X.W. Meng, Y. Wang, J. P. Huang
Department of Physics, Fudan University, Shanghai 200433, China
Introduction
The diffusion and adsorption of gas
molecules in carbon nanotube is of
importance for many applications, the
behaviors of gas molecules in confined
environment is different from the bulk
environment. The dynamical properties of
gas molecules across a carbon nanotube
have not fully understood and are
especially difficult to determine in
experiments. Thus computational methods
are valuable to study the dynamics
properties of gas in porous materials. On
the basis of molecular dynamics
simulations, we investigate the adsorption
properties in a single-walled carbon
nanotube (SWCNT) and transport
properties across the SWCNT in the
presence of O2/ CH4 mixtures. We find
that the adsorption and transport properties
are different with an increasing
concentration of O2.
Results
Mechanism
Adsorption behaviors
Interactions energy
analysis
We find that the interactions
between Methane gas molecules
and the SWCNT are always
stronger than the interactions
between Oxygen and the SWCNT
at the same place, which may be
the reason that the selectivity of
Methane adsorption in the SWCNT
for a larger concentrations range
and easily transported across the
SWCNT compared to Oxygen gas
molecules .
Model
Diffusion behaviors
A Z-directed, uncapped, (10, 0) SWCNT
with diameter 0.772 nm is used to
perpendicularly join the two graphite sheets.
The Lennard-Jones potential parameters of
carbon atoms come from Hummer et al.
The SWCNT and graphite sheets are in a
box (4.652 nm×4.646 nm×6.480 nm) with
200 gas molecules: for Oxygen and
Methane gas mixtures, the concentrations of
Oxygen gas molecules are equal for both
two sides. The concentrations of Oxygen
gas molecules range from 0.07 to 0.9. The
model of Oxygen and Methane we used
come from Arora and Castillo, respectively.
Conclusion
(1) Methane molecules are selected, and
begin to be dominant in the SWCNT for a
large Oxygen gas concentrations range,
however, the total number of Oxygen and
Methane is almost kept at a constant in the
SWCNT.
(2) The number of Methane gas molecules
transported across the SWCNT is
decreased with increasing Oxygen gas
concentrations. However, the number of
Oxygen transported across the SWCNT
is increased with increasing Oxygen gas
concentrations
(3) Methane gas molecules are easily
transported across the SWCNT and the
total number of gas molecules across the
SWCNT is decreased as the Oxygen gas
concentration increases.