"Photocatalysis is a potential tool for environmental and effluent water cleaning. Large band gap semiconductors, first of all TiO2, are commonly employed as photocatalysts. However, most of the photocatalytic materials possess band-gaps corresponding to the Ultra-Violet (UV) wavelengths (220-380 nm) and suffer from low efficiencies due to the high degree of recombination between the photogenerated charges carriers. The challenge is to develop a material with optical band gap in the visible wavelength of the sun’s spectrum (400 nm – 900 nm) and with a suitable flat band potential for efficient charge transfer across the interface. In addition, for many applications it is essential to use photocatalytically active materials in the form of thin films. The proposed work aims at developing a new thin film photocatalytic material to work at visible wavelengths of sun’s spectrum by the modification of TiO2. Two approaches will be followed: (i) nano-mixed phases of wide band gap metal oxides (like WO3 and CuO) and (ii) nano metal cluster (like e.g. Ag-, Cu-, W- clusters) embedded in a wide gap metal oxide as TiO2 is. Both approaches are aimed at influencing the photo-generated carriers and their transport. The nano mixed phases have altogether different band gaps, defect states and defect densities which will influence the electron – hole pair generation with visible wavelengths.
The fabrication of the coatings will be carried out making use of the plasma technology, and especially of sputtering. In fact, this is a very advantageous technique for the deposition of crystalline TiO2 thin films over a wide variety of substrates (e.g. glass, Si-wafer, metal) a low temperatures. Moreover, sputtering is also one of the most feasible methods for the deposition of metal ions and oxide nanoparticles over a thin film matrix, e.g. of TiO2, due to its versatility and the capability of controlling the phisycal properties of the particles by a proper choice of preparation parameters."
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