Tripodal Diglycolamide Research Articles

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. 1,3,5-Triethylbenzene-based tripodal DGA (LI) showed high distribution ratio (D) values for Am3+ and Eu3+ in a mixture of 95% n-dodecane and 5% iso-decanol at 3 M HNO3. Eu/Am separation factors, in the range of 8-10, were obtained at 1 M HNO3 which decreased at higher acidities with the exception of LII which did not show much change. Benzene-1,3,5-triamide-based tripodal DGA (LII) exhibited a high D-value for Pu4+ compared to the other ligands. Slope analysis showed the formation of 1 : 1 or 1 : 2 complexes is dependent on the ligand. The nature of the complexes was further studied with luminescence spectroscopy (Eu complexes) and DFT calculations (Am complexes).

Multi-podant diglycolamides and room temperature ionic liquid impregnated resins: An excellent combination for extraction chromatography of actinides

Extraction chromatography resins, prepared by impregnating two multi-podant diglycolamide ligands, viz. diglycolamide-functionalized calix[4]arene (C4DGA) and tripodal diglycolamide (T-DGA) dissolved in the room temperature ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (RTIL: C4mimTf2N) on Chromosorb-W (an inert solid support), gave excellent results for the removal of trivalent actinides from acidic waste solutions. Distribution coefficient measurements on several metal ions showed selective sorption of Am(III) over hexavalent uranyl ions and other fission product elements such as strontium and cesium. The sorbed metal ions could be efficiently desorbed with a complexing solution containing guanidine carbonate and EDTA buffer. The sorption of Am(III) on both resins followed pseudo-second order rate kinetics with rate constants of 1.37×10−6 and 6.88×10−7g/cpmmin for T-DGA and C4DGA resins, respectively. The metal sorption on both resins indicated the Langmuir monolayer chemisorption phenomenon with Eu(III) sorption capacities of 4.83±0.21 and 0.52±0.05mg per g of T-DGA and C4DGA resins, respectively. The results of column studies show that these resins are of interest for a possible application for the recovery of hazardous trivalent actinides from dilute aqueous solutions.

Polymer inclusion membrane containing a tripodal diglycolamide (T-DGA): Characterization and sorption isotherm studies

Polymer inclusion membranes (PIMs) of the composition, 25.6% T-DGA (tripodal diglycolamide), 53.9% NPOE (2-nitrophenyloctyl ether), and 20.5% CTA (cellulose triacetate) were prepared and characterized using thermogravimetric analysis, X-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission infrared mapping microscopy (TIMM) using Fourier transform infrared (FT-IR) spectroscopy. Uptake of Am3+ was found to be higher than that of Eu3+ and >82% uptake of Am3+ was seen with the PIM of the composition mentioned above. The batch sorption study of Eu3+ (used as a surrogate of Am3+) by this PIM was investigated in 1 M HNO3 and the data were fitted with different conventional kinetic and isotherm model equations. The sorption followed pseudo-second order (Ho) kinetic model suggesting a two-step uptake process, a fast chemical reaction followed by a slow diffusion process. The experimental data were best fitted with a three-parameter model, i.e., the Redlich-Peterson isotherm model. A comparison is made with results obtained with T2EHDGA-based PIMs reported earlier.

Polymer Inclusion Membrane Containing a Tripodal Diglycolamide Ligand: Actinide Ion Uptake and Transport Studies

A cellulose triacetate (CTA)-based polymer inclusion membrane (PIM) containing a C-pivot tripodal diglycolamide (T-DGA) as the carrier extractant and 2-nitrophenyl octyl ether (NPOE) as the plasticizer shows potential for the uptake of actinides from acidic feed solutions. The uptake of actinides (Am3+, Pu4+, Th4+, UO22+) was studied at 1 M HNO3 with PIMs containing 25.6% T-DGA, 53.9% NPOE, and 20.5% CTA. The metal ion uptake followed the trend: Pu4+ > Am3+ > Th4+ > UO22+, which was in synch with the trend reported previously with PIMs containing N,N,N′,N′-tetrakis(2-ethylhexyl) diglycolamide (T2EHDGA) as the carrier. The sorbed actinide ion could be desorbed from the PIMs using a solution of α-hydroxy-iso-butyric acid (AHIBA). Transport studies carried out with 1 M HNO3 as the feed and 1 M AHIBA (at pH 3.0) as the receiver phase showed the trend: Am3+ > Pu4+ > Th4+ > UO22+, which was different than that observed from the uptake studies. Membrane stability was found to be reasonably good.

Diglycolamide-Based Solvent Systems in Room Temperature Ionic Liquids for Actinide Ion Extraction: A Review

Abstract This review article gives a comprehensive account of the extraction of actinide ions using room temperature ionic liquid-based solvent systems containing diglycolamide (DGA) or functionalized DGA extractants. These extractants include multiple DGA-functionalized ligands such as tripodal DGA (T-DGA) and DGA-functionalized calix [4]arenes (C4DGA). Apart from metal ion extraction behaviour, other important features of the ionic liquid-based solvent systems such as separation behaviour, luminescence spectroscopic results, thermodynamics of extraction and radiolytic stability of the ionic liquid-based solvents are also reviewed. Results from studies on DGA-functionalized task-specific ionic liquids (TSIL) are also included in this review article.

