Water confined in mesoporous silica glasses: Influence of temperature ion adsorption/desorption hysteresis loop and fluid structure

In natural as well as industrial processes, water is frequently confined in silica porous materials with pore sizes in the nanometer scale. Understanding the confinement effects on the fluid properties is a fundamental issue, helpful to optimize the industrial processes. The molecular simulation is a powerful tool to study complex polar fluid like water at the atomic scale. The water adsorption/desorption properties in a mesoporous silica glass are investigated by means of Grand Canonical Monte Carlo simulations (GCMC). The SPC and PN TrAZ potential are used to describe water-water and water-silica interactions. The numerical sample of mesoporous silica glass (pore size: 3.6 nm) was obtained by off-lattice reconstruction, known to reproduce in a realistic way the geometrical complexity of high specific surface Vycor (pore size distribution, pore interconnections, etc). The intermolecular potential is shown to reproduce the experimental data at 300 K (adsorption isotherm and isosteric heat of adsorption). The water structure is analyzed and confinement effects are emphasized. The temperature influence is studied: the hysteresis loop is shown to shrink with an increase in temperature.