–clays: preparation, characterization, and materials applications
Section snippets
Background
The most common question asked in regards to this work is “Why bother to make organo-clays synthetically when natural clays are so abundant and so easily modified with organics?” One aim of this review is to address this question, whose answer lies mainly in designed materials applications. Variables such as purity, composition, reproducibility, and specifically designed features can be often controlled better this way than by using natural clay specimens, which, among other certain drawbacks,
General synthetic details
Precursor clay gels are of the composition:to correlate with the ideal hectorite composition (Grim, 1968):where R=monovalent organic salt and Ex=exchangeable cation (Ex=Li,R from this gel). Syntheses were not successful when the cited amount of R=LiF=0.66 mol was used (Barrer and Dicks, 1967). A typical (scaled-down) reaction begins by dissolving 0.72 mmol of organic (monovalent) in water and adding 4.8 mmol LiF with stirring.
Materials applications
At least two quite different applications arise depending upon the fate of the template in the synthetic organo-clay. First, if the organic molecule or polymer is used with the intention of acting as templates of pore structure, then the organic template is removed after the modified clay has been crystallized. Upon template removal, the now porous materials are examined for their use as potential catalysts and catalyst supports. If, on the other hand, the templates are allowed to remain as a
Summary
Let us once again address the question posed at the very beginning of this article: Why bother to create synthetic polymer–clay materials? In addition to the variables already discussed (purity, compositional variety, reproducibility) are those of tunability and other designer properties, such as pore size, aspect ratio, and layer charge. The tunability of the MSCs with respect to pore size, for example, has an advantage over the similar M41S class of materials in that the synthetic procedure
Acknowledgements
Several collaborators have contributed greatly to the progress of this overall project, including Langqiu Xu, P. Thiyagarajan, Christopher L. Marshall, Kang Song, James R. Brenner, Di Wei, Delwin L. Elder, Gerry W. Zajac (BP-Amoco), Randall E. Winans, Sönke Seifert, Roseanne Csencsits, David Gregory, and Robert E. Botto (all of ANL unless otherwise stated). The helpful comments of R. Vaia regarding the manuscript are appreciated. This work was performed under the auspices of the U.S. Department
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