Spectroscopic investigations of Eu3+-complexes with ligands containing multiple diglycolamide pendant arms in a room temperature ionic liquid

Fluorescence spectroscopy was used to study the complexation of different ligands containing multiple diglycolamide (DGA) pendent arms such as T-DGA (tripodal diglycolamide), C4DGA (upper rim functionalized calix [4] arene with four DGA moieties), and C8DGA (both side functionalized calix [4] arene with eight DGA moieties) with Eu3+ in ionic liquids such as C4mimNTf2 and C8mimNTf2 (1-alkyl-3-methylimidazolium bis(trifluoromethylsulphonyl)imide). Mainly five sets of emission profiles were observed in all the spectra (1st set at~580nm assigned as the 5D0→7F0 transition, 2nd set at~593nm assigned as the 5D0→7F1 transition, 3rd set at~613nm assigned as the 5D0→7F2 transition, 4th set at~650nm assigned as the 5D0→7F3 transition, and 5th set at~700nm assigned as the 5D0→7F4 transition). The difference in the spectral features revealed that the nature of the complexes differs significantly from one another. Judd–Offelt constant Ω2, which is a measure of the covalency of the metal–ligand bond, follows the order Eu3+–C4DGA (C8mimNTf2)>Eu3+–C8DGA (C8mimNTf2)>Eu3+–TODGA (C4mimNTf2)>Eu3+–T-DGA (C4mimNTf2)>Eu3+aq. The high intensity of the 5D0→7F2 transitions in all complexes suggests that Eu3+ resides in a highly asymmetric environment. From the splitting patterns of the transitions, the local site symmetry around Eu3+ was found to be C2V for the Eu3+–T-DGA complex in both C4mimNTf2 and a 1:5 acetonitrile–water mixture, C4V for Eu3+–C8DGA and Eu3+–TODGA complexes, and either C1, C2, or CS for the Eu3+–C4DGA complex. A linear relationship between the 5D0–7F1 splitting vs E(5D0–7F0) and E(5D0–7F0) vs E(5D0–7F1) was observed. The crystal field parameters in the different complexes follow the trend Eu3+–C4DGA>Eu3+–TODGA>Eu3+–T-DGA in C4mimNTf2~Eu3+–C8DGA>Eu3+–T-DGA in 5:1 acetonitrile-water mixture.

Two novel extraction chromatography resins containing multiple diglycolamide-functionalized ligands: Preparation, characterization and actinide uptake properties

Two extraction chromatography resins were prepared for the first time by impregnating multiple diglycolamide-functionalized ligands such as diglycolamide-calix[4]arene (C4DGA) and tripodal diglycolamide (T-DGA) on Chromosorb-W, an inert solid support, for the removal of hazardous actinides like Am(III) from radioactive waste solutions at 3M nitric acid. The resins were characterized by SEM, thermal and surface area (BET) analyses. The sorption of Am(III) on the two resins followed pseudo-second order sorption rate kinetics and was exothermic in nature. The sorption of trivalent f-elements proceeded through a chemisorption monolayer phenomenon as analyzed by using several isotherm models. The negative free energy change (ΔG) values of −34.46 and −28.45kJ/mol for T-DGA and C4DGA, respectively, indicate a chemical interaction between the metal ions and the ligands on the surface of the resins. Distribution coefficient measurements of various metal ions showed a selective sorption of trivalent f-elements over hexavalent uranyl ions and other fission product elements. Column studies on breakthrough indicated 0.76 and 0.37mg/g as the breakthrough capacities of the T-DGA and the C4DGA resins, respectively. It was possible to quantitatively elute the loaded metal ion using EDTA solutions.

Unusual transport behaviour of actinide ions with a novel calix[4]arene-tetra-diglycolamide (C4DGA) extractant as the carrier

A calix[4]arene appended with four diglycolamide moieties containing n-octyl groups (C4DGA) was evaluated for the transport of actinide ions such as UO22+, Pu4+, Pu3+, and Am3+ from acidic feed solutions across PTFE flat sheet supported liquid membranes. The supported liquid membrane (SLM) studies were carried out with C4DGA under varying feed acidities, carrier extractant concentrations, and membrane pore sizes. While low pH solutions resulted in no Am3+ transport, quantitative transport of the metal ion was observed when 0.01 M EDTA solution (pH 3.0) was used as the strippant in the receiver phase. The transport efficiency of the carrier solvent system was Pu4+ > Am3+ > Pu3+ ≫ UO22+, which is not in line with those observed for diglycolamide extractants, where Am3+ was extracted to a much higher extent than other actinide ions. The results were compared with those reported earlier for TODGA (N,N,N′,N′-tetra-n-octyldiglycolamide) and tripodal diglycolamide (T-DGA) under identical conditions. Eu3+ transport rates were found out to be significantly higher than those observed with Am3+. The selectivity factors of the C4DGA extractant were compared with those of other DGA-based extractants reported earlier. The diffusion coefficient for the Am(III)–C4DGA complex was obtained experimentally using the lag time method. The stability studies indicated significant deterioration of the liquid membrane with time even after only 3 days of operation.

