In recent years incorporation of plasmonic noble metal nanostructures appear as an attractive approach to enhance the visible light absorption due to direct excitation of the surface
plasmon resonance (SPR) band of the nanoparticles.Plasmonic nanostructures are being increasingly used to
enhance the light harvesting efficiency of photovoltaic devices. For example, Kamat and co-workers demonstrated that the photocurrent generation of nanostructured TiO2 films increases several times in the presence of surface
deposited gold nanoparticles, which promote charge transfer process in the composite systems.In the presence of
photoexcited plasmonic nanoforms, electron injection occurs
from the nanosurface to the conduction band of TiO2 in femtosecond time scale (Figure 6).The positive hole formed
on the nanosurface oxidizes the substrate, whereas the electron in the conduction band of TiO2 reacts further with O2.However, the rapid back electron transfer and consequent charge recombination limit the efficiency of the photocatalytic processes. The size and shape of the metallic nanoparticles have significant effect on the overall efficiency of the process. Kamat and co-workers demonstrated that small sized nanoparticles shift the energy of the Fermi level of the TiO2-nanocomposite
toward more negative value and affect the photocatalytic process due to direct changes in the energetics of the composite systems.Various mechanisms have been proposed to account for the improved photocatalytic efficiency of TiO2−SPR nanostructures, including enhanced light absorption by the
surface plasmons, improved charge separation efficiency, and changes in the energetics of the Fermi level in the composite system arising from the electron storage effects.66 Alloying
noble metal Cu with Pt (Pt−Cu) supported on anatase TiO2 has resulted in a lower work function of metallic platinum,
which in turn facilitates the efficient electron injection from the photoexcited platinum nanoparticles to the conduction band of TiO2 due to lowering the height of Schottky barrier at the interface.The Pt−Cu/TiO2 catalyst exhibited high rate of alcohol oxidation under sunlight irradiation compared to Pt/TiO2 composite.