Co-reporter:Steven Mullens;Joris Roosen;Judith Pype
Industrial & Engineering Chemistry Research December 30, 2015 Volume 54(Issue 51) pp:12836-12846
Publication Date(Web):2017-2-22
DOI:10.1021/acs.iecr.5b03494
The vibrating-nozzle technology is very interesting to very easily and very rapidly produce industrial amounts of functional microspheres. The technology was used to make hybrid alginate–silica microspheres by droplet coagulation. The microspheres were formed starting from suspensions of sodium alginate, and coagulation occurred in an aqueous solution of calcium ions. To enhance the mechanical properties of the alginate raw material, it was combined with two different silica sources: tetramethyl orthosilicate (TMOS) and commercial silica powder. The two different batches of alginate–silica microspheres were fully compared with regard to their morphology, composition, shrinking behavior, and stability in acidic conditions. It was shown that the incorporation of an inorganic matrix resulted in a material with a better stabilized porous structure and a higher resistance in an acidic environment. Both are important when functional particles are designed to be used for adsorption of metal ions, either as a stirred suspension or as a stationary phase in a chromatographic column. A study of the adsorption performance was conducted in batch mode for neodymium(III), a representative element for the group of critical rare-earth elements. The effect of stripping (desorption) on the adsorption performance and reusability was also investigated. The functional alginate–silica microspheres show a sustainable character.
Co-reporter:Kristian Larsson
Journal of Sustainable Metallurgy 2017 Volume 3( Issue 1) pp:73-78
Publication Date(Web):2017 March
DOI:10.1007/s40831-016-0074-4
A solvent extraction system based on the ionic liquid tricaprylmethylammonium nitrate, [A336][NO3], has been investigated for separation of mixtures of rare earth elements (REE) at high total REE concentrations (up to 2 M). The chelating agent EDTA was added to the aqueous nitrate feed solution to increase the separation factors (SFs). This improvement of the SFs is based on the fact that [A336][NO3] extracts the light REE (LREE) stronger than the heavy REE (HREE), whereas a chelating agent forms more stable complexes with the HREE than with the LREE. The combination of these two effects makes that the LREE are even more efficiently extracted than in the absence of a chelating agent. The most efficient separation of the LREE La–Nd from the other REE was obtained using a total initial REE concentration of 1 M, an EDTA concentration of 0.2 M, and a total nitrate concentration of 11 M. Stripping of the extracted REE from the ionic liquid phase could be done using water.
Co-reporter:David Dupont and Koen Binnemans
Green Chemistry 2016 vol. 18(Issue 1) pp:176-185
Publication Date(Web):14 Sep 2015
DOI:10.1039/C5GC01746G
Antimony is becoming an increasingly critical element as the supply-demand gap is expected to exceed 10% over the period 2015–2020. Antimony production is primarily concentrated in China (90%) and as the industrial demand for this metal surges, attention has to turn towards the recovery of antimony from (industrial) waste residues and end-of-life products in order to guarantee a sustainable supply of antimony. Although lamp phosphor waste is usually considered as a source of rare earths, it also contains significant amounts of antimony in the form of the white halophosphate phosphor (Ca,Sr)5(PO4)3(Cl,F):Sb3+,Mn2+ (HALO). HALO phosphor readily dissolves in dilute acidic conditions, making antimony far more accessible than in the main production route which is the energy intensive processing of stibnite ore (Sb2S3). HALO makes up 50 wt% of the lamp phosphor waste, but it has been systematically overlooked and treated as an undesired residue in the efforts to recover rare earths from lamp phosphor waste. In this paper, the feasibility of antimony recovery is discussed and an efficient process is proposed. The HALO phosphor is first dissolved in dilute HCl at room temperature, followed by a selective extraction of antimony with the ionic liquid Aliquat® 336. The remaining leachate is valorized as apatite which is a feed for the phosphate and fertilizer industry. A zero-waste valorization approach was followed, meaning that no residue or waste was accepted and that all the elements were converted into useful products. This paper thus emphasizes the potential of lamp phosphor waste as a secondary source of antimony and describes a sustainable process to recover it. The process can be integrated in lamp phosphor recycling schemes aimed at recovering rare earths.
Co-reporter:Joris Roosen, Stijn Van Roosendael, Chenna Rao Borra, Tom Van Gerven, Steven Mullens and Koen Binnemans
Green Chemistry 2016 vol. 18(Issue 7) pp:2005-2013
Publication Date(Web):10 Nov 2015
DOI:10.1039/C5GC02225H
Bauxite residue (red mud) is a waste residue that results from the production of alumina by the Bayer process. Since it has no large-scale industrial application, it is stockpiled in large reservoirs. Nevertheless, it should be considered as a valuable secondary resource as it contains relatively large concentrations of critical metals like the rare earths, scandium being the most important one. In this work, we investigated the recovery of scandium from real leachates of Greek bauxite residue. In the separation of scandium from the other elements, the biggest challenge arose from the chemical similarities between scandium(III) and iron(III). This hampers high selectivity for scandium, especially because iron, as one of the major elements in bauxite residue, is present in much higher concentrations than scandium. In order to achieve selectivity for scandium, chitosan–silica particles were functionalized with the chelating ligands diethylenetriamine pentaacetic acid (DTPA) and ethyleneglycol tetraacetic acid (EGTA). Both organic ligands were chosen because of the high stability constants between scandium(III) and the corresponding functional groups. The adsorption kinetics and the influence of pH on hydrolysis and adsorption were investigated batchwise from single-element solutions of scandium(III) and iron(III). In binary solutions of scandium(III) and iron(III), it was observed that only EGTA-functionalized chitosan–silica appeared to be highly selective for scandium(III) over iron(III). EGTA–chitosan–silica shows a much higher selectivity over state-of-the-art adsorbents for the separation of scandium(III) from iron(III). The latter material was therefore used as a resin material for column chromatography in order to effectively separate scandium from bauxite residue. Full separation was achieved by eluting the column with HNO3 solution at pH 0.50; at this pH all other elements had already eluted.
Co-reporter:Sven Dewilde, Wim Dehaen and Koen Binnemans
Green Chemistry 2016 vol. 18(Issue 6) pp:1639-1652
Publication Date(Web):02 Nov 2015
DOI:10.1039/C5GC02185E
Poly-p-phenyleneterephthalamide (PPTA) is an aramid polymer with high tensile strength which is currently industrially synthesized in a solvent mixture of N-methylpyrrolidone (NMP) and CaCl2. Due to the toxicity of NMP and the need for a salt to increase the solubility, ionic liquids are suggested as suitable, alternative solvents. A whole series of ionic liquids (ILs) were investigated for their solubilization strength towards PPTA. For this study, small PPTA oligomers were synthesized and used as model compounds in solubility tests with ionic liquids. This study gave insights in the types of cations and anions required for optimal dissolving behavior. Ionic liquids with coordinating anions are a requirement to solubilize PPTA by disrupting the intermolecular hydrogen bond network, just as is the case for cellulose dissolution. Infrared and NMR-spectroscopic studies revealed the interaction of the anions with the hydrogen atoms of the secondary amides of the aramid chains. However, there is no one-to-one relationship between ionic liquids suitable for PPTA and cellulose dissolution. Cations with hydrogen atoms capable of hydrogen bond formation, like imidazolium cations, are poor solvents for PPTA. These cations hamper the anions in using their full potential for coordination with the oligomers. Ammonium and phosphonium ionic liquids which contain only sp3-bonded hydrogen atoms on the cation, do not show a tendency to form hydrogen bonds and dissolve PPTA oligomers much better than their imidazolium analogues. This hypothesis was further confirmed by the fact that substitution of hydrogen atoms by methyl groups on imidazolium and pyridinium cations improves the solvent power of the ionic liquid significantly. This screening test has identified several types of ionic liquids that are able to dissolve larger amounts of the PPTA oligomers on a molar basis than the currently used industrial solvent NMP/CaCl2.
Co-reporter:David Dupont, Evelien Renders, Stijn Raiguel and Koen Binnemans
Chemical Communications 2016 vol. 52(Issue 43) pp:7032-7035
Publication Date(Web):04 May 2016
DOI:10.1039/C6CC02350A
Sulfamic acid (NH3–SO3) is an acidic zwitterion with many applications. N-Alkylated derivatives are introduced, which can be used as a new class of metal extractants R2NH–SO3 and as new super-acidic ionic liquids [R2NH–SO3H][Tf2N]. The synthesis, properties and novel applications of this versatile platform are discussed.
Co-reporter:David Dupont, Evelien Renders and Koen Binnemans
Chemical Communications 2016 vol. 52(Issue 25) pp:4640-4643
Publication Date(Web):01 Mar 2016
DOI:10.1039/C6CC00094K
Strongly acidic (pKa ≈ −3.5) room-temperature ionic liquids (ILs) with –OSO3H functionalized cations are introduced. The strong acidity, easy synthesis, and better physical properties of these R–OSO3H ILs make them excellent alternatives to the well-known sulfonic acid (R–SO3H) ILs, especially in the domain of metal processing.
Co-reporter:Alok Rout and Koen Binnemans
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 23) pp:16039-16045
Publication Date(Web):24 May 2016
DOI:10.1039/C6CP02301K
The ionic liquid trihexyl(tetradecyl)phosphonium thiocyanate has been used for the extraction of the transition metal ions Co(II), Ni(II), Zn(II), and the rare-earth ions La(III), Sm(III) and Eu(III) from aqueous solutions containing nitrate or chloride salts. The transition metal ions showed a high affinity for the ionic liquid phase and were efficiently extracted, while the extraction efficiency of the rare-earth ions was low. This difference in extraction behavior enabled separation of the pairs Co(II)/Sm(III), Ni(II)/La(III) and Zn(II)/Eu(III). These separations are relevant for the recycling of rare earths and transition metals from samarium cobalt permanent magnets, nickel metal hydride batteries and lamp phosphors, respectively. The extraction of metal ions from a chloride or nitrate solution with a thiocyanate ionic liquid is an example of “split-anion extraction”, where different anions are present in the aqueous and ionic liquid phase. Close to 100% loading was possible for Co(II) and Zn(II) up to a concentration of 40 g L−1 of the transition metal salt in the initial aqueous feed solution, whereas the extraction efficiency for Ni(II) gradually decreased with increase in the initial feed concentration. Stripping of Co(II), Zn(II) and Ni(II) from the loaded ionic liquid phase was possible by a 15 wt% NH3 solution. The ionic liquid could reused after extraction and stripping.
Co-reporter:Daphne Depuydt, Arne Van den Bossche, Wim Dehaen and Koen Binnemans
RSC Advances 2016 vol. 6(Issue 11) pp:8848-8859
Publication Date(Web):15 Jan 2016
DOI:10.1039/C5RA22798D
Imidazolium ionic liquids were synthesized from readily available molecules: aldehydes, 1,2-carbonyl components, alkyl amines and acids in a halogen-free procedure. Since the use of enolisable carbonyl functions is not compatible with the modified Debus–Radziszewski reaction, symmetrical 1,3-dialkylimidazolium ionic liquids were made. The use of strong acids, like sulfuric acid, leads to protonation of the amine, low yields and side products that are difficult to remove. Changing the acid in the synthesis to acetic acid greatly improved the isolated yield and produced pure imidazolium acetate ionic liquids. From these imidazolium acetate compounds, many other ionic liquids could be prepared using different metathesis strategies. These strategies were dependent on the acidity of the conjugate acid of the anion, the acid volatility and the hydrophilicity of the used reagents and resulting ionic liquid. The following anions were introduced: bis(trifluoromethylsulfonyl)imide ([Tf2N]−), p-toluenesulfonate (tosylate, [TsO]−), bis(2-ethylhexyl)phosphate ([DEHP]−) and nitrate ([NO3]−). The impact of the different anions on the properties of the ionic liquids was investigated.
Co-reporter:Jeroen Sniekers;Ken Verguts;Dr. Neil R. Brooks;Dr. Stijn Schaltin;Dr. Thanh Hai Phan;Dr. Thi Mien TrungHuynh; Luc VanMeervelt; Steven DeFeyter; Jin Won Seo; Jan Fransaer; Koen Binnemans
Chemistry - A European Journal 2016 Volume 22( Issue 3) pp:1010-1020
Publication Date(Web):
DOI:10.1002/chem.201504123
Abstract
New nickel-containing ionic liquids were synthesized, characterized and their electrochemistry was investigated. In addition, a mechanism for the electrochemical synthesis of nanoparticles from these compounds is proposed. In these so-called liquid metal salts, the nickel(II) cation is octahedrally coordinated by six N-alkylimidazole ligands. The different counter anions that were used are bis(trifluoromethanesulfonyl)imide (Tf2N−), trifluoromethanesulfonate (OTf−) and methanesulfonate (OMs−). Several different N-alkylimidazoles were considered, with the alkyl sidechain ranging in length from methyl to dodecyl. The newly synthesized liquid metal salts were characterized by CHN analysis, FTIR, DSC, TGA and viscosity measurements. An odd-even effect was observed for the melting temperatures and viscosities of the ionic liquids, with the complexes with an even number of carbon atoms in the alkyl chain of the imidazole having a higher melting temperature and a lower viscosity than the complexes with an odd number of carbons. The crystal structures of several of the nickel(II) complexes that are not liquid at room temperature were determined. The electrochemistry of the compounds with the lowest viscosities was investigated. The nickel(II) cation could be reduced but surprisingly no nickel deposits were obtained on the electrode. Instead, nickel nanoparticles were formed at 100 % selectivity, as confirmed by TEM. The magnetic properties of these nanoparticles were investigated by SQUID measurements.
Co-reporter:David Dupont;Sander Arnout;Peter Tom Jones
Journal of Sustainable Metallurgy 2016 Volume 2( Issue 1) pp:79-103
Publication Date(Web):2016 March
DOI:10.1007/s40831-016-0043-y
Antimony has become an increasingly critical element in recent years, due to a surge in industrial demand and the Chinese domination of primary production. Antimony is produced from stibnite ore (Sb2O3) which is processed into antimony metal and antimony oxide (Sb2O3). The industrial importance of antimony is mainly derived from its use as flame retardant in plastics, coatings, and electronics, but also as decolourizing agent in glass, alloys in lead-acid batteries, and catalysts for the production of PET polymers. In 2014, the European Commission highlighted antimony in its critical raw materials report, as the element with the largest expected supply–demand gap over the period 2015–2020. This has sparked efforts to find secondary sources of antimony either through the recycling of end-of-life products or by recovering antimony from industrial process residues. Valuable residues are obtained by processing of gold, copper, and lead ores with high contents of antimony. Most of these residues are currently discarded or stockpiled, causing environmental concerns. There is a clear need to move to a more circular economy, where waste is considered as a resource and zero-waste valorization schemes become the norm, especially for rare elements such as antimony. This paper gives a critical overview of the existing attempts to recover antimony from secondary sources. The paper also discusses the possibility of waste valorization schemes to guarantee a more sustainable life cycle for antimony.
