A new route for the fabrication of an ultrathin film of a PdO-TiO2 composite photocatalyst

Ultrathin PdO-TiO2 composite films have been prepared for the first time by thermal decomposition of the multilayer Langmuir-Blodgett (LB) films of octadecyl amine-metal (Ti and/or Pd) ion complexes. The composite oxide film has been characterized by various spectroscopic techniques and compared with the pure ultrathin TiO2 film. The results of X-ray diffraction (XRD) and Raman spectroscopy reveal the formation of a mostly crystalline anatase phase in the pure TiO2 thin film whereas separate phases of PdO and TiO2 in the composite thin film. Crystallite sizes of 4-7 nm have been estimated from the XRD line broadening. Atomic force microscopy images also reveal oriented aggregates of nanocrystallites in the ultrathin films. The results of absorption spectroscopy have shown allowed direct transitions in both films. Pure TiO2 and the composite films have been compared for their ability to act as photocatalysts in hydrogen generation from a methanol-water mixture. It is found that the composite film has a uniform hydrogen generation rate for a long period of time and shows drastic enhancement in hydrogen production as compared to pure TiO2 film. This is because Pd in the composite film acts as an electron trapping centre and thereby decreases the recombination process in the oxide catalyst. The present study demonstrates the potential of the LB technique to fabricate high quality composite metal oxide films useful for photocatalytic hydrogen generation.