Shibuya et al.
[26] reported the preparation of well-ordered WO3 nanotrees which are
composed of WO3 nanotrucks and WO3 nanobranches on tungsten
plate substrate. Similarly,Zhang et al. [27] synthesized hexagonal structured
WO3 films with tree-like morphology on tungsten foils. The film
thickness and the crystal structure of the film can be controlled by changing
the duration and annealing temperature, respectively.However, the
opacity of the tungsten plate substrate limits its photoelectrochemical
properties. Recently, Su et al. [28] synthesized hexagonal WO3 nanowire
arrays on fluorine doped tin oxide (FTO) substrates by hydrothermal
method. They demonstrated that nanowire or nanoflake arrays are selectively
deposited by adjusting the composition of precursor solutions.
Zhang et al. [29] obtained hexagonal WO3 nanowire arrays and microbricks
on FTO-coated glass with the addition of ammonium sulfate. To
date, controlling the orientation, morphology, growth density and diameter
distribution of well-alignedWO3 nanorod/nanowire arrays by hydrothermal
approach is still the most challenging issues. However, detailed
studies are inadequate up to now. So, it is necessary to explore systematically
the effects of preparing conditions on the growth of well-aligned
WNRs on transparent substrates.