Phase-Mediated Heavy Metal Adsorption from Aqueous Solutions Using Two-Dimensional Layered MoS₂

An understanding of the impacts regarding different phases of inorganic materials on heavy metal removal is indispensable, owing to the intrinsic structure of materials that can affect its properties. In this study, the distinct adsorption behaviors of heavy metals (Pb(II) and Cu(II)) on different phases of MoS₂ (metallic phase (1T) and semiconducting phase (2H)) were theoretically and experimentally investigated. According to the computational results, both Pb(II) and Cu(II) have formed more stable complexes on 1T-MoS₂ compared to those on 2H-MoS₂ due to the lower adsorption energy (E_ad). This phenomenon indicates that Pb(II) and Cu(II) were more preferably adsorbed onto 1T-MoS₂. Based on the results of the computational studies, two-dimensional (2D) MoS₂ nanosheets with identical 1T and 2H phases were synthesized via a facile hydrothermal reaction. As we surmised, 1T-MoS₂ achieved excellent Pb(II) and Cu(II) adsorption capacities, which were 147.09 and 82.13 mg/g at 298 K, respectively, compared to those of 2H-MoS₂ (i.e., 64.16 and 50.74 mg/g at 298 K). Moreover, 1T-MoS₂ has shown other superior properties, such as (i) ultrafast adsorption kinetics and (ii) great anti-interference activity toward other existing cations, compared to 2H-MoS₂. Extensive computations and characterizations of MoS₂-Pb and -Cu adsorption complexes illustrated that the active S sites were indispensable for heavy metal adsorption. Overall, for the first time, we provide evidence that 1T-MoS₂ is more functional in heavy metal removal compared to 2H-MoS₂, which can guide and expand the applications of MoS₂-based adsorbents in environmental remediation.