Environmental applications. Heterogeneous photocatalysis attracted worldwide a growing interest and appeared in the middle of the 1980s, first to be promising for the purification of contaminated wastewater containing organic pollutants and for the removal of air contaminants. Since, the application of photocatalysis in the field of gaz phase treatment has raised a growing interest. Considered as a laboratory process for many years, it is now enjoying unprecedented development resulting from simultaneous efforts by research laboratories and industrials in the search for innovative solutions to the environmental treatment of liquid and gaseous effluents, and surfaces. Selected examples of gaz phase treatment and surface decontamination will be presented.

Energy applications. The direct conversion of solar energy though an energy carrier (fuel), storable and usable upon request, appears as an interesting alternative. Photocatalysis – through water dissociation (water-splitting)- is an innovative and promising way to produce pure hydrogen from renewable energy sources (light energy) .Some specific examples will be given and discussed in photoelectro- and photo- catalytic systems. Dye-sensitized solar cells (DSSCs) based on nanocrystalline titania (TiO₂) electrodes constitute a potentially alternative to traditional inorganic silicon based photovoltaics and have been studied extensively over the past two decades. Among different kinds of nanostructured TiO₂ semiconductors, vertically aligned TiO₂ nanotubes are studied because of their special electrical and optical properties as possible components for DSSCs devices.

Photocatalytic nanomaterials. Photocatalysis requires the use of semiconductor materials with suitable band gaps as catalysts, with energy being supplied by the direct absorption of light rather than by thermal heating as in conventional catalysis. Among the semiconductors used, TiO₂ is currently the most attractive and efficient, with a high photocatalytic efficiency due to its high quantum yield, stability toward photocorrosion and chemicals, insolubility in water, low toxicity, and low cost. Its band gap energy of 3.2 eV leads to photoexcitation requiring wavelengths less than ca. 385 nm, corresponding to a UV irradiance. This point is one of the main drawback in photocatalytic and photoconversion in the case of solar (mainly visible light) energy conversion. Different strategies to shift the TiO2 absorption range from UV to visible light (doping, co-doping, addition of metal NPs to induce plasmonic effects, …) will be presented

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