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Imaging Water Dissociation on TiO(2)(110).
I M Brookes1, C A Muryn, G Thornton
1Surface Science Research Centre and Chemistry Department, Manchester University, Manchester M13 9PL, United Kingdom.
Physical Review Letters
|January 22, 2002
Summary
Water adsorption and dissociation on titanium dioxide (TiO2) surfaces were studied. At low temperatures, water binds to titanium atoms, and upon warming, it breaks down into bridging hydroxyls, indicating a role for oxygen vacancies in the process.
Area of Science:
- Surface Science
- Materials Chemistry
- Catalysis
Background:
- Understanding water-surface interactions is crucial for catalysis and materials science.
- Titanium dioxide (TiO2) is a widely studied semiconductor with applications in photocatalysis and gas sensing.
- The adsorption and dissociation of water on TiO2 surfaces are fundamental processes influencing its reactivity.
Purpose of the Study:
- To identify the specific adsorption site of water molecules on the TiO2(110)-(1 x 1) surface.
- To investigate the dissociation products of water and their locations at elevated temperatures.
- To elucidate the role of surface defects, specifically oxygen vacancies, in the water dissociation pathway.
Main Methods:
- Scanning tunneling microscopy (STM) was employed to achieve atomic-scale resolution.
- Experiments were conducted at controlled temperatures (150 K and 290 K) to study adsorption and dissociation.
- Surface characterization focused on identifying adsorption sites and dissociation product locations.
Main Results:
- Water molecules were observed to adsorb on rows of fivefold coordinated titanium (Ti) atoms at 150 K.
- By 290 K, adsorbed water dissociated to form bridging hydroxyl groups.
- Terminal hydroxyl groups were not observed, suggesting a specific dissociation mechanism.
Conclusions:
- The adsorption site of water on TiO2(110)-(1 x 1) is identified as fivefold coordinated Ti atoms.
- Water dissociation at 290 K leads to the formation of bridging hydroxyls, not terminal ones.
- Bridging oxygen vacancies are implicated as key participants in the water dissociation pathway on this surface.