Complexation and Extraction of Trivalent Actinides and Lanthanides by Triazinylpyridine N-Donor Ligands

Preparation and characterization of a novel macroporous silica-bipyridine asymmetric multidentate functional adsorbent and its application for heavy metal palladium removal

The effective removal of heavy metal ¹⁰⁷Pd(II) from highly active liquid waste (HLW) is very valuable for reducing its hazardous and risk to public health and environment. For this purpose, a novel silica-bipyridine multidentate functional adsorbent was synthesized by vacuum infusing a new asymmetric N-donor ligand CA-MTBP (bipyridine derivative) into the macroporous SiO₂-P support. SEM, N₂ adsorption-desorption isotherms, TGA, XRD, FT-IR, ²⁹Si solid-state NMR and XPS spectroscopy were utilized to systematically characterize the physicochemical properties of the adsorbent. The characterization results indicated that CA-MTBP was successfully immobilized onto the pores of SiO₂-P by intermolecular interaction. Strong hydrogen-bonding interactions identified by single crystal structure of the ligand and ²⁹Si NMR may play a key role in achieving this immobilization. TGA and TOC studies showed that CA-MTBP/SiO₂-P had excellent thermal stability and highly HNO₃ resistance. EDS and XPS investigations provided directly evidences for Pd(II) being selectively adsorbed onto the adsorbent. The adsorbent had excellent adsorption capability, fast adsorption kinetics and high selectivity for Pd(II) over other typical tested metals in HNO₃ media.

The role of the 5f valence orbitals of early actinides in chemical bonding

One of the long standing debates in actinide chemistry is the level of localization and participation of the actinide 5f valence orbitals in covalent bonds across the actinide series. Here we illuminate the role of the 5f valence orbitals of uranium, neptunium and plutonium in chemical bonding using advanced spectroscopies: actinide M4,5 HR-XANES and 3d4f RIXS. Results reveal that the 5f orbitals are active in the chemical bonding for uranium and neptunium, shown by significant variations in the level of their localization evidenced in the spectra. In contrast, the 5f orbitals of plutonium appear localized and surprisingly insensitive to different bonding environments. We envisage that this report of using relative energy differences between the 5fδ/φ and 5fπ*/5fσ* orbitals as a qualitative measure of overlap-driven actinyl bond covalency will spark activity, and extend to numerous applications of RIXS and HR-XANES to gain new insights into the electronic structures of the actinide elements.

A thermodynamical and structural study on the complexation of trivalent lanthanides with a polycarboxylate based concrete superplasticizer

The complexation of trivalent lanthanides with a commercial polycarboxylate based concrete superplasticizer (Glenium® 51) is investigated using different spectroscopic techniques. Time-resolved laser fluorescence spectroscopy (TRLFS) in combination with a charge neutralization model is used to determine temperature dependent conditional stability constants (log β'(T)) for the complexation of Eu(iii) with Glenium® 51 in 0.1 mol kg^-1 NaCl solution in the temperature range of 20-90 °C. Only one complex species is observed, and log β'(T) (given in kg per mol eq) shows a very slight increase with temperature from 7.5 to 7.9. The related conditional molar reaction enthalpy (Δ_rH'_m) and entropy (Δ_rS'_m) obtained using the Van't Hoff equation show that the complexation reaction is slightly endothermic and entropy driven. The thermodynamic investigations are complemented by structural data for complexes formed with Gd(iii) or Tb(iii) and Glenium® 51 using extended X-ray absorption fine structure (EXAFS) spectroscopy. The results imply a non-chelate coordination of the trivalent metals through approximately three carboxylic functions of the polycarboxylate comb polymer which are attached predominantly in a bidentate fashion to the lanthanide under the given experimental conditions.

Studies on neptunium complexation with CMPO- and diglycolamide-functionalized ionic liquids: experimental and computational studies

A CMPO-functionalized task-specific ionic liquid provided significantly greater extraction of Np⁴⁺ than of NpO₂²⁺, which is of interest for radioactive waste treatment.