Co-reporter:Koen Binnemans
Coordination Chemistry Reviews 2015 Volume 295() pp:1-45
Publication Date(Web):1 July 2015
DOI:10.1016/j.ccr.2015.02.015
•Europium(III) compounds often show an intense red photoluminescence.•Eu3+ is a spectroscopic probe for the symmetry of a lanthanide site.•Eu3+ has a non-degenerate ground state (7F0) and excited state (5D0).•The information content of europium(III) spectra is high.•Lifetime measurements allow determining the number of coordinated water molecules.The trivalent europium ion (Eu3+) is well known for its strong luminescence in the red spectral region, but this ion is also interesting from a theoretical point of view. Due to the even number of electrons in the 4f shell (4f6 configuration), the crystal-field perturbation by the crystalline host matrix lifts partly or completely the degeneracies of the 2S+1LJ levels. The Eu3+ ion has the great advantage over other lanthanide ions with an even number of 4f electrons that the starting levels of the transitions in both the absorption and the luminescence spectrum are non-degenerate (J = 0). Moreover, the interpretation of the spectra is facilitated by the small total angular momentum J of the end levels in the transitions. The number of lines observed for the 5D0 → 7FJ transitions in the luminescence spectrum or the 5DJ ← 7F0 transitions in the absorption spectrum allows determining the site symmetry of the Eu3+ ion. This review describes the spectroscopic properties of the trivalent europium ion, with emphasis on the energy level structure, the intensities of the f–f transitions (including the Judd–Ofelt theory), the decay times of the excited states and the use of the Eu3+ ion as a spectroscopic probe for site symmetry determination. It is illustrated how the maximum amount of information can be extracted from optical absorption and luminescence spectra of europium(III) compounds, and how pitfalls in the interpretation of these spectra can be avoided.
Co-reporter:Sofía Riaño and Koen Binnemans
Green Chemistry 2015 vol. 17(Issue 5) pp:2931-2942
Publication Date(Web):10 Mar 2015
DOI:10.1039/C5GC00230C
A procedure for the efficient extraction and separation of rare earths and other valuable elements from used NdFeB permanent magnets is presented. In a first step, an iron free leachate is prepared from an used magnet using nitric acid. Cobalt is separated through a liquid–liquid extraction in aqueous nitrate media using as organic phase the ionic liquid trihexyl(tetradecyl)phosphonium nitrate which is easily prepared from the commercially available ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos® IL 101). Afterwards neodymium and dysprosium are successfully separated using ethylenediaminetetraacetic acid (EDTA) as a selective complexing agent during liquid–liquid extraction with the same ionic liquid. Different parameters of the separation process such as shaking speed, time, temperature, pH effect and concentration of complexing agents were optimized. The designed process allowed the separation of these three elements efficiently in few steps. The separated rare earths and cobalt were precipitated with oxalic acid and then calcined in order to form the oxides. Nd2O3, Dy2O3 and CoO were obtained with purities of 99.6%, 99.8% and 99.8%, respectively. Recycling of the employed ionic liquid for reuse in rare earths separation was also demonstrated.
Co-reporter:David Dupont and Koen Binnemans
Green Chemistry 2015 vol. 17(Issue 4) pp:2150-2163
Publication Date(Web):02 Mar 2015
DOI:10.1039/C5GC00155B
The continuous miniaturization of electric motors, hard disks and wind turbines is causing an increasing demand for high-performance neodymium–iron–boron magnets (NdFeB). The supply risk for the rare-earth elements (REEs) used in these magnets is a growing concern and has sparked the development of recycling schemes for these end-of-life products. In this paper a new recycling process for (microwave) roasted NdFeB magnets is proposed, based on the carboxyl-functionalized ionic liquid: betainium bis(trifluoromethylsulfonyl)imide, [Hbet][Tf2N]. Using the thermomorphic properties of the [Hbet][Tf2N]–H2O system, a combined leaching/extraction step was designed. The change from a homogeneous system during leaching (80 °C) to a biphasic system at room temperature causes the dissolved metal ions to distribute themselves amongst the two phases. The valuable elements (Nd, Dy, Co) are thus separated from the iron with high separation factors. The stripping was done very efficiently using oxalic acid to precipitate the REE(III) and cobalt(II) ions while transferring the iron(III) from the ionic liquid to the water phase as a soluble oxalate complex. The cobalt (present in certain magnets) was removed by treating the mixed (REE/Co) oxalate precipitate with aqueous ammonia. The remaining REE oxalate was then calcined to form the REE oxides (99.9% pure). The ionic liquid is regenerated during the stripping step and contamination of the water phase was avoided by salting-out the ionic liquid with Na2SO4. This innovative recycling process features a combined leaching/extraction in mild conditions using a reusable acidic ionic liquid and an energy-efficient microwave roasting of the magnets. These aspects all contribute towards the green character of this process which can be considered as a sustainable and efficient alternative to mineral acid leaching and solvent extraction.
Co-reporter:David Dupont and Koen Binnemans
Green Chemistry 2015 vol. 17(Issue 2) pp:856-868
Publication Date(Web):28 Nov 2014
DOI:10.1039/C4GC02107J
The supply risk for certain rare-earth elements (REEs) has sparked the development of recycling schemes for end-of-life products like fluorescent lamps. In this paper a new recycling process for lamp phosphor waste is proposed based on the use of the functionalized ionic liquid betainium bis(trifluoromethylsulfonyl)imide, [Hbet][Tf2N]. This innovative method allows the selective dissolution of the valuable red phosphor Y2O3:Eu3+ (YOX) without leaching the other constituents of the waste powder (other phosphors, glass particles and alumina). A selective dissolution of YOX is useful because this phosphor contains 80 wt% of the REEs although it only represents 20 wt% of the lamp phosphor waste. The proposed recycling process is a major improvement compared to currently used hydrometallurgical processes where the non-valuable halophosphate (HALO) phosphor (Sr,Ca)10(PO4)6(Cl,F)2:Sb3+,Mn2+ is inevitably leached when attempting to dissolve YOX. Since the HALO phosphor can make up as much as 50 wt% of the lamp phosphor waste powder, this consumes significant amounts of acid and complicates the further processing steps (e.g. solvent extraction). The dissolved yttrium and europium can be recovered by a single stripping step using a stoichiometric amount of solid oxalic acid or by contacting the ionic liquid with a hydrochloric acid solution. Both approaches regenerate the ionic liquid, but precipitation stripping with oxalic acid has the additional advantage that there is no loss of ionic liquid to the water phase and that the yttrium/europium oxalate can be calcined as such to reform the red Y2O3:Eu3+ phosphor (purity >99.9 wt%), effectively closing the loop after only three process steps. The red phosphor prepared from the recycled yttrium and europium showed excellent luminescent properties. The resulting recycling process for lamp phosphor waste consumes only oxalic acid and features a selective leaching, a fast stripping and an immediate revalorization step. Combined with the mild conditions, the reusability of the ionic liquid and the fact that no additional waste water is generated, this process is a very green and efficient alternative to traditional mineral acid leaching.
Co-reporter:Bieke Onghena, Tomas Opsomer and Koen Binnemans
Chemical Communications 2015 vol. 51(Issue 88) pp:15932-15935
Publication Date(Web):07 Sep 2015
DOI:10.1039/C5CC06595J
A [P44414][Cl]–NaCl–H2O ionic liquid-based aqueous biphasic system shows promising results for the separation of cobalt(II) and nickel(II) by homogeneous liquid–liquid extraction. The extracting phase consists of a hydrophilic ionic liquid that is salted-out by sodium chloride, indicating that there is no need for using hydrophobic ionic liquids.
Co-reporter:Daphne Depuydt, Liwang Liu, Christ Glorieux, Wim Dehaen and Koen Binnemans
Chemical Communications 2015 vol. 51(Issue 75) pp:14183-14186
Publication Date(Web):31 Jul 2015
DOI:10.1039/C5CC05649G
Ionic liquids with an ether-functionalised cation and the bis(2-ethylhexyl)phosphate anion show thermomorphic behaviour in water, with a lower critical solution temperature. These ionic liquids are useful for homogeneous liquid–liquid extraction of first-row (3d) transition metals.
Co-reporter:David Dupont, Stijn Raiguel and Koen Binnemans
Chemical Communications 2015 vol. 51(Issue 43) pp:9006-9009
Publication Date(Web):27 Apr 2015
DOI:10.1039/C5CC02731D
New sulfonic acid functionalized ionic liquids (SAFILs) with bis(trifluoromethylsulfonyl)imide anions were synthesized. These ionic liquids are strong Brønsted acids and can solubilize metal oxides. Water-immiscible SAFILs were used as organic phases in solvent extraction studies.
Co-reporter:Alok Rout and Koen Binnemans
Dalton Transactions 2015 vol. 44(Issue 3) pp:1379-1387
Publication Date(Web):19 Nov 2014
DOI:10.1039/C4DT02766C
Trivalent rare-earth ions were extracted from nitric acid medium by the neutral phosphine oxide extractant Cyanex 923 into ionic liquid phases containing the bis(trifluoromethylsulfonyl)imide anion. Five different cations were considered: 1-butyl-3-methylimidazolium, 1-decyl-3-methylimidazolium, methyltributylammonium, methyltrioctylammonium and trihexyl(tetradecyl)phosphonium. The extraction behavior of neodymium(III) was investigated as a function of various parameters: pH, extractant concentration, concentration of the neodymium(III) ion in the aqueous feed and concentration of the salting-out agent. The loading capacity of the ionic liquid phase was studied. The extraction efficiency increased with increasing pH of the aqueous feed solution. The extraction occurred for all ionic liquids via an ion-exchange mechanism and the extraction efficiency could be related to the solubility of the ionic liquid cation in the aqueous phase: high distribution ratios for hydrophilic cations and low ones for hydrophobic cations. Addition of nitrate ions to the aqueous phase resulted in an increase in extraction efficiency for ionic liquids with hydrophobic cations due to extraction of neutral complexes. Neodymium(III) could be stripped from the ionic liquid phase by 0.5–1.0 M nitric acid solutions and the extracting phase could be reused. The extractability of other rare earths present in the mixture was compared for the five ionic liquids.
Co-reporter:Tom Vander Hoogerstraete, Neil R. Brooks, Bieke Onghena, Luc Van Meervelt and Koen Binnemans
CrystEngComm 2015 vol. 17(Issue 37) pp:7142-7149
Publication Date(Web):13 Aug 2015
DOI:10.1039/C5CE01270H
Crystals of hydrated bis(trifluoromethylsulfonyl)imide (Tf2N) salts of the naturally occurring trivalent rare-earth ions were grown from aqueous solution and analysed by X-ray diffraction. Their structures can be classified into three main groups. The lighter lanthanides La–Gd (except Sm) have a cubic crystal structure with the formula Ln(H2O)3(Tf2N)3, which has Tf2N anions coordinating in a bidentate fashion. The middle and heavy lanthanides (Sm, Tb, Dy, Er, Yb) have a monoclinic crystal structure with formula Ln(H2O)5(Tf2N)3, where the Tf2N anions are coordinating in a monodentate fashion. The heavy lanthanides Gd–Lu (except Tb, Tm) crystallise with very large unit cells making structural identification difficult. Partial structure solution of one of these compounds indicates that the structures contain fully hydrated Ln3+ ions and very disorderd Tf2N anions. Y was found to behave as the heavy lanthanides and Sc was found in a crystal structure of formula [Sc(H2O)7][Tf2N]3·H2O. In addition, La was found in a hexagonal crystal structure of formula La(H2O)3(Tf2N)3·2.5H2O, when a small amount of residual HTf2N was present during crystallisation.
Co-reporter:Daphne Depuydt, Wim Dehaen, and Koen Binnemans
Industrial & Engineering Chemistry Research 2015 Volume 54(Issue 36) pp:8988-8996
Publication Date(Web):August 26, 2015
DOI:10.1021/acs.iecr.5b01910
The use of ionic liquids (ILs) as solvents for extraction of metals is a promising development in separation science and technology; yet, the viscosities of ionic liquids (ILs) can be so high that long reaction times are required to reach the equilibrium state. An aqueous biphasic system (ABS) consisting of the nonfluorinated carboxyl-functionalized phosphonium IL [P444C1COOH]Cl and a 16 wt % NaCl solution is described. The IL-rich phase of the aqueous biphasic system has a very low viscosity, in comparison to the pure IL [P444C1COOH]Cl. This system has excellent extraction properties for scandium. Different extraction parameters were investigated, including contact time and metal loading. The influence of the pH on the solubility of the IL cation in the water-rich phase was determined via quantitative 1H NMR. The stripping of scandium with oxalic acid from the IL phase was also investigated. A plausible extraction mechanism is proposed where three IL cations are deprotonated to form zwitterionic compounds that can coordinate scandium(III) ions.
Co-reporter:Bieke Onghena and Koen Binnemans
Industrial & Engineering Chemistry Research 2015 Volume 54(Issue 6) pp:1887
Publication Date(Web):January 22, 2015
DOI:10.1021/ie504765v
The ionic liquid betainium bis(trifluoromethylsulfonyl)imide [Hbet][Tf2N] was used for the extraction of scandium from aqueous solutions. The influence of several extraction parameters on the extraction efficiency was investigated, including the initial metal concentration, phase ratio, and pH. The extraction kinetics was examined, and a comparison was made between conventional liquid–liquid extraction and homogeneous liquid–liquid extraction (HLLE). The stoichiometry of the extracted scandium complex was determined with slope analysis. Scandium(III) is extracted as a complex with zwitterionic betaine in a 1:3 stoichiometry, with three bis(trifluoromethylsulfonyl)imide counterions. Upon extraction of scandium(III), proton exchange occurs and three protons are transferred to the aqueous phase. Scandium is an important minor element present in bauxite residue (red mud), the waste product that results from the industrial production of alumina by the Bayer process. To evaluate the suitability of [Hbet][Tf2N] for the selective recovery of scandium(III) from red mud leachates, the extraction of other metals present in the leachates (La(III), Ce(III), Nd(III), Dy(III), Y(III), Fe(III), Al(III), Ti(IV), Ca(II), Na(I)) was considered. It was shown that the trivalent lanthanide ions, yttrium(III) and the major elements aluminum(III), titanium(IV), calcium(II), and sodium(I), are all poorly extracted, which is advantageous for the selective recovery of scandium(III) from red mud. Iron(III) showed an extraction behavior similar to that of scandium(III). Scandium recovery was examined from a multielement rare-earth solution. Scandium could be separated from the other rare-earth elements by extraction with [Hbet][Tf2N] and subsequent scrubbing of the loaded ionic liquid phase to remove coextracted metal ions. The extracted scandium was recovered from the ionic liquid phase by using back-extraction with hydrochloric acid or precipitation stripping with oxalic acid.
Co-reporter:David Dupont, Daphne Depuydt, and Koen Binnemans
The Journal of Physical Chemistry B 2015 Volume 119(Issue 22) pp:6747-6757
Publication Date(Web):May 15, 2015
DOI:10.1021/acs.jpcb.5b02980
Hydrophobic (water-immiscible) ionic liquids (ILs) are frequently used as organic phase in solvent extraction studies. These biphasic IL/water extraction systems often also contain metal salts or mineral acids, which can significantly affect the IL trough (un)wanted anion exchange and changes in the solubility of IL in the aqueous phase. In the case of thermomorphic systems, variations in the cloud point temperature are also observed. All these effects have important repercussions on the choice of IL, suitable for a certain extraction system. In this paper, a complete overview of the implications of metal salts on biphasic IL/water systems is given. Using the Hofmeister series as a starting point, a range of intuitive prediction models are introduced, supported by experimental evidence for several hydrophobic ILs, relevant to solvent extraction. Particular emphasis is placed on the IL betainium bis(trifluoromethylsulfonyl)imide [Hbet][Tf2N]. The aim of this work is to provide a comprehensive interpretation of the observed effects of metal salts, so that it can be used to predict the effect on any given biphasic IL/water system instead of relying on case-by-case reports. These prediction tools for the impact of metal salts can be useful to optimize IL synthesis procedures, extraction systems and thermomorphic properties. Some new insights are also provided for the rational design of ILs with UCST or LCST behavior based on the choice of IL anion.
