On the adsorption of elemental mercury on single-atom TM (TM = V, Cr, Mn, Co) decorated graphene substrates

Abstract

Mercury pollution from coal-fired power plants is a severe environmental issue globally. Although integrated removal facilities can achieve ultra-low emissions, there is still a need to develop efficient adsorbents to remove mercury, especially elemental mercury. Single-atom catalysts (SACs), which have high activity and selectivity for adsorption, provide a promising option to do this. However, it remains unknown what would be the best, most effective SAC to be used for mercury removal. Density functional theory (DFT) calculations were conducted to investigate the adsorption characteristics of elemental mercury by single atom transition metals (TMs), in particular vanadium (V), chromium (Cr), manganese (Mn), and cobalt (Co), supported on different graphene substrates (single vacancy, single vacancy doped with three nitrogen, double vacancy, double vacancy doped with four nitrogen). Moreover, the projected density of states, electronic density difference, electronic localization function, electrostatic potential and Fermi softness were analyzed. It is found that the relationship between the distance between the elemental mercury and TM atom (dHg-TM) and adsorption energy is linear. The electrostatic potential can roughly evaluate the adsorption energy. The Fermi softness provides a good descriptor for the adsorption activity of single-atom TM supported on different graphene substrates. Furthermore, this research lays the foundation to develop efficient SAC-based adsorbents to remove elemental mercury.