Role of surface-purity in photocatalytic activity of nanocrystalline anatase–titania processed via polymer-modified sol–gel

Nanocrystalline titania powders have been synthesized via conventional and modified sol–gel using an alkoxide precursor for different R, the ratio of molar concentration of water to that of alkoxide precursor, and calcination temperature. The apparent first-order reaction rate-constant obtained for the powder synthesized via conventional sol–gel is comparable with that of commercial Degussa-P25. Conventional sol–gel has been modified using the hydroxypropyl cellulose polymer to increase the specific surface area of the photocatalyst; and hence, to further enhance its photocatalytic activity. Although higher specific surface area and smaller average nanocrystallite size have been obtained for the powders synthesized via modified sol–gel, they exhibit reduced photocatalytic activity relative to that of powders synthesized via conventional sol–gel. The deactivation of the present photocatalyst has been explained on the basis of reduced surface-purity of the powders after processing via modified sol–gel as induced by the presence of surface-residual organic compounds.