For the first time, anatase TiO2 twin crystals have
been synthesized by a simple hydrothermal method. The samples are
characterized using X-ray diffraction, scanning electron microscopy,
high-resolution transmission electron microscopy, selected area electron
diffraction, ultraviolet–visible diffused reflectance spectra,
and nitrogen sorption isotherms. It is found that a prolonged reaction
time significantly contributes to the structure evolution and that
twin crystals form via the oriented attachment (OA)- and Ostwald ripening
(OR)-controlled secondary growth mechanism. Remarkably, the photoactivity
of TiO2 twin crystals is 2.57 and 8.74 times higher than
that of single-crystalline anatase TiO2 nanosheets and
rutile TiO2, respectively. This has been mainly ascribed
to the unique twin crystal structure. This work is a big step toward
further improvement of the photocatalytic properties of of TiO2.
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