Hydrogen-induced self-assembly of helical carbon nanostructures from ethanol over SiO2 catalysts

Helical carbon nanostructures from ethanol over silica are successfully prepared through the addition of hydrogen during chemical vapor deposition. The helical structure formation appears to occur through hydrogen etching reactions enabling graphitic caps between neighboring tubes to merge, triggering the self-assembly of a helical structure. The experimental data is supported by thermodynamic calculations which correlate the hydrogen radical concentration with the observed efficiency of helical structure formation. Moreover, the calculations show an increase in water vapor content as one increases hydrogen addition. This can account for the improved crystallinity of the samples with higher hydrogen doses. (C) 2011 American Institute of Physics. [doi:10.1063/1.3587184]