Probing carbon micropore size distribution by nucleus independent chemical shift

Abstract

Accurate determination of micropore size distribution is a challenging problem especially of subnanometer-sized micropores. Here, a simple room temperature method is introduced for determining micropore size distribution of activated carbons based on 1H nuclear magnetic resonance (NMR) of adsorbed water under magic angle spinning (MAS). The observed NMR peak shift is determined by the mechanism of nucleus independent chemical shift (NICS). Density functional theory computation of NICS yields a quantitative relationship between the observed peak shift and the micropore size. This relationship provides a direct link between the 1H MAS NMR lineshape and micropore size distribution. Such NICS NMR porometry technique is shown to be useful for characterizing micropore structures of highly carbonized activated carbons.