Sulfonated carbon nanotubes as a strong protonic acid catalyst

gests that the diffusion can be rate-governed in the micro-pores, as the channel dimensions imply very low macropore diffusion resistance. The distinct positions of oxygen and nitrogen spectra appearing at different frequencies demonstrate a significant difference in the diffusion rate constants, which cannot be explained by the minute difference between these sorptives in the main channels. The observed FR spectra can therefore be attributed in principle to intracrystalline diffusion. The resulting kinetic response exhibits selectivity in the sorption rate, which also shows that sorption is controlled primarily by micropore diffusion. Selectivity for oxygen is most pronounced for PS700, where the ratio of oxygen/nitrogen diffusion rates is almost 5. In PS1000 the oxygen diffusion rate increases by a factor of 5 relative to that in PS700, but its selectivity with respect to nitrogen is practically lost. These findings are consistent with the SAXS and gas adsorption results, which show an increase in the pore size with increasing temperature of treatment. Five different commercially available CMSs were recently found by FR to exhibit selectivity ratios ranging from 1.2 to 24 [13]. The present results show that the PS700, whose characteristic micropore slit width from nitrogen adsorption and SAXS is approximately 0.33 nm, is a promising candidate for air separation.