1. Multi-modal Diffusion Mechanisms in Porous Carbons
Keith E. Gubbins, Department of Chemical & Biomolecular Engineering, North Carolina State University
Raleigh, NC 27695
Diffusion of a Binary Mixture in a (7,7) Carbon Nanotube
The carbon nanotube is of a sufficient diameter that neon (blue) can pass itself and argon (green) but argon cannot pass itself or neon. Argon diffuses in a slower single-file diffusion mechanism while neon diffuses in a faster 3-dimensional diffusion mechanism. The diffusion rate of neon is orders of magnitude larger than that for argon.
Diffusion in Activated Carbon
Diffusion in a Carbon Nanotube Bundle
At the lowest pressures argon adsorbs and diffuses in the smallest pores of the material. The energy barrier needed for an argon atom to escape into larger pores is sufficiently high that the argon atoms are trapped in the small pores for long periods of time. Consequently the diffusion coefficient is orders of magnitude slower than it is in a bulk fluid.
The diffusion rates of argon atoms inside the nanotube are orders of magnitude faster than for the atoms trapped in the interstices between the nanotubes. The interstitial atoms exhibit a slower single-file diffusion mechanism while the atoms diffusing inside the nanotube exhibit a faster 3-dimensional diffusion mechanism.