Single crystalline orthorhombic phase tungsten trioxide monohydrate (O-WO 3 •H 2 O, space group: Pmnb) nanoplates with a clear morphology and uniform size distribution have been synthesized by the hydrothermal method and fabricated on the surface of fluorine doped tin oxide (FTO) coated glass substrates with selective exposure of the crystal facet by the finger rubbing method. The rubbing method can easily arrange the O-WO 3 •H 2 O nanoplates along the (020) facet on the FTO substrate. The O-WO 3 •H 2 O nanoplate can be converted to monoclinic phase WO 3 (γ-WO 3 , space group: P21/n) with dominant crystal facet of (002) without destroying the plate structure. Crystal morphologies, structures, and components of the powders and films have been determined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman, X-ray photoelectron spectroscopy, etc. The band gap energies of the O-WO 3 •H 2 O and γ-WO 3 nanoplates were determined as ca. 2.26 and 2.49 eV, respectively. Photoelectrochemical properties of the films with (002) dominant crystal facet have also been checked for discussion of further application in water oxidation. The advantage of (002) facet dominant film was investigated by comparing to one spin-coated γ-WO 3 thin film with the same thickness via photoelectrochemical characterizations such as photocurrent, incident photon to current efficiency, and electrochemical impedance spectroscopy.
HIGHLIGHT
This journal isThe photocatalysis, chromism, and sensing capabilities of nanostructured tungsten oxides, such as tungsten trioxide (WO 3 ), its suboxides (WO x , 0
The capping agent plays a critical function in anisotropic
crystal
growth to induce polyhedral morphology of a nanocrystal. Uniform and
single-crystalline α-Fe2O3 polyhedral
nanoparticles in the hexagonal single crystal system named truncated
hexagonal bipyramid for the first time were successfully synthesized
by a facile one-step hydrothermal method with the aid of carboxymethyl
cellulose and hydrazine molecules. The appearance and crystal structure
of these iron oxide nanoparticles were characterized in detail by
physicochemical methods. The results show that the as-synthesized
α-Fe2O3 particles are bound by 12 same-side
crystalline facets {101} and two other same facets {001} at the tops.
These obtained iron oxide particles belong to a pure hematite phase,
and the particle size is around 400 nm. The optical property of the
as-synthesized product was analyzed, and the determined indirect band
gap value E
g is 2.08 eV. The magnetic
property studies of truncated hexagonal bipyramid hematite particles
have shown that this kind of α-Fe2O3 possess
a weak ferromagnetism under the T
M, and
the saturation points do not reach up to the maximum applied magnetic
field. Role of the reactants was discussed and investigated systematically
in the work. Furthermore, a schematic illustration for the probable
formation of this α-Fe2O3 morphology in
whole of the synthetic process was also proposed.
Photocurrents of different structures of α-Fe2O3 photoanodes, prepared by calcination of electrodeposited α-Fe films, are enhanced by Co–Pi co-catalyst.
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