Effect of Annealing Temperature on Microstructure and UV Light Photocatalytic Activity of TiO2 Films Grown by Atmospheric Pressure CVD

Titanium dioxide (TiO2) films are deposited on quartz substrates by atmospheric pressure (AP)CVD, and then annealed under simulated air (80% nitrogen, 20% oxygen) at temperatures from 600 to 900 degrees C to investigate the change in microstructure and the effect on the photocatalytic activity on the simulated pollutant stearic acid. The as-deposited TiO2 film is mainly composed of pure anatase phase while the rutile phase is detected only after annealing the film at 900 degrees C for 1h. The photocatalytic activity of the annealed films on stearic acid under UV irradiation is found to deteriorate after the films are annealed at temperatures above 700 degrees C. This decrease in photocatalytic performance is observed to be the result of two possible mechanisms induced by the annealing temperature. The first mechanism is the increase in defect concentration (O- and Ti vacancies) in the annealed TiO2 films for annealing temperatures below 800 degrees C, and the second mechanism is the formation of large rutile grains at a higher temperature, 900 degrees C. The effect of annealing on the photocatalytic properties of TiO2 thin films produced using atmospheric pressure CVD is investigated. Photocatalytic degradation of stearic acid shows a decrease caused by two mechanisms: an increase in defects states (O- and Ti vacancies) resulting in recombination of electrons and holes, and formation of large rutile grains with limited heterojunction semiconductor effects with anatase film.