Advances in Materials Science Research Volume 34,

Chapter 3 Computer Study of the removal of Heavy Metals from Graphene

Nova Science Publishers, Inc., pp 115-156

Alexander Y. Galashev

Abstract - Efficient removal of hazardous heavy metals from the environment is an important problem, since most of these metals are highly toxic. Recently, graphene began to be used for the removal of environmental pollutants. Graphene is ineffective as an absorbent unless it is repeatedly used. This raises the problem of graphene cleaning for removal of the deposited materials. The method of molecular dynamics has been used to study the removal of copper, lead, and mercury from graphene by irradiating the target using a beam of Ar13 or Xe13 clusters with energies of 5—30 eV at angles of incidence 0°, 45°, 60°, and 90°. It is obtained that the cluster energy should be in the interval 20 — 30 eV for effective graphene cleaning in case of its copper contamination. There is no cleaning effect at vertical incidence (θ = 0°) of Ar13 clusters. The bonrbardrnents at 45° and 90° incident angles are the most effective ones at a moderate and big amount of deposited copper respectively. The complete removal of lead from graphene with hydrogenated edges and bivacancies was achieved at the angle of incidence of Xe13 clusters equal to 45°. A major part of the film was separated from graphene in the form of an island, which, after separation, was transformed into a three-dimensional structure. The stresses present in the graphene sheet changed in the course of bombardment, but the stressed state retained after the bombardment was terminated. The type of the distribution of stresses in graphene indicates the absence of enhancement of the stressed state in the course of bombardment. The bombardment at angles of incidence of clusters less than 75° substantially enhances the rouglmess of graphene. The complete removal of mercury from graphene with hydrogenated edges was achieved at the angles of incidence of clusters equal to 45° and 60° with the energies of the beam EXe > 15 and 10 eV, respectively. The film of mercury, which has a tendency to become rolled up into a drop, is separated from graphene in the form of single atoms, dimers, trimers, and spherical droplets. In the course of the bombardment, mercury exhibits a weak cohesion with graphene. The bombardment at the angle of incidence of clusters equal to 45° leads to the lowest roughness of graphene. The bornbardrnents in the entire range of the angles of cluster incidence (0° — 90°) have resulted in no significant damages in the hydrogenated edges of the graphene sheet after its cleaning from both lead and mercrury. Thus. the purification of graphene from heavy metals can be performed by bombardment with noble gas clusters.

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