Sequestration of Np4+ and NpO22+ ions by using diglycolamide-functionalized azacrown ethers in C8mim·NTf2 ionic liquid: Extraction, spectroscopic, electrochemical and DFT studies

•Two aza-macrocycle based multiple DGA ligands were used for the extraction of Np(IV) and Np(VI) from nitric acid feeds.•Room temperature ionic liquid, used as the diluent, resulted in improved metal ion extraction.•The extraction of Np(IV) was significantly higher than that of Np(VI) based on its higher ionic potential.•The bonding in the extracted species was explained by DFT and spectrophotometric analysis.•Extraction of Np4+ is by ‘cation-exchange’ mechanism, whereas NpO22+ extraction is by a ‘solvation’ mechanism.