MOLECULAR-SIEVE BEHAVIOR OF ACTIVATED CARBONS

Analysis of data for the adsorption of various molecular probe molecules on a number of different microporous carbons has revealed an empirical relationship between log(n(0)) and log(V-m), where n(0)/mmol g(-1) is the micropore capacity for a given adsorptive and V-m/cm(3) mol(-1) the corresponding adsorptive molar volume. It is shown that observed differences in the linearity and slope of the log(n(0)) vs log(V-m) plots can be rationalised on the basis of different types of molecular sieve behaviour and that analysis of the plots should therefore be able to provide useful information relating not only to the micropores themselves but also to the micropore entrances. It is also concluded that the adsorption of nitrogen is atypical while, with regard to water vapour adsorption, the results indicate that adsorption only occurs in pores of slit-width greater than or equal to 0.37 nm (rather than the previously suggested value of greater than or equal to 0.5 nm), due to the fact that a stable hydrogen-bonded structure is not able to form in narrower ports.