New Greener and Sustainable Methodology for Direct Sequestering and Analysis of Uranium Using a Maline Supramolecular Scaffold and Mechanistic Understanding through Speciation and Interaction Studies

Research, based on the development of an economical innovative green technology, is the quintessential requirement for the advancement of the nuclear fuel cycle (NFC). The present studies show that Maline, with a preorganized supramolecular scaffold, would be considered as the workhorse for its potential efficacy in diverse facets of the NFC, specifically as an elegant metal hijacker for processing of uranium (U) matrices, designer solvent for green analysis of U, and a promising U chelator for a greener alternative for the cleanup of U contamination. Seven U matrices (UO₃, UN, UO₂, Rb₂U(SO₄)₃, U metal, U₃Si₂, and (U, Pu)O₂) were dissolved in Maline without any external additives and cyclic voltammetry was performed to investigate the redox speciation, viz., redox thermodynamics (Eₚ and Eᶠ) and kinetic (D₀, k⁰, and αn) parameters and mechanistic electron transfer of the dissolved U species. To get an insight into the molecular speciation, the structural analysis on UO₃ dissolved in Maline was conducted by extended X-ray absorption fine structure, which indicates an interesting observation of the formation of UO₂²⁺ kind of species with malonic acid and H₂O at equatorial coordination. Molecular dynamics and density functional theory simulations were carried out to acquire diffusion, optimized structure, binding energy, and molecular orbital diagram of U species in Maline, to corroborate the experimental results and to shed light on the hydrogen-bond network in Maline with aqueous dilution. The interaction of uranyl with Maline was probed by luminescence, absorption spectroscopy, and calorimetry titration. Green analysis methodology was developed based on Maline digestion followed by voltammetric determination of U in nuclear material samples. Green chemistry metrics were evaluated to authenticate the greener aspects of the present methodology. The present developed methodology of direct sequestration and analysis of U matrices represents an appropriate replacement of the existing method, viz., hazardous acidic processing of U matrices followed by biamperometry analysis.