Organic/inorganic nanohybrids by surface functionalization of inorganic nanostructures are attracting a great deal of research interest. Halloysite is a naturally occurring aluminosilicate clay mineral with a hollow nanotube structure. It has a 1:1 Al:Si ratio and a stoichiometry of Al2Si2O5(OH)4.nH2O, with siloxane groups at the outside and aluminol groups in the inside of the tube. In this study, the authors propose several novel techniques for surface modification of halloysite nanotubes and apply to the (organic materials/halloysite) nanohybrid. The selective hydrophobization of the inner surface of tubular halloysite was developed. Aqueous phosphonic acid was found to bind on aluminol sites at the tube lumen and did not bind the tube’s outer siloxane surface. NMR and FTIR spectroscopy of selectively modified tubes proved binding of octadecyl phosphonic acid within halloysite lumen through bidentate and tridentate P-O-Al linkage. Selective modification of the halloysite clay lumen creates inorganic micelle-like architecture with hydrophobic aliphatic chain core and hydrophilic silicate shell. An enhanced adsorption capacity of the modified halloysite toward hydrophobic derivatives of ferrocene and flame retardant was shown. This demonstrates that different inner and outer surface chemistry of clay nanotubes can be used for selective modification, enabling different applications, from water purification to drug immobilization and controlled release. We also demonstrate the use of a catecholic anchor (DOPA) for selective modification of inner surface of halloysite nanotube. Aqueous DOPA can bind to the aluminol groups at the tube lumen while does not bind the siloxane external surface under the same condition. Surface-initiated atom transfer radical polymerization (SI-ATRP) was performed through selectively adsorbed DOPA to graft a layer of polymer brush into the nanotube lumen. Furthermore, by using halloysite nanotube, we prepared fluorine-free liquid marbles. Halloysite was modified with octadecyltrimethoxysilane. The surface-modified halloysite formed pincushion agglomerates on the surface of the liquid droplets, which create superhydrophobic surface similar to that of the plant gall surface prepared by aphids. As a result, the liquid marbles showed high mechanical strength upon impact without the use of low surface energy fluoroalkyl or fluorine-modified materials.

Design and characterization of (organic material/halloysite nanotube) hybrids

251st National Meeting (2016)

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