Extraction of Am(iii) using novel solvent systems containing a tripodal diglycolamide ligand in room temperature ionic liquids: a ‘green’ approach for radioactive waste processing

Extraction of Am3+ from acidic feed solutions was investigated using novel solvent systems containing a tripodal diglycolamide (T-DGA) in three room temperature ionic liquids (RTIL), viz. [C4mim][NTf2], [C6mim][NTf2] and [C8mim][NTf2]. Compared to the results obtained with N,N,N′,N′-tetra-n-octyl diglycolamide (TODGA), T-DGA gave significantly higher distribution coefficients in these RTILs. The DAm values decreased with increasing carbon chain length in the RTILs, which was related to the solubility of the RTIL in the aqueous phase. The distribution studies included the effect of equilibration time, aqueous phase acid concentration variation and T-DGA concentration variation. In general, significantly higher equilibration times were observed for the extraction systems, which was partly due to the viscous RTIL phase and partly due to the slow conformational changes of the T-DGA ligand during complexation. Apart from Am3+, extraction of Pu4+, UO22+, Eu3+, Sr2+ and Cs+ was also investigated, since they have significant implications in radioactive waste processing. Stripping studies indicated >99% stripping in three stages using 0.5 M EDTA or DTPA in 1 M guanidine carbonate. Slope analysis indicated the extraction of 1 : 1 complexed species of Am(III) with T-DGA. Time resolved laser fluorescence spectroscopy (TRLFS) studies showed a strong complexation with no inner-sphere water molecules in the Eu(III)–T-DGA complexes for [C4mim][NTf2] as the diluent. Radiolytic degradation studies of the solvent systems containing T-DGA in the three RTILs were also carried out and while the DAm values decreased marginally when the solvents were exposed to 500 kGy absorbed dose, a relatively sharp decrease (60%) was seen when the solvents were exposed further to 1000 kGy absorbed dose, suggesting the possibility of recycling. Extraction studies were also carried out at varying temperatures and the thermodynamic parameters were calculated.

Evaluation of a novel tripodal diglycolamide for actinide extraction: Solvent extraction and SLM transport studies

A novel tripodal diglycolamide (T-DGA) extractant in a diluent mixture (10:1 n-dodecane– iso-decanol) was evaluated for the extraction of actinide ions such as UO 2 2+, Np(IV), Pu(IV), and Am(III) and fission product element ions such as Cs + and Sr 2+ from acidic feed solutions. Conditions for quantitative extraction and stripping were found out for the actinide ions other than UO 2 2+ which is poorly extracted. Solvent extraction studies were carried out at varying concentrations of the extractant and nitric acid using Am(III) and were compared with the results obtained with TODGA ( N, N, N′, N′-tetraoctyldiglycolamide), a representative diglycolamide extractant proposed for actinide partitioning. The extracted species was found out to be Am(NO 3) 3·2T-DGA (o) at higher T-DGA concentrations, while mixed 1:1 and 1:2 species were observed at lower T-DGA concentrations. The prevalence of 1:2 species in the present case as compared to the 1:1 species reported in a similar system was attributed to the low dielectric constant diluent medium used in the present study. Supported liquid membrane studies were also carried out using the T-DGA under varying feed acidities, carrier extractant concentration and compared with TODGA under identical conditions. The transport rates are dependent on the strippant used in the receiver phase and a 0.01 M EDTA solution (pH 3.0) was found to yield quantitative transport of Am(III) using T-DGA as compared to dilute nitric acid, which was efficiently used for the TODGA system in an earlier study. The transport efficiency of the carrier solvent system was Am(III) > Pu(IV) ≫ Np(IV) > UO 2 2+. The diffusion parameters were calculated for the T-DGA system and compared with the experimentally determined parameters.

Tripodal diglycolamides as highly efficient extractants for f-elements

A series of new ligands bearing three diglycolamide functions preorganized at the C-pivot and trialkylphenyl platforms was synthesized. They are very efficient extractants for Am3+ and Eu3+ with an up to five times relative extraction ability for Eu3+. The distribution coefficients are up to 1000 times increased upon alkylation or arylation of the N-position of the diglycolamide moieties. The tripodal diglycolamides show a 1 : 1 metal to ligand stoichiometry as proven with three independent methods for the complexation of the 3-pentyl N-substituted diglycolamide ligand with Eu3+ (K = 2.5 × 105 M−1 in acetonitrile–water). A cage-like cryptand, containing three diglycolamide units, was prepared using a Eu3+ templated synthesis. However, it does not exhibit improved extraction properties.