Hydrothermal synthesis of WO3 films on the TiO2 substrates and their photochromic properties

Tungsten oxide (WO3) films have been prepared on the synthesized TiO2 substrates from a sodium tungsten precursor via a hydrothermal method. X-ray diffraction, scanning electron microscopy and transmission electron microscopy analyses were used to investigate the effect of precursor concentrations on the structures and morphologies of the films. Ordered WO3 films were successfully synthesized on the as-grown TiO2 substrates. With the concentrations increasing from 0.001 M to 0.024 M, the morphologies of the films changed from multi-layer laminated structure to ladder-shaped lamellar structure finally columnar structure. The results also showed that with an increase in precursor concentration, the observed absorptions at 365 nm of the films increased until precursor concentration of 0.016 M, and then decreased with higher concentration. The film obtained with precursor concentration of 0.016 M on the TiO2 substrate had the best photochromic properties.