Growth and optimization of carbon nanotubes in activated carbon by catalytic chemical vapor deposition

Abstract

High yield synthesis of carbon nanotubes in activated carbon by Ni-catalyzed chemical vapor deposition is demonstrated and a parametric study on the effect of the most crucial experimental conditions on the growth is performed. Reaction temperature, time and carbon precursor flow rate were systematically varied and their influence on nanotube size, uniformity, density, growth rate, and yield was evaluated. In situ monitoring of growth evolution was achieved by a microbalance system connected on-line to the reaction zone. The porous structure of the support provides high surface area for catalyst particle deposition and improved catalyst particle dispersion properties, while its composition appeared to enhance nanotube yield. The resulting carbon nanotube-loaded activated carbons were characterized by scanning and transmission electron microscopy, Raman spectroscopy, while the pore transformation after nanotube growth was evaluated by mercury and nitrogen porosimetry. A strong effect of the reaction temperature was found on nanotube growth leading to an optimal value of 750 °C, while for a reaction duration longer than 5 min the growth rate was continuously suppressed, the nanotube size distribution was broaden, and the formation of amorphous carbon was favored. Controlled oxidation experiments on the outer surface of the impregnated activated carbon support were performed in order to remove outer layers and observe the catalyst morphology, content, and activity in the inner parts of the material. The composites produced in the present work, combining the exciting characteristics of carbon nanotubes with those of activated carbon, are anticipated to contribute to the development of novel composite materials based on carbon nanotubes with enhanced physical, chemical and electronic characteristics for important applications such as in catalysis, energy, and environment.