Diamond/Aqueous Electrolyte Interface: Experimental and Theoretical Approaches

This study investigatesthe effects of pH, ionic strength, and temperature on the diamond/aqueoussodium chloride interface. Analysis were performed on both (100) diamond single crystal (flat surfaces) and diamond colloidal particles. While both surfaces types exhibit a similar affinity for potential-determining ions (H+ and OH–), distinct differences were observed in their thermodynamic parameters regarding the distribution of H+ and OH– ions between the interfacial layer and the bulk solution. Specifically, reactions on flat surfaces were found to be entropically unfavorable and exhibit a low endothermic contribution. In contrast, colloidal particles displayed an opposite trend, although the overall value of Gibbs free energy was comparable to that calculated for flat surfaces. Additionally, two distinct ion effects were identified when examining the influence of ionic strength: interfacial water layer compression in the case of flat surfaces and asymmetric counterion association for colloids. These effects were determined to be mutually competitive. To obtain this data, we measured the inner surface potential of diamond in an aqueous electrolyte solution for the first time using a diamond single crystal electrode (DSCrE). Furthermore, the microscopic structure of the interfacial layer near the (100) and (111) diamond crystal planes was studied using localized QM/MM molecular dynamics simulations.