Diffusion driven layer-by-layer assembly of graphene oxide nanosheets into porous three-dimensional macrostructures.

Despite recent progress in preparing numerous types of nanosheets, it remains a difficult challenge to assemble the tiny building blocks into functional macroscale architectures suitable for practical applications. Here we introduce a diffusion driven layer-by-layer assembly process and demonstrate its application for the construction of graphene oxide sheets into various three-dimensional structures. This process involves complexation of the negatively charged graphene oxide sheets and positively charged branched polyethylenimine at a given interface. We find that the diffusion of branched polyethylenimine molecules allows the complex to continuously grow into foam-like frameworks with tunable porosities. Furthermore, the assembly process is quite robust and can be utilized in various configurations such as to create free-standing architectures with tailored shapes or patterned films on a substrate. With such useful features, we believe that this technique may serve as a valuable tool for the assembly of nanomaterials.