Coupled Heterojunction Sn2Ta2O7@SnO2: Cooperative Promotion of Effective Electron Hole Separation and Superior Visible-light Absorption

In this work, a novel heterostructure integrated by two wide-band gap semiconductors, SnO2 and Sn2Ta2O7, is successfully prepared via a hydrothermal approach. Hollow Sn(2)Ta(2)O7 spheres were first formed, and small SnO2 particles were then well-dispersed onto the outside surface of the spheres, forming a p-n heterostructure. This heterostructure exhibits a higher potential edge that yielded enhanced photoredox ability. Further, the heterostructure is of Z-type with a consistent internal electric field direction, which effectively separates the photogenerated electron-hole pairs. Although both component semiconductors do not absorb visible light, the resulted p-n heterostructure is surprisingly observed to show an outstanding photocatalytic performance under visible light illumination. Such a visible light response is concluded to be the consequence of the impurity band formed by Sn2+ doped in SnO2 and Sn4+ in Sn2Ta2O7 via in situ redox. The existence of coupled Sn2+ and Sn4+ ions in p-n heterostructure is responsible for the absence of defects and the regenerated catalytic activities. The findings reported here may provide an approach to fabricate the new types of photocatalysts with a synergetic promotion for visible light absorption and sustained photocatalytic activities by coupling different wide-band semiconductors.