Two-dimensional WS2 as a new mercury removal material: Mercury conversion pathway and effect of defect

Two-dimensional tungstenite (WS2) has great potential to efficiently control gaseous Hg-0 release, because of its wide surface area and the high affinity between mercury and sulfur in WS2. The mercury species adsorption and conversion mechanism over raw and defective WS2(001) surface was investigated on the basis of density functional theory (DFT). The results show that S-defect site on the WS2 surface exhibits more outstanding ability than S-top site to strongly adsorb Hg-0. The oxidizing mercury species (HgO, HgS, HgCl and HgBr) are much easier to be adsorbed by WS2 than elemental mercury, with higher adsorption energy (from -76.09 to -182.59 kJ/mol). The reaction path in the formation of HgS includes a two-step process on S-WS2: Hg-0 -> HgS(ads) -> HgS. In the first reaction step, the energy barrier of surface reaction between elemental mercury and defective S-WS2 is just 4.02 kJ/mol. The second desorption step is an endothermic process and the rate-determining step. The verifying experiment show that WS2 has excellent mercury removal ability at low reaction temperatures under different kinds of flue gas environment. In the whole, WS2 is one of most promising sorbent materials, which can be used for the efficient control of gaseous mercury.

Automated summary

The study shows that WS2 surface's sulfur defect site exhibits stronger adsorption ability for Hg-0 than the sulfur top site; oxidizing mercury species are easier to be adsorbed by WS2, with higher adsorption energy; the formation of HgS involves a two-step process on S-WS2.