Oxidative Immobilization of Gaseous Mercury by [Mo₃S(S₂)₆]^2--Functionalized Layered Double Hydroxide

Every year, thousands of tons of gaseous mercury are released globally, prompting the World Health Organization (WHO) in 2020 to designate mercury as one of the top 10 chemicals posing severe health risks. Therefore, removal of Hg⁰ from the environment is imperative. Our study introduces [Mo₃S(S₂)₆]^2- ≡ [Mo₃S₁₃]^2--functionalized layered double hydroxide nanoparticles, (LDH-Mo₃S₁₃), as an excellent sorbent for gaseous Hg⁰. This material achieved a remarkable sorption capacity of ∼2.33 × 10³ mg/g for gaseous elemental Hg⁰. Such an enormously high sorption capacity makes this material the lead non-platinum-based Hg⁰ gas sorbent known to date. Although sulfides of the Mo₃S(S₂)₆ species of LDH predominantly serve as active sites for capturing gaseous Hg, their integration is essential for the accessibility of gaseous Hg⁰ to the individual reactive active site between the LDH lamella. A heterogeneous reaction between the Hg⁰ vapor and the solid LDH-Mo₃S₁₃ sorbent enables the oxidation of gaseous Hg⁰ to Hg²⁺, and the reduction of the S₂^2- groups to 2S^2- yields redox-driven formation of the nanocrystalline HgS onto the solid sorbents. Density functional theory (DFT) calculations provide further insights into the interactions between Hg⁰ and S, indicating adsorption energy ranging from −8 to −19 kJ/mol. Moreover, the overall reaction enthalpy was calculated as −4048 kJ/mol, suggesting the spontaneous formation of HgS. This investigation unveils an atomistic understanding of the redox-driven interactions between Hg⁰ vapor and Mo₃S(S₂)₆ species as well as the remarkably high mercury sorption capacity of LDH-Mo₃S₁₃, highlighting the potential of metal sulfide-functionalized LDHs for the efficient immobilization of gaseous elemental mercury.