Selective modification of inner surface of halloysite nanotubes: a review

In this paper, we review the chemical strategies used for the modification of the inner surface of halloysite nanotubes (HNTs). The HNTs are nanotubular materials formed by rolling up the 1:1 aluminosilicate clays, where the composition is similar with kaolin. Owing to many virtues, including the high ratio of length to diameter, large cavity volume, desirable biocompatibility, and low cost, the HNTs have been applied to numerous promising domains. The modification of the outer surface is usually intended to decrease the HNT dispersal in aqueous media. Considering that the selective modification for the inner surface gives excellent prospects for hybrid HNT-based materials, herein, we explore the advances in the selective modification of the inner surface that expanded the applications of the HNTs.