Sol-gel SiO2/TiO2 bilayer films with self-cleaning and antireflection properties

We report here that a facile sol-gel dip-coating technique can be used to fabricate a SiO(2)/TiO(2) bilayer film with self-cleaning and antireflection properties. The bottom SiO(2) layer acts as an antireflection coating due to its lower refractive index; the top TiO(2) layer acts as a self-cleaning coating generated from its photocatalysis and photo-induced superhydrophilicity. The maximal transmittance Of SiO(2)/TiO(2) bilayer film at normally incident light can be reached 96.7%, independent of the high refractive index and coverage of TiO(2) nanoparticles. However, the photocatalytic activity of the bilayer film shows a close dependence on coverage of TiO(2) nanoparticles. After illuminated by ultraviolet light, the SiO(2)/TiO(2) bilayer films are superhydrophilic with water contact angle less than 2 degrees, which favors greatly the self-cleaning function of the films. (C) 2008 Elsevier B.V. All rights reserved.