Dicyclohexano-18-crown-6 Research Articles

Charge transfer across the ionic liquid/oil interface: Facilitated ion transfer and electron transfer

Facilitated ion transfer (FIT) and electron transfer (ET) across the ionic liquid (IL)/oil (O) interface between ethylamine nitrate (EAN) and 1,4-dichlorobutane (DCB) have been electrochemically studied. Cyclic voltammograms (CVs) for the FIT of Li+ cation in IL by dicyclohexano-18-crown-6 (DCH18C6) across the IL/O interface formed at a micropipette tip show that the onset of the FIT current is significantly shifted due to the facilitation beyond the potential window limit and that the current is proportional to the concentration of DCH18C6 in O limited by the diffusion of DCH18C6 inside the micropipette. CVs for the ET from supporting electrolyte anions in O to NO3−, the IL anion of EAN, across the IL/O interface studied using a closed-bipolar cell show that NO3− in EAN has an ability to oxidize tetraphenylborate ions in O but not tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ions, the latter of which have more oxidation resistance.

Optimization of synergistic extraction of calcium ion via an emulsion liquid membrane using dicyclohexano-18-crown-6 and D2EHPA carriers: A design of experiment study

Calcium ions play an important role in various fields, with their stable isotopes being of particular importance in medical research and in the production of superheavy metals. Emulsion liquid membranes (ELMs) offer a promising alternative to conventional methods for metal ion extraction due to their remarkable mass transfer rates. However, the effectiveness of crown ethers as carriers in ELM processes has been hindered by their limited ability to extract calcium ions. The aim of this study is to optimize the extraction of calcium ions using an ELM containing dicyclohexano-18-crown-6 (DC18C6) as a carrier and di-(2-ethylhexyl) phosphoric acid (D2EHPA) as a synergistic carrier. To achieve this objective, a two-level fractional factorial design (FFD) was initially implemented to screen the key factors. Subsequently, a central composite design (CCD) was employed to optimize the four identified key factors. The CCD method yielded a quartic regression model for calcium extraction efficiency. The optimum values were: DC18C6 concentration at 0.035 mol/L, feed phase pH of 4, a feed/emulsion volume ratio of 2.3, and a W/O/W stirring time of 23.4 min. Under these optimal conditions, DC18C6 exhibited negligible extractability, while D2EHPA achieved an extraction efficiency of 62.2%. Combining both carriers, however, significantly increased the extraction efficiency to 97.3%, indicating a synergistic effect that enhanced the extraction of Ca(II) ions. Furthermore, the selectivity of the ELM towards Ca(II) ions was examined in binary solutions of Ca(II)/Li(I), Ca(II)/Na(I), and Ca(II)/Mg(II). The ELM demonstrated selectivity for Ca(II) over Li(I), Na(I), and Mg(II) with separation factors of 4.4, 2.0, and 8.1, respectively. It is noteworthy that the combination of carriers positively influenced calcium selectivity exclusively in the Ca(II)/Mg(II) solution. Conversely, no noticeable effect on selectivity was observed in the Ca(II)/Li(I) solution, while the combination had an adverse effect on calcium selectivity in the Ca(II)/Na(I) solution.

Free Energy Calculations and Conformational Analysis of Dibenzo-30-crown-10 with Sm2+, Eu2+, and Three Halide Salts in THF Using the AMOEBA Force Field.

