Halloysite nanotubes based heterogeneous solid acid catalysts
There is increasing interest in clay minerals such as halloysite nanotubes (HNTs) due to their biocompatibility, availability and potential applications in the field of catalysis. Halloysite nanotubes can be modified on both the surfaces to tune its properties, explicitly its innumerable applicability in the field of catalysis. The outer surface of halloysite nanotubes is fit for functionalization to develop halloysite catalysts which creates a valuable provision for endorsing catalytic applications with tunable properties. Furthermore, the occurrence of an empty lumen unlocks new perspectives for the creation of nanostructures with synergistic catalytic effects. This class of compounds displayed promising catalytic performances and up to now, halloysite based catalysts have been useful for promoting several chemical transformations. Keeping in view, the excellent catalytic performance of these nanotubes as catalysts or catalyst supports, the main focus of this review article is to unveil the research on halloysite nanotubes for the preparation of solid acids and their applications in acid catalytic processes.