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Fig. 6 SEM images of anatase single crystals (a) and TiO
2
microspheres composed of
nanosheets with (001) facets (d), inset is the magnified surface of a microsphere. b The size
distribution of anatase single crystals in (a). c The degree of truncation (B/A, A and B denote
lengths of the side of the bipyramid and the side of the square {001} 'truncation' facets,
respectively) of anatase single crystals in (a). e The corresponding photodegradation of methyl
orange (MO) of (d). (Reprinted with permission from Ref. a-c [
130
], d, e [
134
]. Copyright
Nature Publishing Group and Wiley-VCH)
resulting TiO
2
nanosheets. Due to the high percentage of reactive (001) facets, the
synthesized NSs loaded with 1 wt% Pt from photochemical reduction of water in
the presence of methanol as a scavenger showed a H
2
evolution rate of
7381 lmol h
-1
g
-1
under UV-vis light [
22
]. Xiang et al. reported that the flower-
like TiO
2
microsphere films with about 30 % exposed (001) facets were directly
synthesized on the Ti foil in a dilute aqueous HF solution by a simple one-pot
hydrothermal process and exhibited tunable photocatalytic selectivity toward
decomposition of azo dyes by modifying the surface of TiO
2
microspheres as well as
by varying the degree of etching of (001) facets [
133
]. Zhang et al. synthesized
anatase TiO
2
microspheres with exposed mirror-like plane (001) crystalline facets
via a facile low-temperature hydrothermal method. The improved light harvesting
efficiency, attributed to the superior light scattering ability of the TiO
2
microsphere
film, gave such microsphere photoanodes better overall light conversion efficiency
of 7.91 % in DSSCs, which is 1.2 times the overall efficiency (6.73 %) obtained
from the P25 photoanode [
135
].
Most of the hydrothermal syntheses reported so far have been carried out in the
acidic environment with the addition of concentrated hydrofluoric acid, which is
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