Low-temperature treatment for preservation and separation of graphene dispersions

Graphene nanosheets prepared by liquid-phase exfoliation tend to aggregate easily and irreversibly in most solvents due to van der Waals forces and high surface energy. This article presents a facile, low-cost and novel approach for the preservation and separation of graphene dispersions by adjusting the temperature and solvent. Using IPA-water mixtures can realize green production of graphene nanosheets, and different physicochemical parameters are achievable by changing the proportion of components. Two valid methods for improving stability were discussed in depth: low-temperature storage as a liquid and as a solid. When graphene dispersions are stored in a liquid phase, agglomeration of nanosheets in mixed solvents can be effectively retarded by strong viscous resistance induced by low temperatures. Frozen powder prepared by liquid nitrogen maintains the nanosheets in a dispersed state and is suitable for long-term preservation in the solid phase in ordinary freezers. Furthermore, rapid separation of graphene nanosheets is a challenging problem that retards industrial production. Flocculation induced by slow freezing can accelerate solid–liquid separation, offering a novel approach to obtain easily dispersed powders. Various patterns could be printed on paper and poly(ethylene terephthalate) by a simple and low-cost screen printing technique using the graphene powder, providing a new platform for scalable, low-cost printing of electronics. Consequently, this scalable and simple strategy can be satisfactorily applied to the preservation and separation of graphene and is expected to extend to other nanomaterials, including MoS₂ and h-BN.