Thermal Modification of the Molybdenum Disulfide Surface for Tremendous Improvement of Hg²⁺ Adsorption from Aqueous Solution

The adsorption of Hg²⁺ on thermally modified molybdenum disulfide was explored in this work. The X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) results revealed that thermal treatment led to partial oxidation of MoS₂ to MoO₃ and a creation of edge defects on the surface of molybdenum disulfide. The density functional theory (DFT) calculation indicated that the oxidative etchings were terminated with oxygen atoms, and both the vacancy and perfect surface could be oxidized during thermal treatment. The batch tests indicated that thermal treatment enabled the surface of molybdenum disulfide to be highly reactive as Hg²⁺ adsorbent. The adsorption rate and capacity of 500 °C heated molybdenum disulfide were 17.6 times faster and 11-fold higher compared to that of molybdenum disulfide without thermal modification. The tremendous enhancement of Hg²⁺ adsorption was significantly related to the oxidation of molybdenum disulfide and the increase of atom activity on the surface. The oxidation could provide O active sites to strongly adsorb Hg through the formation of the Hg–O complex, while the increased activity greatly improved the affinity of Hg to molybdenum disulfide. This work suggests that thermal modification is an efficient method to increase the removal capacity of heavy metals on molybdenum disulfide