Ultrahigh-throughput exfoliation of graphite into pristine ‘single-layer’ graphene using microwaves and molecularly engineered ionic liquids

Abstract

Graphene has shown much promise as an organic electronic material but, despite recent achievements in the production of few-layer graphene, the quantitative exfoliation of graphite into pristine single-layer graphene has remained one of the main challenges in developing practical devices. Recently, reduced graphene oxide has been recognized as a non-feasible alternative to graphene owing to variable defect types and levels, and attention is turning towards reliable methods for the high-throughput exfoliation of graphite. Here we report that microwave irradiation of graphite suspended in molecularly engineered oligomeric ionic liquids allows for ultrahigh-efficiency exfoliation (93% yield) with a high selectivity (95%) towards ‘single-layer’ graphene (that is, with thicknesses <1 nm) in a short processing time (30 minutes). The isolated graphene sheets show negligible structural deterioration. They are also readily redispersible in oligomeric ionic liquids up to ~100 mg ml–1, and form physical gels in which an anisotropic orientation of graphene sheets, once induced by a magnetic field, is maintained.

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Figure 1: Microwave-assisted liquid-phase exfoliation of graphite in ionic liquids.
Figure 2: Graphite exfoliation on microwave irradiation.
Figure 3: Microscopic visualization and analysis of isolated graphene sheets.
Figure 4: Structural integrity of isolated graphene sheets.
Figure 5: Physical properties of isolated graphene and its dispersion in IL2PF6.

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Acknowledgements

We acknowledge the Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Specially Promoted Research on the Physically Perturbed Assembly for Tailoring High-Performance Soft Materials with Controlled Macroscopic Structural Anisotropy (25000005) and the JSPS FIRST Program for Innovative Basic Research Toward the Creation of a High-performance Battery. We thank E. Silver for generous discussion. SEM, TEM and XPS were conducted at the Research Hub for Advanced Nano Characterization, The University of Tokyo, supported by the Ministry of Education, Culture, Sports, Science and Technology, Japan. We also acknowledge the ImPACT Program of the Council for Science, Technology and Innovation (Cabinet Office, Government of Japan).

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M.M. and Y.S. designed and performed all the experiments. C.P., T.F. and T.A. co-designed the experiments. M.M. and T.A. analysed the data and wrote the manuscript.

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Correspondence to Takuzo Aida.

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The authors declare no competing financial interests.

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Matsumoto, M., Saito, Y., Park, C. et al. Ultrahigh-throughput exfoliation of graphite into pristine ‘single-layer’ graphene using microwaves and molecularly engineered ionic liquids. Nature Chem 7, 730–736 (2015). https://doi.org/10.1038/nchem.2315

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