Sorption behaviour of Pu4+ and PuO22+ on amido amine-functionalized carbon nanotubes: experimental and computational study

Amido amine-functionalized multi-walled carbon nanotubes (MWCNT-AA) were used for efficient and selective solid phase separation of plutonium( iv ) and plutonium( vi ). Langmuir, Freundlich, Dubinin-Radushkevich (D-R), and Tempkin isotherms were employed for understanding the sorption mechanism and Lagergren first order kinetics, an intra-particle diffusion model, and pseudo second order kinetics were applied to understand the sorption kinetics. The sorption proceeded through monolayer coverage of MWCNT-AA with capacities of 91.2 mg g −1 and 89.4 mg g −1 for Pu 4+ and PuO 2 2+ , respectively following a Langmuir isotherm while the sorption kinetics followed a pseudo second order reaction with rate constants of 3.86 × 10 −5 and 3.19 × 10 −5 g mg −1 min −1 for Pu 4+ and PuO 2 2+ respectively. This MWCNT-AA showed high radiolytic stability and a method was developed for almost quantitative back extraction of plutonium in both the oxidation states from MWCNT-AA. Finally, the sorbent MWCNT-AA was employed for processing synthetic high level waste solution obtained from a research reactor origin. Moreover, density functional theory calculation was performed to examine the coordination and interaction behaviour of Pu 4+ and PuO 2 2+ ions towards MWCNT-AA. The present DFT study reveals that Pu is deca-coordinated (two from each of four nitrates and one AA) in the case of Pu 4+ and octa-coordinated (two from each of two nitrates and one AA, and one from each of two oxo groups) in PuO 2 2+ . The calculated free energy of complexation was found to be almost three times higher for Pu 4+ than PuO 2 2+ both in the gas and aqueous phase, which thus confirms the experimentally observed higher sorption of Pu 4+ compared to PuO 2 2+ by MWCNT-AA. Amido amine-functionalized multi-walled carbon nanotubes (MWCNT-AA) were used for efficient and selective solid phase separation of plutonium( iv ) and plutonium( vi ).