Simulation of the interface of (1 0 0) rutile with aqueous ionic solution

The interface of the rutile (1 0 0) surface with NaCl solutions has been simulated by classical molecular dynamics. In contrast to earlier simulations the protonation and hydroxylation equilibriums have been adjusted for different pH values (4, 7.4, and 9). The short range order close to the surface is described by two water layers with some orientational order and intermediate layers of positive or negative ions depending on the surface charge. A Stern model is confirmed with a dense layer of counterions on the charged TiO2 surface and a diffuse layer, which only consists of few ions in our system. The increase of orientational order of the water molecules close to the surface is described by an exponential function with a decay parameter of 1.9 Å, superposed by a damped oscillation which is independent of the pH value. The diffusion is significantly slower than in the bulk within a range of 13 Å from the surface. We propose a common approach for describing the different z-dependences of orientational order and of the diffusion coefficients.