Process-Intensified Pb(II) Removal from Complex Matrices Using an Ultrasound-Assisted Magnetic Fe3O4@γ-Chitosan–Gallic Acid Nanocomposite

Abstract A magnetically recoverable Fe3O4@γ-chitosan-gallic acid (Fe3O4@Chi-GA) nanocomposite was engineered as a sustainable bioadsorbent for Pb(II) removal from complex environmental and consumer matrices. The material was synthesized via sequential surface functionalization of Fe3O4 nanoparticles with γ-chitosan and gallic acid, introducing abundant oxygen- and nitrogen-containing functional groups to enhance metal binding affinity. Comprehensive characterization (FTIR, XRD, TG/DTG, TEM, EDS, DLS, and BET) confirmed successful fabrication and favorable physicochemical properties. Ultrasound-assisted adsorption was employed to intensify mass transfer and reduce equilibrium time. The operating conditions governing Pb(II) adsorption were optimized through response surface methodology (RSM) employing a central composite design (CCD). At the optimized conditions of 0.02 g adsorbent, 50 °C, 10 min of sonication, and pH 5, an equilibrium adsorption capacity (qe) of 16.91 mg g–1 was obtained. Equilibrium data were most appropriately fitted by the Langmuir model, which yielded a maximum adsorption capacity (Qmax) of 19.72 mg g–1 and indicated predominantly monolayer adsorption. Moreover, the pseudo-second-order model provided a strong fit to the kinetic data (R2 = 0.9861), implying that chemical interactions contributed substantially to the adsorption process. Thermodynamic analysis further revealed that Pb(II) uptake was spontaneous and endothermic. Importantly, the nanocomposite demonstrated rapid magnetic separation, structural stability, and reusability over six cycles with minimal performance loss. Application to real samples, including beverages, cosmetic products, and wastewater, resulted in Pb(II) removal efficiencies of 75.92–85.40%, highlighting robustness against matrix interference. These findings demonstrate the potential of Fe3O4@Chi-GA as an efficient, reusable, and scalable adsorbent for ultrasound-enhanced heavy metal removal in complex systems.