UV- or visible-light-induced degradation of X3B on TiO2 nanoparticles: Theinfluence of adsorption

Photodegradation of a textile dye X3B using either UV (lambda greater than or equal to 320 nm) or visible light (lambda greater than or equal to 450 n m) over three catalysts of highly adsorptive TiO2 nanoparticles in water ha s been examined. All the adsorption isotherms demonstrated-the Langmuir typ e behavior. The common observation was confirmed that for all the reactions induced by UV or Visible light, the apparent initial rate of X3B loss in t he aqueous phase increased with the initial equilibrated concentration of X 3B. However, this correlation was changed when the rate was determined by t he decreased concentration both in the aqueous phase and on the catalyst su rface. This increase of real initial rate with the initial equilibrated con centration was observed only in the visible-light-induced reaction over TiO 2 of Degussa P25. For all the other reactions, especially under UV irradiat ion, the real initial rate was found to increase only initially and then de crease with the initial equilibrated concentration. The result suggests tha t there is a screening effect by the adsorbed dye in the TiO2 photocatalyti c reaction and a solution filter effect in the photosensitized reaction. Mo reover, the photosensitized photodegradation of X3B was found to be also de pendent on the physical properties of TiO2, but interestingly the relative activity among the catalysts was similar to that demonstrated in the photoc atalytic reaction.