Study of the interaction of formic acid, formaldehyde and formamide with the bulk terminated (1×1) and reconstructed (2×1) surfaces of rutile TiO_2(011)

摘要

The nature of interactions of formaldehyde (HCHO), formamide (NH_2CHO) and formic acid (HCOOH) is studied for the bulk terminated TiO_2 (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 η~2 (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 η~1 (O) adsorption seen for formaldehyde (0.23 eV). The reasons for this weak adsorption are examined. The arrangement of surface 0 atoms in the (011 )R forces longer Ti- O_(adsorbate) 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.