Diglycolamides Research Articles

Synthesis, characterization and uptake studies of diglycolamic acid and diglycolamide analogs adsorbents for extraction of rare earth elements

Tetraalkyldiglycolamides are known for their high extracting efficiency of rare earth elements (REEs) from nitric acid solutions (1–6 mol/L). Nevertheless, solid-phase extractants based on diglycolamides (DGA) are poorly studied for REEs extraction. This paper explores the design and synthesis of novel REEs adsorbents by grafting silica with diglycolic acid-based ligands. The newly developed solid-phase materials were investigated for their potential to effectively separate REEs from various media. The functionalization of the silica with different ligands was quantified, and the adsorbents' extraction capacities and selectivity for REEs over Calcium (Ca2+), Aluminium (Al3+) and Iron (Fe3+) were evaluated. Si-NH-DGA emerged as the most efficient adsorbent for Gd3+ extraction, exhibiting a remarkable capacity of 44 mg/g at pH 4–6. However, modifications involving ether oxygen substitution with a methylamino group or sulfur led to reduced extraction efficiencies. Si-NH-DGA-NMe2 demonstrated strong binding of REEs in nitric acid solutions (1–3 mol/L HNO3) with corresponding adsorption capacities for Y3+, La3+, Gd3+ and Yb3+ being 16.3, 14.2, 22.8, and 30.2 mg/g, respectively. Furthermore, it displayed remarkable selectivity for REEs over Ca2+. The equilibrium extraction for Gd occurred within 60 min for Si-NH-DGA and Si-NH-DGA-NMe2 under their respective optimal conditions. Disodium EDTA solution demonstrated a high stripping efficiency for Gd3+ in the Si-NH-DGA-NMe2 column extraction, yielding a significant concentration factor (CF = 85). In the same column, following five cycles of loading/stripping of Gd3+, there was an average capacity loss of 6%. Si-NH-DGA-NMe2 emerged as a promising material for solid-phase extraction from concentrated nitric acid solutions, characterized by high capacity and good selectivity towards middle and heavy REEs. This structure has the potential to be further optimized for the development of a solid-phase extraction column for REEs separation and purification. The findings also highlight the potential of Si-NH-DGA-NMe2 as a candidate for REEs adsorption for potential industrial applications and the purification of acidic waste solutions.

Development of a highly efficient gadolinium(III) potentiometric sensor using two aza-crown ether-based multiple diglycolamides (DGAs)

The present investigation deals with the development of two polyvinyl chloride- (PVC) based potentiometric sensors for gadolinium(III) ion with two multiple diglycolamide (DGA) ligands with the DGA moieties tethered onto aza-crown ethers as ionophores, 2-nitrophenyl octyl ether (NPOE) as the plasticizer and sodium tetraphenylborate (NaTPB) as ionic additive. The ionophores are a tripodal DGA ligand containing a triaza-9-crown-3 core (LI) and a tetrapodal DGA ligand with a tetraaza-12-crown-4 as the scaffold (LII). The polymer inclusion membranes (PIMs) were tested for gadolinium ion detection in a mildly acidic solution (pH 3.0 ± 0.1). The PIM containing an optimized composition of 7.8% LI, 29.6% PVC, 60.5% NPOE, 2.1% NaTPB exhibited a linear response behaviour from 7.2 × 10−7 to 4.9 × 10−3 M Gd3+ with a slope of 19.8 ± 0.4 mV/decade and a limit of detection (LOD) of 6.0 × 10−7 M. The sensor showed fast response time (<20 s) and a lifetime of at least two months. It exhibited good tolerance to monovalent/divalent interfering ions and moderate to poor tolerance to trivalent ions. The effect of temperature on the selectivity coefficient of Gd3+ over La3+ was determined which indicated a decreasing trend with temperature. The concentration of Gd3+ in the inner filling solution (IFS) had a significant effect on the sensor sensitivity and on the detection limit. The other sensor containing LII performs poorly as a potentiometric sensor. The physical characterization of the membranes was done using thermogravimetry (TGA), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and photoluminesce (PL) spectroscopy. A PL study was performed using Eu3+ as a surrogate probe for Gd3+ as the latter ion does not show luminescence properties. The PL spectra suggest the presence of a single analyte ion species in the membrane. The sensor containing LI can be used as an indicator electrode for the potentiometric titration of Gd3+ which indicated a recovery of 94.6 ± 4.3% of Gd3+ for triplicate measurements and the results match well with the complexometric titration result using xylenol orange as a colorimetric indicator for the endpoint detection.

