Halloysite as support matrices: a review

Abstract

Developing new applications of natural resources is an interesting area of science. Clay minerals are very versatile materials and have attracted more attention due to their wide applications in various fields for more than a decade. Naturally occurring clay minerals offer a great potential, due to their specific structure (layered and three-dimensional), in several technological applications based on the adsorptive and ionic exchange properties. Halloysite nanotubes (HNTs) are naturally occurring clays with nanotubular structures. Various features such as nanoscale lumens, high length-to-diameter ratio, and low-hydroxyl-group density on the surface of halloysite make them an attractive alternative to other materials; simultaneously, their abundance and cheap cost enhance their utility. Applications of halloysite include various fields such as controlled drug release, nanotemplating, sorption, and fabrication of polymer nanocomposites. Recently, because of features like higher reactivity, higher cationic exchange, and tubular geometry, halloysite has been recognized as an attractive candidate to perform as a catalytic support for polymerization as well as immobilization reactions. The unique structure of HNT provides not only support to catalyst but it also enhances the performance of HNT-supported catalyst for various applications. Numerous studies suggest that halloysite and catalyst complex exhibit tremendous performance for the recovery of catalyst complex as well as for easy and safe administration of catalyst. In continuum, HNTs should be material of interest as a support for various structural and functional applications.