Three-dimensional ruthenium-doped TiO₂ sea urchins for enhanced visible-light-responsive H₂ production

Three-dimensional (3D) monodispersed sea urchin-like Ru-doped rutile TiO₂ hierarchical architectures composed of radially aligned, densely-packed TiO₂ nanorods have been successfully synthesized via an acid-hydrothermal method at low temperature without the assistance of any structure-directing agent and post annealing treatment. The addition of a minuscule concentration of ruthenium dopants remarkably catalyzes the formation of the 3D urchin structure and drives the enhanced photocatalytic H₂ production under visible light irradiation, not possible on undoped and bulk rutile TiO₂. Increasing ruthenium doping dosage not only increases the surface area up to 166 m² g^-1 but also induces enhanced photoresponse in the regime of visible and near infrared light. The doping introduces defect impurity levels, i.e. oxygen vacancy and under-coordinated Ti³⁺, significantly below the conduction band of TiO₂, and ruthenium species act as electron donors/acceptors that accelerate the photogenerated hole and electron transfer and efficiently suppress the rapid charge recombination, therefore improving the visible-light-driven activity.