Tailoring moieties in sulfide-intercalated layered double hydroxides for efficient and stable removal of Cu2 + and Pb2+ in wastewater

In this study, four kinds of organosulfide-intercalated layered double hydroxides (LDH) with regulated amine structures were synthesized via the co-precipitation method, using diethylenetriamine (DETA), melamine (MEL), L -arginine (ARG) and diethylamine (DEA) as amine sources to react with carbon disulfide to prepare dithiocarbamate-based organosulfides. The structure and morphology of the adsorbents were characterized by XRD, FT-IR, SEM, and XPS, and their adsorption performances for Cu 2+ and Pb 2+ in aqueous solution were systematically investigated. The results indicate that the adsorption processes of copper and lead ions onto all four adsorbents conform more closely to the pseudo-second-order kinetic model and the Langmuir isotherm model, suggesting that the adsorption process was mainly controlled by the active sites and supplemented by surface precipitation. Among them, MEL-S@LDH exhibited the optimal adsorption capacity and dynamic adsorption performance due to the π-conjugated structure of triazine ring, which was also confirmed by molecular simulation. The adsorption mechanism involved the formation of stable coordination bonds between dithiocarbamate groups and heavy metal ions, accompanied by the precipitation of metal hydroxides on the surface of LDH layers. These adsorbents showed high selectivity toward Cu 2+ and Pb 2+ under the interference of coexisting ions, and BCR speciation analysis verified the excellent stability of the adsorbed products. This study demonstrates that tuning the amine structure of the intercalant is an effective strategy to enhance the performance of LDH-based adsorbents, with MEL-S@LDH showing particular promise for application in heavy metal wastewater treatment.