High yield production of graphene by liquid phase exfoliation of graphite

TL;DR

Graphene dispersions with concentrations up to approximately 0.01 mg ml(-1), produced by dispersion and exfoliation of graphite in organic solvents such as N-methyl-pyrrolidone are demonstrated.

Abstract

Graphene is at the centre of nanotechnology research. In order to fully exploit its outstanding properties, a mass production method is necessary. Two main routes are possible: large-scale growth or large-scale exfoliation. Here, we demonstrate graphene dispersions with concentrations up to ~0.01 mg/ml by dispersion and exfoliation of graphite in organic solvents such as N-methyl-pyrrolidone. This occurs because the energy required to exfoliate graphene is balanced by the solvent-graphene interaction for solvents whose surface energy matches that of graphene. We confirm the presence of individual graphene sheets with yields of up to 12% by mass, using absorption spectroscopy, transmission electron microscopy and electron diffraction. The absence of defects or oxides is confirmed by X-ray photoelectron, infra-red and Raman spectroscopies. We can produce conductive, semi-transparent films and conductive composites. Solution processing of graphene opens up a whole range of potential large-scale applications from device or sensor fabrication to liquid phase chemistry.

Figures (3)

• Figure 1: A) Dispersions of graphene in NMP, at a range of concentrations ranging from$6-4 \mu \mathrm{~g} / \mathrm{ml}$ (A-E)
• Figure 2: A) SEM image of sieved, pristine graphite (scale:$500 \mu \mathrm{~m}$ ). B) SEM image of sediment after centrifugation (scale: $25 \mu \mathrm{~m}$ ). C), D) and E Bright field TEM images of single layer graphene flakes deposited from GBL, DMEU and NMP respectively (scale: 500 nm ). F) A folded graphene sheet (bright field, deposited from NMP). G) Multi-layer graphene (bright field, deposited from NMP) (scale: 500 nm ). H) A histogram of the number of visual observations of flakes as a function of the number of monolayers per flake for NMP dispersions. This data allows the calculation of the number fraction of monolayers (28%), the mass fraction of monolayers (12%) and the overall yield of graphene ( $0.8 \%$ ) (see table S2 for details).
• Figure 3: A) and B) HRTEM images of solution cast monolayer and bi-layer graphene respectively. C) Electron diffraction pattern of the sheet in A). The peaks are labelled using Miller-Bravais indices. The same labels also apply to the patterns in D) and E). D) and E) Electron diffraction patterns of the sheet shown in B). The pattern in D) was taken from the position marked with the black spot where the sheet is clearly one layer thick. The pattern in E) was taken from the position marked with the white spot where the sheet is clearly two layers thick. F), G) and H) Diffracted intensity taken along the 1-210 to -2110 axis for the patterns shown in C), D) and E) respectively. I) Histogram of the ratios of the intensity of the$\{1100\}$ and $\{2110\}$ diffraction peaks for all the diffraction patterns collected. A ratio greater than 1 is a signature of graphene.