Designing of a spatially separated hetero-junction pseudobrookite (Fe₂TiO₅-TiO₂) yolk-shell hollow spheres as efficient photocatalyst for water oxidation reaction

For the first time, controlled pseudobrookite phase as the yolk and titanium oxide as the shell of hollow spheres were synthesized for the photocatalytic water oxidation. Simple and facile sacrificial hard template strategy was utilized. Firstly, the distribution of TiO₂ in the hollow spheres was controlled by loading aqueous solution of 2, 3, and 5 mol/L TiCl₄ precursor respectively onto carbonaceous template followed by annealing. To prove the Fe³⁺ ions radial penetration into the hydrophobic core of carbonaceous template, we optimized the ethanol to water ratio. The Fe₂TiO₅-TiO₂ yolk-shell hollow spheres exhibited high oxygen evolution reaction (OER) rate up to 148 μmol g⁻¹ h⁻¹ under UV–vis light. This was attributed to the better light harvesting due to the geometry of hollow sphere; charge separation by a thin shell-yolk hetero-junction, a void cavity to access reaction solvent to reactive sites and the hetero-junction of Fe-O-Ti in the hollow structure. These findings suggest that our designed Fe₂TiO₅-TiO₂ yolk-shell hollow spheres are beneficial for the photocatalytic water oxidation.