Arrangement and Mobility of Water in Vermiculite Hydrates Followed by ¹H NMR Spectroscopy

Abstract

The arrangement of water molecules in one- and two-layer hydrates of high-charged vermiculites, saturated with alkaline (Li(+), Na(+)) and alkali-earth (Mg(2+), Ca(2+), Ba(2+)) cations, has been analyzed with (1)H NMR spectroscopy. Two different orientations for water molecules have been found, depending on the hydration state and the sites occupied by interlayer cations. As the amount of water increases, hydrogen bond interactions between water molecules increase at expenses of water-silicate interactions. This interaction favors water mobility in vermiculites. A comparison of the temperature dependence of relaxation times T(1) and T(2) for one and two-layer hydrates of Na-vermiculite shows that the rotations of water molecules around C(2)-axes and that of cation hydration shells around the c-axis is favored in the two-layer hydrate. In both hydrates, the anisotropic diffusion of water takes place at room temperature, preserving the orientation of water molecules relative to the silicate layers. Information obtained by NMR spectroscopy is compatible with that deduced by infrared spectroscopy and with structural studies carried out with X-ray and neutron diffraction techniques on single-crystals of vermiculite.

Dynamic studies of Ormosil membranes

“…They correspond to the simultaneous presence of two types of water molecules. Their respective area is proportional to the amount of both kinds of water inside the sample, while their linewidth is associated with the mobility of the considered water as it could be observed in hydrates [26], gels and superabsorbants [27]. Similar behavior was also already reported in pure hydrated and deuterated POM [28], and associated to the presence of mobile deuterons (mobile water), mobile [D 3 O] + and immobile deuterons (water molecules without mobility).…”

Proton Dynamics in Layered Double Hydroxides: A 1H T1 Relaxation and Line Width Investigation

“…22, 25,43 The observed shortening of T 1 values of the slow relaxing system with increasing RH is consistent with an increase of the mobility of the "mobile" species. 17 The overall shorter T 1b values observed for samples known to contain more watersi.e. Mg 2 Al-NO 3 -and LiAl 2 -Cl - (Figure 3a, Table 1) and GA-LDH samples with decreasing pH of synthesis (Figure 3b, ref 22)sare also consistent with this observation.…”

“…[31][32][33][34] In general, incorporation of water molecules and dissolved species in interlayer galleries or association with solid surfaces reduces their T 1 relaxation times (increases the relaxation rate) relative to the values in bulk solution. 10, 17,18,32 This is because the characteristic frequencies of the vibrational and rotational motions of bulk water are greater than 10 12 Hz and those of diffusional motion are of the order of 10 10 Hz. These frequencies are all much greater than the Larmor frequency, and association with the solid increases the density of states at the Larmor frequency and also allows for greater interaction with paramagnetic centers.…”

“…1-9 1 H NMR is a versatile and effective probe of molecular scale water dynamics. 2,[10][11][12][13][14][15][16][17] Organic species are of comparable interest, but molecular scale study of their adsorption and confinement is more limited. 1,2,[18][19][20] Many of these organic species, including amino acids, carboxylic species, peptides, and larger proteins and molecules of natural organic matter (NOM), occur as anions at neutral to basic pH values and are thus expected to interact strongly with solids having positive structural or pH dependent charges.…”

Computational and Spectroscopic Investigations of the Molecular Scale Structure and Dynamics of Geologically Important Fluids and Mineral-Fluid Interfaces

“…A second, narrow resonance is associated with confined H 2 O that exhibits restricted motion below 10°C. Simulations of the narrow 2 H NMR lineshape below the melting transition show that confined H 2 O experiences fast (> 2 MHz) rotation about the molecular dipole axis, which has been observed in other clays (Conard et al, 1984;Cruz et al, 1978;Ishamaru and Ikeda, 1999;Sanz et al, 2006). Above the melting transition, isotropic and near-isotropic 2 H peaks are observed ( Figure 3).…”