Preparation of multi-walled carbon nanotubes/SiO2 core-shell nanocomposites by a two-step Stober process

The surface modification and functionalisation of multi-walled carbon nanotubes (MWNTs) could provide enhanced properties to MWNTs for highly specific applications which often require solubilisation and dispersion, promotion of functionality, biocompatibility or lower toxicity of MWNTs. Herein, a novel nanocomposite consisting of MWNTs as a core and amorphous silica (SiO2) as a shell is developed. First, the functionalisation of MWNTs with carboxylic functional group (MWNTs-COOH) was obtained via oxidation using the concentrated sulphuric acid/nitric acid mixture (3:1 v/v) treatment. Second, a silica uniform layer was grown on MWNTs-COOH by a two-step Stober process. The core-shell nanostructure is characterised by Fourier-transform infrared spectroscopy, X-ray powder diffraction, transmission electron microscopy, and energy dispersive spectrometer. Experimental results show that a SiO2 shell was uniformly coated on the surface of MWNTs with a thickness of 5-10 nm. The results can have important implications for the preparation of carbon nanotube core-shell nanocomposites in general.