Enhanced remote photocatalytic oxidation on surface-fluorinated TiO2

Area of Science:

• Materials Science
• Environmental Chemistry
• Surface Chemistry

Background:

• Active oxygen species generated on UV-illuminated titanium dioxide (TiO2) surfaces are mobile and can desorb as air-borne oxidants.
• Understanding the factors influencing oxidant desorption is crucial for optimizing photocatalytic oxidation (PCO) processes.

Purpose of the Study:

• To investigate the effect of surface fluorination on TiO2 (F-TiO2) in enhancing the desorption of oxidants for remote PCO.
• To study the remote photocatalytic degradation of stearic acids using F-TiO2 films in ambient air.

Main Methods:

• Fabrication of surface-fluorinated TiO2 (F-TiO2) films.
• Remote PCO experiments using stearic acid-coated glass plates separated by a small gap from the F-TiO2 film.
• Monitoring stearic acid degradation via Fourier transform infrared (FTIR) spectroscopy and gas-chromatographic CO2 production analysis.
• Investigating the influence of surface fluoride concentration, UV intensity, gap distance, relative humidity, H2O2, and ammonia.

Main Results:

• Remote PCO of stearic acids was significantly faster with F-TiO2 compared to pure TiO2, indicating enhanced air-borne oxidant generation.
• Remote PCO activity increased with higher surface fluoride concentration, higher UV intensity, and smaller gap distances.
• Optimal F-TiO2 activity was observed at 50% relative humidity, with no deactivation after repeated reactions.
• CO2 production was enhanced by H2O2 vapor and inhibited by ammonia, suggesting the involvement of hydroxyl radicals (OH).

Conclusions:

• Surface fluorination of TiO2 facilitates the desorption of air-borne oxidants, primarily hydroxyl radicals (OH).
• F-TiO2 exhibits enhanced and stable remote PCO activity, making it promising for air purification applications.
• The study elucidates the mechanism of remote PCO and highlights the role of surface modification in enhancing photocatalytic efficiency.