Temperature-dependent ordering of confined water in MIL-100(Fe) using neutron scattering

MOFs are coordination polymers with an open framework that has potentially accessible pores. In fact, it is this property that allows them to be used as storage systems for different types of molecules. However, the dependence of adsorption on temperature in the liquid phase has been less studied, and it is the aim of this proposal. We propose a neutron total scattering study on MIL-100(Fe) to investigate a sharp, unexpected temperature-induced change in the density of MOF particles immersed in water when transitioning from ~20 ºC to 30 ºC. This was detected via magnetic sustentation experiments on paramagnetic MOF systems during liquid-phase adsorption processes, and we hypothesize an abrupt hydrogen-bonding rearrangement in confined water in that range. By measuring deuterated MIL-100(Fe) fully hydrated with H₂O, D₂O, and 50:50 mixtures at 10 °C and 35 °C, we aim to reconstruct atomistic hydration structures using EPSR modelling at both temperatures. By comparing EPSR-derived pair correlation functions, we aim to assess whether a discrete structural transition in confined water explains the observed macroscopic density changes. This knowledge will have a profound impact in many areas where adsorption from liquid is a key feature including catalysis, capture, separation and controlled release.