Surface charge promotes the synthesis of large, flat structured graphene–(CdS nanowire)–TiO2nanocomposites as versatile visible light photocatalysts

Abstract

Ternary hybrids of (reduced graphene oxide)–(CdS nanowire)–TiO2 nanocomposites (CTG) featuring a large two-dimensional (2D) flat structure have been successfully synthesized via a simple surface charge promoted self-assembly method. Compared to the curly (reduced graphene oxide)–(CdS nanowire) nanocomposites (CG) synthesized by a similar approach, CTG possesses a large 2D flat structure, which not only provides high optical transparency and a large surface area but also facilitates the migration of photogenerated electrons. This large 2D flat structure of CTG leads to increased optical absorption of visible light and increased electrical conductivity as compared to the curly CG, which is attributed to the fact that the large 2D flat structure of reduced graphene oxide (RGO) in CTG provides more efficient contact between light and the RGO sheets and facilitates the transfer of charge carriers. Experimental evidence has proven that negatively charged TiO2 nanoparticles (NPs) both on the surfaces of the CdS nanowires (CdS NWs) and on the RGO sheets can prevent the RGO sheets from becoming curly or aggregated as a result of electrostatic repulsion, thereby forming the large 2D flat structure of CTG. In addition to using RGO as an electron “sink” to improve the transfer of photogenerated electron–hole pairs (EHPs) from CdS NWs, the TiO2 NPs on CdS NWs are able to further boost the transfer of charge carriers in the ternary CTG system due to the suitable energy band match between TiO2 and CdS. Such efficient, spatially separated charge carriers make CTG a versatile visible light photocatalyst for photo-redox processes. This work provides a new, simple strategy to construct these large 2D flat structured RGO-based multi-component composites by using the surface charge properties of materials to efficiently utilize their respective unique electronic properties toward diverse photo-redox processes in both energy conversion and environmental purification.