Photocatalytic hydrogen production with non-stoichiometric pyrochlore bismuth titanate

• Pyrochlore bismuth titanate was synthesized by a sol–gel approach.
• By keeping the pyrochlore structure the Bi/Ti ratio was varied.
• The formed structural vacancies were carefully analyzed by Rietveld refinement.
• The photocatalytic activity was found to increase with the Bi/Ti ratio.
• Photocatalytic activity depends on the TiO distances and the TiOTi angles.

Pyrochlore bismuth titanate (Bi2−xTi0.75x)Ti2O7 was prepared by an aqueous sol–gel method and annealed at different temperatures. Non-stoichiometry was obtained by adjusting the Ti/Bi ratio during synthesis. Additionally the two bismuth titanate phases Bi4Ti3O12 and Bi2Ti4O11 were synthesized. The materials were characterized by X-ray diffraction and UV–vis reflectance spectroscopy. Photocatalytic hydrogen production was tested in the presence of methanol as sacrificial agent after loading the bismuth titanates with nanoparticles of platinum acting as co-catalysts. It was found that stoichiometric Bi2Ti2O7 being completely inactive could be turned into a good photocatalyst by increasing the Ti/Bi ratio to 1.50 corresponding to (Bi1.55Ti0.33)Ti2O7 still crystallizing in a pure pyrochlore phase. The increase in activity is supposed to derive from an optimization of the TiO6-octahedral geometry due to the generation of bismuth and oxygen vacancies in the lattice. If platinum is applied as co-catalyst on (Bi2−xTi0.75x)Ti2O7 samples, stability issues occur during photocatalysis, which are suppressed by coating the platinum particles with a Cr2O3 shell.

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