(32−34) A key point for the technological exploitation of 2D materials is represented by their large-scale production, which still remains challenging. The advent of two-dimensional (2D) materials had a ground-breaking impact on science and technology, (1−13) due to their peculiar properties with high application capabilities in different fields, such as energy storage, (14−22) catalysis, (23−27) optoelectronic devices, (28−31) and gas sensing.
Considering the various advantages of Polarclean over state-of-the-art solvents, including the absence of toxicity and its biodegradability, the validation of superior performances of Polarclean in liquid-phase exfoliation paves the way for sustainable large-scale production of nanosheets of layered materials and for extending their use in application fields to date inhibited by toxicity of solvents (e.g., agri-food industry and desalination), with a subsequent superb impact on the commercial potential of their technological applications. Correspondingly, the density of defects is reduced by 1 order of magnitude by Polarclean-assisted exfoliation, as evidenced by the I(D)/ I(G) ratio in Raman spectra of graphene as low as 0.07 ± 0.01.
The amount of few-layer flakes (with thickness <5 nm) obtained with Polarclean is increased by ∼350% with respect to the case of liquid-phase exfoliation using NMP, maintaining comparable values of the average lateral size, which even reaches ∼10 μm for the case of graphene produced by exfoliation in Polarclean, and of the yield (∼40%). We performed a direct comparison, in the same processing conditions, with liquid-phase exfoliation using N-methyl-2-pyrrolidone (NMP) solvent. Here, we demonstrate the suitability of methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (Rhodiasolv Polarclean) for sonication-assisted liquid-phase exfoliation of layered materials for the case-study examples of WS 2, MoS 2, and graphene. One of the main open challenges is related to the quest of green and bioderived solvents to replace state-of-the-art dispersion media, which suffer several toxicity issues. Liquid-phase exfoliation is the most suitable platform for large-scale production of two-dimensional materials.
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