Photolysis of citrate on the surface of lepidocrocite: An in situ attenuated total reflection infrared spectroscopy study
- Autor(en)
- Paul Borer, Stephan J. Hug, Barbara Sulzberger, Stephan Krämer, Ruben Kretzschmar
- Abstrakt
The photodecomposition of citrate adsorbed to ?-FeOOH (lepidocrocite) was investigated by batch photodissolution experiments and by in situ attenuated total reflection infrared spectroscopy (ATR-FTIR). Batch photodissolution experiments in suspensions of 125 mg/L ?-FeOOH and 100 ?M 14C radio-labeled citrate revealed that the ?-hydroxycarboxylic acid functional group of citrate was selectively photooxidized at pH 4 and pH 6. ATR-FTIR spectra recorded during the irradiation of ?-FeOOH-layers with adsorbed citrate showed that the primary photoproduct of citrate was acetonedicarboxylic acid. In the presence of excess citrate, the adsorbed photoproduct was exchanged in a ligand-exchange reaction indicating that citrate forms stronger surface complexes than acetonedicarboxylic acid. The primary photooxidation reaction was resolved from the subsequent ligand-exchange reaction by the application of a relatively high photon flux (5-10 W/cm2, 300-500 nm). Despite consecutive ligand-exchange reactions, the photoconversion of adsorbed citrate to acetonedicarboxylic acid was almost complete at pH 4 within 22 min. At pH 6, only a small photodecomposition was observed. This result was interpreted in terms of (i) different fractions of inner- and outer-sphere citrate surface, complexes at pH 4 and pH 6 and (ii) different photoreactivity of different inner-sphere complexes. Furthermore, both batch photodissolution experiments and ATR-FTIR spectroscopy revealed that adsorbed acetonedicarboxylic acid was further decomposed to acetoacetate at pH 4 but not at pH 6. This study shows that the photooxidation of adsorbed citrate leads to the same products as the photodecomposition of dissolved ferric-citrate complexes. Moreover, it highlights the potential of ATR-FTIR spectroscopy for investigating photoreactions at iron oxide surfaces at the molecular level. © 2007 American Chemical Society.
- Organisation(en)
- Externe Organisation(en)
- Eidgenössische Technische Hochschule Zürich
- Journal
- The Journal of Physical Chemistry Part C (Nanomaterials and Interfaces)
- Band
- 111
- Seiten
- 10560-10569
- Anzahl der Seiten
- 10
- ISSN
- 1932-7447
- Publikationsdatum
- 2007
- Peer-reviewed
- Ja
- ÖFOS 2012
- 105105 Geochemie, 105904 Umweltforschung
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/4d80a629-7320-4c77-a541-32bfd21be8c0