Quantum Chemistry Study On Adsorption Of Mercury Contaminants By Modified Graphene In Flue Gas Of Coal-fired Power Plant

Under the background of adsorption of toxic heavy metal pollutants and their compounds emitted from coal-fired power plants,the adsorption mechanism of Hg,HgCl,HgCl₂,HgBr,HgBr₂ molecules on the surface of modified graphene was studied based on the adsorption.A variety of stable adsorption configurations of mercury and its compounds on the surface of modified graphene were obtained by ORCA calculation program.Methods such as mayer bond order,reduced density gradient analysis,atoms in molecules theory analysis and electrons in the molecule and localization function were used to study the adsorption interaction of mercury and its compounds on the surface of modified graphene.A basic graphene model was constructed,which is modified by sequentially doping metal atom osmium?Os?,iridium?Ir?,platinum?Pt?,silver?Ag?,vanadium?V?at its central position,and the modified grapheme were used to adsorb Hg,HgCl,HgCl_2,HgBr,and HgBr₂.The calculation results show that the adsorption of elemental Hg on the surface of pure grapheme model is physical adsorption,the graphene modified by metal atom improves the ability of adsorpbtion of Hg but which still belongs to physical adsorption.The adsorption of HgCl,HgCl₂,HgBr and HgBr₂ on the modified grapheme model are chemical adsorption.HgCl is reduced to elemental Hg on Os and V modified grapheme.On Pt modified grapheme model surface,the adsorption energy HgCl is the largest and the configuration is the most stable.The adsorption of Pt-modified graphene is the most stable,and the adsorption energy is the largest.The interaction of Hg and Pt atom is between the open-shell and closed-shell interaction.HgBr is reduced to elemental Hg on Os,V modified grapheme model surface.In the HgBr Pt-graphene configuration,the interaction between Hg and Pt is strong and the adsorption energy is the highest.The adsorption of HgBr₂ on Pt,Ag and V modified graphene is chemical adsorption,while the adsorption energy of HgBr₂ on the surface of Os,Pt and V modified graphene is greater than the adsorption energy of HgBr₂ on Ir and Ag modified grapheme model surface.Due to the adsorption configurations of mercury and its compounds on Pt-modified graphene model surface are most stable,Pt graphene is re-modified by doping with nitrogen,in detail,one to three nitrogen atoms are doped separately.The results show that the increase of the number of doped nitrogen atoms,the adsorption ability of grapheme model to elemental mercury is significantly increased,when the adsorption amount of nitrogen atom reaches to three,the adsotpion energy of Hg N3-Pt-graphene configuration is the largest,and the interaction between Hg and Pt belongs to chemical adsorption.The interaction between HgCl and modified graphene is chemical adsorption and the adsorption energy is the highest when grapheme doped two nitrogen atoms.The interaction between HgCl₂ and modified graphene is chemical adsorption and the adsorption energy is the highest when graphene doped three nitrogen atoms,the interaction between Hg and Pt is metal covalent bonds.When grapheme model doped with three nitrogen atoms,the adsorption configuration of HgBr modified graphene has the largest adsorption energy,and doped one or two nitrogen atoms has little effect on the adsorption energy.The adsorption of HgBr₂ on the surface of nitrogen-doped platinum-modified graphene is chemical adsorption,and its adsorption energy is greatly improved compared with undoped nitrogen,and its adsorption energy is maximized when three nitrogen atoms are doped.Modified graphene can promote the adsorption of elemental mercury and its compounds,especially when platinum-modified graphene doped with nitrogen atoms can perform well adsorption ability.By analyzing the chemical bonds and adsorption energy between the adsorbents,a reliable and good new adsorbent material was proposed.