Carbon, oxygen, hydrogen, and carbon monoxide suction by graphene capillaries: A theoretical study

We present an analytical study to evaluate the suction forces acting on the C, O, and H atoms and the CO molecule due to the presence of open-edge graphene capillaries using the Lennard-Jones potential, and the key results were verified using molecular dynamics and ab initio calculations. Results show that a suction force pulls the atoms and molecules toward the capillary center. The C, O, and H atoms find the most stable position at the capillary center when d is lower than 6.85, 6.45, and 5.85 Å, respectively. Similarly, the same occurs at interlayer distances of 6.70 and 7.65 Å for horizontally and vertically oriented CO molecules, respectively. Those values indicate the shorter interlayer distances that permit the entrance of such atoms and molecules into the inner part of graphene capillaries. For capillaries with an interlayer distance (d) of 10 Å, the central plane within the capillary layers is a region of unstable equilibrium. In contrast, two planes of stable equilibrium planes are located close to the graphene layers, at 2.0. These results were confirmed by molecular dynamics, which showed a higher density of CO molecules within the capillary, where horizontally oriented molecules accumulate around ∼3.4 Å from the graphene layer. This orientation and position were obtained as the most stable using ab initio calculations, where a CO charge gain of only 9.3×10−3e was obtained. The theoretical approach and general view of our analytical results can be helpful for further developments concerning the nanofiltration of liquids and gases.