The development of highly crystalline single-phase Bi20TiO32 nanoparticles for light driven oxygen evolution

• Visible light responsive and pure phase Bi20TiO32 has been successfully synthesized.
• Chelating agent and precursors have an effect on the material properties.
• The grain size of Bi20TiO32 depends on the ratio of citric acid to metal ions.
• Photocatalytic activity of Bi20TiO32 for O2 evolution can be enhanced by co-catalysts.
• The as-prepared Bi20TiO32 sample shows excellent stability during oxygen evolution.

The oxygen-producing photocatalysts play a critical role in the development of the artificial Z-scheme photocatalysis. Bismuth titanates have various complex forms, among which Bi20TiO32 could be an ideal oxygen evolution photocatalyst, but one has been suffering from its metastable structure and the complicate preparation. Herein, pure phase Bi20TiO32 samples were successfully synthesized by a simple sol–gel method followed by calcination of precursors. The effects of chelating agent, source of Bi and Ti precursor's composition have been studied. By combining bismuth nitrate, titanium isopropoxide, and citric acid, highly crystalline Bi20TiO32 was obtained after calcination since citric acid helps the formation of a stable complex in the sol–gel preparation with slow hydrolysis reactions due to highly steric hindrance in titanium isopropoxide. The effect of citric acid to metal ion ratio in this synthesis has been studied and optimized. It was found that only calcinations at 375 °C produced a pure phase while others did not. Here we first reported that pure Bi20TiO32 with high crystallinity was obtained with 1:1 ratio of citric acid to metal ions and it showed the highest photocatalytic activity of oxygen evolution under the illumination. The effects of grain size and co-catalyst on Bi20TiO32 photocatalytic activity of the as-prepared samples have been studied. More generally, it suggests the incorporation of bismuth into a simple oxide of wide band gap via the simple sol–gel method as a strategy to design photocatalysts with excellent properties.

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