Unveiling the dual roles of the intercalation of [MoS4]2− clusters in boosting heavy metal capture by Ca–Al layered double hydroxide

Abstract

Heavy metals such as Pb(II) and Cd(II) are ubiquitously present in aquatic and soil environments and pose a critical threat to the environment and human health. Herein, we report a strategy to prepare high-performance adsorbent materials by assembling [MoS₄]²⁻ groups between the lamellae of CaAl-LDHs (LDH/MoS₄) for Pb(II) and Cd(II) removal. The assembling of LDH/MoS₄ was achieved by a facile coprecipitation and anion exchange method. The intercalation with [MoS₄]²⁻ not only expanded the interlayer spacing but also created more active sites for the capture of the targeted heavy metals. The obtained LDH/MoS₄ nanocomposites demonstrated enormous adsorption capacities of 1202.1 and 678.3 mg g⁻¹ for Pb(II) and Cd(II), respectively. The excellent adsorption of Pb(II) and Cd(II) by LDH/MoS₄ could be attributed to the following: Pb(II) and Cd(II) can form strong M–S covalent bonds with the [MoS₄]²⁻ clusters, and Cd(II) can easily undergo lattice substitution with Ca(II) on the layer of LDHs owing to the similar ionic radius of Ca(II) and Cd(II). Moreover, density functional theory (DFT) calculations further verified the adsorption mechanisms of Pb(II) and Cd(II) sorption. Altogether, its facile fabrication and rapid and ultrahigh adsorption efficiencies demonstrate the importance of LDH/MoS₄ in the simultaneous removal of multiple heavy metal ions in practical applications.