Figure 1. Synthesis of SrTiOmeso crystals by Topotactic Epitaxial Growth
Using the spaces in mesocrystals, SrTiO3 mesocrystals are synthesized from TiO2 mesocrystals using a one-step hydrothermal process.

Figure 2: The structure of SrTiO3 mesocrystals
(a)Electron microscopy image of SrTiO3 mesocrystals obtained during a 24-hour hydrothermal reaction. The nanocrystals are arranged facing the same direction.
(b)Electron microscopy image of SrTiO3 mesocrystals after 48-hours of hydrothermal reaction. The surface nanocrystals have grown in size. We can see that regardless of size and position, the nanocrystals forming the mesocrystal face the same direction.
Figure 3: Water-splitting reaction under ultraviolet light
Compared to the SrTiO3 nanocrystals (black) which are mostly the same structure and size, the SrTiO3 mesocrystals (red) demonstrate a high water-splitting efficiency. Mixed-oxide of rhodium and chromium was used as the co-catalyst.
Figure 4: SrTiO3 mesocrystal light emission
(a)Light emission from SrTiO3 mesocrystals obtained in a 24-hour hydrothermal reaction. A weak light is seen equally throughout apart from the crystal edges.
(b)Light emission from SrTiO3 mesocrystals obtained in a 48-hour hydrothermal reaction. They shine strongly due to the electrons gathered around the large crystals on the surface. The light emitted has a wavelength of 405nm.

Figure 5: Hydrogen synthesis in SrTiO3 mesocrystals
(a)The electrons produced under ultraviolet light move between the nanoparticles in the mesocrystal, gather around the comparatively large nanocrystals exposed on the surface, and reduce the hydrogen ions.
(b)In the nanocrystals that aggregated with a disordered structure, most of the electrons and electron holes recombine and disappear, so the amount of hydrogen produced is low.
Paper Information
Topotactic Epitaxy of SrTiO3 Mesocrystal Superstructures with Anisotropic Construction for Efficient Overall Water Splitting

Peng Zhang, Tomoya Ochi, Mamoru Fujitsuka, Yasuhiro Kobori, Tetsuro Majima, Takashi Tachikawa

Angewandte Chemie International Edition
Related Information

(Molecular Photoscience Research Center)