Ab-initio investigation of thermoactivated directional transport of hydrogen molecules inside narrow carbon nanotubes

Using the pseudopotential DFT and the empirical potential methods we calculate the potential acting to the hydrogen molecules in narrow single-wall carbon nanotubes (SWCNT) (6,0),(7,0) and (3,3). The potential forms a goffered potential surface and can be approximated as V(z, r, phi) approximate to V-0 sin(2 pi z/a) + V(r). We show that in these SWCNTs transport of molecules is given mainly by thermoactivated hoppings between minima of the periodic potential along the tube axis. Taking into account that hydrogen density distribution inside nanotube is stationary and assuming the temperature is changed linearly along the SWCNT length we show that the H-2 density is sufficiently variated, especially for the case of (6,0)SWCNT where the density on both SWCNT ends are different at similar to 30 times when the temperature is changed along the SWCNT from 300K to 1200K. Suppose that H2 molecules can penetrate in the both open SWCNT ends, the molecules would move in the direction of the temperature decreasing. This effect may be used potentially to build up a molecular pump driven by the temperature gradient along narrow nanotube. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim