Oxidizer gases effects on the diameter controlled synthesis of carbon nanotubes

In this study, the influence of oxidizers on the synthesis of carbon nanotubes by C₂H₄ decomposition over Fe catalyst has been investigated. CO₂, O₂, and H₂O were used as oxidizers to control catalyst particle formation and their sizes during the pretreatment stage. The same oxidizers were also employed in the growth stage to maintain the catalyst particle size and remove amorphous carbon formation to keep the catalyst particle active. The results of scanning electron microscopy indicated that the average diameters of nanotubes decreased from 13.4 ± 1.2 nm to 6.2 ± 0.5 nm, and extremely dense nanotubes were obtained when a small amount of CO₂ was added. Adding O₂ significantly decreased the areal carbon nanotube density while widening the diameter distribution. H₂O addition resulted in larger average diameters and made the growth strongly dependent on pretreatment conditions. Within the parameters tested for catalyst pretreatment and CNT growth processes, CO₂ appeared to be the best choice as a weak oxidizing assistant. The strong dependency of the average diameter on pretreatment conditions highlighted that pretreatment is a crucial step in determining the final diameters and their distribution.