Research On The Adsorption Mechanism Of Elemental Mercury By Transition Metal Selenides

The situation of mercury（Hg）pollution in China is currently grim.As one of the largest anthropogenic sources of Hg emissions,the control of Hg pollution from coal combustion has always attracted the attention of international community.Among various Hg sorbents,metal selenide（MSe）has excellent elemental mercury（Hg⁰）adsorption performance,but its Hg⁰ adsorption mechanism is still unclear.In this paper,the Hg⁰ adsorption mechanism by various sites over metal selenide were systematically explored.Firstly,for the M sites over metal selenide,the effects of M site type on Hg⁰ adsorption were studied by DFT.When Hg⁰ was adsorbed at M sites over MSe₂（101）surface（M=Fe,Co,and Cu）,the octahedral coordination of M sites was recovered.The adsorption strength of Hg⁰ at M sites was determined by the number of electrons in antibonding orbital e_g^*,which was inversely proportional to the binding strength.The interaction between Hg⁰ and the Se sites over MSe₂（101）surface was weak,which was attributed to the repulsion of Se 4p orbital to Hg⁰.Surface M sites could not only react with Hg⁰ to form amalgam,but synergize with surface Se sites to facilitate the formation of HgSe.The effects of flue gas component Se⁰ on Hg⁰ adsorption were explored by constructing FeS₂（100）surface,and it was found that the presence of Se⁰could promote the Hg⁰ adsorption by Fe site.Inspired by the DFT calculations,the Se-enriched FeSe₂（101）surfaces were constructed to explore the synergistic effects of Fe and Se sites in Hg⁰ adsorption.The direct Hg⁰ adsorption over Se₁ sites was weak,but the co-presence of Se₁and Fe sites could effectively immobilize Hg⁰.For the Se sites over metal selenide,the important role of unsaturation in Hg⁰ adsorption was proved through the combination of DFT and experiments.The Cu FeSe₂ sample with abundant unsaturated Se（Se^-）sites were synthesized by a liquid-phase reduction method.According to the adsorption kinetic simulation,the Hg⁰ equilibrium adsorption capacity and initial adsorption rate of the Cu FeSe₂ sample were as high as 526.7 mg·g^-1and 900.71μg·g^-1·min^-1.Based on the XPS and DFT results,the excellent Hg⁰ adsorption performance of Cu FeSe₂ was attributed to abundant surface Se^-sites,which decreased from 46.1%to 41.6%after Hg⁰ adsorption.