What if the Electrical Conductivity of Graphene Is Significantly Deteriorated for the Graphene-Semiconductor Composite-Based Photocatalysis?

Abstract

The extraordinary electrical conductivity of graphene has been widely regarded as the bible in literature to explain the activity enhancement of graphene-semiconductor composite photocatalysts. However, from the viewpoint of an entire composite-based artificial photosynthetic system, the significant matter of photocatalytic performance of graphene-semiconductor composite system is not just a simple and only issue of excellent electrical conductivity of graphene. Herein, the intentional design of melamine resin monomers functionalized three-dimensional (3D) graphene (donated as MRGO) with significantly deteriorated electrical conductivity enables us to independently focus on studying the geometry effect of MRGO on the photocatalytic performance of graphene-semiconductor composite. By coupling semiconductor CdS with graphene, including MRGO and reduced graphene oxide (RGO), it was found that the CdS-MRGO composites exhibit much higher visible light photoactivity than CdS-RGO composites although the electrical conductivity of MRGO is remarkably much lower than that of RGO. The comparison characterizations evidence that such photoactivity enhancement is predominantly attributed to the restacking-inhibited 3D architectural morphology of MRGO, by which the synergistic effects of boosted separation and transportation of photogenerated charge carriers and increased adsorption capacity can be achieved. Our work highlights that the significant matter of photocatalytic performance of graphene-semiconductor composite is not a simple issue on how to harness the electrical conductivity of graphene but the rational ensemble design of graphene-semiconductor composite, which includes the integrative optimization of geometrical and electrical factors of individual component and the interface composition.