Iron oxide nanoparticle impregnated mesoporous silicas as platforms for the growth of carbon nanotubes

Iron oxide nanoparticles have been deposited on the exterior of and inside the pores of hexagonal mesoporous silica by a direct synthesis technique with iron phthalocyanine as precursor. Iron loadings were between 0.4 wt.% – 3.2 wt.%. XPS and Mössbauer spectroscopic studies showed that the initial form of the iron oxide nanoparticles was [Fe2O3]. Samples of these iron-loaded materials were stirred in nitric acid to remove the iron oxide existing on the exterior surface of the silica. No significant loss in mesophase ordering was seen in the TEM, PXRD or nitrogen physisorption analysis of the acid washed samples. Both as-prepared and acid-washed silicas were used to grow multi-walled carbon nanotubes (MWCNTs) from acetylene feedstock in a catalytic chemical vapour deposition reactor at 800 °C. In both systems the density of the carbon nanotubes (CNTs) was found to increase with increasing metal loadings. Whereas the as-prepared samples produced CNTs with a range of diameters from 10 nm to 90 nm, the acid treated samples showed CNTs with much more uniform diameters between 5 nm – 15 nm. Raman spectroscopy of the products showed that the carbon nanotubes were highly graphitised and of good quality.