Surface Modification and Functionalization of Halloysite Nanotubes Using Self-Assembly Methods

Abstract

Halloysite nanotubes (HNTs) are a type of natural occurring clay materials with nanotubular structure and having large outer diameter. The structure of HNTs demonstrated that Si-O groups are exposed on the outer surface and theirs surface charge show negative under neutral condition. HNTs have multi-walled nanotubes with an interlayer spacing of 10 Å that can be used for various applications, such as, additives in polymers and plastic, electronic components, drug delivery vehicles, adsorption of toxic compounds in water, and cosmetics. In this study, to enhance the adsorption ability of HNTs, we try to widen the interlayer spacing of HNTs by the insertion of a guest species in the interlayer region of HNTs with preservation of the layered structure, which is called intercalation. HNTs were intercalated by sodium acetate (SA_HNTs) and dimethyl sulfoxide (DMSO_HNTs). SA_HNTs were intercalated resulting from electrostatic repulsion in interlayers and DMSO_HNTs were intercalated by new hydrogen bonding with S=O groups and hydroxyl group of interlayers. It is expected that the intercalated HNTs significantly affect the adsorption of dye molecules because the spacing of interlayers was widened. Intercalation and adsorption ability of HNTS for dye molecules were characterized by Fourier transformed infrared spectroscopy (FT-IR), Ultraviolet-visible spectroscopy (UV), X-ray diffraction (XRD). FT-IR measurements demonstrated that the intercalation of HNTs was confirmed by the presence of C=O vibration peak at 1420 cm-1 and S=O vibration peak at 1043 cm−1. From UV measurements, Raw_HNTs, SA_HNTs and DMSO_HNTs show significant difference in adsorption of dye molecules. We found that the intercalated HNTs for adsorption of dye molecules are more effective than Raw_HNTs. We also synthesized dispersed palladium nanoparticles (PdNP) on magnetic HNTs (Pd-MHNTs). In this study, we synthesized the magnetic HNTs (MHNTs) that supported PdNP through strong electrostatic attraction after outer surface modification with 3-aminopropyl triethoxysilance (APTES). The fabrication of well dispersed palladium nanoparticles ranging in diameter 2~3 nm on MHNTs (Pd-MHNTs) involved attachment of Iron oxide (Fe3O4) nanoparticles on HNTs via a one-step co-precipitation method and modified the outer surface concentration by APTES amino groups and subsequent in situ reduction of Pd. All the processes are simple and eco-friendly without use of additional toxic reagents and complicated treatment. Pd-MHNTs exhibited excellent catalytic ability toward the reduction of 4-nitrophenol more than Pd-HNTs. Because of the iron oxide nanoparticles, Pd-MHNTs were possible to have lager surface area to synthesize PdNP on outer surface. In addition, the catalytic system can be easily recycled for several cycles based on its nice magnetic properties.