Past, Present and Future Perspectives on Halloysite Clay Minerals

Abstract

Halloysite nanotubes (HNTs), clay minerals belonging to the kaolin groups, are emerging nanomaterials which have attracted the attention of the scientific community due to their interesting features, such as low-cost, availability and biocompatibility. In addition, their large surface area and tubular structure have led to HNTs’ application in different industrial purposes. This review reports a comprehensive overview of the historical background of HNT utilization in the last 20 years. In particular it will focus on the functionalization of the surfaces, both supramolecular and covalent, following applications in several fields, including biomedicine, environmental science and catalysis.

Synthesis and Characterization of Nanomaterial Based on Halloysite and Hectorite Clay Minerals Covalently Bridged

“…100 nm and a Ht one of ca. 25 nm [ 6 ], the result is coherent with the two clays bonded. Close observations revealed the presence of halloysite nanotubes covered by hectorite clay (black arrow in the figure).…”

“…Halloysite possesses different charged surfaces: positive in the inner lumen, where mostly of aluminum hydroxide groups are present; negative on the external surface, which consists in silicon dioxide. HNTs can be selectively functionalized at the inner and/or outer surfaces leading to the synthesis of several interesting nanomaterials [ 2 , 3 , 4 , 5 , 6 ]. The most important feature of HNTs is their empty lumen which acts as a nanocontainer for the encapsulation of several biologically active species [ 4 , 7 , 8 ].…”

Application of Halloysite Nanotubes in Cancer Therapy—A Review

“…Among the nanoclays, halloysite is proposed most often in the anticancer applications, mainly due to its unique structure, ability to load drugs via either adsorption [ 25 ] or intercalation [ 26 ], as well as because of its ability to provide the tunable release [ 27 ] and the rare possibility to accommodate simultaneously two different drugs with dissimilar physicochemical properties [ 28 ]. The nanotubular structure of halloysite allows the encapsulation of a vast variety of drugs [ 29 , 30 , 31 ]. The outer surface of halloysite nanotubes (HNTs) may be easily modified in order to adjust the properties crucial for a carrier (charge, polarity) [ 32 ] to introduce biologically relevant molecules (ligands, antibodies) [ 33 , 34 ] or to attach larger molecules/nanoparticles (e.g., magnetic particles, quantum dots) [ 35 , 36 ].…”

Study of Uptake Mechanisms of Halloysite Nanotubes in Different Cell Lines

“…They have been reported to have a good biocompatibility and safety profile following the cellular internalization. [8][9][10][11][12] Due to their properties, HNTs could be used for the encapsulation of drugs, biologically active molecules 3,[13][14][15][16][17][18][19] and as potential non-viral vector for oral gene therapy. 12,20 Moreover, thanks to their large specific surface area, high biocompatibility and nanotubular structure, HNTs are used as support materials and for the loading and controlled release study of various substances.…”