Crown ether complexes have been tailored for use in industrial separations of lanthanides (Ln) as a part of rare earth mining and refining. Dibenzo-30-crown-10 (DB30C10) is one of the most efficient complexants for the separation of rare earth mixtures based on the cation size. To understand the origin of this complexation, molecular dynamics (MD) simulations of DB30C10 have been performed using different combinations of divalent Sm and Eu and three halide salts Cl-, Br-, and I- in tetrahydrofuran (THF) solvent. DB30C10 was parameterized here for the polarizable atomic multipole optimized energetics for biomolecular simulation (AMOEBA) force field, and the existing parameters of THF, Sm2+, and Eu2+ were employed from our previous efforts. The large conformational fluctuations present in the DB30C10 systems were found to be dependent both on the identity of the lanthanide and halide complexes. For Cl- and Br- systems, there were no observed conformational changes at 200 ns, while in I- systems, there were two conformational changes with Sm2+ and one with Eu2+ within that same timeframe. In SmI2-DB30C10, there were three stages of conformational changes. In the first stage, the molecule is unfolded, in the second stage, the molecule is partly folded, and finally, in the third stage, the molecule is completely folded. Lastly, the Gibbs binding free energies of DB30C10 with SmBr2 and EuBr2 have been computed, which resulted in nearly identical ΔGcomp values for each lanthanide with Sm2+ being slightly more favorable. Considering the folding mechanism of the SmI2 system with DB30C10, the Gibbs binding free energies of DB30C10 and dicyclohexano-18-crown-6 (DCH18C6) with SmI2 were calculated separately and compared to probe their complexation affinities, in which the former was found to be more favorable.

Experimental and theoretical studies (DFT) on technetium extraction as HTcO4 using dicyclohexano-18-crown-6 in a blend of isodecyl alcohol and n-dodecane from acidic medium

Fundamental studies on technetium extraction from acid medium using a versatile supramolecule, dicyclohexano-18-crown-6 (DCH18C6) in isodecyl alcohol-n-DD diluent system from acidic nuclear waste have been reported here. It was observed that the maximum extraction (DTc ∼ 2.03) and ∼99% recovery of technetium can be achieved when an organic phase of 0.4 M DCH18C6 in 50% isodecyl alcohol + n-dodecane was used to extract technetium from 4.0 M HNO3 solution followed by three successive stripping contact with water. Two types of mechanisms are found to be operative depending on the acidity of feed solution, an extraction mechanism like, H+aq. + TcO4−aq. + DCH18C6org = HTcO4.DCH18C6org up to 4.0 M feed acidity and HTcO4.DCH18C6org + H +aq. + NO3−aq = DCH18C6org.HNO3 + TcO4−aq.+ H +aq. for feed acidity beyond 4.0 M HNO3. Almost identical interaction energies of adducts DCH18C6-HTcO4 & DCH18C6–HNO3 obtained in the DFT calculations. The extraction is driven by low hydration energy of pertechnate compared to nitrate up to 4.0 M HNO3 and beyond 4.0 M HNO3 concentration of nitrate dominates the hydration energy effect causing decrease in the technetium extraction irrespective of the equal interaction energies.

Extraction of rubidium ion from brine solutions by dicyclohexano-18-crown-6 / ionic liquid system

Abstract Separation among rubidium and potassium ions from salt lake brines remains challenging. In this work, a typical room temperature ionic liquid 1-ethyl-3-metyhlimidazaolium bis(trifluoromethylsulfonyl)imide ([C2mim+][NTf2 –]) was used as diluent and synergistic extractant, dicyclohexano-18-crown-6 (DCH18C6) was used as extractant to extract rubidium ions from brine solutions which contain high concentrations of potassium ions was investigated. Under the optimal conditions, the single extraction efficiency of rubidium ions was up 93.63%. The thermodynamic parameters of the rubidium ion extraction were obtained. Based on the slope analysis method, the extracted species in the organic phase were ascertained as 1:1 complex. UV-visible has been performed to investigate the ion concentration of ionic liquid before and after the interaction of metal ions and ligands. Rubidium ions in [Rb · DCH18C6]+ complex were stripped by 2.5 mol · L–1 NH4NO3. The extraction system offers high efficiency, simplicity and environmentally friendly application prospect to separate rubidium from brine solutions.