Co-reporter:Dr. Tom VerHoogerstraete;Jonas Blockx;Hendrik DeCoster ;Dr. Koen Binnemans
Chemistry - A European Journal 2015 Volume 21( Issue 33) pp:11757-11766
Publication Date(Web):
DOI:10.1002/chem.201500825
Abstract
In a conventional solvent extraction system, metal ions are distributed between two immiscible phases, typically an aqueous and an organic phase. In this paper, the proof-of-principle is given for the distribution of metal ions between three immiscible phases, two ionic liquid phases with an aqueous phase in between them. Three-liquid-phase solvent extraction allows separation of a mixture of three metal ions in a single step, whereas at least two steps are required to separate three metals in the case of two-liquid-phase solvent extraction. In the triphasic system, the lower organic phase is comprised of the ionic liquid betainium- or choline bis(trifluoromethylsulfonyl)imide, whereas the upper organic phase is comprised of the ionic liquid trihexyl(tetradecyl)phosphonium bis(trifluoromethylsulfonyl)imide. The triphasic system was used for the separation of a mixture of tin(II), yttrium(III), and scandium(III) ions.
Co-reporter:Koen Binnemans;Peter Tom Jones
Journal of Sustainable Metallurgy 2015 Volume 1( Issue 1) pp:29-38
Publication Date(Web):2015 March
DOI:10.1007/s40831-014-0005-1
Maintaining the balance between the demand by the economic markets and the natural abundance of the rare-earth elements (REEs) in ores constitutes a major challenge for manufacturers of these elements. This is the so-called balance problem (or balancing problem). The ideal situation is a perfect match between the demand and (production) supply of REEs, so that there are no surpluses of any of the REEs. The balance problem implicates that the rare-earth industry has to either find new applications for REEs that are available in excess, or needs to search for substitutions for REEs that have limited availability and that are high in demand. Different solutions are proposed to solve the balance problem: diversification of REE resources, recycling and urban/landfill mining, substitution, reduced use and new high-volume applications. No single solution can solve the balance problem, but a combination of different strategies can. It is illustrated that the issue of thorium in REE ores is also directly related to the balance problem: presently, thorium is considered as radioactive waste, but this waste could be turned into a valuable resource by using thorium in a thorium-based nuclear fuel cycle.
Co-reporter:Tom Vander Hoogerstraete and Koen Binnemans
Green Chemistry 2014 vol. 16(Issue 3) pp:1594-1606
Publication Date(Web):07 Jan 2014
DOI:10.1039/C3GC41577E
A solvent extraction process with the ionic liquid trihexyl(tetradecyl)phosphonium nitrate has been developed to extract rare earths and separate them from nickel or cobalt. The process is environmentally friendlier than traditional solvent extraction processes, since no volatile and flammable diluents have to be used. Compared to conventional ionic liquid metal extraction systems, the advantage of using the new ionic liquid is that expensive and persistent fluorinated ionic liquids can be avoided. The ionic liquid can be prepared by a simple metathesis reaction from the commercially available ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101). The extraction is facilitated by an inner salting-out effect of a highly concentrated metal nitrate aqueous phase. Feed solutions containing 164 g L−1 cobalt(II) and 84 g L−1 samarium(III), or 251 g L−1 nickel(II) and 61 g L−1 lanthanum(III) were tested. Percentage extractions of more than 99% were obtained for the rare earths and after a subsequent scrubbing step, the purity of the rare earth in the loaded ionic liquid phase was 99.9%. Complete stripping and regeneration of the ionic liquid could be performed using no chemicals other than pure water. Special attention was paid to the viscosity of the loaded ionic liquid phase and the kinetics of the extraction process, because the high viscosity and the slow mass transfer are the reasons why non-fluorinated ionic liquids have always been diluted in the past with conventional hydrophobic organic solvents such as kerosene, toluene or chloroform. The extraction mechanism of the rare earths samarium and lanthanum was studied and it was shown that different anionic complexes are formed. Lanthanum(III) is extracted at maximal loading via the hexakis anionic complex [La(NO3)6]3−, whereas samarium(III) is extracted at maximal loading via the pentakis anionic complex [Sm(NO3)5]2−. The difference in electrical charge of the anions has a pronounced effect on the viscosity of the ionic liquid phases. The separation of lanthanum and samarium from nickel or cobalt, out of highly concentrated metal salt solutions by solvent extraction, is of importance for the recycling samarium–cobalt permanent magnets or nickel metal hydride (NiMH) batteries.
Co-reporter:Joris Roosen, Jeroen Spooren and Koen Binnemans
Journal of Materials Chemistry A 2014 vol. 2(Issue 45) pp:19415-19426
Publication Date(Web):16 Sep 2014
DOI:10.1039/C4TA04518A
Chitosan–silica hybrid adsorbents were prepared and functionalized with ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA). The method consisted of sol–gel hybridization of chitosan and silica, followed by the addition of anhydrides to graft EDTA- and DTPA-ligands on the amine groups of the chitosan moieties in the hybrid particles. The resulting adsorbents were characterized by a range of analytical techniques: FTIR, BET, SEM, TGA, ICP and CHN. Coordination of Eu(III) to immobilized EDTA- and DTPA-groups was investigated by luminescence spectroscopy. The adsorption performance of the chitosan–silica adsorbents was investigated for Nd(III) as a function of the contact time, the pH of the aqueous feed and the adsorbent mass. Stripping and reusability studies were performed for both EDTA-chitosan–silica and DTPA-chitosan–silica. Differences in affinity amongst the rare-earth ions were investigated for DTPA-chitosan–silica in mono-component solutions of five rare earths (La, Nd, Eu, Dy and Lu). The order of affinity was in agreement with the trend in stability constants for the respective rare-earth ions with non-immobilized DTPA (bearing five available carboxylic acid groups). Multi-element mixtures were used to determine the selectivity of the adsorption process. Special attention was paid to separation of Nd and Dy, since these elements are relevant to the recovery of rare earths from End-of-Life permanent magnets.
Co-reporter:Joris Roosen and Koen Binnemans
Journal of Materials Chemistry A 2014 vol. 2(Issue 5) pp:1530-1540
Publication Date(Web):18 Nov 2013
DOI:10.1039/C3TA14622G
Chitosan, which is derived from chitin by deacetylation, is one of the most promising biopolymers for adsorption of metal ions from diluted waste streams. By functionalization of chitosan with ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA) groups, it is possible to obtain a material that is much less soluble in acidic aqueous solutions than native chitosan. The coordinating EDTA and DTPA ligands are very efficient for binding of rare-earth (lanthanide) ions. The functionalization was achieved by reaction of chitosan with EDTA bisanhydride or DTPA bisanhydride. The binding of lanthanide ions to functionalized chitosan was investigated by FTIR (binding of Nd3+) and luminescence spectroscopy (binding of Eu3+). Comparison of the luminescence decay times of the europium(III) coordinated chitosan complexes swollen in water and in heavy water allowed determination of the hydration number of the coordinated Eu3+ ion. Batch adsorption tests for the uptake of neodymium(III) from aqueous nitrate solutions were performed for EDTA-chitosan and DTPA-chitosan. Different experimental parameters such as the adsorption kinetics, loading capacity and pH of the aqueous feed were investigated. The modified chitosan materials are much more effective for adsorption of rare earths than unmodified chitosan. It was shown that adjustment of the pH of the aqueous feed solution allows achieving selectivity for adsorption of rare-earth ions for mixtures containing two different ions. After stripping of the metal content, the modified chitosans could be reused for new adsorption experiments. Medium pressure liquid chromatography (MPLC) with DTPA-chitosan/silica as the stationary phase and a dilute nitric acid solution as eluent was used for the separation of the following mixtures of rare-earth ions: Nd3+/Ho3+, Pr3+/Nd3+ and Pr3+/Nd3+/Ho3+. The experiments show that separation of the rare-earth ions is feasible with DTPA-chitosan/silica, without the need for using solutions of chelating agents as eluents.
Co-reporter:David Dupont, Ward Brullot, Maarten Bloemen, Thierry Verbiest, and Koen Binnemans
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 7) pp:4980
Publication Date(Web):March 18, 2014
DOI:10.1021/am406027y
Magnetic (Fe3O4) and nonmagnetic (SiO2 and TiO2) nanoparticles were decorated on their surface with N-[(3-trimethoxysilyl)propyl]ethylenediamine triacetic acid (TMS-EDTA). The aim was to investigate the influence of the substrate on the behavior of these immobilized metal coordinating groups. The nanoparticles functionalized with TMS-EDTA were used for the adsorption and separation of trivalent rare-earth ions from aqueous solutions. The general adsorption capacity of the nanoparticles was very high (100 to 400 mg/g) due to their large surface area. The heavy rare-earth ions are known to have a higher affinity for the coordinating groups than the light rare-earth ions but an additional difference in selectivity was observed between the different nanoparticles. The separation of pairs of rare-earth ions was found to be dependent on the substrate, namely the density of EDTA groups on the surface. The observation that sterical hindrance (or crowding) of immobilized ligands influences the selectivity could provide a new tool for the fine-tuning of the coordination ability of traditional chelating ligands.Keywords: EDTA; lanthanides; magnetic nanoparticles; magnetite; metal recovery; rare earths;
Co-reporter:Tom Vander Hoogerstraete, Steven Jamar, Sil Wellens, and Koen Binnemans
Analytical Chemistry 2014 Volume 86(Issue 3) pp:1391
Publication Date(Web):January 4, 2014
DOI:10.1021/ac403583u
An accurate quantitative determination of halide ions X (X = Cl, Br, I) in aqueous solution by total reflection X-ray fluorescence (TXRF) is not possible using the traditional acidic internal standards. In general, the standard solutions are highly acidic (e.g., Ga(NO3)3 in HNO3) to avoid precipitation of hydroxides of the standard element and to obtain a stable and reliable standard. In acidic solutions, dissolved halide salts can exchange their cation for a proton. The resulting volatile HX compounds can evaporate during the drying procedure of the TXRF sample preparation. In this technical note, we show that an alkaline Cu(NH3)4(NO3)2 standard can be used for the determination of chlorine, bromine and iodine without facing problems of HX evaporation.
Co-reporter:Tom Vander Hoogerstraete, Steven Jamar, Sil Wellens, and Koen Binnemans
Analytical Chemistry 2014 Volume 86(Issue 8) pp:3931
Publication Date(Web):March 17, 2014
DOI:10.1021/ac5000812
The determination and quantification of halide impurities in ionic liquids is highly important because halide ions can significantly influence the chemical and physical properties of ionic liquids. The use of impure ionic liquids in fundamental studies on solvent extraction or catalytic reactions can lead to incorrect experimental data. The detection of halide ions in solution by total reflection X-ray fluorescence (TXRF) has been problematic because volatile hydrogen halide (HX) compounds are formed when the sample is mixed with the acidic metal standard solution. The loss of HX during the drying step of the sample preparation procedure gives imprecise and inaccurate results. A new method based on an alkaline copper standard Cu(NH3)4(NO3)2 is presented for the determination of chloride, bromide, and iodide impurities in ionic liquids. The 1-butyl-3-methylimidazolium ([C4mim]) ionic liquids with the anions acetate ([C4mim][OAc]), nitrate ([C4mim][NO3]), trifluoromethanesulfonate ([C4mim][OTf]), and bis(trifluoromethylsulfonyl)imide ([C4mim][Tf2N]) were synthesized via a halide-free route and contaminated on purpose with known amounts of [C4mim]Cl, [C4mim]Br, [C4mim]I, or potassium halide salts in order to validate the new method and standard.
Co-reporter:Marc Steichen, Neil R. Brooks, Luc Van Meervelt, Jan Fransaer and Koen Binnemans
Dalton Transactions 2014 vol. 43(Issue 32) pp:12329-12341
Publication Date(Web):16 Jun 2014
DOI:10.1039/C4DT00182F
New homoleptic and heteroleptic zinc(II)-containing liquid metal salts with N-alkylimidazole (AlkIm) ligands and bis(trifluoromethylsulfonyl)imide (Tf2N−) anions are described. The general formulae of the complexes are [Zn(AlkIm)6][Tf2N]2 and [Zn(AlkIm)6−x(AlkIm′)x][Tf2N]2. Single-crystal X-ray diffraction revealed that, in the solid state, the cations consist of octahedral zinc(II) centres. The heteroleptic complexes contain two different N-alkylimidazole ligands. The melting points of the liquid metal salts are below or slightly above room temperature. The dependence of the melting points, viscosity and crystal structure on the alkyl chain length of the N-alkylimidazole ligand for the homoleptic complexes and on the ratio of the two N-alkylimidazole ligands AlkIm and AlkIm′ for the heteroleptic compounds is discussed. The possibility of incongruent melting and the presence of a mixture of the four-coordinate zinc(II) centre and neutral ligands is discussed. The new zinc(II)-containing liquid metal salts have been used as non-aqueous electrolytes for electrodeposition of zinc. A highly reversible deposition–stripping behaviour was found. Zinc electroplating was possible at very high current densities of more than −200 mA cm−2 in unstirred solutions. Compact and highly crystalline zinc deposits were obtained.
Co-reporter:Bieke Onghena, Jeroen Jacobs, Luc Van Meervelt and Koen Binnemans
Dalton Transactions 2014 vol. 43(Issue 30) pp:11566-11578
Publication Date(Web):09 Jun 2014
DOI:10.1039/C4DT01340A
The ionic liquid choline bis(trifluoromethylsulfonyl)imide, [Chol][Tf2N], was used for the extraction of neodymium(III), in combination with choline hexafluoroacetylacetonate, [Chol][hfac], as the extractant. The binary mixture of [Chol][Tf2N] and water shows temperature-dependent phase behavior, with an upper critical solution temperature of 72 °C. A novel extraction technique, homogeneous liquid–liquid extraction (HLLE), was applied to this solvent system. HLLE is based on the use of thermomorphic solvent mixtures and has the advantage of forming a homogeneous phase during mixing. Extraction is not kinetically hindered by an interface and the extraction equilibrium is reached faster than in the case of heterogeneous mixing in conventional solvent extraction. Several extraction parameters were studied for the extraction of neodymium(III) with [Chol][hfac]: temperature, pH, extractant concentration and loading of the ionic liquid phase. A speciation study was performed to determine the stoichiometry of the extracted neodymium(III) complex and a plausible extraction mechanism is proposed. Neodymium is extracted as a tetrakis hexafluoroacetylacetonate complex with one choline cation as counter ion. The crystal structure of the extracted complex showed the presence of a coordination bond between the choline counter ion and the neodymium(III) center, resulting in a coordination number of nine. The stripping of the loaded neodymium and the influence of acid and extractant concentrations on the phase behavior of the [Chol][Tf2N]–H2O system were investigated.
Co-reporter:Sil Wellens, Neil R. Brooks, Ben Thijs, Luc Van Meervelt and Koen Binnemans
Dalton Transactions 2014 vol. 43(Issue 9) pp:3443-3452
Publication Date(Web):06 Dec 2013
DOI:10.1039/C3DT53024H
Metal oxides were found to dissolve in different imidazolium ionic liquids with a hydrogen atom in the C2 position of the imidazolium ring, but not if a methyl substituent was present in the C2 position. The crystal structure of the product that crystallised from an ionic liquid containing dissolved silver(I) oxide showed that this was a silver(I) carbene complex. The presence of carbenes in solution was proven by 13C NMR spectroscopy and the reactions were also monitored by Raman spectroscopy. The dissolution of other metal oxides, namely copper(II) oxide, zinc(II) oxide and nickel(II) oxide, was also studied in imidazolium ionic liquids and it was found that stable zinc(II) carbenes were formed in solution, but these did not crystallise under the given experimental conditions. A crystalline nickel(II) carbene complex could be obtained from a solution of nickel(II) chloride dissolved in a mixture of 1-butyl-3-methylimidazolium and 1-ethyl-3-methylimidazolium acetate.
