Halloysite Based Core-Shell Nanosystems: Synthesis and Application

Halloysite aluminosilicate nanotubes are natural clay systems with unique scrolled structure. It is a tubular form of kaolinite with a length of 0.4–1.5 μm, outer diameter of 50–90 nm, and inner lumen of 10–30 nm. Halloysite was found to be a good carrier for chemical inhibitors, drugs and metal clusters templated on the nanotubes for catalyst preparation. Nanoparticles or nanorods of Au, Ag, Pt, Co, Ni, Cu, Ru, or their oxides as well as CdS and CdSe were selectively synthesized on the surface or in the inner lumens of these clay nanotubes. Such nanostructured core-shell mesocatalysts showed enhanced chemical activity in many chemical reactions (i.e., oxidation, reduction, hydrogenation, cross-coupling, and oil-refining processes). Good dispersibility of functionalized halloysite makes it an efficient surface active catalyst in biphase reactions. In polymeric composites, it has been used as a container for active chemicals providing self-healing and anticorrosion protection and also drug delivery for long-lasting sustainable release. Low toxicity of this tubular clay makes it a perfect nanocarrier for medical and biological applications. Halloysite is a cheap abundantly available nanomaterial; it is not limited to laboratory experimentations but could be scaled up for industrial applications.