Applying a microfluidic device to improve the Ca2+ separation performance of the liquid–liquid extraction process

This study investigates the application of extraction solvent in a new microfluidic apparatus to separate calcium ions (Ca2+). Indeed, a serpentine microfluidic device has been utilized to separate calcium ions. The flow regime map shows that it is possible to completely separate organic and aqueous phases using the serpentine microfluidic device. The suggested microfluidic device reaches the extraction efficiency of 24.59% at 4.2 s of the residence time. This research also employs the Box–Behnken design (BBD) strategy in the response surface methodology (RSM) for performing the modeling and optimization of the suggested extraction process using the recorded experimental data. Flow rate and pH of the aquatic phase as well as Dicyclohexano-18-crown-6 (DC18C6) concentration are those independent features engaged in the model derivation task. The optimum values of pH 6.34, the DC18C6 concentration of 0.015 M, and the flow rate = 20 µl/min have been achieved for the aquatic phase. The results indicated that the extraction efficiency of Ca2+ is 63.6%, and microfluidic extraction is 24.59% in this optimum condition. It is also observed that the microfluidic extraction percentage and experimental efficiency achieved by the suggested serpentine microchannel are higher than the previous separation ranges reported in the literature.

Molecular Dynamics and Free Energy Calculations of Dicyclohexano-18-crown-6 Diastereoisomers with Sm2+, Eu2+, Dy2+, Yb2+, Cf2+, and Three Halide Salts in Tetrahydrofuran and Acetonitrile Using the AMOEBA Force Field.

With the continual development of lanthanides (Ln) in current technological devices, an efficient separation process is needed that can recover greater amounts of these rare elements. Dicyclohexano-18-crown-6 (DCH18C6) is a crown ether that may be a promising candidate for Ln separation, but additional research is required. As such, molecular dynamics (MD) simulations have been performed on four divalent lanthanide halide salts (Sm2+, Eu2+, Dy2+, and Yb2+) and one divalent actinide halide salt (Cf2+) bound to three diastereoisomers of DCH18C6. Dy2+, Yb2+, Cf2+, DCH18C6, and tetrahydrofuran (THF) solvent were parameterized for the AMOEBA polarizable force field for the first time, whereas existing parameters for Sm2+ and Eu2+ were utilized from our previous efforts. A coordination number (CN) of six for Ln2+/An2+-O solvated in THF indicated that the cations interacted almost entirely with the oxygens of the polyether ring. A CN of one for Ln2+/An2+-N solvated in acetonitrile for systems containing iodide suggested that the N atom of acetonitrile was competitive with I- for cation interactions. Fluctuation between five and six CNs for Dy2+ and Yb2+ suggested that although the cations remained in the polyether ring, the size of the ring may not be an ideal fit as these cations possess comparatively smaller ionic radii. Gibbs binding free energies of Sm2+ in all DCH18C6 diastereoisomers solvated in THF were calculated. The binding free energy of the cis-syn-cis diastereoisomer was the most favorable, followed by cis-anti-cis, and then trans-anti-trans. Finally, two major types of conformation were observed for each diastereoisomer that were related to the electrostatic interactions and charge density of the cations.

Sr(ii) extraction by crown ether in HFC: entropy driven mechanism through H2PFTOUD.

The solvent extraction of Sr(ii) was carried out using dicyclohexano-18-crown-6 (DCH18C6) and two HFC mixed solvents MS1 and MS2, where MS1 was composed of 30/60 (w/w)% trans-1,2-dichloroethylene/HFC-43 (HFC-43: 1,1,1,2,2,3,4,5,5,5-decafluoropentane) and MS2 was 5/95 (w/w)% heptane/HFC-43. Nitric acid and perfuruoro-3-6-9-trioxaundecane-1,11-dioic acid (H2PFTOUD) were used to study the effect of acid on the extraction. The maximum distribution ratio of Sr(ii) (DSr) observed for H2PFTOUD conditions was ∼180, and >10 times larger than aqueous nitric acid conditions. The DSr value was influenced by concentrations of the DCH18C6, Sr(ii), and acid, and by temperature. The composition of extracted complexes was estimated using slope analysis as an Sr(ii)–anion–DCH18C6 ratio of ∼1 : 2 : 1. From the extended X-ray absorption fine structure (EXAFS) measurements of Sr(ii) in the aqueous and organic phases, it is inferred that regardless of the acid used, DCH18C6 coordinates to the first coordination sphere of the Sr(ii) extracted complexes and Sr(ii) is hydrated (complexation with H2PFTOUD cannot be distinguished) in the aqueous phase. Thermodynamic data were significantly changed by choice of acid, i.e., both enthalpy and entropy values were negative for nitric acid conditions, on the other hand, entropy values were large and positive for H2PFTOUD conditions. These results have demonstrated that the combination of HFC solvent and crown ether is applicable for metal extraction.

