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°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°C for 1 h. The photocatalytic activity of the annealed films on stearic acid underUVirradiation is found to deteriorate after the films are annealed at temperatures above 700°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°C, and the second mechanism is the formation of large rutile grains at a higher temperature, 900°C.