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In addition to solvent extraction experiments, the extensive molecular dynamics simulations have been performed for aqueous (water + uranyl ion + nitrate ion + nitric acid) organic (tributyl phosphate (TBP) + dodecane) biphasic systems in order to gain molecular insights of uranium extraction process. The simulation results well corroborate with the experimental observations. An attempt has been made to uncover the location of uranyl-TBP complexation by systematically studying the distribution of the complexes at the interface, mixed phase and the bulk phases. From the distribution constant profile, the extraction of UO2+2 ions to the organic phase was predicted to increase with increase in UO2+2 ion concentration. The experimentally observed bell shaped profile of distribution constant for uranyl extraction vs. acid concentration was first time captured by the MD simulations. The interface thickness was seen to be increased with increase in uranyl concentration. On the other hand, the inverse bell-shaped curve of interfacial thickness was noticed with increasing acid concentration. The extraction of uranyl ions was predicted to be proportional to the interface thickness. Finally, the stoichiometry distribution of UO2+2ions and UO2+2-TBP complex, their hydration characteristics, and structural orientation was explored in the different zones of biphasic system. The MD results show that the UO2+2-TBP complexation happens at the interface not in the organic phase as recently reported by the vibrational sum frequency generation experiment. However, reorganization of UO2+2-TBP complex was observed while migration from interface to the bulk organic phase. More, simulations and experimental studies are needed further to resolve the issue of uranyl ion complexation at the interface.

The present investigation demonstrated the efficient sorption of NpO 2 + and NpO 2 2+ on amidoamine functionalized multiwalled carbon nanotube via chemisorption following Langmuir isotherm. A pseudo second order kinetics were found to follow with the rate constant 5.13 × 10 −4 and 3.85 × 10 −4 mg g −1 min −1 for NpO 2 + and NpO 2 2+ , respectively. The radiolytic stability of the sorbent and the back extraction of the neptunium from the sorbent have been investigated. Computational study was also carried out to optimize the structure of the amidoamine functionalized carbon nanotube and its complex of NpO 2 + and NpO 2 2+ . The amidoamine and all the nitrate anions are coordinated to the neptunyl centre in bidentate mode resulting to six-coordinated and octa-coordinated complex for NpO 2 + and NpO 2 2+ , respectively. The theoretically calculated value of ΔG of NpO 2 2+ sorption is found to be higher than that of NpO 2 + which is in good congruence with the experimentally observed higher adsorption capacity for NpO 2 2+ over NpO 2 + .

Poly(amidoamine) dendrimer functionalized carbon nanotube was demonstrated as highly efficient sorbent of the Pu4+ from radioactive waste solution. The second generation dendrimer was found to have more efficiency as compared to the 1st generation might be due to the availability of more functionality for coordinating to the Pu4+ ion. Analysis of different isotherm models revealed that, Langmuir isotherm was predominantly operating through chemi-sorption (with the sorption energy 10.07 and 16.95 kJ mol−1 for 1st and 2nd generation dendrimer) with the sorption capacity 89.22 mg g−1 and 92.48 mg g−1 for 1st and 2nd generation dendrimer, respectively. Analysis of different sorption kinetics model revealed that the sorption proceeded via pseudo 2nd order reaction. The 2nd generation dendrimer was found to be radiolytically more stable while oxalic acid was found to be suitable for quantitative back extraction of Pu4+.

Poly(amidoamine) dendrimer functionalized carbon nano tubes were synthesized, characterized and used for the sorption of americium from aqueous acidic waste solution. The sorption of Am3+ has been found to take place through pseudo second order kinetics with the rate constants of 8.61E-05 and 5.38E-05 mg g−1 min−1for 1st and 2nd generation, respectively, followingLangmuir isotherm. The MWCNT-PAMAMG1 and MWCNT-PAMAMG2 have high radiolytic stability. The stripping study revealed that EDTA can be effectively used for almost quantitative back extraction of metal ion from both generation of dendrimer. Luminescence investigation revealed the presence of single species with no inner sphere water molecule. The 1st generation dendrimer complex was found to be more asymmetric compared to the 2nd generation. The analysis of Judd Offelt parameters and evaluation of photo-physical properties were carried out to understand the complexation of Am3+ with these sorbents.

Extraction of metal ions (i.e., Cs+, K+, Na+, and Rb+) in the presence of ionophore such as dibenzo-18-crown-6 (DB18C6) from the nitrobenzene–water biphasic system is reported by COSMO-RS (conductor-like screening model for real solvents) predictions, molecular dynamics simulation, along with experimental validation. The predicted values of selectivity as obtained for the Na+–DB18C6 complex were 4.571, 4.877, and 4.947 at 298.15, 308.15, and 318.15 K, respectively. This was then confirmed by the experimental distribution coefficient (D) as obtained in the diluent systems along with by varying the metal ion to crown ether ligand (M–L) mole ratios: 10:1 (0.1 M M+ and 0.01 M DB18C6), 1:1 (0.01 M M+ and 0.01 M DB18C6), and 1:10 (0.001 M M+ and 0.01 M DB18C6). The experimentally determined values of DNa (i.e., 0.059, 0.060, and 0.056) were found to be very large as compared to the values of DCs (i.e., 0.001, 0.010, and 0.024) in the nitrobenzene phase. It indicates an excellent extraction ability of DB18C6 for Na+. The rate of phase separation for the Cs+NO3– system was slow as compared to other metal ion systems. The binding energies, free energies, and nonbonded interaction energies of the complexed metal ion in solution were calculated with both explicit and implicit solvent models. A higher interaction energy between Na+–DB18C6 complex and nitrobenzene was observed (i.e., −289.92 in the explicit model and −143.12 kcal/mol in the implicit model) when compared with other metal ions (i.e., Cs+, K+, and Rb+).