Separation and enrichment of Rb(I) in dicyclohexano 18 crown 6(DCH18C6)/PVC polymer inclusion membrane assisted by electric field

The effective extraction of liquid rubidium resources such as salt lake brine and seawater and the recovery of rubidium(I) at the end of the extraction process of lithium resources have always been a challenge in the industry. Two series of polymer inclusion membranes(PDA-PIM and PDT-PIM) were prepared to study the separation and enrichment of Rb(I). PDA-PIM and PDT-PIM used polyvinyl chloride (PVC) and dicyclohexano 18 crown 6(DCH18C6) as carriers, and tricaprylmethylammonium chloride (Aliquat 336) and trioctylphosphine oxide (TOPO) as a plasticizer, respectively. The optimal mass ratio (W/W) of PDA-PIM and PDT-PIM were P25D3.5A25 and P25D3.5T1, respectively. The applied electric field is a core condition for the mass transfer and separation of Rb(I). With the increase of voltage, the permeability coefficient P of Rb(I) and the separation factor (S) relative to Na(I) and K(I) increases. At 180 V, the PRb of PDA-PIM and PDT-PIM were 12.08 and 2.39 µm/s, and the SRB/NA were 11.21 and 14.44. After four mass transfer cycles of PDT-PIM, PRb only decreased by 4.6%. In addition, after 81.5 h of mass transfer, the enrichment ratio of Rb(I) was 3.02 times. These results show the excellent stability and mass transfer performance of PDT-PIM. It's of great significance for low concentration Rb(I) extraction.

Cover Feature: Study on the Isotope fractionation of Zinc in Complexation with Macrocyclic Polyethers (Z. Anorg. Allg. Chem. 6/2021)

The isotope fractionation of Zn was studied by liquid-liquid extraction with aqueous phase of ZnCl2/ HCl and organic phase of crown ethers(CEs), benzo15-crown-5(B15C5), benzo-18-crown-6(B18C6) and Dicyclohexano-24-crown-8(DC24C8)/1,2-dichloroethane. The isotope enrichment factor of the isotope pair 66Zn-64Zn was found to be ϵ66=−0.24 to −0.52‰ in the order of B15C5≥B18C6>DC24C8. The magnitude of ϵ66 was well explained by using the isotope fractionation factors obtained by density functional theory method for Zn chlorides and ZnCl2/CE model molecules. More details can be found in the Article by Toshiyuki Fujii, Chizu Kato, Brandon Mahan, and Frédéric Moynier.

Ionic liquid (IL) cation and anion structural effects on the extraction of metal ions into N-alkylpyridinium-based ILs by a macrocyclic polyether

ABSTRACT Previous studies of the effect of IL cation/anion hydrophobicity and the nature of the aqueous phase anion on the partitioning of alkali and alkaline earth cations between an acidic aqueous phase and 1,3-dialkylimidazolium-based or quaternary ammonium-based ILs in the presence of a crown ether have revealed significant similarities between the behavior of the two IL families. To further explore the generality of these observations and their potential application in the rational design of ILs for use as replacements for the molecular diluents typically employed as extraction solvents, the extraction of several metal ions (Na+, Sr2+ and Ba2+) from nitric and hydrochloric acid solutions by dicyclohexano-18-crown-6 (DCH18C6) into a series of N-alkylpyridinium-based ILs (Cn-pyr+ ILs) has been studied. Although much of the extraction behavior observed in these systems is consistent with that seen for the 1,3-dialkylimidazolium and quaternary ammonium-based ILs, certain observations, in particular the effect of IL cation hydrophobicity on divalent metal ion extraction from HNO3 by N-alkylpyridinium-ILs bearing long (dodecyl- and tetradecyl-) alkyl chains, cannot be fully explained by the established three-path model for metal ion partitioning. Instead a complete description of metal ion extraction in these systems requires consideration of the aggregation of the IL cation in the aqueous phase. The effects of this aggregation on the efficiency and selectivity of metal ion extraction into Cn-pyr+ ILs by the crown ether are systematically explored.