Ab-initio evaluation of acid influence on chemical stability of hydrophilic diglycolamides.

Diglycolamides (DGA) form one of the most promising groups of organic ligands used in bio-inspired solvent extraction processes of lanthanide and actinide ions. Continuous experimental and theoretical research is still performed in order to further improve their application properties including their chemical stability in the real extraction environment. This work provides results of our theoretical approach focused on inclusion of an acid influence on the DGAs chemical structure, treated in frame of the density functional theory. Three different models describing the acid action are proposed and investigated in attempt to increase the resulting accuracy of the chemical stability predictions based on verified theoretical descriptors. The procedure is applied and tested on the set of selected hydrophilic DGA representatives. Comparison of the model results obtained with and without acid action shows that two types of protection effects may occur: a 'direct' protection, accompanied by an explicit change of the ligand stability indicators, and an 'indirect' one consisting in reaction of acid molecules with radicals preceding the contact of latter with the extracting ligands. The possibility of the direct acid protection route is supported by the significant decrease of the Fukui charges found with the acid models included. On the other hand, there is in general no significant difference of trends in the calculated chemical stability descriptors suggesting that an indirect mechanism must be also considered in order to explain the experimentally observed protective role of acids on the chemical stability of investigated DGA derivatives.

Recent Progress on the Structure-Performance Relationship between Diglycolamide Extractants and f-Elements

ABSTRACT Diglycolamides (DGAs) belong to the class of “CHON” type compounds and can form tridentate complexes with metal ions. DGA-based extractants are a subject of great interest in actinide partitioning due to their exceptionally high affinity for trivalent actinides and lanthanides. Since the separation performance of DGAs are closely related to their molecular structures, many structure-modification schemes have been proposed such as the attachment of different alkyl substituents to an amidic N atom or anchoring multiple DGA arms onto a scaffold. In this paper, literature reports that describe the effects of such modifications on the structure and performance of DGAs are summarized. By comparing the extraction and separation properties of DGA extractants with different structures, the relationship between the structure and properties of DGAs is discussed. Such work should be helpful for gaining a more comprehensive, accurate and in-depth understanding of the relationship between structure and property of DGAs to be developed. It should also be beneficial for the structural design of more new DGA extractants.

Structure Activity Relationship Approach toward the Improved Separation of Rare-Earth Elements Using Diglycolamides.

The separation of adjacent lanthanides continues to be a challenge worldwide because of the similar physical and chemical properties of these elements and a necessity to advance the use of clean-energy applications. Herein, a systematic structure-performance relationship approach toward understanding the effect of N-alkyl group characteristics in diglycolamides (DGAs) on the separation of lanthanides(III) from a hydrochloric acid medium is presented. In addition to the three most extensively studied DGA complexants [N,N,N',N'-tetra(n-octyl)diglycolamide, TODGA; N,N,N',N'-tetra(2-ethylhexyl)diglycolamide, TEHDGA; N,N'-dimethyl-N,N'-di(n-octyl)diglycolamide, DMDODGA], 12 new extracting agents with varying substitution patterns were designed to study the interplay of steric and electronic effects that control rare-earth element extraction. Subtle changes in the structure around diglycolamide carbonyl oxygen atoms result in dramatic shifts in the lanthanide extraction strength and selectivity. The effects of the chain length and branching position of N-alkyl substituents in DGAs are elaborated on with the use of experimental, computational, and solution-structure characterization techniques.

