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Metal–organic frameworks (MOFs) are a class of compounds with modern-age technological importance due to diverse structural topologies, porosity, and modularity. ZIF-67 has been synthesized for efficient extraction of f cations in different oxidation states (UO22+, Th4+ and Eu3+) from aqueous pH medium exhibiting the trend in sorption efficiency as: KdTh(6.19 × 103) > KdU (5.20 × 103) > KdEu (1.58 × 103) in accordance to their chemical potential. Langmuir isotherm was found to be predominate with sorption capacity 85.9 mg g−1, 137.4 mg g−1 and 50.6 mg g−1 for U, Th and Eu, respectively. The sorption predominantly proceeded via pseudo 2nd order rate kinetics with rate constants: k2U ~0.089 g mg−1 min−1, k2Th ~0.011 g mg−1 min−1 and k2Eu ~0.04 g mg−1 min−1. The processes were found to be spontaneous as revealed from negative ΔG values; and endothermic in nature (ΔHU ~10.5 kJ mol−1; ΔHTh ~12.8 kJ mol−1; ΔHEu ~8.3 kJ mol−1). The sorption proceeded via the formation of an inner sphere complex as indicated from their enhancement in the entropy values on sorption due to the release of water molecules. The Density Functional Theory (DFT) predicted selectivity using binding energy (ZIF-67-Eu3+ ~ -60.90 eV, ZIF-67-Th4+ ~ -70.78 eV, ZIF-67-Th4+ ~ -69.52 eV) is in line with the experimental selectivity of Th4+ > UO22+ > Eu3+. Total density of states (TODS) and Projected density of States (PODS) were estimated in order to understand the interaction between the ZIF-67 and f cations. [ABSTRACT FROM AUTHOR]

Selective and efficient separation of pertechnetate (TcO 4 - ) from nuclear waste is desirable for the safe and secure management of radioactive waste. Here, we have projected dibenzo-18-crown-6 ether (DB18C6) in a highly polar nitrobenzene medium for enhancing the removal efficiency of 99 Tc from reprocessing plant low level waste (LLW). An effort was made to determine the stoichiometry of metal-ligand complex by slope ratio method, revealing that one ligand (DB18C6) binds with one TcO 4 - moiety. Optimum ligand concentration for 99 Tc extraction was evaluated. Relevant interference of the anions was studied systematically. The effect of solution pH was analysed on the extraction efficiency of 99 Tc. A kinetic study was carried out for maximum extraction of metal ions. A quantitative stripping study was also achieved for metal ions with a suitable stripping solution. After evaluation of all essential parameters, selectivity and feasibility studies were finally carried out with actual low level reprocessing plant waste to demonstrate a laboratory scale process for effective separation of TcO 4 - ions. Density functional theory (DFT) calculations were carried out to understand the nature of the complexation of TcO 4 - ion with DB18C6 in different solvents systems and to elucidate the key aspect behind ionic selectivity and enhanced the 99 Tc extraction efficiency of DB18C6 in the studied diluent systems. The Δ E and Δ G values for different modeled complexation reactions were evaluated systematically. From the calculated free energy of complexation of TcO 4 - with DB18C6, it was observed that the consideration of explicit solvent plays a vital role in predicting the experimental selectivity., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)