398442 Molecular Simulation of Bismuth Telluride Exfoliation in an Ionic Liquid Solvent

Monday, November 17, 2014
Galleria Exhibit Hall (Hilton Atlanta)
Thomas Ludwig1, Zhongtao Zhang1, Haley Gordon2,3, Hung-Ta Wang1 and C. Heath Turner1, (1)Chemical and Biological Engineering, The University of Alabama, Tuscaloosa, AL, (2)Chemistry, St. Mary's College, Notre Dame, IN, (3)Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN

Nanosheets of bismuth telluride (Bi2Te3) are of great research interest because of their potential usefulness in diverse material applications, such as thermoelectrics, heterogeneous catalysis, and superconductors. One proposed method of their fabrication is by ionic liquid (IL) assisted exfoliation. ILs display unique and tunable solvation properties, and they are considered to be green alternatives to conventional solvents. In this work, molecular simulations are used to probe the mechanism of exfoliation of nanosheets of Bi2Te3 in the ionic liquid [BMIM]Cl. We study the thermodynamics, kinetics, and structure of the exfoliation process over a wide temperature range. We observe spontaneous exfoliation without artificial forces, allowing a kinetics-based estimate of the apparent activation energy of exfoliation. We also estimate the surface free energy of Bi2Te3, and the results are comparable to experiment. The structure of the IL solvation layers is found to be strongly ordered, with density oscillations near the interface alternating in charge. This is consistent with the observed stability of experimental dispersions of Bi2Te3, as well as previous simulation results. We find that surface free energy is independent of the size of the Bi2Te3 model used, which implies that the size of the system studied is adequate to describe experimental scale systems and to predict effective exfoliation conditions. The methods used are extensible to other ILs, and our current and future results should accelerate the experimental search for an effective exfoliation process for the manufacture of Bi2Te3 nanosheets.

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