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

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. alpha-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 alpha-Fe2O3. The photocatalytic performance of TiO2 would be inhibited when compositing with alpha-Fe2O3 due to the alpha-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 alpha-Fe2O3 in a core-shell nanoparticle for enhancing visible-light photocatalysis. Heterostructured TiO2@alpha-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 alpha-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 alpha-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@alpha-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.