Origin of enhanced water adsorption at ⟨1(1)over-bar0⟩ step edge on rutile TiO2(110) surface

Water adsorption behavior at < 1 (1) over bar0 > step edges on rutile TiO2 (110) surface has been investigated using density-functional theory calculations. We find that the < 1 (1) over bar0 > edge exhibits significantly enhanced water adsorption, especially dissociative adsorption, as compared to the pristine (110) surface and < 001 > step edge. The origin for the enhanced water adsorption is found to be due to the existence of fourfold coordinated Ti atoms (Ti-4c) at the < 1 (1) over bar0 > step edge, which lead to charge transfer to adsorbates more easily than fivefold coordinated Ti atoms on the (110) surface and < 001 > step edge. Furthermore, due to the local configuration of the dissociative mode, the charge transfer occurs more easily from Ti-4c to the hydroxyl group 1 pi orbital, which considerably increases the adsorbate-substrate interaction. As a result, the < 1 (1) over bar0 > step edge favors dissociative water adsorption, making it more reactive to water than the (110) surface and < 001 > edge. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4753951]