Regulation of the Sulfur Environment in Clusters to Construct a Mn-Sn2S6 Framework for Mercury Bonding.

Abstract

The remarkable chemical activity of metal-sulfur clusters lies in their unique spatial configuration associated with the abundant unsaturated-coordination nature of sulfur sites. Yet, the manipulation of sulfur sites normally requires direct contact with other metal atoms, which inevitably changes the state of the coordinated sulfur. Herein, we facilely construct a Mn-Sn2S6 framework by regulating the sulfur environment of the [Sn2S6]4- cluster with metal ions. Mn-Sn2S6 showed superior removal performance to gaseous elemental mercury (Hg0) at low temperatures (20-60 °C) and exhibited high resistance against SO2. Moreover, Mn-Sn2S6 can completely remove liquid Hg2+ ions with low or high concentrations from acid wastewater. In addition, the adsorption capacities of Mn-Sn2S6 toward Hg0 and Hg2+ reached 21.05 and 413.3 mg/g, respectively. The results of physico-chemical characterizations revealed that compared with Cu2+, Co2+, and Fe2+, the moderate regulation of Mn2+ led to the special porous spherical structure of Mn-Sn2S6 with uniform element distribution, due to the difference of electrode potentials [Eθ(Mn2+/Mn) < Eθ(S/S2-) < Eθ(Sn4+/Sn2+)]. The porous structure was beneficial to Hg0 and Hg2+ adsorption, and the presence of Mn4+/Mn3+ and S1- promoted the oxidation of Hg0, resulting in stable HgS species. The constructed Mn-Sn2S6, thus, is a promising sorbent for both Hg0 ang Hg2+ removal and provides guidelines for cluster-based materials design and tuning.