Nano Anatase TiO 2 Quasi-Core-Shell Homophase Junction Induced by a Ti 3+ Concentration Difference for Highly Efficient Hydrogen Evolution.

The fabrication of heterojunctions or homojunctions between semiconductors is a controllable strategy to facilitate charge separation in photocatalysis. The homophase junctions exhibit atomic-level contact for the fast-speed charge transfer via inducing the built-in electric fields. Herein, a new concept of TiO ₂ quasi-core-shell homophase junction induced by a Ti ³⁺ concentration difference for remarkably enhancing photocatalytic activity is proposed. Nano anatase TiO ₂ quasi-core-shell homophase junctions are constructed between the interior with high Ti ³⁺ concentration (quasi-core) and the surface with no detected Ti ³⁺ (quasi-shell). Diverse Ti ³⁺ concentration differences are obtained via regulating the mass ratio of the Ti source. The nano anatase TiO ₂ quasi-core-shell homophase junctions exhibit improved photocatalytic hydrogen evolution compared with commercial anatase nanoparticles. To be specific, the maximum hydrogen evolution rate of 50.02 mmol/h/g is 25.4 times superior to that of commercial anatase nanoparticles under solar illumination. Besides, the photocatalytic activity remains stable (H ₂ evolution rate of 49.21 mmol/h/g, activity loss of <2%) after five cycles of catalytic test. The promoted photocatalytic activities are ascribed to the constitution of a built-in electrical field between the quasi-shell and quasi-core induced by the band bending, which accelerates the spatial charge separation and suppresses the recombination of carriers. Moreover, the atomic-level contact at the homophase junction interface provides smooth channels for carrier transfer, resulting in more effective separation and transfer of photogenerated electrons and holes. The synthesis of nano anatase TiO ₂ quasi-core-shell homophase junctions provides new insights into the efficient separation and transfer of photogenerated carriers for photocatalytic applications.