title: Layer-by-layer TiO(2)/WO(3) thin films as efficient photocatalytic self-cleaning surfaces.
abstract: New TiO2/WO3 films were produced by the layer-by-layer (LbL) technique and successfully applied as self-cleaning photocatalytic surfaces. The films were deposited on fluorine doped tin oxide (FTO) glass substrates from the respective metal oxide nanoparticles obtained by the sol-gel method. Thirty alternative immersions in pH = 2 TiO2 and pH = 10 WO3 sols resulted in ca. 400 nm thick films that exhibited a W(VI)/Ti(IV) molar ratio of 0.5, as determined by X-ray photoelectron spectroscopy. Scanning electron microscopy, along with atomic force images, showed that the resulting layers are constituted by aggregates of very small nanoparticles (<20 nm) and exhibited nanoporous and homogeneous morphology. The electronic and optical properties of the films were investigated by UV-vis spectrophotometry and ultraviolet photoelectron spectroscopy. The films behave as nanoscale heterojunctions, and the presence of WO3 nanoparticles caused a decrease in the optical band gap of the bilayers compared to that of pure LbL TiO2 films. The TiO2/WO3 thin films exhibited high hydrophilicity, which is enhanced after exposition to UV light, and they can efficiently oxidize gaseous acetaldehyde under UV(A) irradiation. Photonic efficiencies of ξ = 1.5% were determined for films constituted by 30 TiO2/WO3 bilayers in the presence of 1 ppm of acetaldehyde, which are ∼2 times higher than those observed for pure LbL TiO2 films. Therefore, these films can act as efficient and cost-effective layers for self-cleaning, antifogging applications.
authors.affiliation: Instituto de Química, Universidade Federal de Uberlandia , Uberlândia, Minas Gerais 38400-902 Brazil.
authors.forename: Antonio Otavio T
authors.initials: AO
authors.lastname: Patrocinio
authors.forename: Leonardo F
authors.initials: LF
authors.lastname: Paula
authors.forename: Roberto M
authors.initials: RM
authors.lastname: Paniago
authors.forename: Janna
authors.initials: J
authors.lastname: Freitag
authors.forename: Detlef W
authors.initials: DW
authors.lastname: Bahnemann
keywords: TiO2/WO3 films; layer-by-layer; metal oxides films; photocatalysis; self-cleaning