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Nano Research 2016, 9(6): 1709-1722 https://doi.org/10.1007/s12274-016-1065-2
Research Article | Issue | Published: 08 April 2016

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

Show Author's Information HeungBo Sim,  JiYong Lee,  Byeongho Park,  Sun Jun Kim,  Shinill Kang,  WonHyoung Ryu( ),  Seong Chan Jun( )
School of Mechanical EngineeringYonsei University, Seoul, 120-749Republic of Korea
Keywords:
liquid-phase exfoliation, MoS2 nanosheet, freeze-dried silk fibroin powder, amount of suspended MoS2 sheet, stabilized dispersion
Cite this article:
Sim H, Lee J, Park B, et al. High-concentration dispersions of exfoliated MoS2 sheets stabilized by freeze-dried silk fibroin powder. Nano Research, 2016, 9(6): 1709-1722. https://doi.org/10.1007/s12274-016-1065-2
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Abstract Full text Electronic supplementary material About this article

Liquid-phase exfoliation (LPE) is an attractive method for the scaling-up of exfoliated MoS2 sheets compared to chemical vapor deposition and mechanical cleavage. However, the MoS2 nanosheet yield from LPE is too small for practical applications. We report a facile method for the scaling-up of exfoliated MoS2 nanosheets using freeze-dried silk fibroin powders. Compared to MoS2 dispersion in the absence of silk fibroin powder, sonicated MoS2 dispersions with silk fibroin powder (MoS2/Silk dispersion) show noticeably higher exfoliated MoS2 nanosheet yields, with suspended MoS2 concentrations in MoS2/Silk dispersions sonicated for 2 and 5 h of 1.03 and 1.39 mg·mL–1, respectively. The MoS2 concentration in the MoS2/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 MoS2 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 MoS2 nanosheets spin-cast from MoS2 /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 MoS2 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 MoS2 nanosheets stabilize dispersions by enhancing solvent-material interactions. The large quantities of exfoliated MoS2 nanosheets suspended in the as-synthesized dispersions can be utilized for the fabrication of vapor and electrochemical devices requiring high MoS2 nanosheets contents.


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About this article

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

Show Author's information HeungBo Sim, JiYong Lee, Byeongho Park, Sun Jun Kim, Shinill Kang, WonHyoung Ryu( ), Seong Chan Jun( )
School of Mechanical EngineeringYonsei University, Seoul, 120-749Republic of Korea

Abstract

Liquid-phase exfoliation (LPE) is an attractive method for the scaling-up of exfoliated MoS2 sheets compared to chemical vapor deposition and mechanical cleavage. However, the MoS2 nanosheet yield from LPE is too small for practical applications. We report a facile method for the scaling-up of exfoliated MoS2 nanosheets using freeze-dried silk fibroin powders. Compared to MoS2 dispersion in the absence of silk fibroin powder, sonicated MoS2 dispersions with silk fibroin powder (MoS2/Silk dispersion) show noticeably higher exfoliated MoS2 nanosheet yields, with suspended MoS2 concentrations in MoS2/Silk dispersions sonicated for 2 and 5 h of 1.03 and 1.39 mg·mL–1, respectively. The MoS2 concentration in the MoS2/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 MoS2 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 MoS2 nanosheets spin-cast from MoS2 /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 MoS2 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 MoS2 nanosheets stabilize dispersions by enhancing solvent-material interactions. The large quantities of exfoliated MoS2 nanosheets suspended in the as-synthesized dispersions can be utilized for the fabrication of vapor and electrochemical devices requiring high MoS2 nanosheets contents.

Keywords: liquid-phase exfoliation, MoS2 nanosheet, freeze-dried silk fibroin powder, amount of suspended MoS2 sheet, stabilized dispersion

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Publication history
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Acknowledgements

Publication history

Received: 09 December 2015
Revised: 31 January 2016
Accepted: 06 March 2016
Published: 08 April 2016
Issue date: June 2016

Copyright

© Tsinghua University Press and Springer-Verlag Berlin Heidelberg 2016

Acknowledgements

Acknowledgements

This work was partially supported by the Priority Research Centers Program (No. 2009-0093823), the Basic Science Research Program (No. 2013063062), the Korean Government (MSIP) (No. 2015R1A5A1037668) through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (MEST).

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