Co-reporter:Alok Rout and Koen Binnemans
Dalton Transactions 2014 vol. 43(Issue 8) pp:3186-3195
Publication Date(Web):04 Dec 2013
DOI:10.1039/C3DT52541D
The solvent extraction of trivalent rare-earth ions and their separation from divalent transition metal ions using molten salt hydrates as the feed phase and an undiluted fluorine-free ionic liquid as the extracting phase were investigated in detail. The extractant was tricaprylmethylammonium nitrate, [A336][NO3], and the hydrated melt was calcium nitrate tetrahydrate, Ca(NO3)2·4H2O. The extraction behavior of rare-earth ions was studied for solutions of individual elements, as well as for mixtures of rare earths in the hydrated melt. The influence of different extraction parameters was investigated: the initial metal loading in the feed phase, percentage of water in the feed solution, equilibration time, and the type of hydrated melt. The extraction of rare earths from Ca(NO3)2·4H2O was compared with extraction from CaCl2·4H2O by [A336][Cl] (Aliquat 336). The nitrate system was found to be the better one. The extraction and separation of rare earths from the transition metals nickel, cobalt and zinc were also investigated. Remarkably high separation factors of rare-earth ions over transition metal ions were observed for extraction from Ca(NO3)2·4H2O by the [A336][NO3] extracting phase. Furthermore, rare-earth ions could be separated efficiently from transition metal ions, even in melts with very high concentrations of transition metal ions. Rare-earth oxides could be directly dissolved in the Ca(NO3)2·4H2O phase in the presence of small amounts of Al(NO3)3·9H2O or concentrated nitric acid. The efficiency of extraction after dissolving the rare-earth oxides in the hydrated nitrate melt was identical to extraction from solutions with rare-earth nitrates dissolved in the molten phase. The stripping of the rare-earth ions from the loaded ionic liquid phase and the reuse of the recycled ionic liquid were also investigated in detail.
Co-reporter:Alok Rout and Koen Binnemans
Dalton Transactions 2014 vol. 43(Issue 4) pp:1862-1872
Publication Date(Web):04 Nov 2013
DOI:10.1039/C3DT52285G
A new non-fluorinated malonamide-based ionic liquid extractant was synthesized and investigated for the extraction behavior of europium(III) and other trivalent rare-earth ions from nitric acid medium. The extractant was the functionalized ionic liquid trihexyl(tetradecyl)phosphonium N,N,N′,N′-tetra(2-ethylhexyl)malonate, [P66614][MA], and it was used in combination with the non-fluorinated ionic liquid trihexyl(tetradecyl)phosphonium nitrate, [P66614][NO3], as diluents. The extraction behavior of europium in this ionic liquid solution was studied as a function of various parameters such as the pH, concentration of the extractant, the type of acidic medium, temperature, concentration of the salting-out agent and the metal concentration of the aqueous feed. The extraction behavior of [P66614][MA] in [P66614][NO3] was compared with that of [P66614][MA] in the chloride-containing ionic liquid diluent trihexyl(tetradecyl)phosphonium chloride, [P66614][Cl] (Cyphos IL 101). The nitrate system was found to be superior. Marked differences in extraction behavior were observed between [P66614][MA] and the molecular malonamide extractant N,N,N′,N′-tetra(2-ethylhexyl)malonamide (TEHMA), i.e. the compound from which the anion of the ionic liquid extractant was prepared. The extraction behavior of other rare earths (La, Ce, Nd, Sm, Ho, Yb) and some transition metals (Ni, Co, Zn) was investigated using this functionalized ionic liquid. A good separation of the rare earths from the transition metals could be achieved. For the rare earths, the extraction efficiency increases over the lanthanide series. The effects of thermodynamic parameters, the stripping of europium(III) from the ionic liquid and the reusability of the functionalized ionic liquid were studied in detail.
Co-reporter:Jeroen Sniekers, Neil R. Brooks, Stijn Schaltin, Luc Van Meervelt, Jan Fransaer and Koen Binnemans
Dalton Transactions 2014 vol. 43(Issue 4) pp:1589-1598
Publication Date(Web):24 Oct 2013
DOI:10.1039/C3DT52416G
New cationic silver-containing ionic liquids were synthesized and used as non-aqueous electrolytes for the electrodeposition of silver layers. In the liquid state of these ionic liquids, a silver (I) cation is coordinated by pyridine-N-oxide (py-O) ligands in a 1:3 metal-to-ligand ratio, although in some cases a different stoichiometry of the silver center crystallized out. As anions, bis(trifluoromethanesulfonyl)imide (Tf2N), trifluoromethanesulfonate (OTf), methanesulfonate (OMs) and nitrate were used, yielding compounds with the formulae [Ag(py-O)3][Tf2N], [Ag(py-O)3][OTf], [Ag(py-O)3][OMs] and [Ag(py-O)3][NO3], respectively. The compounds were characterized by CHN analysis, FTIR, NMR, DSC, TGA and the electrodeposition of silver was investigated by cyclic voltammetry, linear potential scans, scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX). With the exception of [Ag(py-O)3][Tf2N], which melts at 108 °C, all the silver(I) compounds have a melting point below 80 °C and were tested as electrolytes for silver electrodeposition. Interestingly, very high current densities were observed at a potential of −0.5 V vs. Ag/Ag+ for the compounds with fluorine-free anions, i.e. [Ag(py-O)3][NO3] (current density of −10 A dm−2) and [Ag(py-O)3][OMs] (−6.5 A dm−2). The maximum current density of the compound with the fluorinated anion trifluoromethanesulfonate, [Ag(py-O)3][OTf], was much lower: −2.5 A dm−2 at −0.5 V vs. Ag/Ag+. Addition of an excess of ligand to [Ag(py-O)3][OTf] resulted in the formation of the room-temperature ionic liquid [Ag(py-O)6][OTf]. A current density of −5 A dm−2 was observed at −0.5 V vs. Ag/Ag+ for this low viscous silver salt. The crystal structures of several silver complexes could be determined by X-ray diffraction, and it was found that several of them had a stoichiometry different from the 1:3 metal-to-ligand ratio used in their synthesis. This indicates that the compounds form crystals with a composition different from that of the molten state. The electrochemical properties were measured in the liquid state, where the metal-to-ligand ratio was 1:3. Single crystal X-ray diffraction measurements showed that silver(I) is six coordinate in [Ag(py-O)3][Tf2N] and [Ag(py-O)3][OTf], while it is five coordinate in the other complexes. In [Ag3(py-O)8][OTf]3, there are two different coordination environments for silver ions: six coordinate central silver ions and five coordinate for the outer silver ions. In some of the silver(I) complexes, silver–silver interactions were observed in the solid state.
Co-reporter:Tom Vander Hoogerstraete, Bart Blanpain, Tom Van Gerven and Koen Binnemans
RSC Advances 2014 vol. 4(Issue 109) pp:64099-64111
Publication Date(Web):14 Nov 2014
DOI:10.1039/C4RA13787F
A chemical process which consumes a minimum amount of chemicals to recover rare-earth metals from NdFeB magnets was developed. The recovery of rare-earth elements from end-of-life consumer products has gained increasing interest during the last few years. Examples of valuable rare earths are neodymium and dysprosium because they are important constituents of strong permanent magnets used in several large or growing application fields (e.g. hard disk drives, wind turbines, electric vehicles, magnetic separators, etc.). In this paper, the rare-earth elements were selectively dissolved from a crushed and roasted NdFeB magnet with a minimum amount of acid, further purified with solvent extraction and precipitated as pure oxalate salts. The whole procedure includes seven steps: (1) crushing and milling of the magnet into coarse powder, (2) roasting to transform the metals into the corresponding oxides, (3) the selective leaching of the rare-earth elements with acids (HCl, HNO3) to leave iron behind in the precipitate, (4) extracting remaining transition metals (Co, Cu, Mn) into the ionic liquid trihexyl(tetradecyl)phosphonium chloride, (5) precipitating the rare earths by the addition of oxalic acid, (6) removing the precipitate by filtration and (7) calcining the rare-earth oxalates to rare-earth oxides which can be used as part of the feedstock for the production process of new magnets. The magnet dissolution process from the oxides utilized four molar equivalents less acid to dissolve all rare earths in comparison with a dissolution process from the non-roasted magnet. Moreover, the less valuable element iron is already removed from the magnet during the dissolution process. The remaining transition metals are extracted into the ionic liquid which can be reused after a stripping process. Hydrochloric acid, the side product of the rare-earth oxalate precipitation process, can be reused in the next selective leaching process. In this way, a recycling process consuming only air, water, oxalic acid and electricity is developed to recover the rare earths from NdFeB magnets in very high purity.
Co-reporter:Alok Rout, Ernesto Rezende Souza and Koen Binnemans
RSC Advances 2014 vol. 4(Issue 23) pp:11899-11906
Publication Date(Web):14 Feb 2014
DOI:10.1039/C3RA48045C
Europium(III) was extracted by bis(2-ethylhexyl)diglycolamic acid (DEHDGA) dissolved in the non-fluorinated ionic liquid tetraoctylammonium dodecyl sulphate, [N8888][DS]. The extraction behaviour of europium(III) was investigated as a function of various parameters: pH, extractant concentration, concentration of the europium(III) ion in the aqueous feed and concentration of the salting-out agent. A comparison was made with extraction of europium(III) by the acidic extractants bis(2-ethylhexyl)phosphoric acid (D2EHPA) and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) in tetraoctylammonium dodecyl sulphate. DEHDGA was found to be the best extractant in these experimental conditions. The ionic liquid diluent has been compared with tetraoctylammonium dodecylbenzene sulphonate and trihexyl(tetradecyl)phosphonium dodecyl sulphate. The extraction efficiency increased with increasing pH of the aqueous feed solution up to a maximum at pH 5, followed by a decrease in efficiency at higher pH values. Europium(III) was found to be extracted by a proton exchange mechanism. Europium(III) could be stripped from the ionic liquid phase by 1 M nitric acid.
Co-reporter:Alok Rout and Koen Binnemans
Industrial & Engineering Chemistry Research 2014 Volume 53(Issue 15) pp:6500-6508
Publication Date(Web):March 25, 2014
DOI:10.1021/ie404340p
The extraction behavior of neodymium and other rare earths from nitric acid media by the functionalized ionic liquid trioctylmethylammonium dioctyl diglycolamate, [A336][DGA], was investigated. The nonfluorinated ionic liquid trioctylmethylammonium nitrate, [A336][NO3], was used as diluent. The extraction behavior of neodymium(III) in this ionic liquid solution was carried out as a function of various parameters such as the pH, concentration of the extractant, type of acidic media, temperature, concentration of salting-out agent, and concentration of the aqueous feed. The extraction behavior of [A336][DGA] in [A336][NO3] was compared with that of [A336][DGA] in the chloride-containing ionic liquid diluent [A336][Cl] (Aliquat 336). The distribution ratios obtained in [A336][DGA] were compared with those observed in molecular extractant N,N-dioctyl diglycol amic acid (HDGA), from which the anion of the ionic liquid extractant was prepared. The distribution ratio for extraction of neodymium(III) by [A336][DGA] in [A336][NO3] was higher than that for extraction by HDGA in [A336][NO3], at pH values >2. The effects of thermodynamic parameters, the stripping of neodymium(III) from the ionic liquid, and the reusability of the functionalized ionic liquid were studied in detail. The general applicability of the extraction system was illustrated by the extraction of lanthanide(III) ions other than neodymium(III).
Co-reporter:Alok Rout, Sil Wellens and Koen Binnemans
RSC Advances 2014 vol. 4(Issue 11) pp:5753-5758
Publication Date(Web):14 Nov 2013
DOI:10.1039/C3RA46261G
It is shown that rare earths can be distributed between two immiscible ionic liquids, allowing the transfer of the rare earths from one ionic liquid phase to another. The ionic liquid 1-ethyl-3-methylimidazolium chloride was used as the initial feed phase and the ionic liquid trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate (Cyphos IL 104) as the extracting phase. The rare earths could be recovered from the extracting phase by stripping with a 2 M HNO3 solution. The ionic liquids could be regenerated for reuse in the next extraction step. This ionic liquid–ionic liquid extraction system can be used for the separation of rare earths from nickel, because nickel is not extracted under these experimental conditions. Such a separation process is relevant for the recycling of valuable metals from nickel metal hydride (NiMH) batteries. Direct dissolution of rare-earth oxides in 1-ethyl-3-methylimidazolium chloride was possible, provided that a small amount of concentrated hydrochloric acid was added to the ionic liquid.
Co-reporter:Kallidanthiyil Chellappan Lethesh, Wim Dehaen and Koen Binnemans
RSC Advances 2014 vol. 4(Issue 9) pp:4472-4477
Publication Date(Web):02 Dec 2013
DOI:10.1039/C3RA45126G
Ionic liquids with the bis(2-ethylhexyl)dimethylammonium cation, [BEDMA]+, were prepared by a halide-free route starting from the readily available secondary amine bis(2-ethylhexyl)amine. The following anions were considered: chloride, bromide, iodide, nitrate, hydrogensulphate, dihydrogenphosphate, formate, acetate, propionate, trifluoroacetate, methyl sulphate, methanesulphonate, tosylate, isonicotinate, nicotinate and picolinate. Several of the compounds are room-temperature ionic liquids, albeit with a high viscosity. All ionic liquids are soluble in water. The ionic liquids are very stable in strongly alkaline medium. No signs of decomposition could be observed by contact of the chloride ionic liquid with 50 wt% sodium hydroxide, even after prolonged heating at 80 °C. The high stability against strong bases is attributed to the branched structure of the quaternary ammonium cation, which blocks the Hofmann elimination reaction.
Co-reporter:David Dupont, Jakob Luyten, Maarten Bloemen, Thierry Verbiest, and Koen Binnemans
Industrial & Engineering Chemistry Research 2014 Volume 53(Issue 39) pp:15222-15229
Publication Date(Web):September 3, 2014
DOI:10.1021/ie502546c
Core–shell Fe3O4@SiO2 nanoparticles were prepared with a modified Stöber method and functionalized with N-[(3-trimethoxysilyl)propyl]ethylenediamine triacetic acid (TMS-EDTA). The synthesis was optimized to make core–shell nanoparticles with homogeneous and thin SiO2 shells (4.8 ± 0.5 nm) around highly superparamagnetic Fe3O4 cores (14.5 ± 3.0 nm). The core–shell Fe3O4@SiO2(TMS-EDTA) nanoparticles were then used for the extraction and separation of rare-earth ions. By comparing them with previously published results for Fe3O4(TMS-EDTA) and SiO2(TMS-EDTA) nanoparticles, it was clear that the core–shell nanoparticles combine the advantage of magnetic retrieval observed for Fe3O4(TMS-EDTA) nanoparticles with the higher selectivity observed for SiO2(TMS-EDTA). The advantages of the SiO2 shell include a lower specific weight and a larger grafting density compared to Fe3O4 surfaces, but also the improved resistance to acidic environments required for the stripping of rare-earth ions.
