Enhanced photocatalytic hydrogen production with synergistic two-phase anatase/brookite TiO₂ nanostructures

Highly crystalline pure brookite and two-phase anatase/brookite TiO ₂ nanostructures were synthesized via a simple hydrothermal method with titanium sulfide as the precursors in sodium hydroxide solutions. The control of the phase composition has been demonstrated via solution concentration and reaction time, and the phase transformation mechanism has been elucidated. Photocatalytic activities of the as-synthesized two-phase anatase/brookite TiO₂, pure anatase nanoparticles, and pure brookite nanoplates were appraised via photocatalytic hydrogen evolution in aqueous methanol solution. Results have shown that the photocatalytic activity is higher for the two-phase anatase/brookite TiO₂ and brookite nanoplates as compared to pure anatase nanoparticles despite the lower surface areas of the two-phase anatase/brookite TiO₂ and brookite nanoplates. From the Mott-Schottky analysis, brookite phase is shown to have a more cathodic conduction band edge potential than anatase phase, which leads to more energetically favorable hydrogen reduction. Moreover, femtosecond transient absorption spectroscopy measurements suggests that the photoexcited electrons transfer from brookite to anatase phase - leading to further enhancement of the photocatalytic activity. In comparison with the highly active two-phase commercial benchmark P25, our synthesized two-phase anatase/brookite TiO ₂ is 220% more active when measured by the H₂ yield per unit area of the photocatalyst surface.