Synthesis of sulfonated magnetic polymer microspheres via seed swelling polymerization for green and efficient selective adsorption of La3+

Lanthanum (La), as a core and widely applied light rare earth element, possesses irreplaceable strategic value in key technological fields such as permanent magnets, catalysis, and optics. However, its green and efficient separation and purification remain significant challenges. In this study, sulfonated magnetic polymer microspheres (Fe 3 O 4 @PGMA-DVB-SO 3 H) were successfully synthesized for the first time through a simultaneous seed swelling polymerization strategy followed by sulfonation. Oleic acid-modified Fe 3 O 4 nanoparticles were successfully encapsulated within a crosslinked poly(glycidyl methacrylate-divinylbenzene) (PGMA-DVB) matrix, resulting in microspheres with uniform morphology, excellent dispersibility, and strong magnetic separability. The introduction of –SO 3 H groups provided abundant active sites, thereby enabling high selectivity for La 3+ over other competing rare earth ions, with the separation factor between La 3+ and Lu 3+ increasing progressively as sample concentration increased. Adsorption experiments revealed a maximum La 3+ adsorption capacity of 51.3 mg/g at pH 4.0 and room temperature, with the process following pseudo-second-order kinetics and exhibiting Langmuir-type isotherm behavior. Thermodynamic analysis indicated that the adsorption was spontaneous and endothermic. After five consecutive adsorption-desorption cycles, the adsorption efficiency of the magnetic nanospheres remained as high as 85%. FT-IR, XPS, and SEM-EDS characterizations, combined with density functional theory (DFT) calculations, revealed that the Fe 3 O 4 @PGMA-DVB-SO 3 H microspheres exhibited significant selectivity for La 3+ , which was primarily governed by stable electrostatic interactions and multi-site coordination between La 3+ ions and surface functional groups. This study presents a novel and scalable strategy for constructing green, efficient, and reusable magnetic functional adsorption materials with high selectivity toward the light rare earth element La.