Enhanced Selective Adsorption of Lanthanum(III) by Dual-Site Polymeric Ion-Imprinted Nanoparticles from Aqueous Media

Selective recognition and separation of rare-earth elements (REEs) is considered a real challenge for the RE industry. In this work, two dual-site ion-imprinted polymers (IIP-AM and IIP-MAA) were synthesized via a radical copolymerization method for the removal of La(III) from aqueous solutions. The structures of samples were characterized and confirmed with various kinds of techniques, including IR, X-ray diffraction, field emission scanning electron microscopy, Brunauer–Emmett–Teller, thermogravimetry analysis, and X-ray photoelectron spectroscopy (XPS). Adsorption studies reveal that the pseudo-second-order kinetic model and the Langmuir isotherm model were well-fitted with the adsorption of La(III), showing high adsorption capacities of 45.65 and 50.05 mg/g for IIP-AM and IIP-MAA, respectively, after 120 min at pH = 5.5 and 25 °C. Impressively, the fabricated IIPs possess remarkable selectivity between La(III) and other REEs, as well as excellent reusability after five successive adsorption–regeneration cycles with less than 9% reduction of capacities. The adsorption mechanism indicates that the surface complexation and electrostatic attraction contribute to the adsorption of La(III) based on the characterization analysis of XPS, elemental mapping, and energy-dispersive spectrometry, as well as density functional theory calculations. Accordingly, these samples with tailored ion-imprinted cavities and abundant active O sites entirely exhibit the potentials for the selective recovery of REEs from aqueous solutions.