Solvent Exfoliation of Transition Metal Dichalcogenides: Dispersibility of Exfoliated Nanosheets Varies Only Weakly between Compounds
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Graeme Cunningham, Mustafa Lotya, Clotilde S. Cucinotta, Stefano Sanvito, Shane D. Bergin, Robert Menzel, Milo S. P. Shaffer and Jonathan N. Coleman, Solvent Exfoliation of Transition Metal Dichalcogenides: Dispersibility of Exfoliated Nanosheets Varies Only Weakly between Compounds, ACS Nano, 6, 4, 2012, 3468-3480Download Item:
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Abstract:
We have studied the dispersion and exfoliation of four inorganic layered compounds, WS2,
MoS2, MoSe2 and MoTe2 in a range of organic solvents. The aim was to explore the relationship
between the chemical structure of the exfoliated nanosheets and their dispersability. Sonication
of the layered compounds in solvents generally gave few-layer nanosheets with lateral
dimensions of a few hundred nanometers. However the dispersed concentration varied greatly
from solvent to solvent. For all four materials the concentration peaked for solvents with surface
energy close to 70 mJ/m2, implying that all four layered compounds have surface energy close to
this value. Inverse gas chromatography measurements showed MoS2 and MoSe2 to have surface
energies of ~75 mJ/m2, in good agreement with dispersability measurements. However, this
method suggested MoTe2 to have a considerably larger value of surface energy (~120 mJ/m2).
While surface energy based solubility parameters are perhaps more intuitive for 2-dimensional
materials, Hansen solubility parameters are probably more useful. Our analysis shows the
dispersed concentration of all four layered materials to show well-defined peaks when plotted as
a function of Hansen?s dispersive, polar and H-bonding solubility parameters. This suggests that
we can associate Hansen solubility parameters of ~ P ? 18 MPa1/2, ~ D ? 8.5 MPa1/2 and ~ H ? 7
MPa1/2 with all four types of layered material. Knowledge of these properties allows the
estimation of the Flory-Huggins parameter, ?, for each combination of nanosheets and solvent.
We found that the dispersed concentration of each material falls exponentially with ? as
predicted by solution thermodynamics. This work shows that solution thermodynamics and
specifically solubility parameter analysis can be used as a framework to understand the
dispersion of 2-dimensional materials. Finally, we note that in good solvents such as cyclohexylpyrrolidone, the dispersions are temporally stable with >90% of material remaining dispersed after 100 h.
Sponsor
Grant Number
Science Foundation Ireland (SFI)
G20267
Author's Homepage:
http://people.tcd.ie/sanvitoshttp://people.tcd.ie/berginsh
http://people.tcd.ie/colemaj
http://people.tcd.ie/mlotya
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ACS Nano6
4
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Nanoscience & MaterialsDOI:
http://dx.doi.org/10.1021/nn300503eLicences: