Enhanced photocatalytic hydrogen generation over ZrO2-TiO2-CdS hybrid structure.

Hybrid photocatalysts with suitable band structures are expected to show enhanced photocatalytic activity as compared to their constituent single phase compounds due to their improved physico-chemical properties. Here, we report an enhanced photocatalytic activity of a new composite photocatalyst comprising of ZrO2, TiO2, and CdS. This hybrid catalyst exhibits increased photocatalytic activity for hydrogen generation from water as compared to their constituent compounds. The photocatalytic activity decreases in the order: ZrO2-TiO2-CdS>TiO2-CdS>ZrO2-CdS>CdS>ZrO2-TiO2≈TiO2>ZrO2. An apparent quantum efficiency of 11.5% is obtained for ZrO2-TiO2-CdS with Pd as co-catalyst. Absorption edge of the composite is slightly blue shifted compared with that of pure CdS. Photoluminescence lifetime studies indicate an increased lifetime for the charge carriers in the composite sample as compared to that of pure CdS. Transmission electron microscopy images reveal that the particle size of the composite is much less than that of single phase CdS. The enhanced photocatalytic activity of the composite is attributed to the decreased particle size of CdS and increased lifetime of the charge carriers resulting from the efficient interfacial transfer of photogenerated electrons at the CdS/TiO2 and CdS/ZrO2 interface.

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

Ultrathin PdO-TiO(2) 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 TiO(2) film. The results of X-ray diffraction (XRD) and Raman spectroscopy reveal the formation of a mostly crystalline anatase phase in the pure TiO(2) thin film whereas separate phases of PdO and TiO(2) 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 TiO(2) 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 TiO(2) 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.

A rapid method for the synthesis of nitrogen doped TiO2 nanoparticles for photocatalytic hydrogen generation.

A facile, fast, and economic method of doping TiO2, synthesized by conventional precipitation route with N has been developed. By this method, stable N doped TiO2 can be prepared within a short duration of time. The method adopted was to treat the TiO2 powder synthesized by simple precipitation with trioctyl amine (TOA) at 320 degrees C for 2 hours followed by calcination at 400 degrees C for 2 hours to obtain the N-doped TiO2. The sample along with NiO as co-catalyst showed significant photocatalytic activity for hydrogen generation from aqueous methanol solution under sunlight type irradiation. This synthesis method opens up a fast and easy route for doping the existing TiO2 or other wide band gap oxide semiconductors with nitrogen so that they can exhibit enhanced photocatalytic activity under solar irradiation.