Using a minimal model approach for interpreting the intermediate scattering function, F(Q, t), to analyze quasi-elastic neutron scattering (QENS) data from interlayer water as a function of temperature in the 2D-layered clay minerals montmorillonite (Mt) and hectorite (Ht) a clear difference in behavior was observed. This was related to the polarization effect induced on the water molecules by both the exchangeable cation and surface charge within the interlayer. Although crucial for improving the wide range of industrial applications of clays as well as for explaining water uptake and retention by clays such information is neither obtained straightforwardly by other experimental methods nor fully accounted by molecular dynamics simulations. Furthermore, analysis of the evolution of the fitted parameters as a function of temperature shows that hydrogen atoms have a relaxation with a smaller average motional amplitude for Mt. Physically this can be explained as stronger hydrogen-bonding by water at the interlayer surfaces in Mt. These results allow for a novel and realistic description of these nanomaterials at the atomic scale, which is crucial for improving functional properties. These findings also prove that this new approach to modeling QENS captures subtle changes hidden in the spectra.

Developing new technologies for carbon sequestration and long-term carbon storage is important. Clay minerals are interesting in this context as they are low-cost, naturally abundant, can adsorb considerable amounts of CO 2 , and are present in storage sites for anthropogenic carbon. Here, to better understand the intercalation mechanisms of CO 2 in dehydrated and hydrated synthetic Na-fluorohectorite clay, we have combined powder X-ray diffraction, inelastic and quasi-elastic neutron scattering, and density functional theory calculations. For dehydrated Nafluorohectorite, we observe no crystalline swelling or spectroscopic changes in response to CO 2 , whereas for the hydrated case, damping of the librational modes related to the intercalated water was clearly observed. These findings suggest the formation of a more disordered water coordination in the interlayer associated with highly confined water molecules. From the simulations, we conclude that intercalated water molecules decrease the layer−layer cohesion energy and create physical space for CO 2 intercalation. Furthermore, we confirm that interlayer confinement reduces the Na + hydration number when compared to that in bulk aqueous water, which may allow for proton transfer and hydroxide formation followed by CO 2 adsorption in the form of carbonates. The experimental results are discussed in the context of previous and present observations on, a similar smectite, Ni-fluorohectorite, for which it is established that CO 2 attaches to the edge of nickel hydroxide islands present in the interlayer.

Quasi-elastic neutron scattering (QENS) from bulk-water at 300 K, measured on the IRIS backscattering neutron spectrometer (ISIS, UK), is interpreted using the jump diffusion model (JDM), a “minimalistic” multi-timescale relaxation model (MRM) and molecular dynamics simulations (MD). In the case of MRM data analysis is performed in the time domain, where the relaxation of the intermediate scattering function is described by a stretched Mittag-Leffler function, Eα(−(|t|/τ)α). This function displays an asymptotic power law decay and contains the exponential relaxation function as a special case (α = 1). To further compare the two approaches, MD simulations of bulk water were performed using the SPCE force field and the resulting MD trajectories analysed using the nMoldyn software. We show that both JDM and MRM accurately describe the diffusion of bulk water observed by QENS at all length scales, and confirm that MD simulations do not fully describe the quantum effects of jump diffusion.