Interlamellar space configuration under variable environmental conditions in the case of ni-exchanged montmorillonite: quantitative XRD analysis

Interlamellar space organization of low-charge montmorillonite was studied by modeling of X-ray diffraction (XRD) patterns recorded under controlled relative humidity (RH) conditions on Ni saturated specimens. The quantitative XRD investigation, based on an indirect method consisting of the comparison of experimental 00l reflections with the other calculated from structural models, is used to characterize eventual nanostructural changes along c* axis of Ni-exchanged montmorillonite. This method allowed us to determine, respectively, the relative layer types contribution, the layer thickness, nanoconfiguration of the interlamellar space, and position, amount, and organization of water molecules and exchangeable cations. Obtained theoretical models exhibit heterogeneous hydration state which is the dominating character detected all over studied cycles. Along RH cycle a modification in the main structure of the host materials is performed and the presence of a mixed layer structure (MLS) is noted. The hydration hysteresis at the low and the high RH range can be explained by fluctuations in the water retention mechanism and hydration heterogeneities created within the smectite crystallite.