Clinoptilolite/electrolyte interface probed by a classical molecular dynamics simulations and batch adsorption experiments

Abstract Classical molecular dynamics (CMD) simulations were used to describe clinoptilolite/electrolyte interface with an atomistic resolution. The most abundant (010) surface cut was chosen together with two forms of clinoptilolite (CL) skeleton: neutral siliceous form (CL-SIL) and charged natural form with aluminum substitutions (CL-SUB). Structural properties of adsorbed water molecules, sodium, and ammonium cations are described in very detail and compared to the experimental findings. It is shown that the structure of water molecules and ions near the surface is significantly influenced by the framework charge. To improve our understanding of CL(010)/electrolyte interactions, umbrella sampling (US) simulations were performed to get free energies of adsorption of Na+ and NH4+ cations. These are compared with complementary experimental numbers obtained by batch adsorption experiments. The qualitative agreement was found but the origins of quantitative disagreement are discussed.