Co-reporter:K. Binnemans, P.T. Jones
Journal of Rare Earths 2014 Volume 32(Issue 3) pp:195-200
Publication Date(Web):March 2014
DOI:10.1016/S1002-0721(14)60051-X
This vision paper discusses the advantages and disadvantages of the three main options for the recycling of rare-earth elements from end-of-life fluorescent lamps: (1) direct re-use of the lamp phosphor mixture; (2) separation of the lamp phosphor mixture into the different phosphor components; (3) recovery of the rare-earth content. An overview is given of commercial activities in Europe in the domain of recycling of materials from end-of-life fluorescent lamps and the recovery of rare earths from these lamps. The collection of end-of-life fluorescent lamps is currently driven by a legal framework that prohibited the release of mercury to the environment. The contaminations of the lamp phosphor powders by mercury and by small glass particles of crushed fluorescent lamps are limiting factors in the recycling process. Research should be directed to an advanced clean-up of the reclaimed lamp phosphor fraction, and in particular to the removal of mercury and glass fragments. The recovery of rare earths from the lamp phosphors could be facilitated by taking advantage of the differences in resistance of the different lamp phosphors by chemical attack by inorganic acids and bases.The advantages and disadvantages of different approaches to the recycling of fluorescent lamps are compared
Co-reporter:Sandra D. Hojniak, Ian P. Silverwood, Asim Laeeq Khan, Ivo F. J. Vankelecom, Wim Dehaen, Sergei G. Kazarian, and Koen Binnemans
The Journal of Physical Chemistry B 2014 Volume 118(Issue 26) pp:7440-7449
Publication Date(Web):June 4, 2014
DOI:10.1021/jp503259b
Novel difunctionalized ionic liquids (ILs) containing a triethylene glycol monomethyl ether chain and a nitrile group on a pyrrolidinium or imidazolium cation have been synthesized and incorporated into supported ionic liquid membranes (SILMs). These ILs exhibit ca. 2.3 times higher CO2/N2 and CO2/CH4 gas separation selectivities than analogous ILs functionalized only with a glycol chain. Although the glycol moiety ensures room temperature liquidity of the pyrrolidinium and imidazolium ILs, the two classes of ILs benefit from the presence of a nitrile group in different ways. The difunctionalized pyrrolidinium ILs exhibit an increase in CO2 permeance, whereas the permeances of the contaminant gases rise negligibly, resulting in high gas separation selectivities. In the imidazolium ILs, the presence of a nitrile group does not always increase the CO2 permeance nor does it increase the CO2 solubility, as showed in situ by the ATR-FTIR spectroscopic method. High selectivity of these ILs is caused by the considerably reduced permeances of N2 and CH4, most likely due to the ability of the −CN group to reject the nonpolar contaminant gases. Apart from the CO2 solubility, IL–CO2 interactions and IL swelling were studied with the in situ ATR-FTIR spectroscopy. Different strengths of the IL–CO2 interactions were found to be the major difference between the two classes of ILs. The difunctionalized ILs interacted stronger with CO2 than the glycol-functionalized ILs, as manifested in the smaller bandwidths of the bending mode band of CO2 for the latter.
Co-reporter:Gijs Vanhoutte ; Neil R. Brooks ; Stijn Schaltin ; Bastiaan Opperdoes ; Luc Van Meervelt ; Jean-Pierre Locquet ; Philippe M. Vereecken ; Jan Fransaer
The Journal of Physical Chemistry C 2014 Volume 118(Issue 35) pp:20152-20162
Publication Date(Web):August 11, 2014
DOI:10.1021/jp505479x
Lithium-containing solvate ionic liquids [Li(L)n][X], with ligands L = 1,2-dimethoxyethane (G1, monoglyme) or 1-methoxy-2-(2-methoxyethyl)ether (G2, diglyme) (with n = 1, 2 or 3) and with anions X = bis(trifluoromethylsulfonyl)imide (Tf2N–), bromide (Br–) or iodide (I–), were synthesized and used as electrolytes for the electrodeposition of lithium metal. Very high lithium-ion concentrations could be obtained, since the lithium ion is part of the cationic structure of the solvate ionic liquids. Without stirring, current densities up to −26 A dm–2 at a potential of −0.5 V vs Li/Li+ were registered during cyclic voltammetry. The formation of a solid–electrolyte interface during electrodeposition of lithium from [Li(G1)2][Tf2N] was studied by electrochemical quartz microbalance and Auger electron spectroscopy. SEM pictures revealed uniform and nondendritic lithium deposits.
Co-reporter:Sil Wellens, Ben Thijs and Koen Binnemans
Green Chemistry 2013 vol. 15(Issue 12) pp:3484-3485
Publication Date(Web):04 Oct 2013
DOI:10.1039/C3GC41328D
A batch of the protic ionic liquid pyrrolidinium nitrate exploded while drying it under reduced pressure at 110 °C, using a rotary evaporator with an oil bath.
Co-reporter:Tom Vander Hoogerstraete, Sil Wellens, Katrien Verachtert and Koen Binnemans
Green Chemistry 2013 vol. 15(Issue 4) pp:919-927
Publication Date(Web):26 Feb 2013
DOI:10.1039/C3GC40198G
An environmentally friendly process for the separation of the transition metals copper, cobalt, iron, manganese and zinc from rare earths by solvent extraction with the ionic liquid trihexyl(tetradecyl)phosphonium chloride has been developed. The solvent extraction process is carried out without the use of organic diluents or extra extraction agents and it can be applied as a sustainable hydrometallurgical method for removing transition metals from neodymium–iron–boron or samarium–cobalt permanent magnets. The recycling of rare earths is of high importance because of the possible supply risk of these elements in the near future. The method was tested for the removal of cobalt and iron from samarium and neodymium, respectively. The highest distribution ratios for cobalt and iron were found with 8.5 and 9 M HCl. At the tested conditions, the concentrations of neodymium and samarium in the ionic liquid were below 0.5 mg L−1 (0.5 ppm), even for feed concentrations of 45 g L−1. The separation factors of Nd/Fe and Sm/Co are 5.0 × 106 and 8.0 × 105, respectively. The percentage extraction of iron is still higher than 99.98% at loadings of the ionic liquids with 70 g L−1 of iron. The viscosity of the ionic liquid containing the tetrachloroferrate(III) complex [FeCl4]− is lower, and less depending on the feed concentration, than in the case with a tetrachlorocobaltate(II) anion [CoCl4]2−. After extraction, cobalt can be stripped very easily from the ionic liquid phase with water. However, due to the very high distribution ratio, iron could only be stripped by forming a water-soluble iron complex with ethylenediaminetetraacetic acid (EDTA). Also the possibility to extract chromium, nickel, aluminium, calcium and magnesium with trihexyl(tetradecyl)phosphonium chloride has been investigated, but the distribution ratios of these elements are very low in the tested conditions.
Co-reporter:Sil Wellens, Remi Goovaerts, Claudia Möller, Jan Luyten, Ben Thijs and Koen Binnemans
Green Chemistry 2013 vol. 15(Issue 11) pp:3160-3164
Publication Date(Web):10 Sep 2013
DOI:10.1039/C3GC41519H
A continuous ionic liquid extraction process using the ionic liquid trihexyl(tetradecyl)phosphonium chloride (Cyphos® IL 101) has been developed for the selective extraction of cobalt from nickel. The performance of this continuous extraction process is competitive with that of currently applied industrial processes. Moreover, the elimination of volatile odorous compounds from the extraction phase leads to environmentally friendlier and healthier working conditions.
Co-reporter:Sil Wellens, Ben Thijs, Claudia Möller and Koen Binnemans
Physical Chemistry Chemical Physics 2013 vol. 15(Issue 24) pp:9663-9669
Publication Date(Web):12 Apr 2013
DOI:10.1039/C3CP50819F
The proof-of-principle for the separation of metals by solvent extraction using two mutually immiscible ionic liquids is given. Cobalt was extracted from the ionic liquid 1-ethyl-3-methylimidazolium chloride to the ionic liquid trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate. A distribution ratio of 44 was obtained. Cobalt could be selectively separated from nickel, with a separation factor of 207. The extraction mechanism was elucidated using UV-VIS absorption measurements. The mutual solubility between the two ionic liquids was determined by 1H NMR. Processing steps such as washing, stripping and regeneration of the ionic liquid phases are discussed.
Co-reporter:Alok Rout, Justyna Kotlarska, Wim Dehaen and Koen Binnemans
Physical Chemistry Chemical Physics 2013 vol. 15(Issue 39) pp:16533-16541
Publication Date(Web):24 Jul 2013
DOI:10.1039/C3CP52218K
The ionic liquids 1-hexyl-3-methylimidazolium bis(2-ethylhexyl)phosphate, [C6mim][DEHP], 1-hexyl-1-methylpyrrolidinium bis(2-ethylhexyl)phosphate, [C6mpyr][DEHP], and tetrabutylammonium bis(2-ethylhexyl)phosphate, [N4444][DEHP], were prepared and characterized using 1H and 13C NMR spectroscopy. The extraction behavior of neodymium(III) from nitrate medium by these ionic liquids, diluted with the room temperature ionic liquids 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C6mim][NTf2], 1-hexyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [C6mpyr][NTf2], and tributylmethylammonium bis(trifluoromethylsulfonyl)imide, [N1444][NTf2], was studied. The distribution ratio of neodymium(III) was measured as a function of various parameters, such as pH, concentration of the ionic liquid extractant, nature of diluents, concentration of ionic liquid cations and nitrate anions in the aqueous phase. The extraction behavior was compared with that obtained for a solution of the molecular extractant bis(2-ethylhexyl)phosphoric acid (DEHPA) in an ionic liquid diluent. The extraction of neodymium(III) in the ionic liquids [C6mim][DEHP] and [C6mpyr][DEHP] showed markedly different extraction properties in comparison with that of the quaternary ammonium analogue [N4444][DEHP], especially concerning the pH dependence of the extraction process. These results show that the extraction process can be tuned by the selection of the ionic liquid cation. The extraction experiments also included the trivalent rare-earth ions lanthanum(III), cerium(III), praseodymium(III), ytterbium(III) and yttrium(III). Studies of the stripping behavior and the reusability of the ionic liquids were carried out, which indicate that the ionic liquids can be reused with no loss in activity.
Co-reporter:Sandra D. Hojniak, Asim Laeeq Khan, Oldamur Hollóczki, Barbara Kirchner, Ivo F. J. Vankelecom, Wim Dehaen, and Koen Binnemans
The Journal of Physical Chemistry B 2013 Volume 117(Issue 48) pp:15131-15140
Publication Date(Web):November 7, 2013
DOI:10.1021/jp409414t
Supported ionic liquid membranes (SILMs) are promising tools for the separation of carbon dioxide from other gases. In this paper, new imidazolium, pyrrolidinium, piperidinium, and morpholinium ionic liquids with a triethylene glycol side chain and tosylate anions, as well as their symmetrical dicationic analogues, have been synthesized and incorporated into SILMs. The selectivities for CO2/N2 and CO2/CH4 separations have been measured. The selectivities exhibited by the dicationic ionic liquids are up to two times higher than the values of the corresponding monocationic ionic liquids. Quantum chemical calculations have been used to investigate the difference in the interaction of carbon dioxide with monocationic and dicationic ionic liquids. The reason for the increased gas separation selectivity of the dicationic ionic liquids is two-fold: (1) a decrease in permeance of nitrogen and methane through the ionic liquid layer, presumably due to their less favorable interactions with the gases, while the permeance of carbon dioxide is reduced much less; (2) an increase in the number of interaction sites for the interactions with the quadrupolar carbon dioxide molecules in the dicationic ionic liquids, compared to the monocationic analogues.
Co-reporter:Tom Vander Hoogerstraete, Bieke Onghena, and Koen Binnemans
The Journal of Physical Chemistry Letters 2013 Volume 4(Issue 10) pp:1659-1663
Publication Date(Web):April 29, 2013
DOI:10.1021/jz4005366
Binary mixtures of the ionic liquid betainium bis(trifluoromethylsulfonyl)imide and water show an upper critical solution temperature. This solvent system has been used to extract metal ions by phase-transition extraction, using zwitterionic betaine as extractant. The system is efficient for the extraction of trivalent rare-earth, indium and gallium ions. This new type of metal extraction system avoids problems associated with the use of viscous ionic liquids, namely, the difficulty of intense mixing of the aqueous and ionic liquid phases by stirring.Keywords: gallium; indium; ionic liquids; phase transitions; rare earths; solvent extraction; thermomorphic behavior;
Co-reporter:Daphne Depuydt;Dr. Neil R. Brooks;Dr.Ir. Stijn Schaltin;Dr. Luc VanMeervelt;Dr.Ir. Jan Fransaer;Dr. Koen Binnemans
ChemPlusChem 2013 Volume 78( Issue 6) pp:578-588
Publication Date(Web):
DOI:10.1002/cplu.201300063
Abstract
The synthesis, structure and electrochemical properties of several silver-containing liquid metal salts have been investigated. These ionic liquids comprise of a silver-containing cation with a silver centre coordinated by two or more alkylamine ligands and a bis(trifluoromethylsulfonyl)imide (Tf2N) anion. With the monodentate amines tert-butylamine (tBuAm), iso-butylamine (iso-BuAm), sec-butylamine (sec-BuAm), 2-ethylhexylamine (2-EtHexAm), di(2-ethylhexyl)amine and piperidine (pip), compounds with the formula [Ag(L)2][Tf2N] are formed, several of which are room-temperature ionic liquids and all melt at or below 100 °C. In the case of [Ag(L)2][Tf2N] (L=tBuAm, iso-BuAm and pip), single-crystal X-ray diffraction shows that, in the solid state, the silver centres are two-fold coordinated by two amine ligands and the anion and cation exist as separated ion pairs. With ethylenediamine (en), two different compounds were formed, depending on the silver-to-ligand ratio and their structures were elucidated by X-ray diffraction. [Ag(en)][Tf2N] has a very high melting point and is polymeric in the solid state, with en ligands coordinated to different silver(I) centres, creating one-dimensional chains. [Ag(en)2][Tf2N], on the other hand, is a room-temperature ionic liquid, with four-coordinate silver(I) centres, but is actually polymeric in the solid state. The electrodeposition behaviour of [Ag(2-EtHexAm)2][Tf2N] and [Ag(en)2][Tf2N] was investigated both at room temperature and at 90 °C and it was possible to achieve very high current densities in unstirred solutions and to electrodeposit closed, crack-free, silver coatings. A crystal of [Ag2(en)Cl2] was obtained from a solution of [Ag(en)][Tf2N] in deuterochloroform and its structure is described.
Co-reporter:K. Binnemans;P. T. Jones;K. Van Acker;B. Blanpain;B. Mishra;D. Apelian
JOM 2013 Volume 65( Issue 7) pp:846-848
Publication Date(Web):2013 July
DOI:10.1007/s11837-013-0639-7
TMS has forged cooperative agreements with several carefully selected organizations that actively work to benefit the materials science community. In this occasional series, JOM will provide an update on the activities of these organizations. This installment, by the Center for Resource Recovery & Recycling (CR3), focuses on the importance of recycling of rare earths to mitigate the so-called Balance Problem. The CR3 is a research center established by Worcester Polytechnic Institute, Colorado School of Mines, and KU Leuven. Twenty-eight corporations and national laboratories along with support from the U.S. National Science Foundation’s Industry University Cooperative Research Center (I/UCRC) program are sponsors of the center.
Co-reporter:Sil Wellens, Ben Thijs and Koen Binnemans
Green Chemistry 2012 vol. 14(Issue 6) pp:1657-1665
Publication Date(Web):13 Apr 2012
DOI:10.1039/C2GC35246J
A green solvent extraction process for the separation of cobalt from nickel, magnesium and calcium in chloride medium was developed, using undiluted phosphonium-based ionic liquids as extractants. Cobalt was extracted to the ionic liquid phase as the tetrachlorocobaltate(II) complex, leaving behind nickel, magnesium and calcium in the aqueous phase. Manganese is interfering in the separation process. The main advantage of this ionic liquid extraction process is that no organic diluents have to be added to the organic phase, so that the use of volatile organic compounds can be avoided. Separation factors higher than 50000 were observed for the cobalt/nickel separation from 8 M HCl solution. After extraction, cobalt can easily be stripped using water and the ionic liquid can be reused as extractant, so that a continuous extraction process is possible. Up to 35 g L−1 of cobalt can be extracted to the ionic liquid phase, while still having a distribution coefficient higher than 100. Instead of hydrochloric acid, sodium chloride can be used as a chloride source. The extraction process has been upscaled to batch processes using 250 mL of ionic liquid. Tri(hexyl)tetradecylphosphonium chloride, tri(butyl)tetradecylphosphonium chloride, tetra(octyl)phosphonium bromide, tri(hexyl)tetradecylphosphonium bromide and Aliquat 336 have been tested for their performance to extract cobalt from an aqueous chloride phase to an ionic liquid phase. Tri(hexyl)tetradecylphosphonium chloride (Cyphos IL 101) turned out to be the best option as the ionic liquid phase, compromising between commercial availability, separation characteristics and easiness to handle the ionic liquid.
