Photocatalytic composite thin films with controlled optical properties based on TiO2, WO3 and rGO

Abstract

The work investigates the self-cleaning and optical properties of composite thin films based on titanium dioxide (TiO2), tungsten oxide (WO3) and reduced graphene oxide (rGO) sprayed on glass substrates, using dispersions of sol-gel powders. Two sets of films were obtained, using different processing parameters for deposition. The thin films in the first set (Route 1) are obtained through layer-by-layer deposition of TiO2-rGO and WO3-rGO coatings, varying their order in the composite. The second set (Route 2) contains one-batch deposited films from a mixed TiO2-WO3-rGO powder. The coatings are uniform and continuous, with several aggregates at the surface. All films are photoactive under simulated solar radiation at low irradiance value (34 W/m2) in phenol (ph) and methylene blue (MB) removal from low concentrated solutions (10 ppm). The higher photocatalytic efficiencies recorded during the MB removal (28%) compared to ph (16%) may be the result of the photocatalyst dye sensitization. The improved adsorption of both pollutants on the one-batch films is directly correlated with their wetting properties (water contact angle of ∼11°). Transmittance values higher than 80% and reflectance lower than 15% in the UV–VIS region for all films recommends them for deposition on glazing, as there is little light absorption or scattering. Overall, the Route 2 (one-batch) samples exhibited lower water contact angles (11° compared to 18–20° for Route1) and higher photocatalytic efficiency in both methylene blue (29% compared to ∼20%) and phenol (17% compared to ∼10%) removal. Therefore, they are better suited as self-cleaning layers/coatings on glazing compared to the layer-by-layer deposited films.