Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5397246 | Journal of Electron Spectroscopy and Related Phenomena | 2006 | 12 Pages |
Abstract
The adsorption of oxalate, malonate and succinate on anatase, rutile and lepidocrocite, was studied by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) at aqueous concentrations of 200 μM between pH 9 and 3. Clear spectral differences between the aqueous species and the surface adsorbed species for all three dicarboxylates are taken as strong evidence for inner-sphere adsorption. The characteristically different spectra on each oxide reveal surface specific interactions and could be used as a diagnostic tool, e.g., to probe the relative abundance of anatase and rutile on the surface of TiO2 samples. Spectral changes between pH 7.0 and 3.0 show that two to three different surface complexes of oxalate and one to three surface complexes of malonate and succinate are formed on each of the three surfaces. While the exact structures of each complex can currently not be derived, important differences between the dicarboxylates can be identified. Only adsorbed oxalate exhibits two strong bands above 1670 cmâ1, as expected for a five- (bidentate chelating) or six-membered (bidentate bridging) ring structure with one oxygen of each carboxylic group coordinated to surface sites and two CO double bonds pointing away from the surface. The absence of clear CO double bond vibrations above 1620 cmâ1 show that malonate and succinate adsorb differently, with one or both of the carboxylic groups independently forming monodentate hydrogen bonded, bidentate chelating (four-ring) or bidentate bridging (five-ring) structures. Oxalate is the only one of the three dicarboxylates that formed additional surface complexes at low pH on rutile and anatase and lead to rapid dissolution of lepidocrocite below pH 5.0.
Related Topics
Physical Sciences and Engineering
Chemistry
Physical and Theoretical Chemistry
Authors
Stephan J. Hug, Detlef Bahnemann,