Engineering sulfur-rich MoS2 adsorbent with abundant unsaturated coordination sulfur sites for gaseous mercury capture from high-concentration SO2 smelting flue gas.

• A high-performance MoS x adsorbent with sulfur-rich feature was prepared. • The number of unsaturated coordination sulfur sites decides Hg0 adsorption. • The as-prepared MoS x -6–220 possesses the best performance for Hg0 capture. • The final adsorption product is formed through a transformation from Hg-Mo amalgam to HgS. Gaseous elemental mercury (Hg0) removal is desirable for the green and high-quality development of nonferrous metal smelting industry. Developing a simple and feasible method to prepare high-performance adsorbent is still challenging. Herein, a sulfur enrichment strategy was proposed to prepare molybdenum sulfide (MoS x) with abundant unsaturated coordination sulfur sites. Benefiting the sulfur-rich feature, the Hg0 sequestration capacity of prepared MoS x is markedly enhanced compared with commercial MoS 2. The characterization results of MoS x demonstrate an ideal structural property and abundant unsaturated sulfur ligands, which assures a desired performance for Hg0 adsorption. Among these adsorbents, MoS x -6–220 exhibits the best Hg0 capture performance, which presents a Hg0 adsorption efficiency of nearly 100 % and average adsorption rate of 6.41 μg/g/min. The theoretical saturated adsorption capacity of MoS x -6–220 reaches 53.03 mg/g, higher than other conventional metal sulfides. The typical compositions in the smelting flue gas have almost little impact on Hg0 adsorption. The experimental and characterization results confirm that the impressive performance is primarily attributed to the enormous quantity of unsaturated coordination sulfur sites, rather than S/Mo stoichiometry. Moreover, the density functional theory calculation results further demonstrate the high adsorption activity of unsaturated coordination sulfur site for Hg0 immobilization. Hg0 adsorption pathway shows that Hg0 is first adsorbed on the top of Mo atom in the form of Hg-Mo amalgam, then the adsorbed Hg would migrate to unsaturated coordination sulfur ligand and bond with it to form stable HgS product, thereby realizing the permanent immobilization of Hg0. This work not only provide a promising strategy to prepare high-performance metal sulfide adsorbents, but also give deep insight into the Hg0 adsorption and conversion mechanism at the molecular level. [ABSTRACT FROM AUTHOR]