Theoretical elucidation of rare earth extraction and separation by diglycolamides from crystal structures and DFT simulations

Diglycolamides (DGAs) show excellent application prospects for the extraction and separation of rare earth metals from highly radioactive liquid wastes and rare earth ores. The extraction ability of DGAs for rare earth ions in nitrate or chloride media increases with increasing atomic number of the rare earth metal. To understand the origin of this phenomenon, three binuclear crystals [Ln(TEDGA)3][Ln(NO3)6] of N,N,N′,N′-tetraethyldiglycolamide (TEDGA) with rare earth ions La(III), Pr(III) and Eu(III) were prepared and characterized crystallographically. The three complexes belong to the triclinic crystal system, P-1 space group. The bond lengths of Ln–Oamide are significantly shorter than those of Ln–Oether in the same crystal. The Ln–Oamide and Ln–Oether bond lengths gradually decrease with increasing atomic number of the rare earth ion. The dihedral angle formed by TEDGA and metal ions through the tridentate coordination gradually increases with increasing metal ion atomic number, tending toward the formation of sizeable planar coordination structures for the most massive rare earth ions. The structures of the compounds formed by the extractant and metal ion were optimized by means of DFT simulations. We find that the interaction between TEDGA and the rare earth ion is dominated by electrostatic interaction by analyzing binding energy, WBIs, Mulliken charge, natural electron configurations, and molecular orbital interaction. The covalent component of the Ln–O bonds of the complexes increases with increasing metal atomic number. The observed increase in extraction and separation capacity of diglycolamides for rare earth ions with increasing atomic number might be due to the formation of two five-member rings by one tridentate ligand. The rare earth ions with large atomic numbers tend to form planar structures with large dihedral angles with DGA ligands.

Separation of Pr(III) and Fe(III) by unsymmetrical diglycolamides from nitric acid media

A systematic structural separation study was carried out for the separation of Pr(III) and Fe(III) from nitric acid medium with unsymmetrical diglycolamides (DGAs). Four kinds of diglycolamides, N,N′-di-methyl-N,N′-di-dodecyl diglycolamide (DMDDdDGA), N,N′-di-ethyl-N,N′-di-dodecyl diglycolamide (DEDDdDGA), N,N′-di-propyl-N,N′-di-dodecyl diglycolamide (DPDDdDGA) and N,N′-di-butyl-N,N′-di-dodecyl diglycolamide (DBDDdDGA) with different alkyl substituent were synthesized and characterized. The effect of the structure of extractant on the separation of iron and praseodymium was studied. A high separation coefficient of Pr(III) and Fe(III) was obtained by DMDDdDGA in a wide range of nitric acid concentration, which shows good application prospect in the recovery and purification of rare earth.

Application of quantum mechanical simulations for studying the radiolytic stability of prospective extractants in the nuclear fuel cycle

Diglycolamides (DGA) play a crucial role in the advanced spent nuclear fuel reprocessing. This work extends the portfolio of theoretically calculated properties of such organic extractants related to the radiolytic stability in the partitioning processes. The radiolytic stability of selected DGA ligands (TMDGA, TEDGA, Me-TEDGA, and Me2-TEDGA) was studied by the theoretical simulation methods based on quantum mechanics. As the most suitable indicator, the calculated Fukui functions were in good correlation with the trend of increased stability with increasing molecular weight. The Fukui charges also brought the explanation why TMDGA most likely does not degrade in the ether group, unlike the other ligands.

Aggregation Behavior of Alkyldiglycolamides in n-Dodecane Medium during the Extraction of Nd(III) and Nitric Acid

Diglycolamides (DGAs) are promising reagents for the separation of trivalent actinides and lanthanides from the nitric acid medium. The alkyl group attached to DGAs plays an important role in deciding the extraction and third phase formation behavior of trivalents in DGAs. To understand the role of alkyl group (varied from hexyl to dodecyl) attached to DGA, the extraction behavior of Nd(III) from the nitric acid medium was studied in 0.2 M alkyl DGA in n-dodecane (n-DD). The organic phase obtained after extraction was subjected to dynamic light scattering (DLS) studies to explore the behavior of reverse micelles (or aggregates) formed in the organic phase. The data were compared with the self-aggregation behavior of DGAs in n-DD. The results revealed that the aggregate size and their distribution in n-DD increased with increase in the extraction of nitric acid and Nd(III) in organic phase for all DGAs. However, at certain conditions of loading of HNO3 and Nd(III) the organic phase underwent splitting into...

