Hierarchically structured micro−/macro-porous Ni-MOF-74/polyacrylate composite beads with in situ MOF growth for high capacity Pb(II) removal from water

The practical implementation of metal-organic frameworks (MOFs) for water purification is often hindered by their powdery nature, limited processability, and mass-transfer limitations in dynamic systems. Herein, we report the in-situ growth of Ni 2 (dobdc) within a macroporous tetraethylenepentamine (TEPA)-functionalized polyacrylate (PA) matrix to fabricate hierarchically porous composite beads for the efficient removal of Pb(II) from water. The polymer support not only enabled the formation of mechanically stable, recoverable bead-shaped adsorbents suitable for fixed-bed operation but also directed the growth of smaller, more uniformly dispersed Ni-MOF-74 crystals than those of the pristine MOF synthesized without polymer support. The resulting composite bead integrates the intrinsic microporosity of Ni 2 (dobdc) with the polymer's macroporous architecture, thereby generating hierarchical transport pathways that facilitate access for adsorption and diffusion. XRD, SEM-EDS, FT-IR, XPS, TGA, and N 2 sorption confirmed the successful formation of the hierarchical MOF-polymer architecture and the preservation of the crystalline MOF structure within the beads. The Ni 2 (dobdc)@PA beads retain substantial porosity, a BET surface area of 593 m 2 g −1 , and a pore volume of 0.22 cm 3 g −1 . Batch adsorption experiments demonstrated rapid Pb(II) adsorption kinetics, achieving >85% removal within 15 min and near-complete removal within 25 min. Equilibrium data are well described by the Langmuir model, yielding a high Pb(II) adsorption capacity (q max = 598.8 mg g −1 ). The composite beads maintain remarkable Pb(II) uptake in binary-ion systems and show excellent regeneration stability. Fixed-bed experiments further substantiated the practical applicability of the structured adsorbent under dynamic flow conditions, delivering an overall Pb(II) removal efficiency of 87.3% for a 1000 mL influent at a flow rate of 1.0 mL min −1 . Post-adsorption characterization by FT-IR and XPS supported a surface-complexation-dominated mechanism enabled by the hierarchically porous bead architecture. This work provides a promising route toward scalable, processable MOF-based adsorbents for continuous heavy-metal removal from water.