Correlation of TiO2 photocatalytic activity and diffuse reflectance spectra

Photocatalytic activity of TiO2 samples prepared by aqueous hydrolysis of T iCl4 and deposition with NH3 in gaseous acetone photocatalytic oxidation ha s been found dependent on calcination temperature. The activity reaches its maximum at calcination temperature 450 degreesC and then decreases, all th e samples being anatase. The photocatalytic activity of the samples in a se ries of different calcination temperatures correlates well with reflectance of the samples in the visible light region. The increase in calcination te mperature from 320 to 500 degreesC results in the growth of TiO2 crystallit es, decrease in BET surface area, slight changes in lattice parameters, and removal of weak surface Bronsted acid centers that are speculated to be OH groups. TiO2 prepared by deposition with NaOH exhibits much higher photoca talytic activity. The only paramagnetic species detected in the TiO2 sample s was NO that resulted from oxidation of lattice-captured NH3. No NO was de tected in TiO2 prepared by deposition with NaOH. The concentration of NO in creases steadily with calcination temperature as indicated by ESR spectra. The observed correlation of diffuse reflectance and photocatalytic activity was attributed to opposite effects of the increase of crystallinity and re moval of surface water and hydroxyl groups. (C) 2001 Elsevier Science B.V. All rights reserved.