Silica coating of vapor grown carbon fibers

Silica coatings have been applied to vapor grown carbon fibers (VGCFs) by a liquid phase deposition process. Unlike the coating of single walled carbon nanotubes, the addition of a surfactant to “solubilize” the VGCFs results in an extremely non-uniform coating consisting of spherical silica aggregated around the tubes. As was observed for fullerenes, hydroxylation of the surface of the VGCF appears to be key to the formation of a uniform silica coating. Irrespective of the type of VGCF, heating a suspension of VGCFs in nitric acid to dryness (Type II) gave us the best results in terms of silica growth around the VGCF and there is a correlation between the percent of hydroxyls present on the VGCF surface and on the type of growth that occurs on the VGCF. Nitric acid treatment of VGCFs for 1 day in solution were precipitated with acetone (Type III treatment), and then coated with silica. This acid treatment made the coated fibers highly soluble in EtOH.