Metal–organic frameworks for radionuclide sequestration from aqueous solution: a brief overview and outlook

¹³⁷Cs, ⁹⁰Sr, ²³⁸U, ⁷⁹Se, and ⁹⁹Tc sequestrations from aqueous solution by metal–organic framework materials are summarized in this Frontier article.

Hydrophilic 2,9-bis-triazolyl-1,10-phenanthroline ligands enable selective Am(iii) separation: a step further towards sustainable nuclear energy

An exciting new family of hydrophilic ligands for the selective extraction of Am(iii) from spent nuclear fuel are reported herein.

Th(iv) and Ce(iv) napthylsalophen sandwich complexes: characterization of unusual thorium fluorescence in solution and solid-state

The synthesis, characterization, and surprising electronic spectroscopy of two ML₂ sandwich complexes, where M = Ce(iv) or Th(iv) and L = napthylsalophen²⁻ are described.

A novel highly selective ligand for separation of actinides and lanthanides in the nuclear fuel cycle. Experimental verification of the theoretical prediction

Predicted by DFT simulation dilactams (B) are selective and efficient extractants for the separation of Eu³⁺ and Am³⁺.

4,4′-Di-tert-butyl-6-(1H-tetrazol-5-yl)-2,2′-bipyridine: modification of a highly selective N-donor ligand for the separation of trivalent actinides from lanthanides

In the present work, the complexation and extraction behaviour of HN₄^tbubipy towards An(iii) and Ln(iii) is studied by spectroscopy, solvent extraction, and QM calculations.

Separation of Am3+ and Eu3+ using hexa-n-octylnitrilo triacetamide (HONTA): complexation, extraction, luminescence, EXAFS and DFT studies

Solvent extraction and complexation of Am³⁺ and Eu³⁺ were studied using HONTA.

Synthesis and characterization of uranium(iv) tetrachloro complexes in bis-pyrazolylpyridine ligand environments

The most intriguing feature in structures2a–2dis the out-of-plane shift of the U ion from the chelate's three coordinating N atoms (grey background: molecular plane), as exemplarily shown for2band2d.

Extraction of minor actinides, lanthanides and other fission products by silica-immobilized BTBP/BTPhen ligands

Novel BTBP [bis-(1,2,4-triazin-3-yl)-2,2′-bipyridine]/BTPhen [bis-(1,2,4-triazin-3-yl)-1,10-phenanthroline] functionalized silica gels have been developed to extract minor actinides, lanthanides and other fission products.

Noncovalent immobilization and surface characterization of lanthanide complexes on carbon electrodes

Surface immobilization and spectroscopic characterization of redox-active molecular lanthanide complexes is demonstrated on carbon electrodes.

Separation of rare earths and other valuable metals from deep-eutectic solvents: a new alternative for the recycling of used NdFeB magnets

Neodymium and dysprosium can be separated using a new extraction system based on a deep-eutectic solvent and Cyanex® 923 diluted in toluene.

Benzene-centered tripodal diglycolamides: synthesis, metal ion extraction, luminescence spectroscopy, and DFT studies

Three benzene-centered tripodal diglycolamides (Bz-T-DGAs) were synthesized and evaluated for actinide, lanthanide, and fission product ion extraction.

Characterization of Lanthanide Complexes with Bis-1,2,3-triazole-bipyridine Ligands Involved in Actinide/Lanthanide Separation

