MOLECULAR SIMULATION OF FLUID ADSORPTION IN BUCKYTUBES

We report grand canonical Monte Carlo (GCMC) molecular simulation studies of simple fluid adsorption in buckytubes. Buckytubes are graphitic tubes with internal diameters of 1-5 nm and a regular pore structure. Adsorption isotherms and isosteric heats of adsorption are shown for argon and nitrogen in a microporous buckytube at 77 K, for argon and nitrogen in a mesoporous buckytube at 77 K, and for argon in a mesoporous buckytube at 55 K. The smaller buckytube shows type I adsorption behavior. Layering and hysteresis (type VI and IV adsorptions, respectively) are observed for the larger buckytube. A temperature of 77 K is shown to be below the critical temperature for capillary condensation and above the critical temperature for layering transitions for both nitrogen and argon adsorption. A temperature of 55 K is shown to be below the critical temperature for layering transitions for argon adsorption. Argon adsorption at 77 K in an open-ended mesoporous model buckytube is also presented. A comparison is made with argon adsorption at 77 K in a ''semiinfinite'' model buckytube of the same diameter. The open-ended model gives a narrower, more rounded hysteresis loop.