Self-assembled TiO2 agglomerates hybridized with reduced-graphene oxide: A high-performance hybrid photocatalyst for solar energy conversion

Abstract

Spherical TiO2 agglomerates incorporated with reduced-graphene oxide (rGO) sheets were fabricated using aerosol assisted self-assembly. Compared to that of conventional graphene–TiO2 composites, the new hybrid geometry of the self-assembled agglomeration of TiO2 and rGO enabled a porous structure, a more efficient charge separation through interconnected TiO2 nanoparticles and rGO, and improved the contact between TiO2 and rGO to maximize the role of rGO as an electron reservoir. The as-prepared rGO–TiO2 composites were characterized with a diverse range of analytical techniques, and their photocatalytic activity was tested in terms of H2 production and gaseous CH3CHO degradation. The incorporation of the rGO sheets into the TiO2 agglomerates promoted the photocatalytic H2 production and CH3CHO oxidation; our results showed that the performance of our systems is directly proportional to the content of rGO (when added up to 10 wt%). This finding confirmed that rGO, acting as an electron collector and mediator, can facilitate charge-pair separation; only a small light-shielding effect by rGO was observed. Furthermore, open-circuit potential decay measurements revealed that the presence of rGO in the agglomerated TiO2 can significantly suppress charge recombination; this further confirmed the role of rGO as an effective electron conduit. The new geometry of the rGO–TiO2 composite proposed in this work shows several advantages compared to various types of graphene–TiO2 composites previously reported, such as the stronger electronic coupling between rGO sheets and TiO2, minimized light-shielding effect by rGO (even when a relatively large amount of rGO is used), and facile scale-up for mass production. Therefore, our rGO–TiO2 composite can be considered as a promising hybrid photocatalyst for solar energy conversion.