Morphology of carbon nanoclusters prepared by catalytic disproportionation of carbon monoxide

Catalytic disproportionation of carbon monoxide has long been established as a method for producing graphitic deposits. Using this method, a set of samples was prepared under a variety of the process parameters: temperature, CO/CO{sub 2} ratio, hydrogen partial pressure, and duration of reaction. The morphology of the product has been characterized using both scanning electron microscopy and transmission electron microscopy, with similarities found between the CO disproportionation deposits, and the nanoclusters produced by arc discharge. In particular, the analysis revealed multiwalled, concentric hollow core nanotubes in which the layers are separated by 0.34 nm, the distance associated with separation between graphitic basal planes.The catalytically produced nanotubes are in general much longer than those typically produced in an arc discharge while other properties are almost identical. Their morphology depends on the choice of the process parameters, particularly the partial pressure of hydrogen. With no hydrogen present, only closed forms of carbon deposits such as multiwalled nanotubes are produced. As the partial pressure of hydrogen is increased, the filament-type carbon deposits with open edges are observed. The number of open edges increases with increasing H{sub 2} concentration. However, for a given hydrogen concentration, the number of open edges decreases as the reaction temperature is raised. Extending the reaction time creates longer nanotubes, reaching an average length of10 {micro}m after 48 h. Employing this low-temperature method for the production of nanotubes, one can expect ultimately to establish control of their morphology through variations of easily tunable process parameters.