Abstract
Liquid-phase exfoliation (LPE) is an attractive method for the scaling-up of exfoliated MoS sub(2) sheets compared to chemical vapor deposition and mechanical cleavage. However, the MoS sub(2) nanosheet yield from LPE is too small for practical applications. We report a facile method for the scaling-up of exfoliated MoS sub(2) nanosheets using freeze-dried silk fibroin powders. Compared to MoS sub(2) dispersion in the absence of silk fibroin powder, sonicated MoS sub(2) dispersions with silk fibroin powder (MoS sub(2)/Silk dispersion) show noticeably higher exfoliated MoS sub(2) nanosheet yields, with suspended MoS sub(2) concentrations in MoS sub(2)/Silk dispersions sonicated for 2 and 5 h of 1.03 and 1.39 mg.mL super(-1), respectively. The MoS sub(2) concentration in the MoS sub(2)/Silk dispersion after centrifugation above 10,000 rpm is more than four times that without the silk fibroin. The size of the dispersed silk fibroin is controlled by the change of centrifugation rate, showing the removal of silk fibroin above tens of micrometers in size after centrifugation at 2,000 rpm. Size-controlled silk fibroin biomolecules combined with MoS sub(2) nanosheets are expected to increase the practical use of such materials in fields related to tissue engineering, biosensors and electrochemical electrodes. Atomic force microscopy and Raman spectroscopy provide the height of the MoS sub(2) nanosheets spin-cast from MoS sub(2) /Silk dispersions, showing thicknesses of 3-6 nm. X-ray photoelectron spectroscopy and X-ray diffraction indicate that the outermost surface layer of the hydrophobic MoS sub(2) crystals interact with oxygen-containing functional groups that exist in the hydrophobic part of silk fibroins. The amphiphilic properties of silk fibroin combined with the MoS sub(2) nanosheets stabilize dispersions by enhancing solvent-material interactions. The large quantities of exfoliated MoS sub(2) nanosheets suspended in the as-synthesized dispersions can be utilized for the fabrication of vapor and electrochemical devices requiring high MoS sub(2) nanosheets contents. [Figure not available: see fulltext.]