Related Experiment Videos
UV induced local heating effects in TiO2 nanocrystals.
Thomas Berger1, Oliver Diwald, Erich Knözinger
1Institut für Materialchemie, Technische Universität Wien, Veterinärplatz 1/GA, Vienna A-1210, Austria.
Physical Chemistry Chemical Physics : PCCP
|April 25, 2006
Summary
Photogenerated hole centers trap on titanium dioxide (TiO2) nanocrystal surfaces under UV light, forming one electron-hole pair per particle. This trapping process is influenced by photon energy and can lead to localized heating, impacting photocatalysis.
Area of Science:
- Materials Science
- Photochemistry
- Surface Chemistry
Background:
- Titanium dioxide (TiO2) is a widely studied photocatalyst.
- Understanding charge carrier dynamics is crucial for optimizing photocatalytic efficiency.
- Surface trapping mechanisms play a significant role in photocatalytic reaction pathways.
Purpose of the Study:
- To investigate the trapping of photogenerated hole centers on isolated TiO2 nanocrystals.
- To characterize the dynamics and concentration of trapped charges under UV irradiation.
- To explore the influence of UV irradiance and temperature on charge trapping.
Main Methods:
- Time-resolved electron paramagnetic resonance (TREPR) spectroscopy was used to track trapped hole centers.
- Experiments were conducted on isolated TiO2 nanocrystals at 77 K and low pressures (< 10(-6) mbar).
- UV irradiance was varied to study its effect on trapping dynamics and temperature.
Main Results:
- Photogenerated hole centers were observed to trap on the surface of TiO2 nanocrystals.
- The maximum concentration of trapped charges reached approximately one electron-hole pair per particle, independent of UV irradiance.
- Trapping dynamics were dependent on the number of supra-bandgap photons, and localized heating occurred above 1.55 mW cm(-2).
Conclusions:
- Surface trapping of photogenerated holes is a key process in TiO2 nanocrystals.
- The constant maximum concentration suggests a saturation limit for charge trapping per particle.
- Enhanced non-radiative recombination and heat production contribute significantly to thermal chemistry in photocatalytic cycles.