Effect of Fe3+ doping on the electronic structure and surface hydration properties of quartz

Abstract

In this study, the effects of Fe³⁺ doping on the crystal structure and surface properties of quartz were analyzed using density functional theory (DFT) calculations and molecular dynamics (MD) simulations. The crystal structure, surface model, and adsorption model of the water molecule layer for Fe³⁺-doped α-quartz were established. The DFT calculations reveal that Fe³⁺ doping affects the α-quartz lattice parameters and surface active sites. The adsorption energy near the sites occupied by Fe³⁺ is −66.20 kJ/mol, which is considerably lower than that of the undoped system (−42.35 kJ/mol). This makes it easier for water molecules to be adsorbed on the Fe³⁺-doped α-quartz (001) surface. The frontier orbital energy, electron density difference, charge density, and Mulliken bond population analyses indicate that the presence of Fe³⁺ improves the ability of the (001) surface of α-quartz to attract and bind water molecules. This improvement is mainly due to the formation of hydrogen bonds between the surface hydroxyl groups and water molecules on the surface of Fe³⁺-doped quartz and the equilibrium of the electrostatic interaction between the cation and water molecules. MD simulations show that a hydration layer with a thickness of approximately 8 Å is formed on the surface of Fe³⁺-doped α-quartz. Compared with the undoped system, the hydration film on the surface of the doped system is thicker, indicating that the incorporation of Fe³⁺ impurities in the lattice enhances the surface hydration characteristics of quartz. These results offer theoretical guidance for achieving efficient separation and thorough purification of quartz.