The role of water in zeolite pores: the structure/property relationship for ion exchange

Abstract

Abstract The role of occluded water in the ion exchange selectivity of molecular sieves is studied in detail with Sandia Octahedral Molecular Sieves (SOMS). SOMS exhibit a high selectivity for divalent cations only when the framework Nb(V) are substituted by M(IV) atoms. Vibrational dynamics of the water molecules of the SOMS with varying charge balancing cations and M atoms are studied by inelastic neutron scattering (INS) measurements. The experimental INS spectra were compared with those of ice Ih to characterize the structural changes induced by confinement on the H2O hydrogen-bonding network. Data indicate that with increasing M(IV) content, a tendency of water molecules to restore the bulk-like arrangements and increased solvation effects on the channel cations [ 1 ]. Data are complimented with further characterization by MAS NMR.