Optimised photocatalytic activity of grid-like mesoporous TiO2 films:: effect of crystallinity, pore size distribution, and pore accessibility

Photocatalytic activity of anatase cubic-based ordered mesoporous thin films was related to the morphology of the crystalline porous network obtained upon thermal treatment with a specific incremented sequence. The porosity and pore size distribution of these thin films were investigated with a novel Environmental Ellipsometric Porosimetry (EEP) technique. Network crystallinity was assessed by XRD. In parallel, the evolution of the photocatalytic activity was studied through UV-induced photodegradation of methylene blue and lauric acid within the films at the various steps of the temperature treatment. The photoactivity was linked to the porous characteristics of the films and we concluded that the activity is optimal when the porosity is high and completely accessible, and when the nanoparticle and pore size have dimensions of 7.5 and 5.5 nm respectively. Such an optimal system was obtained after a sequential thermal treatment ending with 10 min at 600 degrees C in air, for which the films adopts an ordered bidirectional grid-like structure.