Speciation of Select f-Elements with Lipophilic Phosphorus Acids and Diglycol Amides in the ALSEP Backward-Extraction Regime

The complexation of HDEHP, HEH[EHP], T2EHDGA, and TODGA and mixtures thereof in n-dodecane with Nd(III), Pm(III), and Am(III), extracted from pH 3 aqueous media, were analyzed by distribution analysis, IR, UV–vis, and X-ray spectroscopies. Appreciable ternary complex formation is seen among HDEHP with DGA components and to a lesser extent with HEH[EHP]. Ternary complex formation constants were determined by absorption spectroscopy and slope analysis. The effect of the adduct formation on the process performance and on the Ln/An selectivity is discussed. It has been shown that the ternary complexes have the tendency to extract larger trivalent cations as Am and Nd over Eu, thus diminishing the overall Ln/Am selectivity of the process. Also, previously unreported extraction constants were derived for HEH[EHP] with Am and Pm as well as coordination information for Nd-HEH[EHP] and Nd-T2EHDGA complexes.

The Radiolysis of CMPO: Effects of Acid, Metal Complexation and Alpha vs. Gamma Radiation

The organophosphorus amide octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO) is proposed for use in fuel cycle separations as a group actinide/lanthanide extractant. Alternative compounds such as the monoamides and diglycolamides (DGAs) proposed for actinide and/or actinide/lanthanide extraction also contain the amidic functional group, but do not contain the CMPO aromatic or phosphoryl groups. Their radiation stability is in the order monoamides > CMPO > DGA for irradiation under similar conditions. Although they produce similar radiolysis products, the kinetics of degradation for CMPO are completely different than for the other amides. CMPO degradation occurs in a zero-order fashion, and the –G-value for the change in [CMPO] is much lower when in the presence of acid. The DGAs and monoamides degrade with pseudo-first-order kinetics and are not protected by acidity. Possible mechanistic reasons for the differences between CMPO and the other amides are discussed, as are the effects of the diluent and metal complexation on CMPO free radical reaction rates. Finally, it is also shown that α-irradiation has much less adverse effects on CMPO degradation than β/γ irradiation, both with respect to –G-values, and radiolysis product generation.

Solvent extraction behavior of trivalent metal ions in diglycolamides having same carbon to oxygen ratio

Various diglycolamides (DGAs), N,N,N’,N’-tetraoctyl diglycolamide (TODGA), N,N-di-2-ethylhexyl-N’,N’-di-octyl diglycolamide (DEHDODGA), N,N,N’,N’-tetra-2-ethylhexyl diglycolamide (TEHDGA), N,N-di-decyl-N’,N’-di-hexyl diglycolamide (D2DHDGA), N,N-di-butyl-N’,N’-di-dodecyl diglycolamide (DBD3DGA), N,N,N’,N’-tetra-hexyl diglycolamide (THDGA), and N,N,N’,N’-tetradecyl diglycolamide (TDDGA) have been synthesized and studied for the extraction of Am(III) and Eu(III) from nitric acid medium. An attempt was made to understand the extraction and third phase formation behavior of trivalent metal ions in these DGAs. Our results revealed that despite having the same carbon to oxygen ratio in these DGAs, the third phase formation behavior and extractions achieved in these DGAs are significantly different.

Understanding nitric acid-induced changes in the arrangement of monomeric and polymeric methacryloyl diglycolamides on their affinity toward f-element ions.

