MICROWAVE-ASSISTED FUNCTIONALIZATION OF HALLOYSITE NANOTUBE SURFACE

Abstract

Halloysite, Al2Si2O5·2H2O, is a naturally occurring two-layered alluminosilicate, chemically similar to kaolin, which has a predominantly high-aspect-ratio hollow tubular structure in the submicrometer range and an internal diameter in the nanometer range. The size of halloysite nanotubes (HNTs), generally varies from 50 to 70 nm in external diameter, ca. 15 nm diameter lumen, and 0.5 to 1 μm in length. Halloysite tubes have aluminol (Al-OH) groups on the internal surface and siloxan groups (Si-O-Si) on the external surface. The very large diameter of the halloysite lumen makes it potentially suitable for the accommodation of a range of guests. In recent reports, for example, the mesoporous lumen of HNTs was used as a nanoreactor to host reactants for nanosynthesis and biomimetic synthesis. Application of halloysite is severely limited by its hydrophilic internal and external surfaces. In order to improve the dispersion of HNTs in polymer matrix and synthesize great promise organic composites, a surface modification of halloysite is required. In this work we have developed a new synthetic method, that consists in the grafting of organosilanes on the external surface by microwave irradiation. The f-HNTs can be employed as polymer filler and they can be subjected to further chemical modification by organic molecules such as ionic liquids.