Study on the Isotope fractionation of Zinc in Complexation with Macrocyclic Polyethers

AbstractIsotope fractionation of Zn was studied via liquid‐liquid extraction with aqueous phase of ZnCl2/HCl and organic phase of crown ethers(CEs), including benzo15‐crown‐5(B15C5), benzo‐18‐crown‐6(B18C6) and Dicyclohexano‐24‐crown‐8(DC24C8)/1,2‐ dichloroethane. The isotope enrichment factor (ϵ66), expressed in permil notation, of the isotope pair 66Zn−64Zn was found to be between −0.24 and −0.52 ‰ in the order of enrichment: B15C5≥B18C6>DC24C8. The magnitude of ϵ66was well explained by theoretical isotope fractionation factors obtained by density functional theory method for zinc chloride and ZnCl2/CE model molecules, and a thermochemical description that correlates ϵ66 with the differences in Gibbs free energy(ΔG) of the exchange reaction, here termed δΔG, based on the mass differences of Zn isotopes involved. Finally, results suggest that ϵ66 may be used as a diagnostic and metric of Zn metabolic derangement, such as in porphyrias.

Proton conduction in hydronium solvate ionic liquids affected by ligand shape.

We investigated the ligand dependence of the proton conduction of hydronium solvate ionic liquids (ILs), consisting of a hydronium ion (H3O+), polyether ligands, and a bis[(trifluoromethyl)sulfonyl]amide anion (Tf2N-; Tf = CF3SO2). The ligands were changed from previously reported 18-crown-6 (18C6) to other cyclic or acyclic polyethers, namely, dicyclohexano-18-crown-6 (Dh18C6), benzo-18-crown-6 (B18C6) and pentaethylene glycol dimethyl ether (G5). Pulsed-field gradient spin echo nuclear magnetic resonance results revealed that the protons of H3O+ move faster than those of cyclic 18C6-based ligands but as fast as those of acyclic G5 ligands. Based on these results and density functional theory calculations, we propose that the coordination of a cyclic ether ligand to the H3O+ ion is essential for fast proton conduction in hydronium solvate ILs. Our results attract special interest for many electro- and bio-chemical applications such as electrolyte systems for fuel cells and artificial ion channels for biological cells.

Radical channels of radiation destruction of macrocyclic component of strontium-selective extractants based on ionic liquids

To study the radiolysis of the extractant composition based on solutions of dicyclohexano-18-crown-6 (DCH18C6) in ionic liquids containing the bis(trifluoromethylsulfonyl)imide anion (NTf2−), we synthesized stereoisomeric DCH18C6•Sr(NTf2)2 complexes as a model of the strontium-containing macrocyclic component of this system and studied the mechanism of their destruction in the solid phase. Three main stages of radiation-chemical transformations were found. At the initial stage of radiolysis after ionization of the complex components, a positive charge is transferred from the macrocycle to the anion, which is induced by the lower ionization potential of NTf2− as compared to the crown ether. This results in the radiation protection of the macrocycle due to the blockage of the polyether ring cleavage, which is observed under radiolysis of “free” DCH18C6. The next stage consists in the accumulation of the —O—•CH—CH2— radicals caused by the reaction of the dissociation products of the NTf2− anion with the crown ether. It intensifies the radiation destruction of the polyether ring. At the final stage, the macrocyclic radicals efficiently scavenge SO2, the molecular product of dissociation of the NTf2− anion, with the formation of sulfonyl-type radicals. The discovered channels of radiation-chemical transformations of the macrocycle in the systems including the NTf2− anion should be considered in the design of new radiation-resistant extractants.

