Binding of Mercury Species and Typical Flue Gas Components on ZnS(110)

Environmentally benign zinc sulfide (ZnS), consisting entirely of active sites, has shown promising efficiency for capturing mercury from flue gas in recent experimental studies. In this work, the binding mechanism of Hg-0 on the ZnS(110) surface was investigated by the density functional theory (DFT) method. Meanwhile, the binding of two additional mercury forms, HgCl and HgCl2, and three essential flue gas components, H2O, SO2, and HCl, and their further effects on the strength of Hg-0 binding on the ZnS(110) surface were also evaluated. The results showed that, consistent with experimental observations, Hg-0 can be chemisorbed on the ZnS(110) surface with binding energies (BEs) as high as-87.80 kJ/mol. The enhanced electrostatic characteristics on the activated surface, especially the Zn sites, are beneficial to exciting the outer-shell electrons of Hg-0 and thereby enhancing the binding strength of the material. HgCl and HgCl2 were found to be chemisorbed with the highest BEs of -174.33 and -132.79 kJ/mol, respectively. Moreover, H2O was found to have a positive effect on Hg-0 binding, whereas SO2 and HCl have negligible effects. Our theoretical calculations demonstrate that ZnS has great potential to serve as a novel soxbent for the efficient removal of mercury from coal-combustion flue gas.