Co-reporter:Murugan Ganapathi, Svetlana V. Eliseeva, Neil R. Brooks, Dimitri Soccol, Jan Fransaer and Koen Binnemans
Journal of Materials Chemistry A 2012 vol. 22(Issue 12) pp:5514-5522
Publication Date(Web):08 Feb 2012
DOI:10.1039/C2JM13925A
Mixtures of acetamide and dimethylsulfone (DMSO2) with dissolved anhydrous transition metal chlorides are introduced as new non-aqueous electrolytes for the preparation of composite metal coatings with embedded hydrophilic particles via an electrolytic co-deposition process. Red-emitting (Eu2O3 and Y2O3:Eu3+), yellow-emitting (Y3Al5O12:Ce3+), green-emitting (Gd2O2S:Tb3+) and blue-emitting (BaMg2Al16O27:Eu2+) rare-earth phosphor particles and yttrium oxide particles have been embedded into thin nickel and cobalt layers. The metal coatings with the rare-earth phosphor particles have a metallic lustre, but show at the same time photoluminescence upon irradiation with UV light. The spectroscopic and photophysical properties of the rare-earth phosphors are not modified by embedding them in the metallic host matrix. Different electrodeposition parameters were optimised in order to obtain well-adherent coatings with a uniform particle distribution. By preparing mixtures of the Y2O3:Eu3+ and Gd2O2S:Tb3+ phosphors, the emission colour could be varied from red to orange and yellow to green, depending on the mixing ratios. Embedding mixtures of yellow and blue phosphors in the metal layer made it possible to produce coatings with white photoemission.
Co-reporter:Peter De Vreese ; Neil R. Brooks ; Kristof Van Hecke ; Luc Van Meervelt ; Edward Matthijs ; Koen Binnemans ;Rik Van Deun
Inorganic Chemistry 2012 Volume 51(Issue 9) pp:4972-4981
Publication Date(Web):April 23, 2012
DOI:10.1021/ic202341m
A deep-eutectic solvent with the properties of an ionic liquid is formed when choline chloride is mixed with copper(II) chloride dihydrate in a 1:2 molar ratio. EXAFS and UV–vis–near-IR optical absorption spectroscopy have been used to compare the coordination sphere of the cupric ion in this ionic liquid with that of the cupric ion in solutions of 0.1 M of CuCl2·2H2O in solvents with varying molar ratios of choline chloride and water. The EXAFS data show that species with three chloride ions and one water molecule coordinated to the cupric ion as well as species with two chloride molecules and two water molecules coordinated to the cupric ion are present in the ionic liquid. On the other hand, a fully hydrated copper(II) ion is formed in an aqueous solution free of choline chloride, and the tetrachlorocuprate(II) complex forms in aqueous choline chloride solutions with more than 50 wt % of choline chloride. In solutions with between 0 and 50 wt % of choline chloride, mixed chloro–aquo complexes occur. Upon standing at room temperature, crystals of CuCl2·2H2O and of Cu(choline)Cl3 formed in the ionic liquid. Cu(choline)Cl3 is the first example of a choline cation coordinating to a transition-metal ion. Crystals of [choline]3[CuCl4][Cl] and of [choline]4[Cu4Cl10O] were also synthesized from molecular or ionic liquid solvents, and their crystal structures were determined.
Co-reporter:Evert Vanecht, Koen Binnemans, Sergiy Patskovsky, Michel Meunier, Jin Won Seo, Linda Stappers and Jan Fransaer
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 16) pp:5662-5671
Publication Date(Web):21 Feb 2012
DOI:10.1039/C2CP23677J
The stability of gold nanoparticles synthesised by sputter deposition has been studied in situ in 1-butyl-3-methylimidazolium ionic liquids with bis(trifluoromethylsulfonyl)imide, tetrafluoroborate, hexafluorophosphate and dicyanamide anions with UV-VIS absorption spectroscopy and transmission electron microscopy. Besides the growth of the gold nanoparticles, two other processes were observed after sputtering, namely aggregation and sedimentation of these nanoparticles. To model the absorption spectra of the sputtered gold nanoparticles, generalized multiparticle Mie calculations were performed. These theoretical calculations confirm the increase in absorbance at longer wavelength for larger aggregates and are in agreement with the experimental observations. It was found that the kinetics of aggregation and sedimentation scale with the viscosity of the ionic liquid. Small amounts of water were found to have a large detrimental influence on the stability of the colloidal suspensions of the gold nanoparticles in ionic liquids. From the large discrepancy between the theoretical and the experimentally observed stability of the NPs, it was concluded that structural forces stabilize the gold nanoparticles. This was also borne out by AFM measurements.
Co-reporter:Neil R. Brooks, Stijn Schaltin, Kristof Van Hecke, Luc Van Meervelt, Jan Fransaer and Koen Binnemans
Dalton Transactions 2012 vol. 41(Issue 23) pp:6902-6905
Publication Date(Web):11 Apr 2012
DOI:10.1039/C2DT30725A
The first examples of structurally characterised mixed-ligand metal-containing ionic liquids (ILs) are presented, synthesised by the use of different N-alkylimidazoles. The cations consist of two-coordinate silver(I) centres ligated by two different N-alkylimidazole ligands. It is shown that the resulting ionic liquids have lower melting points than the single ligand ILs.
Co-reporter:Tom Vander Hoogerstraete, Neil R. Brooks, Bernadette Norberg, Johan Wouters, Kristof Van Hecke, Luc Van Meervelt and Koen Binnemans
CrystEngComm 2012 vol. 14(Issue 15) pp:4902-4911
Publication Date(Web):24 May 2012
DOI:10.1039/C2CE25470K
A series of ionic liquids with copper(II), nickel(II) or cobalt(II)-containing cations have been synthesised and characterised, where possible with single crystal X-ray diffraction. A number of N-methylimidazole (MeIm), N-ethylimidazole (EtIm), N-butylimidazole (BuIm) or N-hexylimidazole (HeIm) ligands are coordinated to the metal centres and bis(trifluoromethyl)sulfonyl imide (Tf2N) anions provide the charge balance. Two types of metal complexes have been analysed. One has the general formula [Cu(AlkIm)4][Tf2N]2 (AlkIm = MeIm, EtIm, BuIm and HeIm) and contains square planar copper(II) centres with longer interactions to oxygen atoms of bis(trifluoromethylsulfonyl)imide anions. The other type of metal complex has a metal:ligand ratio of 1:6, with composition [M(MeIm)6][Tf2N]2 (M = Cu, Ni, Co) and contains octahedral metal centres. The ionic liquids have low melting points and the change in melting points is discussed as a function of alkyl chain length on the imidazole ligand and as a function of the metal centre. The metal–ligand interactions and intermolecular interactions in the crystal structures are analysed and related to the properties of the metal complexes.
Co-reporter:Kallidanthiyil Chellappan Lethesh, Dries Parmentier, Wim Dehaen and Koen Binnemans
RSC Advances 2012 vol. 2(Issue 31) pp:11936-11943
Publication Date(Web):27 Sep 2012
DOI:10.1039/C2RA22304J
Water-soluble ionic liquids can be prepared from halide ionic liquids by a new anion exchange method. This new method for the anion exchange in ionic liquids takes advantage of the strong basicity of phenolate anions (also called phenate anions or phenoxide anions). The principle behind the method is to first prepare the 4-tert-butylphenolate salt of the desired cation, followed by reaction of the 4-tert-butylphenate with a Brønsted acid in a biphasic system formed by water and a water-immiscible organic solvent. The method has been applied to the synthesis of ionic liquids with 1-butyl-3-methylimidazolium, tetrabutylammonium, tetrabutylphosphonium and 1-butyl-1-methylpyrrolidinium cations and a range of anions (formate, acetate, methanesulfonate, tosylate, trifluoroacetate, picolinate, hydrogen dipicolinate, nicotinate, isonicotinate, nitrate, hydrogen sulfate, dihydrogen phosphate). Depending on the nature of the cation, slight modifications of the experimental procedure were required.
Co-reporter:Evert Vanecht, Koen Binnemans, Jin Won Seo, Linda Stappers and Jan Fransaer
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 30) pp:13565-13571
Publication Date(Web):15 Jun 2011
DOI:10.1039/C1CP20552H
The growth of gold nanoparticles (NPs) synthesized by sputter deposition on an ionic liquid surface is studied in situ in the bulk phase of the ionic liquids (ILs) 1-butyl-3-methylimidazolium dicyanamide [C1C4Im][N(CN)2], 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [C1C4Im][Tf2N], 1-butyl-3-methylimidazolium tetrafluoroborate [C1C4Im][BF4], 1-butyl-3-methylimidazolium hexafluorophosphate [C1C4Im][PF6] and 1-butyl-3-methylimidazolium triflate [C1C4Im][TfO]. It is found that primary nanoparticles with a diameter smaller than 2.5 nm are present in the sample immediately after sputtering. Growth of these primary particles proceeds after the end of the sputtering process and stops when the nanoparticles reach a certain size. Depending on the viscosity of the ionic liquid this growth process can proceed several hours to several days. The growth speed is fastest for the least viscous ionic liquid and follows the trend [C1C4Im][N(CN)2] > [C1C4Im][Tf2N] > [C1C4Im][TfO] > [C1C4Im][BF4] > [C1C4Im][PF6]. It is also found that a higher concentration of sputtered gold results in faster growth of the gold nanoparticles. A discussion on the growth mechanism of sputtered gold NPs is included.
Co-reporter:Thomas Cardinaels, Kathleen Lava, Karel Goossens, Svetlana V. Eliseeva, and Koen Binnemans
Langmuir 2011 Volume 27(Issue 5) pp:2036-2043
Publication Date(Web):January 20, 2011
DOI:10.1021/la1047276
The 1,10-phenanthrolinium cation is introduced as a new building block for the design of ionic liquid crystals. 1,10-Phenanthroline, 5-methyl-1,10-phenanthroline, 5-chloro-1,10-phenanthroline, and 4,7-diphenyl-1,10-phenanthroline were quaternized by reaction with 1,3-dibromopropane or 1,2-dibromoethane. The resulting cations were combined with dodecyl sulfate or dioctyl sulfosuccinate anions. The influence of both the cation and anion type on the thermal behavior was investigated. Several of the complexes exhibit mesomorphic behavior, with smectic E phases for the dodecyl sulfate salts and smectic A phases for the dioctyl sulfosuccinate salts. Structural models for the packing of the 1,10-phenanthrolinium and anionic moieties in the liquid-crystalline phases are presented. The ionic compounds show fluorescence in the solid state and in solution.
Co-reporter:Kallidanthiyil Chellappan Lethesh, Kristof Van Hecke, Luc Van Meervelt, Peter Nockemann, Barbara Kirchner, Stefan Zahn, Tatjana N. Parac-Vogt, Wim Dehaen, and Koen Binnemans
The Journal of Physical Chemistry B 2011 Volume 115(Issue 26) pp:8424-8438
Publication Date(Web):May 24, 2011
DOI:10.1021/jp2027675
Two series of 1-alkylpyridinium and N-alkyl-N-methylpiperidinium ionic liquids functionalized with a nitrile group at the end of the alkyl chain have been synthesized. Structural modifications include a change of the alkyl spacer length between the nitrile group and the heterocycle of the cationic core, as well as adding methyl or ethyl substituents on different positions of the pyridinium ring. The anions are the bromide and the bis(trifluoromethylsulfonyl)imide ion. All the bis(trifluoromethylsulfonyl)imide salts as well as the bromide salts with a long alkyl spacer were obtained as viscous liquids at room temperature, but some turned out to be supercooled liquids. In addition, pyrrolidinium and piperidinium ionic liquids with two nitrile functions attached to the heterocyclic core have been prepared. The crystal structures of seven pyridinium bis(trifluoromethylsulfonyl)imide salts are reported. Quantum chemical calculations have been performed on model cations and ion pairs with the bis(trifluoromethylsulfonyl)imide anion. A continuum model has been used to take solvation effects into account. These calculations show that the natural partial charge on the nitrogen atom of the nitrile group becomes more negative when the length of the alkyl spacer between the nitrile functional group and the heterocyclic core of the cation is increased. Methyl or methoxy substituents on the pyridinium ring slightly increase the negative charge on the nitrile nitrogen atom due to their electron-donating abilities. The position of the substituent (ortho, meta, or para) has only a very minor effect on the charge of the nitrogen atom. The 15N NMR spectra of the bis(trifluoromethylsulfonyl)imide ionic liquids were recorded with the nitrogen-15 nucleus at its natural abundance. The chemical shift of the 15N nucleus of the nitrile nitrogen atom could be correlated with the calculated negative partial charge on the nitrogen atom.
Co-reporter:Thomas Cardinaels, Yuki Hirai, Kenji Hanabusa, Koen Binnemans and Takashi Kato
Journal of Materials Chemistry A 2010 vol. 20(Issue 39) pp:8571-8574
Publication Date(Web):01 Sep 2010
DOI:10.1039/C0JM01956A
A red-emitting molecular europium(III) complex has been doped into liquid-crystalline (LC) physical gels consisting of 4-pentyl-4′-cyanobiphenyl (5CB) with amino acid-based gelators. Light scattering cells on the basis of these LC physical gels could be switched between a non-transparent off-state and a transparent on-state by on–off application of electric fields. The gels produced intense red light when they were irradiated with UV-light.
Co-reporter:Hasan Mehdi, Koen Binnemans, Kristof Van Hecke, Luc Van Meervelt and Peter Nockemann
Chemical Communications 2010 vol. 46(Issue 2) pp:234-236
Publication Date(Web):21 Nov 2009
DOI:10.1039/B914977E
Ionic liquids containing the hexafluoroacetylacetonate anion are immiscible with water and they exhibit strong metal-complexing ability.
Co-reporter:Peter Nockemann, Rik Van Deun, Ben Thijs, Diederik Huys, Evert Vanecht, Kristof Van Hecke, Luc Van Meervelt and Koen Binnemans
Inorganic Chemistry 2010 Volume 49(Issue 7) pp:3351-3360
Publication Date(Web):February 25, 2010
DOI:10.1021/ic902406h
Uranium(VI) oxide has been dissolved in three different ionic liquids functionalized with a carboxyl group: betainium bis[(trifluoromethyl)sulfonyl]imide, 1-(carboxymethyl)-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide, and N-(carboxymethyl)-N-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide. The dissolution process results in the formation of uranyl complexes with zwitterionic carboxylate ligands and bis[(trifluoromethyl)sulfonyl]imide (bistriflimide) counterions. An X-ray diffraction study on single crystals of the uranyl complexes revealed that the crystal structure strongly depends on the cationic core appended to the carboxylate groups. The betainium ionic liquid gives a dimeric uranyl complex, the imidazolium ionic liquid a monomeric complex, and the pyrrolidinium ionic liquid a one-dimensional polymeric uranyl complex. Extended X-ray absorption fine structure measurements have been performed on the betainium uranyl complex. The absorption and luminescence spectra of the uranyl betainium complex have been studied in the solid state and dissolved in water, in acetonitrile, and in the ionic liquid betainium bistriflimide. The carboxylate groups remain coordinated to uranyl in acetonitrile and in betainium bistriflimide but not in water.
