Characterization and activity of visible-light driven TiO₂ photocatalyst doped with tungsten

This research aimed to expand the activity of TiO₂ down to the visible light region by modifying the sol-gel conditions and doping with tungsten. The optimum conditions for calcination temperature, acid type, and heating rate were 200°C, HNO₃, and 1°C/min, respectively. The undoped TiO₂ synthesized under these conditions could significantly absorb the visible light whereas the commercial Degussa P-25 could not. The absorptivity decreased sequentially as the wavelength increased from 400 to 700 nm. Within 6 h of 2-W blue-light illumination, 23% of 0.1 mM 2-chlorophenol was removed. The XRD result showed that the crystalline was anatase phase. The visible-light absorption property of the TiO₂ became even better when doped with tungsten. At the optimum W to TiO₂ ratio of 0.5%, the degradation of 0.1 mM 2-chlorophenol increased to 53% indicating a higher photocatalytic activity. Both crystalline and amorphous TiO₂ could exhibit the photocatalytic activity under the visible light region.