Water Confinement in Faujasite Cages: A Deuteron NMR Investigation in a Wide Temperature Range. 2. Spectra and Relaxation at High Temperature

Abstract

Deuteron NMR spectra and spin-lattice relaxation were measured for D2O confined in NaX, NaY, and DY faujasites with various loadings at temperatures ranging from 200 to 310 K with the aim to study molecular mobility of confined water. Hysteresis of spin-lattice relaxation was observed for both DY and NaY(2.4) samples at 500% loading (280 water molecules per unit cell) in a heating-cooling cycle between 264.5 and 277.7 K. The hysteresis is most likely reflecting formation and decomposition of water clusters at different temperature. Spin-lattice relaxation rates obtained from the experiment are consistent with a picture of the fast magnetization exchange between two dynamically different deuteron populations. The observed relaxation behavior as a function of temperature and loading is most likely an effect of interplay between translational and rotational diffusion. Translational diffusion of water molecules is found to be related to the strength of the electrostatic interaction of water oxygen atoms to faujasite sodium cations, whereas water molecule reorientations seem to depend on the strength of hydrogen bonding to faujasite oxygen atoms and the strength of hydrogen bonds between water molecules, at outer and inner positions in water clusters, respectively.

Translational and Rotational Dynamics of Molecules Confined in Zeolite Nanocages by Means of Deuteron NMR

“…The methods applied here in the analysis of deuteron NMR data, obtained for water molecules in confinement, were developed and described before. 29 Some of previous results, supplemented by additional measurements, are summarized in Table 1. The effective quadrupole coupling constant, C Q eff , is a fraction of the static value which amounts to 260 kHz.…”

“…The methods applied here in the analysis of deuteron NMR data, obtained for water molecules in confinement, were developed and described before . Some of previous results, supplemented by additional measurements, are summarized in Table .…”

“…28 We develop and follow the application of 2 H NMR spectroscopy methods outlined before. 29 Translational mobility related features are detected as a set of small molecules was chosen. Shape of motionally averaged spectra displays features related to molecular mobility.…”

“…Evolution of translational and rotational mobilities is the main target. Data for D 2 O are reanalysed and summarized together with complementary new results. We extend our approach to ammonia, methanol, and acetone at low loadings.…”

Dynamics of molecules confined in nanocages. A deuteron NMR study at high temperature

“…Applied here methods in analysis of deuteron NMR data, obtained for moelcules in confinement, were developed and described before for the case of water. 24 Some of previous results, supplemented by additional measurements, are summarized in Table 1. Contributions of Gaussians depend on decreasing temperature, that of narrower one is decreasing.…”