Abstract
Understanding the adsorption and photoactivity of acetic acid and trimethyl acetic acid on TiO2 surfaces is important for improving the performance of photocatalysts and dye-sensitized solar cells. Here we present a structural study of adsorption on rutile TiO2(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 TiO2(110)-1 × 1 can be attributed to an increase in interadsorbate Coulomb repulsion. Exposure of TiO2(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.
Highlights
The interactions of small organic molecules with rutile4−6 and anatase7−9 TiO2 surfaces have been the focus of numerous investigations.10. These act as model systems to elucidate the surface photoactivity associated with applications such as the photocatalytic degradation of organic pollutants.6,11−15 Carboxylate adsorption oadnsoTripOt2iohnasoanlsosurercfaeciveesd.15m−1u7chInattednytei-osnencsointinzeedctesdowlairthcdeylles (DSSC) the dye is typically bound to TiO2 nanoparticles via one or more carboxylate species
Density functional theory (DFT) calculations were employed to study the adsorption of acetate on rutile TiO2(100)-1 × 1, as well as TiO2(110)-1 × 1 for comparison
The scanning tunneling microscopy (STM) results suggest that the resulting carboxylates are bidentate bonded to adjacent Ti5c atoms along the [001] direction
Summary
Since Honda and Fujishima first demonstrated the photoelectrocatalytic capability of TiO2, the material has been widely investigated as a heterogeneous catalyst. The interactions of small organic molecules with rutile− and anatase− TiO2 surfaces have been the focus of numerous investigations. These act as model systems to elucidate the surface photoactivity associated with applications such as the photocatalytic degradation of organic pollutants.− Carboxylate adsorption oadnsoTripOt2iohnasoanlsosurercfaeciveesd.15m−1u7chInattednytei-osnencsointinzeedctesdowlairthcdeylles (DSSC) the dye is typically bound to TiO2 nanoparticles via one or more carboxylate species. Exposure of rutile TiO2(110)-1 × 14,5,19−22 to acetic acid gives rise to a 2 × 1 acetate overlayer at saturation coverage. This results from dissociative adsorption with both oxygens binding to two adjacent surface Ti atoms, with the proton thought to bond to the adjacent surface O atom as a bridging OH species.. As for other TiO2 surfaces, exposure of rutile TiO2(011)-2 × 1 to acetic acid results in 1D clusters predicted by DFT to be a combination of molecular monodentate and dissociative bidentate adsorption.. Density functional theory (DFT) calculations were employed to study the adsorption of acetate on rutile TiO2(100)-1 × 1, as well as TiO2(110)-1 × 1 for comparison.
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