Co-reporter:Kyra Lunstroot, Kris Driesen, Peter Nockemann, Lydie Viau, P. Hubert Mutin, André Vioux and Koen Binnemans
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 8) pp:1879-1885
Publication Date(Web):21 Dec 2009
DOI:10.1039/B920145A
Flexible luminescent polymer films were obtained by doping europium(III) complexes in blends of poly(methyl methacrylate) (PMMA) and the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C6mim][Tf2N]. Different europium(III) complexes have been incorporated in the polymer/ionic liquid matrix: [C6mim][Eu(nta)4], [C6mim][Eu(tta)4], [Eu(tta)3(phen)] and [choline]3[Eu(dpa)3], where nta is 2-naphthoyltrifluoroacetonate, tta is 2-thenoyltrifluoroacetonate, phen is 1,10-phenanthroline, dpa is 2,6-pyridinedicarboxylate (dipicolinate) and choline is the 2-hydroxyethyltrimethyl ammonium cation. Bright red photoluminescence was observed for all the films upon irradiation with ultraviolet radiation. The luminescent films have been investigated by high-resolution steady-state luminescence spectroscopy and by time-resolved measurements. The polymer films doped with β-diketonate complexes are characterized by a very intense 5D0 → 7F2 transition (up to 15 times more intense than the 5D0 → 7F1) transition, whereas a marked feature of the PMMA films doped with [choline]3[Eu(dpa)3] is the long lifetime of the 5D0 excited state (1.8 ms).
Co-reporter:Koen Binnemans
Chemical Reviews 2009 Volume 109(Issue 9) pp:4283
Publication Date(Web):August 4, 2009
DOI:10.1021/cr8003983
Co-reporter:Koen Binnemans
Journal of Materials Chemistry A 2009 vol. 19(Issue 4) pp:448-453
Publication Date(Web):09 Oct 2008
DOI:10.1039/B811373D
Recent progress in the design of low-melting liquid-crystalline metal complexes (metallomesogens) has facilitated the study of the photophysical properties of these compounds in the mesophase. Luminescence in the liquid crystal state has been observed for metallomesogens incorporating lanthanide(III), gold(I), silver(I), copper(I) or zinc(II) ions. An alternative approach to liquid-crystalline metal-containing systems is doping a metal complex in a liquid-crystal host. A fascinating property of these materials is the ability to observe linearly polarized emission.
Co-reporter:Kyra Lunstroot ; Peter Nockemann ; Kristof Van Hecke ; Luc Van Meervelt ; Christiane Görller-Walrand ; Koen Binnemans ;Kris Driesen
Inorganic Chemistry 2009 Volume 48(Issue 7) pp:3018-3026
Publication Date(Web):February 25, 2009
DOI:10.1021/ic8020782
Highly luminescent anionic samarium(III) β-diketonate and dipicolinate complexes were dissolved in the imidazolium ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C6mim][Tf2N]. The solubility of the complexes in the ionic liquid was ensured by a careful choice of the countercation of the samarium(III) complex. The samarium(III) complexes that were considered are [C6mim][Sm(tta)4], where tta is 2-thenoyltrifluoroacetonate; [C6mim][Sm(nta)4], where nta is 2-naphthoyltrifluoroacetonate; [C6mim][Sm(hfa)4], where hfa is hexafluoroacetylacetonate; and [choline]3[Sm(dpa)3], where dpa is pyridine-2,6-dicarboxylate (dipicolinate) and [choline]+ is (2-hydroxyethyl)trimethyl ammonium. The crystal structures of the tetrakis samarium(III) β-diketonate complexes revealed a distorted square antiprismatic coordination for the samarium(III) ion in all three cases. Luminescence spectra were recorded for the samarium(III) complexes dissolved in the imidazolium ionic liquid as well as in a conventional solvent, that is, acetonitrile or water for the β-diketonate and dipicolinate complexes, respectively. These experiments demonstrate that [C6mim][Tf2N] is a suitable spectroscopic solvent for studying samarium(III) luminescence. High-luminescence quantum yields were observed for the samarium(III) β-diketonate complexes in solution.
Co-reporter:Kyra Lunstroot, Kris Driesen, Peter Nockemann, Kristof Van Hecke, Luc Van Meervelt, Christiane Görller-Walrand, Koen Binnemans, Séverine Bellayer, Lydie Viau, Jean Le Bideau and André Vioux
Dalton Transactions 2009 (Issue 2) pp:298-306
Publication Date(Web):13 Nov 2008
DOI:10.1039/B812292J
Ionogels are solid oxide host networks confining at a meso-scale ionic liquids, and retaining their liquid nature. Ionogels were obtained by dissolving lanthanide(III) complexes in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C6mim][Tf2N], followed by confinement of the lanthanide-doped ionic liquid mixtures in the pores of a nano-porous silica network. [C6mim][Ln(tta)4], where tta is 2-thenoyltrifluoroacetonate and Ln = Nd, Sm, Eu, Ho, Er, Yb, and [choline]3[Tb(dpa)3], where dpa = pyridine-2,6-dicarboxylate (dipicolinate), were chosen as the lanthanide complexes. The ionogels are luminescent, ion-conductive inorganic–organic hybrid materials. Depending on the lanthanide(III) ion, emission in the visible or the near-infrared regions of the electromagnetic spectrum was observed. The work presented herein highlights that the confinement did not disturb the first coordination sphere of the lanthanide ions and also showed the excellent luminescence performance of the lanthanide tetrakis β-diketonate complexes. The crystal structures of the complexes [C6mim][Yb(tta)4] and [choline]3[Tb(dpa)3] are reported.
Co-reporter:Kris Driesen, Caroline Vaes, Thomas Cardinaels, Karel Goossens, Christiane Görller-Walrand and Koen Binnemans
The Journal of Physical Chemistry B 2009 Volume 113(Issue 31) pp:10575-10579
Publication Date(Web):July 14, 2009
DOI:10.1021/jp901145z
The luminescence spectra of europium(III) complexes dissolved in the liquid crystal 4′-pentyl-4-cyanobiphenyl (5CB) were investigated. Upon alignment of the europium(III)-doped nematic liquid−crystal host in a liquid−crystal cell with alignment layers, polarization effects were observed in the emission spectra. These polarization effects were visible as differences in the relative intensities of the crystal-field components of the transitions. Although the europium(III) complexes do not need to be liquid−crystalline themselves, some structural anisotropy is required for good alignment in the liquid crystal host and for the generation of linearly polarized light.
Co-reporter:Kyra Lunstroot, Linny Baeten, Peter Nockemann, Johan Martens, Pieter Verlooy, Xingpu Ye, Christiane Görller-Walrand, Koen Binnemans and Kris Driesen
The Journal of Physical Chemistry C 2009 Volume 113(Issue 31) pp:13532-13538
Publication Date(Web):July 9, 2009
DOI:10.1021/jp9015118
Ionic liquids were used as solvents for dispersing luminescent lanthanide-doped LaF3:Ln3+ nanocrystals (Ln3+ = Eu3+ and Nd3+). To increase the solubility of the inorganic nanoparticles in the ionic liquids, the nanocrystals were prepared with different stabilizing ligands, i.e., citrate, N,N,N-trimethylglycine (betaine), and lauryldimethylglycine (lauryl betaine). LaF3:5%Ln3+:betaine could successfully be dispersed in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [C4mpyr][Tf2N], 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate [C4mpyr][TfO], and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C4mim][Tf2N] but only in limited amounts. Red photoluminescence was observed for the europium(III)-containing nanoparticles and near-infrared luminescence for the neodymium(III)-containing systems.
Co-reporter:Kris Driesen, Dries Moors, Jeroen Beeckman, Kristiaan Neyts, Christiane Görller-Walrand, Koen Binnemans
Journal of Luminescence 2007 Volume 127(Issue 2) pp:611-615
Publication Date(Web):December 2007
DOI:10.1016/j.jlumin.2007.03.022
Switching of near-infrared emission was observed for liquid crystal (LC) cells filled with a chiral nematic liquid–crystal mixture (mixture of E7 and cholesteryl nonanoate) doped with luminescent neodymium(III) or ytterbium(III) β-diketonate complexes. The operating principle of the LC cell is based on an electrically induced phase transition from a chiral nematic to a nematic phase. The chiral nematic phase scatters the excitation light more strongly, resulting in more efficient light absorption and intenser photoluminescence.
Co-reporter:Koen Binnemans;Katleen Lodewyckx;Thomas Cardinaels;Tatjana N. Parac-Vogt;Cyril Bourgogne;Daniel Guillon;Bertr Donnio
European Journal of Inorganic Chemistry 2006 Volume 2006(Issue 1) pp:
Publication Date(Web):11 NOV 2005
DOI:10.1002/ejic.200500702
The Schiff base LH3 obtained by condensation of 3-formyl-4-hydroxyphenyl-3,4,5-tris(tetradecyloxy)benzoate with 1,3-diamino-2-propanol reacts with lanthanide(III) acetate salts to form dinuclear complexes of the type Ln2L2 with the trivalent ions from the first half of the lanthanide series (Ln = Nd, Sm, Gd). These stable and neutral metallomesogens exhibit a rectangular columnar mesophase over a broad temperature range. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Co-reporter:Tatjana N. Parac-Vogt Dr.;Antoine Pacco Dr.;Peter Nockemann Dr.;Sophie Laurent Dr.;Robert N. Muller Dr.;Mathias Wickleder Dr.;Gerd Meyer Dr.;Luce Ver Elst Dr. and Dr.
Chemistry - A European Journal 2006 Volume 12(Issue 1) pp:
Publication Date(Web):3 NOV 2005
DOI:10.1002/chem.200500136
Proton nuclear magnetic relaxation dispersion (NMRD) profiles were recorded between 0.24 mT and 1.4 T for lanthanum(III)- and gadolinium(III)-containing [15]metallacrown-5 complexes derived from α-aminohydroxamic acids and with copper(II) as the ring metal. The influence of the different R-groups on the proton relaxivity was investigated, and a linear relationship between the relaxivity and the molecular mass of the metallacrown complex was found. The selectivity of the metallacrown complexes was tested by transmetalation experiments with zinc(II) ions. The crystal structure of the copper [15]metallacrown-5 gadolinium complex with glycine hydroximate ligands is reported.
Co-reporter:Peter Nockemann, Eva Beurer, Kris Driesen, Rik Van Deun, Kristof Van Hecke, Luc Van Meervelt and Koen Binnemans
Chemical Communications 2005 (Issue 34) pp:4354-4356
Publication Date(Web):03 Aug 2005
DOI:10.1039/B506915G
A high quantum yield and an enhanced photostability was found for a europium(III) tetrakis(2-thenoyltrifluoroacetonate) complex after dissolving the complex in a weakly-coordinating imidazolium ionic liquid.
Co-reporter:Antoine Pacco;Tatjana N. Parac-Vogt;Els van Besien;Kristine Pierloot;Christiane Görller-Walr and
European Journal of Inorganic Chemistry 2005 Volume 2005(Issue 16) pp:
Publication Date(Web):14 JUL 2005
DOI:10.1002/ejic.200500241
The conversion of 12-metallacrown-4 complexes with copper(II) in the central cavity to 15-metallacrown-5 complexes with lanthanide(III) ions in the central cavity upon addition of trivalent lanthanide ions was analysed in solution by electrospray ionisation mass spectrometry (ESI-MS), absorption spectrophotometry, circular dichroism and proton NMR spectroscopy. In all cases, copper(II) ions were the ring metals. The lanthanide-induced shifts of the proton resonances in the NMR spectra of different lanthanide(III)-containing 15-metallacrown-5 complexes with tyrosinehydroximate ligands were studied. The dynamics of ligand exchange of α-aminohydroximate-based lanthanide(III)-containing 15-metallacrown-5 complexes were studied in methanol solutions. The ring structure of the 12-metallacrown-4 complex that acts as starting compound for the formation of the 15-metallacrown-5 complexes was optimized by DFT methods using alaninehydroximate as a model ligand. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Co-reporter:Kyra Lunstroot, Kris Driesen, Peter Nockemann, Lydie Viau, P. Hubert Mutin, André Vioux and Koen Binnemans
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 8) pp:NaN1885-1885
Publication Date(Web):2009/12/21
DOI:10.1039/B920145A
Flexible luminescent polymer films were obtained by doping europium(III) complexes in blends of poly(methyl methacrylate) (PMMA) and the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C6mim][Tf2N]. Different europium(III) complexes have been incorporated in the polymer/ionic liquid matrix: [C6mim][Eu(nta)4], [C6mim][Eu(tta)4], [Eu(tta)3(phen)] and [choline]3[Eu(dpa)3], where nta is 2-naphthoyltrifluoroacetonate, tta is 2-thenoyltrifluoroacetonate, phen is 1,10-phenanthroline, dpa is 2,6-pyridinedicarboxylate (dipicolinate) and choline is the 2-hydroxyethyltrimethyl ammonium cation. Bright red photoluminescence was observed for all the films upon irradiation with ultraviolet radiation. The luminescent films have been investigated by high-resolution steady-state luminescence spectroscopy and by time-resolved measurements. The polymer films doped with β-diketonate complexes are characterized by a very intense 5D0 → 7F2 transition (up to 15 times more intense than the 5D0 → 7F1) transition, whereas a marked feature of the PMMA films doped with [choline]3[Eu(dpa)3] is the long lifetime of the 5D0 excited state (1.8 ms).
Co-reporter:Evert Vanecht, Koen Binnemans, Sergiy Patskovsky, Michel Meunier, Jin Won Seo, Linda Stappers and Jan Fransaer
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 16) pp:NaN5671-5671
Publication Date(Web):2012/02/21
DOI:10.1039/C2CP23677J
The stability of gold nanoparticles synthesised by sputter deposition has been studied in situ in 1-butyl-3-methylimidazolium ionic liquids with bis(trifluoromethylsulfonyl)imide, tetrafluoroborate, hexafluorophosphate and dicyanamide anions with UV-VIS absorption spectroscopy and transmission electron microscopy. Besides the growth of the gold nanoparticles, two other processes were observed after sputtering, namely aggregation and sedimentation of these nanoparticles. To model the absorption spectra of the sputtered gold nanoparticles, generalized multiparticle Mie calculations were performed. These theoretical calculations confirm the increase in absorbance at longer wavelength for larger aggregates and are in agreement with the experimental observations. It was found that the kinetics of aggregation and sedimentation scale with the viscosity of the ionic liquid. Small amounts of water were found to have a large detrimental influence on the stability of the colloidal suspensions of the gold nanoparticles in ionic liquids. From the large discrepancy between the theoretical and the experimentally observed stability of the NPs, it was concluded that structural forces stabilize the gold nanoparticles. This was also borne out by AFM measurements.
Co-reporter:Thomas Cardinaels, Yuki Hirai, Kenji Hanabusa, Koen Binnemans and Takashi Kato
Journal of Materials Chemistry A 2010 - vol. 20(Issue 39) pp:NaN8574-8574
Publication Date(Web):2010/09/01
DOI:10.1039/C0JM01956A
A red-emitting molecular europium(III) complex has been doped into liquid-crystalline (LC) physical gels consisting of 4-pentyl-4′-cyanobiphenyl (5CB) with amino acid-based gelators. Light scattering cells on the basis of these LC physical gels could be switched between a non-transparent off-state and a transparent on-state by on–off application of electric fields. The gels produced intense red light when they were irradiated with UV-light.
