Layer-by-Layer TiO₂/WO₃ 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.

Enhanced visible-light-driven photocatalytic performance of mesoporous W-Ti-SBA-15 prepared through a facile hydrothermal route

“…Two intense peaks at 458.5 eV and 464.2 eV in Fig. 6B are relevant to the Ti 2p 3/2 -Ti 2p 1/2 spin-orbit components of Ti 4+ species in TiO 2 lattice [11,19]. The lack of binding-energy peaks corresponding to Ti 3+ species indicates the absence of surface defects [19].…”

“…Especially, it is a suitable candidate to fabricate composites with TiO 2 to create heterojunction structures that facilitate the transfer and separation of photoinduced electrons and holes and hereby inhibit the recombination of charge carriers [9][10][11]. Accordingly, band-gap shrinkage was observed in composites on account of the formation of heterojunction structures [12].…”

Accelerated self-cleaning by Cu promoted semiconductor binary-oxides under low intensity sunlight irradiation

“…Photocatalysis as a useful tool for the self-cleaning of glass, polymer thin films and textile fabric surfaces has recently been reported by Daoud [1][2][3][4], Kiwi [5][6][7][8], Hashimoto/Fujishima et al [9,10], Bahnemann [11][12][13], Radetic [14] and Pakkanen [15]. TiO 2 has been chosen as the standard photocatalyst used in the field of environmental photochemistry due to its stability, effective separation of charges under band-gap irradiation and availability of fairly pure samples.…”

“…There is nowadays a need to develop resistant photocatalysts presenting faster self-cleaning kinetics compared to TiO 2 and composite-TiO 2 surfaces which are too slow for many industrial applications [5][6][7][8][11][12][13]. The second area that needs improvement lies in the fact that most of the self-cleaning films are deposited from colloids on surfaces that are subsequently heated to diffuse and anneal the colloid into the surface at temperatures that fabrics and polymer films do not resist [5][6][7][8][9][10][11][12][13].…”

“…The second area that needs improvement lies in the fact that most of the self-cleaning films are deposited from colloids on surfaces that are subsequently heated to diffuse and anneal the colloid into the surface at temperatures that fabrics and polymer films do not resist [5][6][7][8][9][10][11][12][13]. The deposition/adhesion of this non-uniform low adhesive colloidal TiO 2 films are easily wiped out by finger or cloth since they are not mechanically stable.…”