Effect of Cu(2)O Substrate on Photoinduced Hydrophilicity of TiO(2) and ZnO Nanocoatings

The effect of a Cu(2)O substrate on the photoinduced alteration of the hydrophilicity of TiO(2) and ZnO surfaces was studied. It was demonstrated that the formation of heterostructures Cu(2)O/TiO(2) and Cu(2)O/ZnO strongly changed the direction of the photoinduced alteration of surface hydrophilicity: while both TiO(2) and ZnO demonstrate surface transition to superhydrophilic state under UV irradiation and no significant alteration of the surface hydrophilicity under visible light irradiation, the formation of Cu(2)O/TiO(2) and Cu(2)O/ZnO heterostructures resulted in photoinduced decay of the surface hydrophilicity caused by both UV and visible light irradiation. All observed photoinduced changes of the surface hydrophilicity were compared and analyzed in terms of photoinduced alteration of the surface free energy and its polar and dispersive components. Alteration of the photoinduced hydrophilic behavior of TiO(2) and ZnO surfaces caused by formation of the corresponding heterostructures with Cu(2)O are explained within the mechanism of electron transfer and increasing of the electron concentration on the TiO(2) and ZnO surfaces.