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Solvent-Exfoliated Graphene at Extremely High Concentration

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journal contribution
posted on 2011-08-02, 00:00 authored by Umar Khan, Harshit Porwal, Arlene O’Neill, Khalid Nawaz, Peter May, Jonathan N. Coleman
We describe three related methods to disperse graphene in solvents with concentrations from 2 to 63 mg/mL. Simply sonicating graphite in N-methyl-2-pyrrolidinone, followed by centrifugation, gives dispersed graphene at concentrations of up to 2 mg/mL. Filtration of a sonicated but uncentrifuged dispersion gives a partially exfoliated powder that can be redispersed at concentrations of up to 20 mg/mL. However, this process can be significantly improved by removing any unexfolaited graphite from the starting dispersion by centrifugation. The centrifuged dispersion can be filtered to give a powder of exfoliated few-layer graphene. This powder can be redispersed at concentrations of at least 63 mg/mL. The dispersed flakes are ∼1 μm long and ∼3 to 4 layers thick on average. Although some sedimentation occurs, ∼26–28 mg/mL of the dispersed graphene appears to be indefinitely stable.