Molecular-level insights into the immobilization of vapor-phase mercury on Fe/Co/Ni-doped hierarchical molybdenum selenide.

Abstract

A novel and efficient adsorbent (TM-MoSe2, TM = Fe, Co, Ni) for mercury removal was developed and studied. The adsorption of mercury species (Hg0, HgCl, and HgCl2) and the oxidation of Hg0 by HCl on TM-MoSe2 (001) surface were explored at molecular level by density functional theory (DFT). The results shown that the Hg0 adsorption capacity of MoSe2 was improved by the doping of Fe/Co/Ni, which was also confirmed by experiments. The initial Hg0 removal efficiency of MoSe2-based adsorbents reached 96.4-100.0%. In addition, HgCl was mainly adsorbed on TM-MoSe2 (001) surface in the form of dissociation. The escape of Hg atom from HgCl resulted in the release of Hg0 again. However, HgCl2 could be fixed well on the surface of adsorbent through molecular adsorption or dissociative adsorption. For the oxidation process of Hg0 by HCl, it abided with the Langmuir-Hinshelwood mechanism. In comparison with direct oxidation (Hg → HgCl2), two-step pathway (Hg → HgCl → HgCl2) was an achievable reaction route with lower energy. Furthermore, the Hg → HgCl process was the rate-limiting step of the two-step pathway. The proposed adsorption and oxidation mechanism of mercury species on TM-MoSe2 (001) provide advanced strategies on the development of adsorbents for industrial mercury removal.