Synthesis, Characterization, and Light-Induced Spatial Charge Separation in Janus Graphene Oxide

Janus graphene oxides and Janus graphenes are materials with different functionalization on opposite faces of atomically thin carbon sheets. Owing to their monolayer nature, these Janus sheets show unique properties where the functionalization on one face can modulate the properties on the opposite face. However, few general procedures to create and characterize Janus graphene oxides or Janus graphenes have been reported, and as a consequence these intriguing materials remain largely unexplored. Here we report a general synthesis of Janus graphene oxide, where particles are deposited in situ from molecular precursors on opposite faces of monolayer graphene oxide (GO). We used a silicon wafer and a polymer film to successively expose and protect alternate graphene oxide faces for asymmetric deposition of Pt and TiO2 nanocrystals, thus producing Janus graphene oxide composites (Pt|GO|TiO2). We used electron microscopy of Janus graphene oxide cross-sections to conclusively show that Pt and TiO2 particles are placed on opposite faces of monolayer sheets. Furthermore, we demonstrate the utility of Janus graphene oxide asymmetric chemistry by showing that photogenerated electrons and holes accumulate on opposite faces of the atomically thin sheets. The general nature of the synthesis and characterization protocols enables both production and asymmetry verification of a wide range of Janus graphene oxides and therefore provides a general approach for spatial charge separation across two-dimensional structures and other potential applications.