Pb(II) Adsorption on Amine-Grafted Fe 3 O 4 @MCM-41: Fast Uptake and O-Anchored Binding Revealed by DFT

Fe3O4@MCM-41–NH2 core–shell particles synthesized via coprecipitation and CTAB-templated silica coating with postgrafted APTES demonstrate ordered mesoporosity and magnetic separability. Characterization by XRD, FT-IR, TEM, N2 sorption, and VSM confirms BET surface area of 175 m2·g–1 and strong ferrimagnetism. Under batch conditions (pH 6.0, 25 °C, dose = 0.90 g·L–1), Pb(II) removal reached 94.8% in 60 min (qe = 21.1 mg·g–1), with kinetics following a pseudo-second-order model (k2 = 0.21 mg–1·g·min–1). Equilibrium data were described by Langmuir and Freundlich models; residual-focused metrics indicate mild site heterogeneity. Cluster-DFT calculations (r2SCAN-3c/B3LYP-D3/def2) reveal dominant O-anchored inner-sphere Pb–O complexes on the aminated silica surface in aqueous medium, thermodynamically favored over Pb–N coordination, with amine groups providing secondary environmental-tuning functionality. Multicycle reusability demonstrates robust performance. Overall, Fe3O4@MCM-41–NH2 provides fast Pb(II) uptake, mechanistic clarity via DFT, and practical magnetic recovery with sustained multicycle performance, positioning it as a promising regenerable adsorbent for sustainable wastewater remediation.