Theoretical research on reaction of solid sulfur allotropes with elemental mercury

Element sulfur has proven to be active material for hazardous elemental mercury (Hg-0) removal. However, the underlying mechanism of elemental sulfur reacting with Hg-0 was still unclear. Generally, solid elemental sulfur exists mainly composed of crown-shaped S-8 molecules and traces of S-6, S-7, and S-9 molecules. This research employed quantum chemical calculations and electronic wavefunction analysis to investigate the reaction between branched and cyclic S-n, isomers (n = 6-9) with Hg-0 at the molecular level. Thermodynamic data and kinetics were also computed. It was found that Hg-0 react with branched S-n, isomers would proceed spontaneously with heat release by analyzing reaction Gibbs free energies and enthalpies. Reaction rate constants of branched S-n, molecules are several orders of magnitude higher than those of cyclic S-n, molecules. Moreover, the electronic wavefunction analysis was conducted. The Mayer bond order along the reaction pathway could characterize Hg-S and S-S bonds breaking and formation quantitively. Localized molecular orbitals isosurface maps reflect Hg-S bonds show typical sigma bond characteristics in the products. Localized orbital locator color-filled maps reveal electrons begin to concentrate in the region between Hg and 5 atoms as reactions proceeding forward. In summary, this research would help develop sulfur contained adsorbents with superior Hg-0 removal performance in the future.

Automated summary

This research investigates the reaction mechanism between sulfur and Hg-0 through quantum chemical calculations and electronic wavefunction analysis. It shows that branched S-n isomers react with Hg-0 spontaneously with heat release, and have higher reaction rate constants than cyclic S-n molecules. Furthermore, electronic wavefunction analysis characterizes the breaking and formation of Hg-S and S-S bonds during the reaction process.