Halloysite nanotubes modified by chitosan as an efficient and eco-friendly heterogeneous nanocatalyst for the synthesis of heterocyclic compounds

Halloysite nanotubes (HNTs) are the subset of clay minerals with the same ratio of tetrahedral silicon and octahedral aluminum sheets. The special features of HNTs like tubular morphology, biocompatible, availability and porosity lead to use it in the various application such as drug delivery, catalyst, self-lubrication, and wastewater treatment. Also, HNTs could be modified with different polycation and polyanion due to the different charge of the outer and inner surface of nanotubes. Chitosan as a polycation which obtained by alkaline N-deacetylation of chitin. In recent years, much attention has been paid to this compound due to its unique features such as non-toxic, hydrophilic, biocompatible, biodegradable and antibacterial activity. Because of the biomedical activity of chitosan, it can be used for drug delivery systems, wound healing and tissue engineering. In the structure of chitosan, there are a large number of amine and hydroxyl groups. Therefore, it can be modified by fictionalization with organic and inorganic material. In this study, HNTs modified by chitosan and its catalyst activity was investigated in the synthesis of pyranopyrazole derivatives. The use of efficient, green and reusable nanocatalyst are some advantages of the present work.