Polymer-microsphere coated with MoS2 nanoflowers for the removal of Pb(II) from water: Polydopamine-mediated MoS2 assembly and efficient Pb(II) adsorption

The engineering of macroscopic architectures by loading MoS2 nanosheets onto larger framework materials is an efficient strategy to overcome the limitations preventing the application of nanosized MoS2-based adsorbents for Pb(II) removal. However, the large-scale utilization of these nanocomposites still faces several challenges as a result of their poor stability, slow adsorption kinetics, and low MoS2 utilization. Herein, a practical and efficient nanocomposite (MoS2/PDA/MPS) was prepared by coating MoS2 nanoflowers onto micron-sized polystyrene beads (MPS) via the construction of a strong adhesive polydopamine (PDA) interlayer. The PDA interface can adhere to the MPS surface and immobilize the MoS2 nanopartices, thus facilitating the application of MoS2/PDA/MPS in flow-through systems. Further, the flower-like structure of the MoS2 on the outer surface of the host exposes active sites and facilitates mass transfer compared to those of traditional nanocomposites. Meanwhile, the R-SO3- groups of MPS can enhance permeation and preconcentrate the Pb(II) ions via the Donnan membrane effect, resulting in improved adsorption kinetics and capacity. Batch adsorption experiments revealed that MoS2/PDA/MPS shows fast adsorption kinetics (<45 min), exceptional adsorption capacity (371.7 mg/g, calculated from the Langmuir model at 298 K), and high adsorption selectivity for Pb(II) uptake. The excellent stabilities and reusability of the nanocomposite were tested over 10 adsorption–desorption cycles. In addition, a considerable working capacity (approximately 2000 BV) in synthetic wastewater was observed in fixed-bed column tests, and the used adsorbent could be readily regenerated with a binary NaCl–EDTANa2 solution for reuse without significant capacity loss. Thus, MoS2/PDA/MPS has great applications for the remediation of lead-containing wastewater, and our findings provide new insights into the preparation of efficient MoS2-based adsorbents having practical applications.