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Nano Research

Article Title

High-concentration dispersions of exfoliated MoS2 sheets stabilized by freeze-dried silk fibroin powder

Keywords

MoS2 nanosheet, liquid-phase exfoliation, freeze-dried silk fibroinpowder, amount of suspendedMoS2 sheet, stabilized dispersion

Abstract

Liquid-phase exfoliation (LPE) is an attractive method for the scaling-up ofexfoliated MoS2 sheets compared to chemical vapor deposition and mechanicalcleavage. However, the MoS2 nanosheet yield from LPE is too small for practicalapplications. We report a facile method for the scaling-up of exfoliated MoS2nanosheets using freeze-dried silk fibroin powders. Compared to MoS2 dispersionin the absence of silk fibroin powder, sonicated MoS2 dispersions with silkfibroin powder (MoS2/Silk dispersion) show noticeably higher exfoliated MoS2nanosheet yields, with suspended MoS2 concentrations in MoS2/Silk dispersionssonicated for 2 and 5 h of 1.03 and 1.39 mg·mL–1, respectively. The MoS2concentration in the MoS2/Silk dispersion after centrifugation above 10,000 rpmis more than four times that without the silk fibroin. The size of the dispersed silkfibroin is controlled by the change of centrifugation rate, showing the removal ofsilk fibroin above tens of micrometers in size after centrifugation at 2,000 rpm.Size-controlled silk fibroin biomolecules combined with MoS2 nanosheets areexpected to increase the practical use of such materials in fields related to tissueengineering, biosensors and electrochemical electrodes. Atomic force microscopyand Raman spectroscopy provide the height of the MoS2 nanosheets spin-castfrom MoS2 /Silk dispersions, showing thicknesses of 3–6 nm. X-ray photoelectronspectroscopy and X-ray diffraction indicate that the outermost surface layer of thehydrophobic MoS2 crystals interact with oxygen-containing functional groupsthat exist in the hydrophobic part of silk fibroins. The amphiphilic propertiesof silk fibroin combined with the MoS2 nanosheets stabilize dispersions byenhancing solvent-material interactions. The large quantities of exfoliated MoS2nanosheets suspended in the as-synthesized dispersions can be utilized for thefabrication of vapor and electrochemical devices requiring high MoS2 nanosheetscontents.

Graphical Abstract

Publisher

Tsinghua University Press

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