The complexation of selected trivalent lanthanide ions with derivatives of the tetranitrogen donor ligands 6,6'-bis-1R,1H-1,2,3-triazol-4-yl-2,2'-bipyridines (BTzBPs, R = alkyl or aryl) was investigated in solid state and in solution. An anhydrous solid [Ce(Bn-BTzBP)(NO₃)₃] (Bn = benzene) complex was synthesized and characterized by single-crystal X-ray diffraction. Eu(III) complexes with the 2-ethyl(hexyl) derivative EH-BTzBP in methanol were studied by time-resolved fluorescence spectroscopy. Earlier studies have identified the EH-BTzBP as a potentially useful solvent extraction reagent for the separation of americium from lanthanide metal ions, a challenging component of advanced nuclear fuel cycles for actinide transmutation. To help identify species formed in the extraction process, the influence of 2-bromohexanoic acid (identified as an essential component of the separation system) on Eu(III) complexes was investigated. Comparison with an organic phase after extraction of Eu(III) by EH-BTzBP and 2-bromohexanoic acid showed that both 1:1 and 1:2 (Eu/EH-BTzBP) complexes are involved in the extraction. UV-visible spectrophotometry was used to compare Eu(III) stability constants with those of other Ln(III) complexes.

Extraction of Lanthanide and Actinide Ions from Aqueous Mixtures Using a Carboxylic Acid-Functionalized Porous Aromatic Framework

Porous aromatic frameworks (PAFs) incorporating a high concentration of acid functional groups possess characteristics that are promising for use in separating lanthanide and actinide metal ions, as required in the treatment of radioactive waste. These materials have been shown to be indefinitely stable to concentrated acids and bases, potentially allowing for multiple adsorption/stripping cycles. Additionally, the PAFs combine exceptional features from MOFs and inorganic/activated carbons giving rise to tunable pore surfaces and maximum chemical stability. Herein, we present a study of the adsorption of selected metal ions, Sr(2+), Fe(3+), Nd(3+), and Am(3+), from aqueous solutions employing a carbon-based porous aromatic framework, BPP-7 (Berkeley Porous Polymer-7). This material displays high metal loading capacities together with excellent adsorption selectivity for neodymium over strontium based on Langmuir adsorption isotherms and ideal adsorbed solution theory (IAST) calculations. Based in part upon X-ray absorption spectroscopy studies, the stronger adsorption of neodymium is attributed to multiple metal ion and binding site interactions resulting from the densely functionalized and highly interpenetrated structure of BPP-7. Recyclability and combustibility experiments demonstrate that multiple adsorption/stripping cycles can be completed with minimal degradation of the polymer adsorption capacity.

Modular Approaches to Diversified Soft Lewis Basic Complexants through Suzuki-Miyaura Cross-Coupling of Bromoheteroarenes with Organotrifluoroborates

Remediation or transmutation of spent nuclear fuel obtained as a function of energy production and legacy waste remains a significant environmental concern. Substantive efforts over the last three decades have focused on the potential of soft-Lewis basic complexants for the chemoselective separation of trivalent actinides from lanthanides in biphasic solvent systems. Recent efforts in this laboratory have focused on the concept of modularity to rapidly prepare complexants and complexant scaffolds not easily accessible via traditional linear methods in a convergent manner to better understand solubility and complexation structure/activity function in process-relevant solvents. The current work describes an efficient method for the construction of diversified complexants through multi-Suzuki-Miyaura cross-coupling of bromoheteroarenes with organotrifluoroborates affording efficient access to 22 novel materials in 43-99% yield over two, three, or four cross-couplings on the same scaffold. Optimization of the catalyst/ligand system, application, and limitations are reported herein.

Solvent extraction of americium(iii) and europium(iii) with tridentate N,N-dialkyl-1,10-phenanthroline-2-amide-derived ligands: extraction, complexation and theoretical study

Herein, the extraction and complexation of americium(iii) and europium(iii) with three N,N-dialkyl-1,10-phenanthroline-2-amide analogues were investigated, and theoretical calculations were carried out.

Highly efficient extraction of actinides with pillar[5]arene-derived diglycolamides in ionic liquids via a unique mechanism involving competitive host–guest interactions

A novel extraction mechanism is described.

Selective separation of trivalent f-ions using 1,10-phenanthroline-2,9-dicarboxamide ligands in ionic liquids

1,10-Phenanthroline-2,9-dicarboxamide complexants decorated with alkyl chains and imidazolium cations have been studied for extraction of trivalent f-ions into imidazolium ionic liquids.