Understanding Lanthanide Adsorption on DTPA-Functionalized Magnetic Nanoparticles: A Combined Kinetic, Spectroscopic and Colloidal Study

Lanthanide adsorption on DTPA-functionalized magnetic nanoparticles was investigated using neodymium (Nd³⁺) as a probe, with results extended across the series (La³⁺ to Dy³⁺). A two-step chemisorption mechanism is demonstrated: fast electrostatic complexation (∼61% charge neutralization, transient aggregation) followed by slower inner-sphere chelation (disaggregation). FTIR confirms chemisorption via disappearance of δ(O–H) at 1400 cm⁻¹, a new shoulder at 1585–1575 cm⁻¹, and ν(Ln–O) bands at ∼485 cm⁻¹. Gd³⁺ exhibits exceptional rigidity and the lowest desorption at pH 2 (91%) due to its half-filled 4f⁷ shell. In this work, we successfully performed the adsorption and desorption of several rare earth mixtures, demonstrating the potential for selective separation. Light lanthanides show high recovery (>95%). These results provide a unified framework for lanthanide–DTPA interfacial chemistry.