Bifunctional Monolithic Magnetic Lanthanum-Loaded Polyurea Aerogel for Efficient Fluoride Adsorption and Rapid Separation

Abstract Polyurea aerogel adsorbents suffer from low apparent density due to their high porosity, making rapid solid–liquid separation by gravity sedimentation difficult. To overcome this bottleneck, Fe3O4 magnetic nanoparticles were introduced into the polyurea aerogel framework via in situ coprecipitation. The resulting magnetic lanthanum-loaded polyurea aerogel (MLa-PUA) composite possesses a three-dimensional interconnected porous structure with a specific surface area of 36.24 m2/g. It exhibits a saturation magnetization of 18.29 emu/g with typical superparamagnetic characteristics, enabling magnetic separation within 1 min under an external magnetic field of ∼0.3 T. Static adsorption experiments using ∼3 mm granules obtained by crushing the monolithic aerogel demonstrated that MLa-PUA maintains stable fluoride removal performance over a wide pH range of 2–11 and a temperature range of 25–45 °C. The interference order of coexisting anions follows the sequence: PO43– > CO32– > HCO3– > SO42– > Cl–. The adsorption process fits the Langmuir isotherm model and the pseudo-second-order kinetic equation, reaching equilibrium within 120 min, with a theoretical maximum adsorption capacity of 95.78 mg/g. Mechanistic investigation reveals that ligand exchange is the dominant adsorption mechanism, involving the combination of F– with La3+ to form LaF3. Desorption regeneration experiments identified 1.5 mol/L NaOH as the optimal eluent, achieving a desorption capacity of 34.30 mg/g within 120 min. After six adsorption–desorption cycles, the fluoride removal rate remained above 71%, and the saturation magnetization was retained at 13.78 emu/g. This study successfully endows the lanthanum-loaded polyurea aerogel with rapid magnetic separability through a magnetic functionalization strategy while preserving its high fluoride adsorption capacity, offering a feasible solution for the engineering application of low-density porous adsorbents.