Multilayered ordered mesoporous platinum/titania composite films: does the photocatalytic activity benefit from the film thickness?

Multilayered films of TiO2 with ordered cubic mesoporosity were grown via layer-by-layer deposition on a conductive FTO (F-doped SnO2) substrate by dip-coating and subsequent calcination at 400 degrees C. Since platinum nanoparticles are known to enhance the photocatalytic activity, they were introduced into the TiO2 mesopores by pulsed electrodeposition. Additionally, sandwich-like layers with up to five alternating TiO2 and Pt layers were prepared. The photocatalytic gas-phase oxidation of acetaldehyde served as a test reaction to characterize the activity in the gas phase of both pristine TiO2 as well as Pt/TiO2 single-and multilayer films. The ordered mesoporous pristine TiO2 and Pt/TiO2 nanocomposites exhibited significantly higher photoactivity than commercial Pilkington Activ (TM) glass and dense TiO2 films. Moreover for pristine TiO2 films, those consisting of three layers (about 650 nm in thickness), were shown to be sufficient to achieve a maximum photonic efficiency of zeta = 0.45%. For the Pt/TiO2 system, however, a single-layer film with a total thickness of only about 220 nm exhibited an almost identical activity. Moreover, repetitive experiments demonstrated that the newly prepared photocatalyst films did not suffer from a decrease in the photocatalytic activity, evincing their potential for practical applications.