Pressure Gap In Carbon Nanomaterials? Effect of Temperature and Pressure on the Binding of Simple Molecules to Carbon Nanotubes

The interaction of simple molecules with single wall carbon nanotubes (SWCNTs) and carbon black was shown to depend on the experimental conditions.  For example, acetone dosed to SWCNTs at 100 K and low pressure (~10^-6 Torr) has binding energy of ~75 kJ/mol.  Increasing exposures at 100 K resulted in the filling of adsorption sites with lower energies.  Adsorption of acetone at 300 K and high pressure (~7.6 Torr) results in acetone binding energies of ~120 kJ/ mol.  Similar phenomena were observed for the interaction of 1,3-butadiene and n-butane with SWCNTs.  Experiments suggest that these strongly bound species desorb as intact molecules.  The adsorption under typical UHV conditions (100 K-10^-6 Torr) does allow for molecules to access the sites with highest desorption energy.  Carbon black shows similar behavior to SWCNTs, but with significantly lower capacity for molecular uptake, consistent with its specific surface area and porous structure.