Accelerating directional charge separation via built-in interfacial electric fields originating from work-function differences

In this work, a hierarchical porous SnS 2 /rGO/TiO 2 hollow sphere heterojunction that allows highly-efficient light utilization and shortening distance of charge transformation is rationally designed and synthesized. More importantly, an rGO interlayer is successfully embedded between the TiO 2 hollow sphere shells and outermost SnS 2 nanosheets. This interlayer functions as a bridge to connect the two light-harvesting semiconductors and acts as a hole injection layer in the tandem heterojunction. The induced built-in electric fields on both sides of the interface precisely regulate the spatial separation and directional migration of the photo-generated holes from the light-harvesting semiconductor to the rGO hole injection interlayer. These synergistic effects greatly prolong the lifetime of the photo-induced charge carriers. The optimized tandem heterojunction with a 2 wt% rGO loading demonstrate enhanced visible-light-driven photocatalytic activity for Rhodamine B (RhB) dye degradation (removal rate: 97.3%) and Cr(VI) reduction (removal rate: 97.09%). This work reveals a new strategy for the rational design and assembly of hollow-structured photocatalytic materials with spatially separated reduction and oxidation surfaces to achieve excellent photocatalytic performance. The built-in interfacial electric fields originating from differences in the work-functions facilitate the directional migration of photo-induced holes from the VB of SnS 2 to the rGO hole injection interlayer, leading to efficient charge separation and high photocatalytic activity.