Paper SS-WeA2
The Interaction of Carboxylic Acids with Rutile TiO2 (110) Single Crystal Surfaces: Results from IR-Spectroscopy
Wednesday, November 2, 2011, 2:20 pm, Room 107
| Session: |
Adsorption & Reactions on Oxide Surfaces |
| Presenter: |
Maria Buchholz, Karlsruhe Institute of Technology (KIT), Germany |
| Authors: |
M. Buchholz, Karlsruhe Institute of Technology (KIT), Germany
M.C. Xu, Ruhr-University Bochum, Germany
Y.M. Wang, Ruhr-University Bochum, Germany
A. Nefedov, Karlsruhe Institute of Technology (KIT), Germany
C. Wöll, Karlsruhe Institute of Technology (KIT), Germany
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| Correspondent: |
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The role of oxides is central in many technological areas such as gas sensing, catalysis and thin film growth. Zinc oxide and titanium oxide are also important for photocatalysis and photooxidation, e.g. of CO to CO2[1]. In the Graetzel-cell, organic molecules bound to TiO2-substrates via carboxylate bonds effectively convert photons into electric energy. In last decades numerous IR investigations of oxide powders, including the different modifications of TiO2, have been reported. An unambiguous assignment of the features in the complex IR spectra recorded for molecules bound to the oxide powder particle surfaces, however, is only possible on the basis of data recorded for well-defined reference systems, e.g. surfaces of single crystals. Unfortunately, studies on oxide single crystals are extremely scarce due to the fact that the sensitivity of reflection IR-spectroscopy for molecular adsorbates is two orders of magnitude lower for oxides than for metal single crystals. Only recently was is possible to overcome these technical problems by employing a novel, optimized spectrometer.[2] Here, we will demonstrate the performance of this highly sensitive IRRAS-setup by presenting high-quality IR-spectra obtained for two molecules, benzoic acid and terephthalic acid, adsorbed on rutile TiO2 (110). Owing to the fact that many Dye Sensitized Solar Cells (DSSCs) consist of dyes grafted to the oxide support via carboxylate groups determining and controlling the adsorption of carboxylic acids on oxidic substrates is fundamental to understanding the energy transfer from the molecule to the substrate. For the present experiments, monolayers of terephthalic acid (TPA) and benzoic acid (BA) were first deposited under UHV-conditions on a rutile TiO2 (110) surface at room temperature. Subsequently the sample was transferred in the main chamber and subjected to an analysis in a highly sensitive UHV IRRAS system. While for BA the expected bidentate carboxylate bonding is observed, for TPA the presence of two carboxylic acid groups leads to interesting complications. The IR-spectra allow, in particular, answering the question whether for the flat-lying TPA species observed in scanning probe techniques[3] the carboxylic acid group is still protonated, a question which could not be answered by the results from x-ray absorption spectroscopy[3].
[1] M. C. Xu, Y. K. Gao, E. M. Moreno, M. Kunst, M. Muhler, Y. M. Wang, H. Idriss, C. Wöll, Phys. Rev. Lett. 2011, 106, 138302.
[2] Y. M. Wang, A. Glenz, M. Muhler, C. Wöll, Rev. Sci. Instrum. 2009, 80, 113108.
[3] P. Rahe, M. Nimmrich, A. Nefedov, M. Naboka, C. Wöll, A. Kühnle, Journal of Physical Chemistry C 2009, 113, 17471.