Exploring Water Nanoconfinement in Mesoporous Oxides through Molecular Simulations

Abstract

Mesoporous oxides present highly ordered monodisperse pores (2-50 nm) and high surface area (100-1000 m2/g). The precision achieved in controlling pore dimensions, interconnectivity and morphology in the nanometer range has given rise to unique properties with several technological applications, such as (photo)catalysis, sorption, sensors, biomaterials, all of which involve water interactions. These systems are also very interesting from a fundamental point of view, given that they offer a model in which to study confinement effects in the nanoscale. In this context, there is a persistent need for a precise characterization of the physical-chemical conditions of water inside of the pores, where two key aspects come together: surface and confinement effects. The temporal and spatial limitations of existing experimental techniques constitute an invitation for molecular simulations and modelling. Molecular simulations provide optimal spatial resolution for the study of the structure and dynamics of water within nanopores and the phase transformations it experiences on cooling and heating. In this chapter, the relation between nanoconfinement and properties of water in mesoporous materials, with a focus on phase transitions phenomena (liquid-vapour and solid-liquid equilibria), structure and transport properties were explored. Resorting to different molecular simulation techniques at different scales (atomistic and coarse-grained Molecular Dynamics), the effect of pore size and hydrophilicity on the mentioned phenomenon were reviewed.