Diffusive dynamics of water in ion-exchanged zeolites

In this paper, an incoherent quasi-elastic neutron scattering (IQENS) study of the single-particle dynamics of water in fully hydrated Na-A and Mg50-A zeolites at T=293K and T=333K is presented. In order to probe different time scales, measurements were made at two resolutions, similar to 8 mu eV and similar to 28 mu eV. The high-resolution data allowed us to investigate the slower dynamics, which is mainly translational. The low-resolution spectra were used to probe the faster dynamics and distinguish between diffusional and rotational motion. We found that the partial exchange of Na+ with Mg2+ induces: (a) an increase of the available volume for diffusion; (b) a decrease of the fraction of water molecules taking part in the observed jump diffusion process; and (c) a shortening of the residence time.