Two-Dimensional Molybdenum Disulfide as a Superb Adsorbent for Removing Hg²⁺ from Water

Abstract

One feature of two-dimensional (2D) molybdenum disulfide nanosheets is the huge sulfur-rich surface area, which might lead to the strong adsorption of Hg2+ in water, because the sulfur on the surfaces could strongly bind to Hg2+. In this work, the adsorption of Hg2+ on 2D molybdenum disulfide sheets in water has been studied in order to develop a novel and efficient adsorbent for removing Hg2+ from water. The study was performed through the measurements of adsorption isotherm and kinetics, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy–energy-dispersive spectroscopy (SEM-EDS). The partially oxidized 2D molybdenum disulfide sheets with less than five S–Mo–S layers were prepared through the exfoliation of natural molybdenite. AFM observations illustrated a fast and multilayer Hg2+ adsorption on the surface of 2D molybdenum disulfide. The results of adsorption tests and SEM-EDS have indicated that 2D molybdenum disulfide was a superb adsorbent. The adsorption followed the Freundlich isotherm model and fitted well with pseudo-second-order kinetics model. The excellent Hg2+ capture property was mainly attributed to the complexation of Hg2+ with intrinsic S and oxidation-induced O atom exposed on 2D molybdenum disulfide surfaces, as well as the electrostatic interaction between negatively charged 2D molybdenum disulfide and cation Hg2+.