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

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 10wt%). 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.