Aggregation of Bifunctional Extractants Used for Uranium(VI) Separation

Evaluation of Adsorptive Capture and Release Efficiency of MNPs-SA@Cu MOF Composite Beads Toward U(VI) and Th(IV) Ions from an Aqueous Media

Effluent from nuclear power plants, rocks, and minerals contains hazardous radionuclides that adversely affect human health and seriously threaten the environment. To address this issue, simple, economic, and sustainable magnetite nanoparticle loaded sodium alginate copper metal-organic framework composite beads (MNPs-SA@Cu MOF composite beads) have been designed, and their performance has been evaluated under varying conditions of pH, time, adsorbent dose, and initial concentration and have been studied by batch adsorption studies for optimizing the adsorption conditions. In this work, MNPs-SA@Cu MOF composite beads have been prepared in situ for the adsorptive removal of uranium [U(VI)] and thorium [Th(IV)] ions from an aqueous solution. The synthesized MNPs-SA@Cu MOF composite beads were characterized by model analytical techniques like Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, Brunauer-Emmett-Teller, and thermal gravimetric analysis. Here, 6 mg of adsorbent with 10 mL of 50 mg/L uranium and thorium ion solution at pH 5 was capable of removing the U(VI) and Th(IV) ions with 99.9 and 97.7% removal efficiencies, respectively. The obtained results showed that the adsorption behavior of the adsorbent for U(VI) and Th(IV) follows pseudo-second-order kinetics, and Langmuir isotherm fitted well with a maximum adsorption capacity of 454.54 and 434.78 mg/g, respectively. The adsorption mechanism indicated that electrostatic interaction and hydrogen bonding are the main driving forces for removing the U(VI) and Th(IV) ions. It can be reused for up to 10 adsorption-desorption cycles with minimal loss of removal efficiency. The easy synthesis method of MNPs-SA@Cu MOF composite beads and the high removal efficiency of U(VI) and Th(IV) ions reveal that they can potentially treat radionuclide waste effectively.

Aggregation Behavior of Nitrilotriacetamide (NTAmide) Ligands in Thorium(IV) Extraction from Acidic Medium: Small-Angle Neutron Scattering, Fourier Transform Infrared, and Theoretical Studies

Two tripodal amides obtained from nitrilotriacetic acid with n-butyl and n-octyl alkyl chains (HBNTA(L_I) and HONTA(L_II), respectively) were studied for the extraction of Th(IV) ions from nitric acid medium. The effect of the diluent medium, i.e., n-dodecane alone and a mixture of n-dodecane and 1-decanol, onto aggregate formation were investigated using small angle neutron scattering (SANS) studies. In addition, the influence of the ligand structure, nitric acid, and Th(IV) loading onto ligand aggregation and third-phase formation tendency was discussed.The L_I/L_II exist as monomers (aggregarte radius for L_I: 6.0 Å; L_II:7.4 Å) in the presence of 1-decanol, whereas L_II forms dimers (aggregarte radius for L_II:9.3 Å; L_I does not dissolve in n-dodecane) in the absence of 1-decanol. The aggregation number increases for both the ligands after HNO₃ and Th(IV) loading. The maximum organic concentration (0.050 ± 0.004 M) of Th(IV) was reached without third-phase formation for 0.1 M L_I/L_II dissolved in 20% isodecanol +80% n-dodecane. The interaction of 1-decanol with L_II and HNO₃/Th(IV) with amidic oxygens of L_I/L_II results in shift of carbonyl stretching frequency, as shown by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) studies. The structural and bonding information of the Th-L_I/L_II complex were derived from the density functional theoretical (DFT) studies. The molecular dynamics (MD) simulations suggested that the aggregation behavior of the ligand in the present system is governed by the population of hydrogen bonds by phase modifier around the ligand molecules. Although the theoretical studies suggested higher Gibbs free energy of complexation for Th⁴⁺ ions with L_I than L_II, the extraction was found to be higher with the latter, possibly due to the higher lipophilicity and solubility of the Th-L_II aggregate in the nonpolar media.

Force Field Parameterization of Actinyl Molecular Cations Using the 12-6-4 Model

In this work, a set of 12-6-4 force fields (FFs) parameters were developed for the actinyl molecular cations, AnO2n+ (n = 1, 2), from uranium to plutonium for classical molecular dynamics (MD) for four water models: TIP3P, SPC/E, OPC3, and TIP4Pew. Such a non-bonded potential model taking into account the induced dipole between the metallic center and the surrounding molecules has shown better performances for various cations than the classic 12-6 non-bonded potentials. The parametrization method proposed elsewhere for metallic cations has been extended to these molecular cations. In contrast to the actinyl 12-6 FFs from the literature, the new models reproduce correctly both solvation and thermodynamic properties, thanks to the inclusion of the induced dipole term (C4). The transferability of such force fields was assessed by performing MD simulations of carbonato actinyl species, which are highly implicated in actinide migration or actinide extraction from seawater. A highly satisfying agreement was found when comparing the EXAFS signals computed from our MD simulation to the experimental ones. The set of FFs developed here opens new possibilities for the study of actinide chemistry.