Functional porous graphene materials by pickering emulsion templating: From emulsion stabilization to structural design and fabrication

Graphene oxide (GO) is a water-soluble, oxidized derivative of graphene. It is a precursor to obtain porous graphene materials (PGMs), allowing for the easy fabrication, functionalization, and restoration of graphene properties through reduction into reduced graphene oxide (rGO). Due to the hydrophilic oxygen-containing groups and the hydrophobic sp2 domains, GO flakes are amphiphilic. Thus, GO can stabilize Pickering emulsions where GO-stabilized droplets are dispersed in another immiscible continuous liquid phase. By tuning GO Pickering emulsion templates and removing the liquid phases, PGMs with variable architecture, such as different pore size distribution, pore shape, pore volume, and interconnectivity, can be achieved. Furthermore, both the composition and the distribution of functional additives within PGMs can be tuned via emulsion templating. Emulsion-templated PGMs have high surface area, low mass density, tunable mechanical properties and permeability, and many sites for functionalization, which make them promising materials for a variety of applications, e.g., energy storage, biomedical engineering, sensing, absorption, and separation. This paper reviews the factors affecting GO amphiphilicity, the assembly of GO flakes at emulsion interfaces, the resulting emulsion stabilization by the flakes, and the treatments, such as drying and reduction of GO emulsions, that can be used to obtain PGMs with desirable composition and architecture using Pickering emulsion templating. The latest applications of PGMs are discussed, and research challenges and future opportunities are also proposed.