Semiconductor preparative chemistry has been developed in order to produce nanostructured dispersions  and colloids of titanium dioxide. The materials properties were efficiently, tuned in order to optimize their interaction with light and were applied for photocatalytic environmental cleaning. The colloids (particles with d=10-50 nm) have been used for deposition as nanocrystalline, high surface areas, titania thin films of thickness of 0.5-10 µm. For the preparation of TiO2 thin films, doctor blade sol-gel processes were employed. The film surface parameters  were examined together with a theoretical analysis and data treatment by means of fractal geometry. To increase the photocatalytic efficiency, deposition of metallic species (such as Ag, Au) on the titania was performed. The immobilized photocatalysts are successfully applied in the photodecomposition of organic pollutants, azo-dyes and pesticides. The obtained results are discussed in the light of recent developments in photocatalysis, including fundamental knowledge and practical applications.