Large-scale synthesis of multi-walled carbon nanotubes by microwave CVD

Carbon nanotubes (CNTs) are an interesting class of nanostructures which can be thought of as arising from the folding of a layer of graphite (a graphene sheet) to form a hollow cylinder composed of carbon hexagons. However, practical applications are still limited by the intricate process of synthesis and the inability of present day methods to provide large-scale production of CNTs. Moreover, high-quality nanotubes with functionalization capability with polymers are desired for polymer microelectromechanical systems (MEMS), nanodvices and BioMEMS. In this paper, an innovative CVD approach using microwave energy was developed for the large-scale production of multi-wall carbon nanotubes (MWNTs). Straight and helical CNTs were obtained when acetylene created by a microwave field was decomposed over the cobalt catalyst at 700 °C. Scanning electron microscopy of microwave-driven MWNTs revealed their homogenous nature. High-resolution electron microscopy showed that typically the MWNT has 26 layers. The average diameter of the tubes observed was 20-30 nm. Electron microscope observations showed a higher yield of nanotubes obtained from microwave CVD than the thermal filament CVD method.