Matching energy levels between TiO2 and α-Fe2O3 in a core–shell nanoparticle for visible-light photocatalysis

Abstract

Coupling TiO₂ with other semiconductors is a route to extend the optical response range of TiO₂ and to improve the efficiency of its photon quantum. α-Fe₂O₃ seems compatible with TiO₂ and possesses a high solar-light-harvesting capability that is fifteen times as large as that of TiO₂. However, there is an energy level mismatch between TiO₂ and α-Fe₂O₃. The photocatalytic performance of TiO₂ would be inhibited when compositing with α-Fe₂O₃ due to the α-Fe₂O₃-induced photo-generated carriers trapping and dissipation. The composite acts like a one-way valve, in which photo-generated carriers flow from a thick pipe to a thin one and then jam up. Herein, we achieved the goal of matching the energy levels between TiO₂ and α-Fe₂O₃ in a core–shell nanoparticle for enhancing visible-light photocatalysis. Heterostructured TiO₂@α-Fe₂O₃ core–shell nanoparticles were fabricated by the long-pulsed laser ablation of a titanium target in water followed by a hydrothermal reaction. A well-matched interface between TiO₂ and α-Fe₂O₃ was observed, which promoted photo-generated electrons and holes migration and separation. The energy band of the TiO₂ nanoparticle was demonstrated to be matched with that of α-Fe₂O₃, resulting from the upward shift of its valence band due to the abundant oxygen vacancies and bridging hydroxyls on its surface. In this situation, the “blocked pipe” seems to be dredged effectively and the visible-light photocatalytic methyl orange dyes degradation performance of the TiO₂@α-Fe₂O₃ nanoparticles is improved by a factor of two over that of the as-synthesized TiO₂ nanoparticles. These findings provide new insights into TiO₂ nanostructure photocatalysts and energy band engineering for visible-light photocatalysis.