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 °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™ 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 ζ = 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.