Molecular dynamics simulation of the interface between sulfur mustard and graphene

Using molecular dynamics simulations, the interface between sulfur mustard (SM) which is one of the most toxic chemical warfare agents, and single layer graphene (G) was investigated for the first time to find a new class of adsorbents. Various analyses have been done in order to atomistically understand the adsorption mechanism. Results show that: (1) A solid-like SM layer of 6 A thick is formed near G, and its density approximates to 2.5 times as large as that of the bulk SM; (2) Adsorption is occurred in three layers, and due to two distinct orientations of SM relative to G surface, i.e. parallel and tilted, there are fine structures within first layer; (3) Study of surface self-diffusion shows that the diffusion coefficient of SM molecules on G surface is half of the diffusion coefficient of SM molecules in the bulk. Furthermore, the diffusion coefficient of SM molecules with parallel orientation is half of the diffusion coefficient of tilted SM molecules and the lifetime of parallel orientation in the first adsorption layer is about three times more than that of tilted; (4) Pair interaction energy calculation between SM and G revealed that the adsorption energy of parallel SM molecules (-11.875 kCal/mol) is greater than that of the tilted SM molecules (-6.125 kCal/mol) and parallel orientation is the favorable orientation for adsorption. SM-SM pair interaction energy analysis also revealed that SM-SM pairs near G are more associated than SM-SM pairs in the bulk of SM. In summary, our results clearly show that G can be a good candidate for adsorption of SM and similar toxic chemical warfare agents.