Assembled diglycolamides (DGAs) have a strong affinity toward f-element ions at high nitric acid concentrations. Small angle X-ray scattering studies revealed that nitric acid concentration dependent changes occur in the geometrical arrangement of the DGA units of monomeric methacryloyl-DGA and the corresponding polymeric DGA. Cylindrical aggregates of methacryloyl-DGA were formed in 10:1 n-dodecane:1-decanol (added for solubility reasons) upon equilibration with nitric acid. The lengths and diameters of the cylindrical methacryloyl-DGA aggregates increased on varying the nitric acid concentration from 3 to 4 mol L(-1). This resulted in an increase of the distribution coefficient (D) of Eu(3+) ions from 72 to 197. The physical structure of cross-linked (10 mol %) poly(methacryloyl-DGA) reorganized distinctly upon equilibration with nitric acid. In this case, also the DEu(3+) values increased significantly from 147 mL g(-1) at 1 mol L(-1) HNO3 to ∼4000 mL g(-1) at 4 mol L(-1) HNO3. Hydrogen bonds between the outer sphere of Eu(3+)/Am(3+)/Pu(4+) nitrate and DGA units provide stabilization in the hydrophobic environment. This results in enhancement of their extraction upon increasing nitric acid concentration both in the organic phase as well as in the polymer matrix. Though monomeric and polymeric methacryloyl-DGA are different in their physical assembling, the normalized DI values for a same f-element ion upon varying HNO3 concentrations show remarkably similar patterns in both forms. In addition, the unusual stoichiometry deduced from the slopes of the log D vs log[HNO3] curves at fixed nitrate concentration seems to suggest that the normal extraction mechanism may not be operating in the hydrogen bonded DGA assemblies.

Extraction behavior of trivalent lanthanides from nitric acid medium by selected structurally related diglycolamides as novel extractants

The extraction affinity of trivalent lanthanides, Ln(III), from nitric acid medium has been explored using a series of ten structurally related synthesized diglycolamides (DGA) diluted with toluene. The structure-reactivity relationship with extraction of trivalent lanthanides as well as their atomic number was investigated. The extraction of nitric acid and selected lanthanide ions by N,N,N′,N′-tetradodeceyldiglycolamide (TDDGA), from nitric acid medium was studied in details. Distribution ratio of the trivalent lanthanide ions has been studied as a function of aqueous HNO3 concentrations, DGA concentration, and temperature. The stoichiometry of La(III), Nd(III), and Eu(III) was determined at different nitric acid concentrations by slope analysis of extraction data, and enthalpy change accompanied by extraction was also determined and reported in this work.

Assembled diglycolamide for f-element ions sequestration at high acidity

Diglycolamides (DGA) form reverse-micellar type of supramolecular aggregates upon equilibration with a nitric acid solution that enhances DGA affinity extraordinary towards f-elements. To mimic DGA aggregates, DGA molecules have been preorganized on chemical platforms to form assemblies having a good affinity towards f-elements. However, the synthetic procedures used are quite laborious that limits their large scale applications. To address this problem, a new DGA-bearing monomer N,N-dioctyl,N′-propyl-2-methylacrylamide diglycolamide has been synthesized. This DGA-methacrylate monomer can be polymerized easily, and shows an interesting affinity towards f-element ions both in monomeric and polymeric forms at high nitric acid concentrations. This makes it very promising for the development of fixed-site membranes, resins, and magnetic assemblies for a variety of applications. DGA-methacrylate monomer has been found to assemble on magnetic nanoparticles Fe3O4. DGA-methacrylate coated Fe3O4 particles capture representative trivalent actinide 241Am with a very high efficiency. However, it has been observed that HNO3 induced preorganization of DGA-methacrylate plays an important role in sorption of f-element ions in the polymeric form and self-assembled molecules on the magnetic nanoparticles.

