Surfactant functionalization of carbon nanotubes (CNTs) for layer-by-layer assembling of CNT multi-layer films and fabrication of gold nanoparticle/CNT nanohybrid

This paper describes a new strategy through noncovalent functionalization of multi-walled carbon nanotube (MWNTs) with supramolecular surfactant for layer-by-layer (LbL) assembling MWNT multi-layer film onto indium tin oxide (ITO)-coated glass plate and for attaching gold nanoparticles (GNPs) onto the MWNTs to fabricate GNP/MWNT nanohybrid. Surfactant (i.e., sodium dodecyl sulfate, SDS) can interact with the MWNTs through hydrophobic interaction between the hydrophobic chain of SDS and the sidewall of the MWNTs. Such an interaction essentially leads to noncovalent adsorption of SDS onto the MWNTs, resulting in an enhanced solubilization of the MWNTs in distilled water and providing some negative charges on the tube surface. Both properties make it possible to assemble MWNT multi-layer films onto the ITO plate through an alternative adsorption of oppositely charged SDS-functionalized MWNTs and polyelectrolyte [i.e., poly(diallyldimethylammonium chloride), PDDA] as revealed by scanning electron microscopy (SEM), ultraviolet–visible–near-infrared spectroscopy (UV–vis–NIR), quartz crystal microbalance (QCM), and cyclic voltammetry (CV). The same properties of the SDS-functionalized MWNTs are demonstrated to be useful for mediating the attachment of GNPs onto the tube surfaces to form GNP/MWNT nanohybrid as verified with transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemistry.