Diglycolamic Acid-Functionalized MWCNT-Augmented Polymeric Beads for Efficient Separation of Trivalent Lanthanides and Actinides

Abstract

Diglycolamic acid-functionalized multiwalled carbon nanotubes (DGA-MWCNTs) were augmented onto polysulfone-based polymeric materials for the efficient separation of two representative trivalent lanthanide and actinide ions (Eu3+ and Am3+) from the aqueous acidic streams. The appearance of the carbonyl peak at ∼1665 cm–1 along with the −OH bending band of the carboxylic acid revealed the successful incorporation of the DGA-MWCNT onto polysulfone, which was also evidenced by the change in surface morphology in the scanning electron microscope (SEM) images. While analyzing the uptake data, the maximum separation factor was found for aqueous feeds with pH values in the range of 3.5–5, where the polymer with 3% DGA-MWCNT loading exhibited more than 87% sorption for both Eu3+ and Am3+. The sorption processes predominantly followed pseudo-second-order rate kinetics with estimated rate constants of 1.0 × 10–5 mg g–1 min–1 and 1.8 × 10–5 mg g–1 min–1 for Am3+ and Eu3+, respectively. The uptake data were fitted to isotherm models, viz., Langmuir, Freundlich, Dubinin–Radushkevich, etc., and conformed well to the Freundlich isotherm. The sorption of the metal ions was found to be spontaneous (ΔG Am ∼ −6.3 kJ mol–1, ΔG Eu ∼ −6.8 kJ mol–1), and the overall enhancement in entropy during sorption indicated the formation of inner-sphere complexes. The PS-DGA-MWCNT beads exhibited good radiation stability up to a 500 kGy γ dose, while at 1000 kGy, deterioration in the separation performance was observed. Single contact with 0.1 M EDTA resulted in more than 96% back extraction of Am3+ and Eu3+ from the loaded polymeric beads, whereas quantitative back extraction was achieved after two consecutive contacts.