The extraction of SR2+ with dicyclohexano-18-crown-6 in conventional organic solvent and ionic liquid diluents

90Sr (t1/2 = 28.8 a), one of the most significant fission products in high-level radioactive liquid waste (HLLW), contributes to a large part of the heat load and radiation. Removal of 90Sr from the HLLW is beneficial for the final treatment of nuclear waste. In this paper, the extraction of Sr2+ was carried out using dicyclohexano-18-crown-6 (DCH18C6) in a variety of diluents including conventional organic solvents and novel ionic liquid solvents. The effect of several factors, such as nitric acid concentration, crown ether concentration and initial strontium concentration on the extraction of Sr2+ have been studied comprehensively. The higher distribution ratio and the stripping efficiency of Sr2+ were obtained with the binary diluents consisted of n-octanol and acetylene tetrachloride, which were compared with that using pure n-octanol as diluent. As for the CnmimNTf2 (n = 2, 4, 6) ionic liquid solvent systems, the distribution ratio of Sr2+ was much higher in the nitric acid medium with low concentration than in the traditional solvent systems. The results showed that DC2mimNTf2 > DC4mimNTf2 > DC6mimNTf2, which indicated that shorter carbon chain benefits the extraction of Sr2+.

Insights in uranium extraction from spent nuclear fuels using dicyclohexano-18-crown-6 – Fate of rhenium as technetium homolog

The single extraction of rhenium(VII) and uranium(VI) from nitric acid solution by dicyclohexano-18-crown-6 (DCH) solutions was investigated. The extraction of Re(VII), in the form of perrhenate (ReO4−) anion, was optimum for a nitric acid concentration of 3 M and was explained by the ion-pair extraction of perrhenate anions by the hydroxonium DCH complex. The stoichiometry of the Re(VII) complex was obtained from the distribution data by slope analysis and the extracted specie was identified as {ReO4−(DCH-H3O)+}. The uranyl extraction by DCH solutions was evaluated under the same conditions and the extracted specie was identified as {(NO3−)2(DCH-UO22+)} for a nitric acid concentration above 5 M. The extraction of rhenium(VII) from nitric acid solution by DCH solutions in the presence of large excess of uranium(VI) was then investigated. For a nitric acid concentration of 3 mol/L, the extraction efficiency of perrhenate was found to be almost independent of uranium concentration. Based on the chemical similarities between Re(VII) and Tc(VII), this suggests that DCH could be considered for the separation of technetium (VII)/uranium(VI) from nitric acid solution.

The Extraction of Metal Contaminants Using Supercritical Carbon Dioxide

Conventional decontamination methods utilize water-based systems, which generate high amounts of secondary wastes. Herein, the authors describe an environmentally benign decontamination method using liquid and supercritical CO2. The use of CO2 as a solvent affords effective waste reduction by its ability to be recycled, thereby leaving behind only the contaminants upon its evaporation. In this study, a CO2 solution process was assessed using t-butyl salen (t-salen), dicyclohexano-18Crown6 (DC18C6), 8-hydroxyquinoline (8-HQN), perfluoro-1-octanesulfonic acid tetra-ethylammonium salt (NEt4PFOSA), and pentadecafluorooctanoic acid ammonium salt (NEt4PFOA) to extract spiked radioactive contaminants (Nb, Zr, Co, Sr) from an inert sample matrix, namely with filter paper. With the static extraction method, Sr was extracted with a maximum extraction rate of 97%, and Nb was extracted with a maximum extraction rate of 75%. Additionally, the authors were also able to extract Co and Zr with maximum extraction rates of 73% and 64%, respectively.

