Delivered by Publishing Technology to: University of Waterloo IP: 129.97.58.73 On: Mon, 24 Mar 2014 04:39:53 Copyright: American Scientific Publishers Copyright © 2014 American Scientific Publishers All rights reserved Printed in the United States of America Review Journal of Nanoscience and Nanotechnology Vol. 14, 2121–2134, 2014 www.aspbs.com/jnn Designed Nanostructures of Clay for Controlled Adsorption of Organic Compounds Tomohiko Okada 1 , Yoko Seki 2 , and Makoto Ogawa 2 3 * 1 Department of Chemistry and Material Engineering, Shinshu Univeristy Wakasato 4-17-1, Nagano City, Nagano 380-8553, Japan 2 Graduate School of Science and Engineering, Waseda University Nishiwaseda 1-6-1, Shinjuku-ku, Tokyo 169-8050, Japan 3 Department of Earth Sciences, Waseda University Nishiwaseda 1-6-1, Shinjuku-ku, Tokyo 169-8050, Japan The utilization of smectite clay, swelling layered silicate, as scaffolds for designing functional nano- structures was overviewed. Surface modification of smectites with organoammonium ions has given hydrophobic and microporous nature to uptake nonionic organic contaminants from environments. The states of the adsorbed nonionic organic compounds have been altered and varied by the mod- ification of smectites as shown by the controlled release and specific catalytic reactions. Cationic species have been easily concentrated on smectites from aqueous phase and the states (orientation and distribution) have been controlled by the co-adsorption of both cationic and nonionic species. The functions of smectite-organic intercalation compounds derived from the precisely controlled nanostructures were introduced in this review. Keywords: Smectite, Surface Modification, Organoclay, Nanostructural Design, Adsorption. CONTENTS 1. Introduction ........................................ 2121 2. Surface Modification to Accommodate Nonionic Organic Compounds .......................... 2123 2.1. Organophilic Clays .............................. 2123 2.2. Microporous Organically Pillared Clays ............... 2128 3. Controlled Spatial Distribution of Organic Cations on Smectites by the Co-Adsorption ............... 2131 4. Summary and Future Perspectives ....................... 2132 Acknowledgments ................................... 2132 References and Notes ................................ 2133 1. INTRODUCTION Designed nanostructures on solid surfaces play an impor- tant role in developing materials/functions as adsor- bent/separation, sensor/detection, catalyst/reaction, which are relevant to the environmental purification and moni- toring and medical sciences (bioassay, imaging, and drug delivery). Microporous and mesoporous solids have been investigated as adsorbents and catalysts with molecular selectivity. In order to achieve precise molecular selec- tivity in adsorption/separation and catalysts, efforts have * Author to whom correspondence should be addressed. been made to design the pore shape and size precisely. The preparation of nanoporous inorganic–organic hybrid materials, such as organic moieties attached zeolites 1 and mesoporous silicas, 2–4 and porous coordination com- pounds (designated as porous coordination polymers (PCP) or metal organic frameworks (MOF) 5–8 ) have been reported and the application of these materials in adsorp- tion/separation and gas storage has been actively been investigated. The interlayer space of layered solids is often expand- able (or in some case swellable) to accommodate guest species and the surface properties (interlayer nano- structure) are possible to be modified by the intercala- tion reactions (Fig. 1). 9 10 The “expandable 2-dimensional nanospace” is regarded as a nano-vessel or nano-reaction environment for accommodating various kinds of guest species and their reactions. The confinement of molecules in nanospace brings peculiar phenomena, for example, a natural dye in the interlayer space is stabilized upon degradation. 11 Modification of layered solids has been con- ducted for the uptake of a specific molecule, catalysis with selectivity, efficient photo-induced process, and so on. 12 The spatial distribution of organic species in the interlayer spaces is an important parameter as seen by the efficient J. Nanosci. Nanotechnol. 2014, Vol. 14, No. 3 1533-4880/2014/14/2121/014 doi:10.1166/jnn.2014.8597 2121