Clay Minerals as Natural Nanosheets

Particles with nanometer dimensions (nanoparticles) are all around us. The finest particles of sand are blown by the wind over thousands of kilometers. The finest particles of soils are either eroded by the wind in extremely dry conditions or by water under wet conditions and deposited hundreds of kilometers or more from the origin. The air contains nanoparticles of carbon, ice, and oxides and is often contaminated with organic and inorganic compounds. As natural layered silicates, clay minerals, are available everywhere and cheap, they have been mixed with organic polymers as bulking fillers in the industry. On the other hand, intercalated compounds of layered clay mineral, such as smectite, with organic molecules have been studied in the academia. The intercalated compounds are expecting to have hybridized characters and properties, which are something alike to those of the parent compounds; clay minerals and guest organic molecules, but something different from those of them. Among these nanoparticles in nature, clay minerals take a unique position, not only because of their nanometer size but also because of their shape (clay minerals are layered materials or two-dimensional (2D) materials), ion exchange, and adsorption properties. These properties are the basis for intense research in the transformation of clay minerals into nanomaterials for a variety of technological application and in the incorporation of clay minerals in nanodevices. As clay minerals are natural materials that can be mined, they are cheap. But this comes at a