Photocatalytic reactivity of transparent titania sols prepared by peptization of titanium tetraisopropoxide

Photocatalysis of a transparent aqueous sol, which was prepared by peptizing titanium tetraisopropoxide in nitric acid for 7 days followed by dialysis was examined for the color-fading of methylene blue (MB) and Orange II and for the degradation of 4-chlorophenol (4-CP). Measurements of XRD patterns of the powders obtained by drying the sol indicated the formation of anatase. Under argon-bubbling, MB was degraded via the formation of colorless leuco form and the color of the sol returned to original by bubbling air in the dark. Reaction rates for oxidative degradation of MB under air-bubbling showed maximum at the 0.013 mol-Ti dm−3 in the sol and at pH 4.2. Reaction rates for color-fading of Orange II were higher by a factor of 6.8 than that of MB. The dependence of rates on the concentrations of MB or Orange II in the sol was discussed with the rate law. For the degradation of 4-CP in the sol under the irradiation for 6 h, 92.7% of 4-CP was completely dechlorinated and 69.5% of the initial TOC was decreased.