engleski

Quartz/aqueous electrolyte solution interface: molecular dynamic simulation and surface potential measurements

At the surface of quartz, immersed in aqueous electrolyte solution, surface oxygen and silica atoms react with water molecules to form electrically charged surface sites [1, 2]. Due to charging, the distribution of ions and orientation of water molecules take place and the interfacial layer forms. This, in turn, is important in a variety of different physical and chemical processes, such as adsorption of contaminants, heterogeneous catalysis, mineral dissolution, membrane chemistry etc. We combined the experimental and computational approach to investigate the interfacial properties of quartz/aqueous electrolyte solutions. We measured the inner and electrokinetic zeta potentials, namely quartz single crystal electrode potential (SCrE) [3] and zeta potential obtained via streaming potential measurements (SP). Moreover, molecular dynamics (MD) simulations of investigated systems provide the information regarding orientation and 3D layering of water molecules as well as distribution of ions at interface [2]. Additionally, electrokinetic potentials were calculated by means of equilibrium (EMD) and non-equilibrium (NEMD) molecular dynamics [4]. Zeta potentials obtained from MD simulations qualitatively agree with experimentally obtained surface potentials, suggesting that anions more strongly influence quartz surface properties. Layering and accumulation of water at the interface decreases as pH increases. At pH = 3 weak preferential orientation of water was found. However, at pH = 6 and 9 strong orientational ordering of water molecules were obtained. In this respect, water molecules „feel” the negatively charged quartz surfaces to more extended depths towards the bulk solution which implies propagation of surface properties.

Quartz, ion distribution, interfacial water layer, surface potential, single crystal electrodes, molecular dynamic, electrical interfacial layer

nije evidentirano