Pore size distribution in mesoporous materials as studied by 1H NMR

The pore size distributions of six mesoporous silica materials were determined by measuring the H-1 NMR signal from the non-frozen fraction of confined acetonitrile as a function of temperature. The average pore size distributions determined by NMR agree fairly well with those obtained by N-2 sorption measurements. However, NMR gives a more detailed picture of the pore size distribution revealing three well-defined peaks. The peak at the lower pore size, however, reflects the surface layer rather than a real pore size distribution. The NMR method to determine pore dimensions in the mesoporous range has a potential to become an alternative approach to the conventional gas sorption technique. In practise, however, pore sizes larger than approximately 400 Angstrom in diameter will be difficult to determine accurately due to the inverse dependence between the freezing point depression of the confined liquid and the pore diameter.