Silver-modified titanium dioxide thin films for efficient photodegradation of methyl orange

Silver-modified, rough, high surface area titanium dioxide thin films resulting via a two-step dipping and UV-irradiation process were examined for their catalytic activity towards photodegradation of methyl orange (MO). Optimization of the photocatalyst's performance as a function of the dipping time, irradiation time and the dipping solution concentration was performed. The optimum silver nitrate concentration of the dipping solution was found to be 10(-3) M. The modified materials present enhanced photocatalytic efficiency and can decompose the organic pollutant three-times faster than the undoped original films (Degussa P25). A further Ag+-ion concentration increase in dipping solution results a decrease of the films photocatalyst efficiency due to a shading of the available semiconductor surface by the silver layer. This performance is consistent with the unique structural, morphological, and surface characteristics of the composite silver/titania materials. The lower the average particle size, roughness and fractal dimension, the higher the photodegradation percentage and rate constants. The surface doping effect is synergetic to the charge separation process and the photocatalytic results are explained on the basis of a mechanism involving efficient separation of electron-hole pairs induced by silver-ions (Ag+). Reproducibility tests proved that the photocatalytic activity of the silver-modified films remains intact even after six consecutive experiments of new added pollutant quantities. (C) 2002 Elsevier Science B.V. All rights reserved.