Solvent structure and dynamics as drivers of mineral surface reactivity: insights from molecular dynamics simulations and rare-event methods

Abstract

Mechanistic understanding of correlations between the kinetics of water exchange on cations in solution and the kinetics of mineral dissolution and growth is curtailed by inherent limitations of current experimental and theoretical investigative tools. However, such reactivity trends are often vaguely hypothesized to stem from the influence of ions on solvent structure and dynamics at the mineral-water interface. The methodologies outlined in this dissertation to enhance the sampling of low probability events during molecular dynamics simulations significantly advances our capability to compute rate constants for interfacial reactions and to explore correlations between surface reactivity, solvent structure, and dynamics. ☐ Chapter 1 investigates the mechanisms of water exchange and ion attachment / detachment at kink sites along the obtuse edge directions of the calcite (104) surface. This study identifies the rate limiting steps for ion attachment and detachment along the step edge and reveals both similarities and key mechanistic differences between these reactions and interfacial water exchange reactions. ☐ Chapter 2 expands upon the previous Chapter and investigates the pressure dependence of kink site reaction kinetics in comparison to the kinetics of water exchange in solution. It tests the presumption that interfacial activation volumes, which bear mechanistic significance, reflect those measured for water exchange on aqueous ions. ☐ Chapter 3 investigates the underlying physical basis for the rate-enhancing effects of sodium chloride on the dissolution kinetics of amorphous and crystalline silica using disilicic acid as model. This study demonstrates that sodium chloride enhances the hydrolysis rate by increasing the probability of the transition state complex progression to the product state and establishes a correlation between the hydrolysis rate and the bulk structure of the solution phase.