Understanding the adsorption and
photoactivity of acetic acid and
trimethyl acetic acid on TiO
2
surfaces is important for
improving the performance of photocatalysts and dye-sensitized solar
cells. Here we present a structural study of adsorption on rutile
TiO
2
(100)-1 × 1 and -1 × 3 using Scanning Tunnelling
Microscopy and Density Functional Theory calculations. Exposure of
both terminations to acetic acid gives rise to a ×2 periodicity
in the [001] direction (i.e., along Ti rows), with a majority ordered
c(2 × 2) phase in the case of the 1 × 1 termination. The
DFT calculations suggest that the preference of c(2 × 2) over
the 2 × 1 periodicity found for TiO
2
(110)-1 ×
1 can be attributed to an increase in interadsorbate Coulomb repulsion.
Exposure of TiO
2
(100)-1 × 1 and -1 × 3 to trimethyl
acetic acid gives rise to largely disordered structures due to steric
effects, with quasi-order occurring in small areas and near step edges
where these effects are reduced.
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