Optimizing 2D MoS2 for removal of anionic heavy metals from water: insights from density functional theory study

Abstract

Two dimensional Molybdenum disulfide (2D MoS2) has been identified as a potential candidate for the adsorption of heavy metal (HM) ions. However, approaches that consider doping of the material as a means of enhancing the adsorption capabilities of HM ions are still lacking yet such knowledge is important for the optimisation of 2D MoS2 for the proposed applications. In this study, we used density functional theory and molecular dynamics simulation approaches to investigate the adsorption dynamics of HM ions (Hg+2, Pb+2, Cd+2, Zn+2, Cu+2, Ni+2, and Cr+3) in contaminated water on the surface of 2D MoS2 to unravel how such interactions can be improved with the introduction of S substitutional dopant using O, Cl, P, and Se as potential dopants. From the analysis of adsorption energies, the interactions between the HMs and doped MoS2 surfaces are all negative, implying that they are attractive and spontaneous. The interactions between the P- and Cl-doped 2D MoS2 surfaces and HM ions were more favourable than those between the Se- and O-doped systems. The results showed that Cl-doped 2D MoS2 was more effective for the removal of Hg+2, Cd+2, and Zn+2 HM ions because of their moderate adsorption energies. Furthermore, the analysis of projected density of states showed that the removal of Hg+2, Cd+2, and Zn+2 in water can be attributed to the hybridization of the d- and p-state electrons of the HMs and Cl-doped 2D MoS2 material. Upon thermal treatment, Hg, Cd, and Zn HMs were completely removed from the surface of Cl-doped 2D MoS2 at 322, 371, and 316 K, respectively, rendering the material reusable. This study explores the adsorption dynamics of HMs ions onto doped 2D MoS2 and provides some insights that may guide the realization of 2D MoS2 as a mainstream adsorbents in the removal of HMs in contaminated water.