First-Principles Calculations of Sarin Adsorption on Anatase Surfaces

We report density functional theory calculations investigating the adsorption of the organophosphate nerve agent sarin (GB) on clean (101), (001)-(1 x 4), and (001)-(1 x 1) surfaces of anatase titanium dioxide (TiO2). Our calculations show that GB chemisorbs on all three surfaces by the formation of a dative bond between the phosphoryl oxygen and a five-coordinated titanium atom in the surface. The adsorption of GB on the (001)-(1 x 4) and (001)-(1 x 1) surfaces (-45.1 and -34.8 kcal mol(-1)) is substantially stronger than on the (101) surface (-18.2 kcal mol(-1)). This could be a result of reactive surface states observed within the TiO2 band gap at the (001) surfaces but not the (101) surface. Our calculations show that the GB adsorption passivates these surface states. GB adsorption also breaks a bridging oxygen bond on both (001) surfaces, leading to a titanyl group that is also predicted to occur in adsorption of the simulant dimethyl methylphosphonate (DMMP) on anatase (001). The ordering of the three anatase surfaces by strength of GB adsorption is the same as that predicted for DMMP, while the GB adsorption is predicted to be weaker than DMMP adsorption by 8 kcal mol(-1) on the (001)-(1 x 4) surface and by 3 kcal mol(-1) on the (101) and (001)-(1 x 1) surfaces.