Competition of Hg2+ adsorption and surface oxidation on MoS2 surface as affected by sulfur vacancy defects

Abstract

Two dimensional molybdenum disulfide (2D-MoS2) has been recently developed to be used as superb adsorbents for removing heavy metals from water due to its huge sulfur-rich surface area. In this work, single adsorption and co-adsorption performances of H2O, Hg2+ and O2 on MoS2 surface with and without S-vacancy defects have been theoretically studied to explore the Hg2+ adsorption and surface oxidation through density function theory (DFT) calculations. Moreover, the Hg2+ adsorption and surface oxidation have experimentally studied through atomic force microscopy (AFM) to verify the theoretical calculation results. It has been found that S-vacancy defects make MoS2 surface more reactive, leading to the much stronger adsorption energy of H2O, Hg2+ and O2 on defective MoS2 surface. O2 can only be physically adsorbed on the perfect MoS2 surface, while it bonds to the unsaturated Mo atoms at the vacancy site on defective MoS2 surface. Besides, co-adsorption results illustrate that Hg2+ have priority to react with MoS2 surface than O2 due to the much stronger binding affinity, and surface oxidation occurs only when there are enough reaction sites for the Hg2+ adsorption and surface oxidation simultaneously. These theoretical co-adsorption results are consistent with the experimental Hg2+ adsorption and surface oxidation results obtained by AFM. These findings in this study are of great significance for the development and utilization of MoS2-based nanomaterials as a heavy metal adsorbent.