Tuning the diglycolamides for modifier-free minor actinide partitioning

The unsymmetrical diglycolamides (DGAs) such as N,N-dihexyl-N′,N′-dioctyl-3-oxapentane-1,5-diamide (DHDODGA), N,N-didecyl-N′,N′-dioctyl-3-oxapentane-1,5-diamide (D2DODGA), N,N-didodecyl-N′,N′-dioctyl-3-oxapentane-1,5-diamide (D3DODGA), were synthesized, and characterized by IR, NMR, and mass spectroscopic techniques. The extraction behaviour of Am(III), Eu(III), and Sr(II) by the solutions of these unsymmetrical DGAs in n-dodecane was studied as a function of concentration of nitric acid and DGA. The distribution ratio of Am(III) and Eu(III) increased with increase in the concentration of nitric acid; whereas, the distribution ratio of Sr(II) reached a maximum at 4 M nitric acid followed by decrease at higher acidities. The extraction of Am(III) and Eu(III) in 0.1 M DGA/n-dodecane decreased in the order DHDODGA > D2DODGA > D3DODGA. However, the order changed upon lowering the concentration of DGA. The third-phase formation behaviour of nitric acid and neodymium(III) in 0.1 M DGA/n-dodecane was studied as a function of concentration of nitric acid. The limiting organic concentration of nitric acid and neodymium increased with increase in the chain length of alkyl group attached to amidic nitrogen. Near stoichiometric amount of neodymium(III) was loaded in 0.1 M D3DODGA/n-dodecane without the formation of third-phase from 3 to 4 M nitric acid medium. The study revealed that the unsymmetrical diglycolamides D2DODGA and D3DODGA are superior candidates for partitioning the minor actinides from high-level liquid waste.

Liquid–liquid extraction and pertraction behavior of Am(III) and Sr(II) with diglycolamide carrier extractants

Solvent extraction and supported liquid membrane transport properties of Am(III) and Sr(II) from nitric acid medium using several substituted diglycolamides (DGAs) were investigated in detail. The DGAs studied were N,N,N′N′-tetraamyl diglycolamide (TPDGA), N,N,N′N′-tetrahexyl diglycolamide (THDGA), N,N,N′N′-tetraoctyl diglycolamide (TODGA), N,N,N′N′-tetra(2-ethyl hexyl)diglycolamide (T2EHDGA) and N,N,N′N′-tetradecyl diglycolamide (TDDGA). Effects of feed acidity, phase modifier composition, nature of species were investigated for the solvent extraction of the radionuclides using the DGAs. The trend of Am(III) extraction was TPDGA≫THDGA≫TODGA>TDDGA≫T2EHDGA. The slope analysis method for Am(III) extraction has indicated extracted species containing 4 and 3 molecules of the extractant for TODGA and T2EHDGA, respectively and about two molecules of extractant were found to be associated with the other DGAs. When simulated high level waste was used as the feed, the distribution ratio values decreased significantly.Supported liquid membrane transport of the radionuclides was evaluated to understand the effects of feed acidity, membrane pore size and phase modifier concentration for the DGAs. While the trends for Am(III) transport rate were TPDGA∼THDGA∼TDDGA>TODGA>T2EHDGA and usually 2–5h were needed for quantitative transport (>99%), Sr(II) transport was found to be significant in this time scale. The trend for activation energies of transport of Am(III) was found to be TDDGA>THDGA>TPDGA (with 30% iso-decanol)>T2EHDGA>TODGA.

Solvent Extraction of Various Metals Including Actinides by Bidentate and Tridentate Diamides

Many diamide-type extractants were synthesized and tested for the extraction of actinides (III), (IV), (V) and (VI) . The diglycolamides (DGA) with two amidic oxygen and one ether oxygen, which show the tridentate feature, have the high extractability of actinides (An) . In order to increase the lipophilic property, the diglycolamides with the different functional groups attached to N atoms were synthesized and examined for their extractability. It was found that N, N, N', N'- tetraoctyl-diglycolamide (TODGA) and N, N, N', N'- tetradecyl-diglycolamide (TDDGA) exhibit the satisfactory dissolution into n-dodecane with less solubility in H2O. The results of various metal extractions using TODGA revealed that the divalent, trivalent and tetravalent metals with ionic radius of 90-120 pm gave notably high D values. After elucidation of the effect on substitution of the functional group, the chemical form of DGA to have high performance on An extraction was proposed.