Effect of tungsten on the purification of few-walled carbon nanotubes synthesized by thermal chemical vapor deposition methods

Few-walled carbon nanotubes (FWNTs) were synthesized by the methane chemical vapor deposition (CVD) method using binary catalysts Co/Mo and Co/W supported on MgO. It was found that Mo was not only a promoter for FWNT growth but also active in the formation of multiwalled carbon nanotubes (MWNTs) in our CVD process. W was found to be a better promoter since it was much less active in producing MWNT impurities. As a result, the raw FWNT materials prepared from W-containing catalysts were much more easily purified than those from Mo-containing catalysts. Scanning electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, and transmission electron microscopy were used to characterize both raw materials and purified samples.