Toward an Understanding of Fundamentals Governing the Elemental Mercury Sequestration by Metal Chalcogenides

The lack of fundamental understanding of the chemistry governing elemental mercury (Hg⁰) immobilization over metal chalcogenides (MChals) is the key challenge impeding the interpretations of Hg⁰ behaviors in global cycles. This work therefore made the first endeavor toward the establishment of a roadmap capable of describing and depicting Hg⁰ sequestrations by various MChals. The results suggest that the binding energy between the metal cations and chalcogen anions is a proper descriptor that could predict the immobilization behaviors of Hg⁰ over zinc chalcogenides (ZnS and ZnSe) that exhibit an identical molecular structure, i.e., the lower the binding energy was, the higher the Hg⁰ sequestration performance that was obtained. The validity of this descriptor was further demonstrated over a series of MChals sharing structural similarities. A scaling relationship was thus established, which further proved the Hg⁰ immobilization performance of MChals was generally in reverse proportion to the above-mentioned binding energy. Although there is still a long way toward the proposal of a full roadmap that can predict and depict the Hg⁰ immobilization behaviors over all MChals, this work marks the first step on this road and provides guides for further studies by understanding the fundamentals governing Hg⁰ sequestration over MChals with structural similarities.