Ion-pair extraction-reaction of calcium using Y-shaped microfluidic junctions: An optimized separation approach

In this research, a continuous microsolvent extraction-reaction was developed for the efficient separation of calcium ion. This study gives a preliminary possible practical application of microfluidic devices in chemical exchange reaction for enrichment of 48Ca stable isotope. For this purpose, in the first stage, the hydrodynamic behavior of two immiscible liquids in a simple Y-shaped microfluidic junction is experimentally investigated, and then ion-pair extraction-reaction of Ca2+ using picric acid as a counter-ion and dicyclohexano-18-crown-6 (DC18C6) as a lipophilic ionophore is studied in this microfluidic and conventional batch method. The impact of main process parameters, including concentration of calcium chloride (0.001–0.1 M), picric acid (0.002–0.2 M), and DC18C6 (0.001–0.1 M) on the extraction-reaction efficiency and apparent overall volumetric mass transfer coefficient was comprehensively examined by utilizing response surface methodology (RSM), leading to an optimized condition for the separation of calcium. In addition, by changing the dimensions of microreactors, the influence of contact time and flow rates of both phases on the extraction-reaction efficiency was investigated. The results show that the efficiency varies significantly with changes in reagent concentration. Since the efficiency decreased with increasing the calcium chloride, the existence of a small amount of picric acid and DC18C6 in the organic phase facilitates the extraction-reaction. Moreover, the extraction-reaction is almost accomplished within ∼ 1.5 s with the efficiency of 98.55% by using the microfluidic device whereas the equilibrium condition is obtained in at least 30 min in a batch method. Furthermore, the higher contact time and flow rates result in the higher separation of the calcium ion.

DFT calculation and experimental validation on the interactions of bis(trifluoromethylsulfonyl)imide and hexafluorophosphate with cesium

Bis(trifluoromethylsulfonyl)imide (NTf2−) and hexafluorophosphate (PF6−) are the most frequently used anions for hydrophobic ionic liquids (ILs) which have been considered as promising solvents in the extraction of cesium ions. The interactions of NTf2− and PF6− with Cs+ were explored in this work. The results of DFT calculation indicated that both Cs+ and Cs(18C6)+ prefer to interact with two NTf2− or PF6− anions in gas phase, where 18C6 is 18-crown-6. The complex of Cs(NTf2)2− was observed in electrospray ionization mass spectrometry (ESI-MS), and the complexes of [Cs(18C6)NTf2]2 and [Cs(18C6)PF6]2 were crystallized in which Cs(18C6)+ interacted with two anions. The interactions of NTf2− with cesium resulted in a synergistic effect between dicyclohexano-18-crown-6 (DCH18C6) and NTf2− in the extraction of Cs+ using n-octanol as diluent. However, DFT calculation revealed that the complex Cs(DCH18C6)+ interacted with one NTf2− anion was more thermodynamically stable than that with two anions in organic phase, different from that in gas phase.

Extractive insights in the cesium ion partitioning with bis(2-propyloxy)-calix [4]crown-6 and dicyclohexano-18-crown-6 in ionic liquid-water biphasic systems

We report the molecular dynamics studies on the interfacial behavior of cesium (Cs+) extraction by bis(2-propyloxy)calix [4]crown-6 (BPC6) and dicyclohexano-18-crown-6 (DCH18C6). For the benchmarking study, the phase separation for [BMIM][Tf2N]-water was validated. Thereafter, to understand the mechanism of complexation and the behavior of the crown ether ligand, crown ether (CE) molecules and Cs+NO3− ions were inserted randomly in the ionic liquid (IL)–water biphasic system. It was observed that the 2:1 Cs+-BPC6 complex formed during the simulation was more stable at the interface and was found to diffuse slowly to the IL side of the interface. On the contrary the 1:1 Cs+-DCH18C6 complex was found to be fully solvated in the bulk IL phase. The [BMIM]+ cation was found to partition to the aqueous phase and exchange with Cs+ ion in presence or absence of CE. The solubility, density plots and the snapshots of the [BMIM]+ cation at the IL–water interface indicates the dual cationic exchange. A comparison of the interfacial behavior of Cs+-BPC6 complex and Cs+-DCH18C6 complex in IL–water preformed interface system, depicted that the Cs+-BPC6 complex was stable at the interface till the end of the simulation. One the other hand, the uncomplexed DCH18C6 resided at the interface, while the Cs+ ion diffused to the bulk aqueous phase. The calculated interaction energy of Cs+-BPC6 was found to higher as compared to Cs+-DCH18C6. These results display the importance of the dual cationic exchange properties of IL and the extraction efficiency of CE for extraction of metal ions.