Diffusion of water molecules confined in slits of rutile TiO2(110) and graphite(0001)

Titanium dioxide (TiO₂) is well applied in implant materials because of its biocompatibility while carbon is usually regarded as toxicant to cells. Actually, water-surface interaction has significant influence on the biocompatibility of implant materials. To understand the difference between TiO₂ and graphite on the biocompatibility, molecular dynamics simulations were performed to study the structure and diffusion of water in nano-slits formed by rutile TiO₂(110) and graphite(0001) with the separation distance ranging from 0.8 to 2.0nm. Simulation results show that the residence time of water at TiO₂ surface is considerably longer than that at graphite surface, indicating the stronger interaction between water and TiO₂. Moreover, the microstructure of water molecules absorbed at the TiO₂ and graphite surfaces were analyzed; the bound water molecules at the TiO₂ surface and the hydrogen bond network reduce the diffusivity of water through the TiO₂ slits. Simulation results show that the surface chemistry is crucial to the diffusion of water in nanoscale pores, while geometric size effect may just enhance the chemical effect.