Investigation of dioctahedral smectite hydration properties by modeling of X-ray diffraction profiles: Influence of layer charge and charge location

Abstract

SbId-1 and SbCa-1, respectively) was studied by modeling of X-ray diffraction patterns recorded under controlled relative humidity (RH) for Sr-and/or Ca-saturated specimens. The influence of layer charge and charge location on smectite hydration was studied. Distribution of layers with different hydration states (dehydrated -0W, monohydrated -1W, bi-hydrated -2W, or tri-hydrated -3W) within smectite crystals often leads to two distinct contributions to the X-ray diffraction pattern, each contribution having different layer types randomly interstratified. Structure models are more heterogeneous for beidellite than for montmorillonite. For beidellite, two distinct populations of particles with different coherent scattering domain sizes account for the heterogeneity. Increased hydration heterogeneity in beidellite originates also from the presence of 0W (non-expandable) and of 1W layers under high relative humidity (RH) conditions. Similarly, after ethylene-glycol (EG) solvation, some beidellite layers incorporate only one plane of EG molecules whereas homogeneous swelling was observed for montmorillonite with the systematic presence of two planes of EG molecules.For montmorillonite and beidellite, the increase of layer charge shifts the 2W-to-1W and the 1W-to-0W transitions towards lower RH values. For all samples, layer thickness of 0W, 1W, and 2W layer types was similar to that determined for low-charge SWy-1 montmorillonite (Source Clay SWy-1), and no change of layer thickness was observed as a function of the amount or of the location of layer charge. Layer thickness however increased with increasing RH conditions.

In-Depth Insights into the Key Steps of Delamination of Charged 2D Nanomaterials

“…Even synthetic layered silicates when synthesized at temperatures below 1000 K show a non-uniform intracrystalline reactivity. As a consequence, a large fraction of the stacks does not show osmotic swelling at all, or the separation between adjacent layers varies randomly and a weighted average of the d-spacings is observed which is of limited analytical and practical value (16). Moreover, all the above mentioned materials need to be ion-exchanged and/or purified in some way prior to osmotic swelling.…”

Hydration Properties and Interlayer Organization of Water and Ions in Synthetic Na-Smectite with Tetrahedral Layer Charge. Part 1. Results from X-ray Diffraction Profile Modeling

“…Using a systematic fitting procedure the evolution of layer type abundance and of crystal parameters can be followed accurately along the water vapor desorption isotherm, which allows assessing the specificity of the studied saponite by comparison with previous studies performed on natural smectites. 20,25,26 Structure Models and Crystal Parameters EWolution. The CSDSs along the c* axis (N parameter, Tables 1 and 2) are higher for saponites than for natural smectites.…”

“…A similar CSDS increase with decreasing hydration was already observed as a result of either RH decrease or temperature increase. 20,25,26 It was interpreted as a disruption of some 2W layer stacks owing to weaker electrostatic interactions between layers resulting from increasing interlayer distances upon hydration. Although consistent with this interpretation, the CSDS increase during the 2W-1W transition is less significant than that for Na-saturated low-charge montmorillonite (increase of ∼25% and ∼50%, respectively).…”

“…[21][22][23][24] By fitting positions and profiles of the 00l reflections over a large angular range, the relative proportions of the different layer types can be determined together with the thickness and water content of the different layer types. 20,25,26 These studies showed systematic hydration heterogeneity whatever the interlayer cation, relative humidity (RH), amount, and location of layer charge and temperature.…”

Expansion characteristics of organo montmorillonites during the intercalation, aging, drying and rehydration processes: Effect of surfactant/CEC ratio

“…Although sydration behavior of original montmorillonite has been extensively studied in past two decades [25][26][27][28][29], less attention has been paid to the structural characteristics of wet OMt [30][31][32]. Several previous reports indicated that X-ray diffraction (XRD) is still the most widely used method for characterizing the structure of OMt in water, and the results showed that water molecules can always cause evident swelling of OMt [33][34][35][36].…”