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Ultrafast Surface-Specific Spectroscopy of Water at a Photoexcited TiO2 Model Water-Splitting Photocatalyst
Ellen H G Backus1,2, Saman Hosseinpour2,3, Charusheela Ramanan2,4
1University of Vienna, Faculty of Chemistry, Institute of Physical Chemistry, Währinger Straße 42, 1090, Vienna, Austria.
Angewandte Chemie (International Ed. in English)
|November 27, 2023
Summary
Researchers used advanced spectroscopy to observe water splitting on titanium dioxide (TiO2) photocatalysts. Water molecules dissociate within 20 picoseconds after UV light exposure, forming Ti-OH groups.
Area of Science:
- Photocatalysis
- Surface Chemistry
- Spectroscopy
Background:
- Photocatalytic water dissociation is crucial for energy applications.
- Understanding the hole-mediated oxidation mechanism at the catalyst-water interface is essential.
- High temporal resolution studies are needed to elucidate reaction dynamics.
Purpose of the Study:
- To investigate the molecular-level mechanism of photo-induced water dissociation at the TiO2-water interface.
- To achieve high temporal resolution of interfacial water reactions under realistic conditions.
- To provide insights into the early steps of photocatalytic water splitting.
Main Methods:
- Employed femtosecond time-resolved, surface-specific vibrational sum frequency generation (SFG) spectroscopy.
- Studied the reaction directly at the interface of titanium dioxide (TiO2) and liquid water.
- Focused on interfacial water molecules to track reactions on relevant timescales.
Main Results:
- Observed water dissociation occurring within 20 picoseconds after UV photoexcitation of TiO2.
- The reaction mechanism was consistent across different pH levels (pH 3 and 11).
- Identified the conversion of H2O to Ti-OH groups and deprotonation of existing Ti-OH groups.
Conclusions:
- Provided direct experimental evidence of the early stages of photocatalytic water dissociation.
- The findings offer critical molecular-level insights into interfacial reaction dynamics.
- Results are relevant for designing more efficient photocatalysts for water splitting.
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