Template-free assembly of three-dimensional networks of graphene hollow spheres at the water/toluene interface

• A template-free approach for preparing three-dimensional graphene was developed.
• The three-dimensional network consists of micron-sized hollow spheres of graphene.
• The construction of graphene is based on the Pickering emulsions at the interface.
• The hollow spherical structure of graphene was well preserved after freeze-drying.
• The presence of polyvinyl alcohol is critical for the maintaining the structure.

HypothesisThe Pickering emulsion system, generated by amphiphilic graphene oxide (GO) sheets trapped between water/toluene liquid interfaces, can be directly used for template-free formation of three-dimensional (3D) structure of GO hollow spheres.ExperimentsThe method involves the formation of highly stable micron-sized Pickering emulsions via mild sonication of GO aqueous solution and toluene in the presence of polyvinyl alcohol (PVA), followed by direct freeze-drying of the mixture for preserving the unique 3D hollow spherical structures.FindingsThe 3D structure of interconnected GO hollow spheres, with a diameter in the range ∼2 to 10 μm, has been prepared. Transmission and scanning electron microscopy analyses confirmed the formation of the 3D structure directly from the Pickering emulsion system. The presence of PVA is critical in supporting the GO hollow spherical structures. Raman analysis confirmed the structural integrity of the GO in the 3D products.

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