the principle of photocatalysis is abundantly explained in the literature, after the illumination of semiconductor, generally oxides, with an energy greater than or equal to that of the forbidden band "Band-gap" an electron passes from the valence band (BV) towards the conduction band (BC) thus creating the electron / hole couple. The electron (e-BC) and the hole (h + BV) thus formed will be able to react with the molecules adsorbed on the surface of the semiconductor to give radical species: these are redox reactions governed by the redox potentials of adsorbed reagents and by the position of the valence and conduction bands of the semiconductor