Dynamics of water in synthetic saponite clays: Effect of trivalent ion substitution

Abstract

Saponite clay belongs to the phyllosilicate family and is comprised of layers of Si(IV) tetrahedra and Al(III) or Mg(II) octahedra with definite interlayer spacing. In these systems, the trivalent ion substitutions in the tetrahedral layers lead to negative charge on the layers. Here we report the dynamics of water contained in [Si(6.97)Al(1.03)][Ni(6.00)]O(20)(OH)(4)[Na(1.03)]·28H(2)O (SAP-1) and [Si(7.13)Fe(0.86)][Ni(6.00)]O(20)(OH)(4)[Na(0.86)]·14H(2)O (SAP-2) saponite clays in the temperature range 200-310 K as studied by quasielastic neutron scattering technique. Particularly the effect of the ion substitution towards the dynamics of water is addressed here. Data analysis is carried out using the relaxing cage model. The existence of distribution in relaxation times indicated that the water molecules in saponite clay have a different local environment which leads to complex diffusion behavior. It is found that water exists in a supercooled state in the temperature range up to 235 K. However, some of the water molecules are found to be immobile in the temperature range 240-285 K. The fraction of immobile water decreases with increase in temperature. At higher temperatures, some of the water molecules in the hydration shells or those near the surface start participating in the diffusion process and at 293 K, almost all water molecules contribute to the dynamics. Diffusivity of water in both SAP-1 and SAP-2 are found to be lower in comparison to the bulk, and within the two samples of saponite clay diffusivity in SAP-1 is found to be lower compared to SAP-2; this has been explained on the basis of the charge on the tetrahedral layers and the charge balancing cations in the interlayer spacing.

Modeling the arrangement of particles in natural swelling-clay porous media using three-dimensional packing of elliptic disks

“…Numerous studies have focused on the dynamical properties of water molecules and cations in the interlamellar space of swelling clay minerals [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. However, on larger spatial scales, the presence of strongly anisometric particle shapes and their mutual arrangement in porous media are most often associated with the development of anisotropy in interparticle pore networks [19][20][21].…”

The Impact of Thermal History on Water Adsorption in a Synthetic Nanolayered Silicate with Intercalated Li+ or Na+

“…69 Figure 4 shows the evolution of the interlayer distance d 001 as a function of the RH for the preheated and non-preheated NaFHt and LiFHt samples. In contrast to NiFHt, 61 NaFHt and LiFHt show a step-like process, with transitions between the hydration states occurring within a narrow range of relative humidity values, a behavior which is also observed in natural smectites, such as montmorillonite, 30 saponite, 70 and vermiculite. 17 However, in LiFHt, transitions from 1.5WL to 2WL occur more gradually (both for preheated and nonpreheated samples).…”

Saponites containing divalent transition metal cations in octahedral positions — Exploration of synthesis possibilities using microwave radiation and NMR characterization

“…A priori, different divalent cations can occupy the octahedral positions, but a partial substitution by several trivalent cations being also possible in the structure of saponite (raw saponites mainly contain Mg 2+ , Fe 2+ , Fe 3+ and Al 3+ in these positions). Sodium is usually the charge-balancing interlayer cation, and as it is easily hydrated; the resulting phases usually become hydrated with two water layers (bilayer), both Na + cations and water molecules showing high mobility in the interlayer space (Mitra et al, 2013). In previous works, the microwave-assisted synthesis of saponites containing Ni 2+ , Mg 2+ or Fe 2+ as octahedral cations, also exploring the incorporation of Fe 3+ into the tetrahedral positions has been reported (Trujillano et al, 2009a(Trujillano et al, ,b, 2010(Trujillano et al, , 2011.…”