Figure 2: Photographs of the experimental procedure.

(a) Photographs of the concentration step for MoS₂ nanosheets. After ultrasonication, the MoS₂ dispersion is placed on top of 60% w v⁻¹ iodixanol as a step gradient and then ultracentrifuged at 32 kr.p.m. for 24 h. Subsequently, 60% w v⁻¹ iodixanol is injected to separate the concentrated MoS₂ nanosheets from the aggregates, and then extracted. The dispersion, gradient and injection solution all contain 2% w v⁻¹ F68. (b) Photograph of MoS₂ bands in an ultracentrifuge tube after the first iteration of density gradient ultracentrifugation (DGU). The concentrated MoS₂ solution was diluted by a factor of eight before ultracentrifugation to reveal the position of each band more clearly. (c) Photograph of the ultracentrifuge tubes after the second iteration of DGU. Fractions from the well-defined bands (f7, f17 and f27) and the relatively wider bands (f9, f13 and f23) from the first iteration are collected and used for the second iteration. The fractions from the dashed region are used for characterization.