Study of the interaction of formic acid, formaldehyde and formamide with the bulk terminated (1 × 1) and reconstructed (2 × 1) surfaces of rutile TiO2(011)

The nature of interactions of formaldehyde (HCHO), formamide (NH2CHO) and formic acid (HCOOH) is studied for the bulk terminated TiO2 (011) (1 × 1) surface and its most stable real surface structure the “brookite-like” (2 × 1) reconstruction; denoted (011)R. On the (011) (1 × 1) strong bridging adsorptions are seen for formic acid (1.71 eV) and formamide (1.57 eV) whereas the formaldehyde adsorbs in an η2 (C,O) structure (1.31 eV). On the (011)R there is a marked decrease in binding with only weak monodentate structures seen for formic acid (0.38, 0.27 eV) and formamide (0.44, 0.29 eV) and an η1 (O) adsorption seen for formaldehyde (0.23 eV). The reasons for this weak adsorption are examined. The arrangement of surface O atoms in the (011)R forces longer TiOadsorbate bonds resulting in weak adsorption energy. Charge transfer to the surface is also reduced and in the case of bridging adsorptions the destabilising effect of the surface O atoms is considerable. The crystal field of the titanium surface atoms is examined and the (011) (1 × 1) Ti is found to have a higher proportion of states in the conduction band available to bind to the adsorbate when compared to their counterparts of the (011)R surface.