Liquid-Phase Exfoliation of Two-Dimensional Nanosheets

Liquid-phase exfoliation is a leading top-down route to derive few-layer or monolayer nanosheets from bulk layered materials. It involves the dispersion of powdered or bulk crystals in a liquid medium, followed by the application of mechanical or chemical energy to overcome interlayer van der Waals interactions. Through the judicious selection of solvents or additives whose surface energies approximate those of the target materials, high yields of two-dimensional nanosheets can be achieved. Sonication, shear mixing, microwave irradiation and electrochemical methods have emerged as principal techniques to induce exfoliation, enabling the scalable production of nanosheets of graphene, transition metal dichalcogenides, hexagonal boron nitride and other layered compounds. These ultrathin materials exhibit size-dependent electronic, optical and catalytic properties, lending themselves to applications in energy storage, optoelectronics, catalysis, biomedical sensing and environmental remediation. Advances in green solvents, phase-inversion strategies and biomolecular templating have improved the sustainability and functional versatility of the process, while the integration of exfoliated nanosheets into inks, coatings, heterostructures and composite matrices has broadened the palette of potential device architectures. Challenges remaining include the fine control of lateral flake dimensions, minimisation of structural defects, long-term dispersion stability and the transition from laboratory-scale demonstrations to industrial throughput. Continued innovation in exfoliation media, process intensification and post-exfoliation purification will be central to realising the full promise of two-dimensional materials in commercial technologies.

Research from Nature Portfolio

Recent studies have demonstrated the feasibility of direct exfoliation of layered materials in benign media. Temperature-controlled sonication in pure water has been shown to produce stable dispersions of 2D nanosheets without the need for surfactants, relying on intrinsic surface charges and edge functionalisation to maintain colloidal stability and enabling applications such as inkjet printing on diverse substrates. Phase-inversion strategies driven by supercritical carbon dioxide have delivered efficient exfoliation across a range of bulk materials, exploiting micelle-to-reverse micelle transitions to achieve high yields of single- and few-layer nanosheets for use in conductive papers, fluorescent labelling and polymer reinforcement. In another approach, multivalent biomolecular interactions using dextran have been employed for the simultaneous exfoliation and functionalisation of transition metal dichalcogenide monolayers, generating hybrid nanosheets that combine exfoliation with selective pathogen recognition, thereby expanding the utility of 2D materials in biosensing and diagnostic applications.

Liquid-Phase Exfoliation of Two-Dimensional Nanosheets publication trend

The graph below shows the total number of articles in liquid-phase exfoliation of two-dimensional nanosheets across all publications each year (not limited to Nature Index journals).

Technical terms

Liquid-phase exfoliation (LPE): A top-down method in which bulk layered materials are dispersed in a liquid medium and subjected to mechanical or chemical energy to separate them into ultrathin nanosheets.

Sonication: The use of high-frequency sound waves to induce cavitation and shear forces in a liquid, facilitating the delamination of layered materials.

Supercritical carbon dioxide (scCO₂): A fluid phase of CO₂ above its critical temperature and pressure, used to trigger solvent phase inversion and assist in exfoliation through reversible micelle formations.

Multivalent interaction: The simultaneous binding of multiple ligands to a nanosheet surface, enhancing exfoliation and functionalisation by leveraging multiple weak bonds in concert.

Surfactant: A molecule that adsorbs at interfaces to reduce surface tension, used to stabilise exfoliated nanosheets in dispersion but potentially introducing impurities or requiring removal.

References

1. Direct exfoliation and dispersion of two-dimensional materials in pure water via temperature control. Nature Communications (2015).
2. High-efficiency exfoliation of layered materials into 2D nanosheets in switchable CO2/Surfactant/H2O system. Scientific Reports (2015).
3. 2D transition metal dichalcogenides with glucan multivalency for antibody-free pathogen recognition. Nature Communications (2018).
4. Microwave-Driven Exfoliation of Bulk 2H-MoS2 after Acetonitrile Prewetting Produces Large-Area Ultrathin Flakes with Exceptionally High Yield. ACS Nano (2023).
5. Sustainable Liquid-Phase Exfoliation of Layered Materials with Nontoxic Polarclean Solvent. ACS Sustainable Chemistry & Engineering (2020).
6. Emerging 2D Materials Produced via Electrochemistry. Advanced Materials (2020).