Modeling Adsorption and Transport in Nanotubes with Realistic Defects and Entrance Functional Groups

Thursday, November 11, 2010: 8:50 AM
Seminar Theater (Hilton)
Chandrashekar Shankar1, Prashant Kumar1, Pabitra Choudhury2 and J. Karl Johnson1, (1)Department of Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, PA, (2)Chemical and petroleum engineering, University of Pittsburgh, Pittsburgh, PA

The importance of single- and dual-vacancy defects on diffusion of argon and carbon dioxide through single-walled carbon nanotubes (SWNTs) is investigated using simulation techniques. Physically realistic defects are generated using ab initio density functional theory (DFT) calculations. Constant temperature DFT molecular dynamics calculations are used to mimic the reconstruction of vacancy defect sites. We also investigate the effect of hydrogen termination of the dangling bonds in the defective nanotubes. Atomic center charges are computed using an electrostatic potential fitting method for periodic systems. Adsorption isotherms are computed from classical Monte Caro simulations. We find that the defects have very little effect on the adsorption isotherms. Molecular dynamics methods are used to compute self-, corrected-, and Fickian diffusivities. We compare diffusivities computed for varying types and concentrations of defects with calculations for pristine nanotubes as a function of loading. We also present simulations of water and ion transport through SWNT membranes having various types of functional groups at the ends of the nanotubes. We explore the importance of functional group type and concentration on the flux of water and on the flux of cations and anions through the membranes.

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