(93b) Competitive Adsorption of Ions at Solid-Liquid Interface: Molecular Simulation Study

Interfacial properties like distribution, hydration, and structure of ions at solid - liquid interface dominated by the competitive ions from bulk solution. This phenomenon plays a major role in the areas like the rate of nutrients supply to plants, secondary oil recovery methods and surface catalytic reactions. To understand the competition between ions, we carried out molecular dynamics simulations of monovalent (Na⁺ and Rb⁺) and divalent (Mg²⁺ and Sr²⁺) ions chloride solutions at various concentrations at mica surface. Even though monovalent (Na⁺ and Rb⁺) ions formed monolayer configuration in adsorption region, their isotherm profiles resembled like multilayer adsorption. In the case of divalent ions (Mg²⁺ and Sr²⁺), we observed bilayer configurations in adsorption region and their isotherm profiles showed the early saturation. Our analysis of potential mean force, coverage, and hydration of ions were able to explain the observed isotherm behaviors and competitiveness between the surface ions of mica and cations of solutions at concentrations.