Interface-engineered MnFe2O4/poly(N-(1-naphthyl) ethylene diamine magnetic nanocomposite for high-affinity and recyclable adsorptive removal of 4-nitroaniline from water

Abstract

The release of aromatic amines such as 4-nitroaniline (4-NA) poses persistent environmental and health risks. Here, we synthesize a poly(N-(1-naphthyl) ethylenediamine)-modified manganese ferrite nanocomposite (MnFe₂O₄/PNED) and evaluate its performance as a reusable magnetic adsorbent for 4-NA removal. Structural, morphological, and textural analyses (XRD, SEM/EDX, and N₂ adsorption–desorption) confirm a crystalline spinel MnFe₂O₄ core uniformly wrapped by a thin PNED shell, with BET surface area and total pore volume increasing from 67.3 to 98.5 m² g⁻¹ and from 0.162 to 0.243 cm³ g⁻¹, respectively. Under the examined conditions, the composite delivers higher equilibrium uptake than bare MnFe₂O₄ (q_m up to ∼7.6 vs. ∼6.3 mg g⁻¹) and reaches equilibrium more rapidly, attributable to improved surface functionality/dispersion and mesoporosity. Maximum removal performance was obtained at pH 7, using an adsorbent dose of 0.01 g L⁻¹ and an initial 4-NA concentration of 20 mg L⁻¹. Kinetic data are well described by the pseudo-second-order model—particularly for MnFe₂O₄/PNED (R² = 0.985)—while equilibrium isotherms are best represented by the Langmuir model (R² = 0.9915 for MnFe₂O₄/PNED), indicating monolayer adsorption on energetically uniform sites with stronger affinity on the coated surface, even though the fitted q_m for PNED is slightly lower than that of pristine MnFe₂O₄. Dubinin–Radushkevich analysis yields mean adsorption energies E < 8 kJ mol⁻¹, consistent with physisorption dominated by π–π stacking and hydrogen bonding, with minor Lewis acid–base contributions at surface metal centers.