Computer Study of the Interaction of Mercury with Graphene
Alexander Y. Galashev
Abstract—The contamination ofnatural waters and the lower atmosphere by heavy metal ionscreates a serious ecological problem. Mercury is one of the most toxic heavy metals, because it is not biodegradable. We have studied the physical properties of mercury films on partially hydrogenated imperfect graphene by means of molecular dynamics at 300 K. Films prepared on the basis of three various types of the atomic interaction potential for mercury and other constant interaction potentials are considered. It is shown that the one most promising is the Schwerdtfeger potential function, at which mercury atoms do not fall into the divacancies present on graphene and atom packing with the lowest energy are realized in a liquid film and the film gradually fold into a drop. Another computer experiment has been employed to study rapid heating of a mercury film on graphene containing Stone–Walesdefects. Hydrogenated edges of a graphene sheet withstand heating by 800 K. As the film contracts into a droplet, the horizontal component of the self-diffusion coefficient of Hg atoms monotonically decreases, while the vertical component passes through a deep minimum, which reflects the onset of droplet rising over the substrate. Formation of the droplet leads to a decrease in the blunt contact angle. Temperature–related changes in graphene manifest themselves as a rise in the intensity of additional peaks in the angular distribution of the closest neighbors, oscillatory pattern of the stress acting in its plane, and an almost linear growth of roughness. Molecular dynamics simulation of the bombardment of a target with a Xe13 cluster beam at energies of 5–30 eV and incidence angles of 0°–60° aiming to remove a mercury film from partially hydrogenated imperfect graphene has been performed. The graphene is completely cleaned of mercury at a cluster energy of EXe ≥ 15 eV. Mercury is removed from the graphene film via sputtering of single atoms and droplet detachment. A stress in graphene resulting from forces normal to the sheet plane is noticeably higher than that due to forces acting in its plane. Bombardment at an angle of incidence of 45° is more efficient than that at incidence of 0° and 60° and leads to lower graphene roughness. Thus, mercury can be removed from graphene by heating or bombarding with heavy noble gas clusters.