Co-reporter:Joris Roosen, Jeroen Spooren and Koen Binnemans
Journal of Materials Chemistry A 2014 - vol. 2(Issue 45) pp:NaN19426-19426
Publication Date(Web):2014/09/16
DOI:10.1039/C4TA04518A
Chitosan–silica hybrid adsorbents were prepared and functionalized with ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA). The method consisted of sol–gel hybridization of chitosan and silica, followed by the addition of anhydrides to graft EDTA- and DTPA-ligands on the amine groups of the chitosan moieties in the hybrid particles. The resulting adsorbents were characterized by a range of analytical techniques: FTIR, BET, SEM, TGA, ICP and CHN. Coordination of Eu(III) to immobilized EDTA- and DTPA-groups was investigated by luminescence spectroscopy. The adsorption performance of the chitosan–silica adsorbents was investigated for Nd(III) as a function of the contact time, the pH of the aqueous feed and the adsorbent mass. Stripping and reusability studies were performed for both EDTA-chitosan–silica and DTPA-chitosan–silica. Differences in affinity amongst the rare-earth ions were investigated for DTPA-chitosan–silica in mono-component solutions of five rare earths (La, Nd, Eu, Dy and Lu). The order of affinity was in agreement with the trend in stability constants for the respective rare-earth ions with non-immobilized DTPA (bearing five available carboxylic acid groups). Multi-element mixtures were used to determine the selectivity of the adsorption process. Special attention was paid to separation of Nd and Dy, since these elements are relevant to the recovery of rare earths from End-of-Life permanent magnets.
Co-reporter:Joris Roosen and Koen Binnemans
Journal of Materials Chemistry A 2014 - vol. 2(Issue 5) pp:NaN1540-1540
Publication Date(Web):2013/11/18
DOI:10.1039/C3TA14622G
Chitosan, which is derived from chitin by deacetylation, is one of the most promising biopolymers for adsorption of metal ions from diluted waste streams. By functionalization of chitosan with ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA) groups, it is possible to obtain a material that is much less soluble in acidic aqueous solutions than native chitosan. The coordinating EDTA and DTPA ligands are very efficient for binding of rare-earth (lanthanide) ions. The functionalization was achieved by reaction of chitosan with EDTA bisanhydride or DTPA bisanhydride. The binding of lanthanide ions to functionalized chitosan was investigated by FTIR (binding of Nd3+) and luminescence spectroscopy (binding of Eu3+). Comparison of the luminescence decay times of the europium(III) coordinated chitosan complexes swollen in water and in heavy water allowed determination of the hydration number of the coordinated Eu3+ ion. Batch adsorption tests for the uptake of neodymium(III) from aqueous nitrate solutions were performed for EDTA-chitosan and DTPA-chitosan. Different experimental parameters such as the adsorption kinetics, loading capacity and pH of the aqueous feed were investigated. The modified chitosan materials are much more effective for adsorption of rare earths than unmodified chitosan. It was shown that adjustment of the pH of the aqueous feed solution allows achieving selectivity for adsorption of rare-earth ions for mixtures containing two different ions. After stripping of the metal content, the modified chitosans could be reused for new adsorption experiments. Medium pressure liquid chromatography (MPLC) with DTPA-chitosan/silica as the stationary phase and a dilute nitric acid solution as eluent was used for the separation of the following mixtures of rare-earth ions: Nd3+/Ho3+, Pr3+/Nd3+ and Pr3+/Nd3+/Ho3+. The experiments show that separation of the rare-earth ions is feasible with DTPA-chitosan/silica, without the need for using solutions of chelating agents as eluents.
Co-reporter:Kyra Lunstroot, Kris Driesen, Peter Nockemann, Kristof Van Hecke, Luc Van Meervelt, Christiane Görller-Walrand, Koen Binnemans, Séverine Bellayer, Lydie Viau, Jean Le Bideau and André Vioux
Dalton Transactions 2009(Issue 2) pp:NaN306-306
Publication Date(Web):2008/11/13
DOI:10.1039/B812292J
Ionogels are solid oxide host networks confining at a meso-scale ionic liquids, and retaining their liquid nature. Ionogels were obtained by dissolving lanthanide(III) complexes in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C6mim][Tf2N], followed by confinement of the lanthanide-doped ionic liquid mixtures in the pores of a nano-porous silica network. [C6mim][Ln(tta)4], where tta is 2-thenoyltrifluoroacetonate and Ln = Nd, Sm, Eu, Ho, Er, Yb, and [choline]3[Tb(dpa)3], where dpa = pyridine-2,6-dicarboxylate (dipicolinate), were chosen as the lanthanide complexes. The ionogels are luminescent, ion-conductive inorganic–organic hybrid materials. Depending on the lanthanide(III) ion, emission in the visible or the near-infrared regions of the electromagnetic spectrum was observed. The work presented herein highlights that the confinement did not disturb the first coordination sphere of the lanthanide ions and also showed the excellent luminescence performance of the lanthanide tetrakis β-diketonate complexes. The crystal structures of the complexes [C6mim][Yb(tta)4] and [choline]3[Tb(dpa)3] are reported.
Co-reporter:Neil R. Brooks, Stijn Schaltin, Kristof Van Hecke, Luc Van Meervelt, Jan Fransaer and Koen Binnemans
Dalton Transactions 2012 - vol. 41(Issue 23) pp:NaN6905-6905
Publication Date(Web):2012/04/11
DOI:10.1039/C2DT30725A
The first examples of structurally characterised mixed-ligand metal-containing ionic liquids (ILs) are presented, synthesised by the use of different N-alkylimidazoles. The cations consist of two-coordinate silver(I) centres ligated by two different N-alkylimidazole ligands. It is shown that the resulting ionic liquids have lower melting points than the single ligand ILs.
Co-reporter:Bieke Onghena, Jeroen Jacobs, Luc Van Meervelt and Koen Binnemans
Dalton Transactions 2014 - vol. 43(Issue 30) pp:NaN11578-11578
Publication Date(Web):2014/06/09
DOI:10.1039/C4DT01340A
The ionic liquid choline bis(trifluoromethylsulfonyl)imide, [Chol][Tf2N], was used for the extraction of neodymium(III), in combination with choline hexafluoroacetylacetonate, [Chol][hfac], as the extractant. The binary mixture of [Chol][Tf2N] and water shows temperature-dependent phase behavior, with an upper critical solution temperature of 72 °C. A novel extraction technique, homogeneous liquid–liquid extraction (HLLE), was applied to this solvent system. HLLE is based on the use of thermomorphic solvent mixtures and has the advantage of forming a homogeneous phase during mixing. Extraction is not kinetically hindered by an interface and the extraction equilibrium is reached faster than in the case of heterogeneous mixing in conventional solvent extraction. Several extraction parameters were studied for the extraction of neodymium(III) with [Chol][hfac]: temperature, pH, extractant concentration and loading of the ionic liquid phase. A speciation study was performed to determine the stoichiometry of the extracted neodymium(III) complex and a plausible extraction mechanism is proposed. Neodymium is extracted as a tetrakis hexafluoroacetylacetonate complex with one choline cation as counter ion. The crystal structure of the extracted complex showed the presence of a coordination bond between the choline counter ion and the neodymium(III) center, resulting in a coordination number of nine. The stripping of the loaded neodymium and the influence of acid and extractant concentrations on the phase behavior of the [Chol][Tf2N]–H2O system were investigated.
Co-reporter:Sil Wellens, Neil R. Brooks, Ben Thijs, Luc Van Meervelt and Koen Binnemans
Dalton Transactions 2014 - vol. 43(Issue 9) pp:NaN3452-3452
Publication Date(Web):2013/12/06
DOI:10.1039/C3DT53024H
Metal oxides were found to dissolve in different imidazolium ionic liquids with a hydrogen atom in the C2 position of the imidazolium ring, but not if a methyl substituent was present in the C2 position. The crystal structure of the product that crystallised from an ionic liquid containing dissolved silver(I) oxide showed that this was a silver(I) carbene complex. The presence of carbenes in solution was proven by 13C NMR spectroscopy and the reactions were also monitored by Raman spectroscopy. The dissolution of other metal oxides, namely copper(II) oxide, zinc(II) oxide and nickel(II) oxide, was also studied in imidazolium ionic liquids and it was found that stable zinc(II) carbenes were formed in solution, but these did not crystallise under the given experimental conditions. A crystalline nickel(II) carbene complex could be obtained from a solution of nickel(II) chloride dissolved in a mixture of 1-butyl-3-methylimidazolium and 1-ethyl-3-methylimidazolium acetate.
Co-reporter:Alok Rout and Koen Binnemans
Dalton Transactions 2014 - vol. 43(Issue 8) pp:NaN3195-3195
Publication Date(Web):2013/12/04
DOI:10.1039/C3DT52541D
The solvent extraction of trivalent rare-earth ions and their separation from divalent transition metal ions using molten salt hydrates as the feed phase and an undiluted fluorine-free ionic liquid as the extracting phase were investigated in detail. The extractant was tricaprylmethylammonium nitrate, [A336][NO3], and the hydrated melt was calcium nitrate tetrahydrate, Ca(NO3)2·4H2O. The extraction behavior of rare-earth ions was studied for solutions of individual elements, as well as for mixtures of rare earths in the hydrated melt. The influence of different extraction parameters was investigated: the initial metal loading in the feed phase, percentage of water in the feed solution, equilibration time, and the type of hydrated melt. The extraction of rare earths from Ca(NO3)2·4H2O was compared with extraction from CaCl2·4H2O by [A336][Cl] (Aliquat 336). The nitrate system was found to be the better one. The extraction and separation of rare earths from the transition metals nickel, cobalt and zinc were also investigated. Remarkably high separation factors of rare-earth ions over transition metal ions were observed for extraction from Ca(NO3)2·4H2O by the [A336][NO3] extracting phase. Furthermore, rare-earth ions could be separated efficiently from transition metal ions, even in melts with very high concentrations of transition metal ions. Rare-earth oxides could be directly dissolved in the Ca(NO3)2·4H2O phase in the presence of small amounts of Al(NO3)3·9H2O or concentrated nitric acid. The efficiency of extraction after dissolving the rare-earth oxides in the hydrated nitrate melt was identical to extraction from solutions with rare-earth nitrates dissolved in the molten phase. The stripping of the rare-earth ions from the loaded ionic liquid phase and the reuse of the recycled ionic liquid were also investigated in detail.
Co-reporter:Alok Rout and Koen Binnemans
Dalton Transactions 2014 - vol. 43(Issue 4) pp:NaN1872-1872
Publication Date(Web):2013/11/04
DOI:10.1039/C3DT52285G
A new non-fluorinated malonamide-based ionic liquid extractant was synthesized and investigated for the extraction behavior of europium(III) and other trivalent rare-earth ions from nitric acid medium. The extractant was the functionalized ionic liquid trihexyl(tetradecyl)phosphonium N,N,N′,N′-tetra(2-ethylhexyl)malonate, [P66614][MA], and it was used in combination with the non-fluorinated ionic liquid trihexyl(tetradecyl)phosphonium nitrate, [P66614][NO3], as diluents. The extraction behavior of europium in this ionic liquid solution was studied as a function of various parameters such as the pH, concentration of the extractant, the type of acidic medium, temperature, concentration of the salting-out agent and the metal concentration of the aqueous feed. The extraction behavior of [P66614][MA] in [P66614][NO3] was compared with that of [P66614][MA] in the chloride-containing ionic liquid diluent trihexyl(tetradecyl)phosphonium chloride, [P66614][Cl] (Cyphos IL 101). The nitrate system was found to be superior. Marked differences in extraction behavior were observed between [P66614][MA] and the molecular malonamide extractant N,N,N′,N′-tetra(2-ethylhexyl)malonamide (TEHMA), i.e. the compound from which the anion of the ionic liquid extractant was prepared. The extraction behavior of other rare earths (La, Ce, Nd, Sm, Ho, Yb) and some transition metals (Ni, Co, Zn) was investigated using this functionalized ionic liquid. A good separation of the rare earths from the transition metals could be achieved. For the rare earths, the extraction efficiency increases over the lanthanide series. The effects of thermodynamic parameters, the stripping of europium(III) from the ionic liquid and the reusability of the functionalized ionic liquid were studied in detail.
Co-reporter:Jeroen Sniekers, Neil R. Brooks, Stijn Schaltin, Luc Van Meervelt, Jan Fransaer and Koen Binnemans
Dalton Transactions 2014 - vol. 43(Issue 4) pp:NaN1598-1598
Publication Date(Web):2013/10/24
DOI:10.1039/C3DT52416G
New cationic silver-containing ionic liquids were synthesized and used as non-aqueous electrolytes for the electrodeposition of silver layers. In the liquid state of these ionic liquids, a silver (I) cation is coordinated by pyridine-N-oxide (py-O) ligands in a 1:3 metal-to-ligand ratio, although in some cases a different stoichiometry of the silver center crystallized out. As anions, bis(trifluoromethanesulfonyl)imide (Tf2N), trifluoromethanesulfonate (OTf), methanesulfonate (OMs) and nitrate were used, yielding compounds with the formulae [Ag(py-O)3][Tf2N], [Ag(py-O)3][OTf], [Ag(py-O)3][OMs] and [Ag(py-O)3][NO3], respectively. The compounds were characterized by CHN analysis, FTIR, NMR, DSC, TGA and the electrodeposition of silver was investigated by cyclic voltammetry, linear potential scans, scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX). With the exception of [Ag(py-O)3][Tf2N], which melts at 108 °C, all the silver(I) compounds have a melting point below 80 °C and were tested as electrolytes for silver electrodeposition. Interestingly, very high current densities were observed at a potential of −0.5 V vs. Ag/Ag+ for the compounds with fluorine-free anions, i.e. [Ag(py-O)3][NO3] (current density of −10 A dm−2) and [Ag(py-O)3][OMs] (−6.5 A dm−2). The maximum current density of the compound with the fluorinated anion trifluoromethanesulfonate, [Ag(py-O)3][OTf], was much lower: −2.5 A dm−2 at −0.5 V vs. Ag/Ag+. Addition of an excess of ligand to [Ag(py-O)3][OTf] resulted in the formation of the room-temperature ionic liquid [Ag(py-O)6][OTf]. A current density of −5 A dm−2 was observed at −0.5 V vs. Ag/Ag+ for this low viscous silver salt. The crystal structures of several silver complexes could be determined by X-ray diffraction, and it was found that several of them had a stoichiometry different from the 1:3 metal-to-ligand ratio used in their synthesis. This indicates that the compounds form crystals with a composition different from that of the molten state. The electrochemical properties were measured in the liquid state, where the metal-to-ligand ratio was 1:3. Single crystal X-ray diffraction measurements showed that silver(I) is six coordinate in [Ag(py-O)3][Tf2N] and [Ag(py-O)3][OTf], while it is five coordinate in the other complexes. In [Ag3(py-O)8][OTf]3, there are two different coordination environments for silver ions: six coordinate central silver ions and five coordinate for the outer silver ions. In some of the silver(I) complexes, silver–silver interactions were observed in the solid state.
Co-reporter:Hasan Mehdi, Koen Binnemans, Kristof Van Hecke, Luc Van Meervelt and Peter Nockemann
Chemical Communications 2010 - vol. 46(Issue 2) pp:NaN236-236
Publication Date(Web):2009/11/21
DOI:10.1039/B914977E
Ionic liquids containing the hexafluoroacetylacetonate anion are immiscible with water and they exhibit strong metal-complexing ability.
Co-reporter:David Dupont, Evelien Renders and Koen Binnemans
Chemical Communications 2016 - vol. 52(Issue 25) pp:NaN4643-4643
Publication Date(Web):2016/03/01
DOI:10.1039/C6CC00094K
Strongly acidic (pKa ≈ −3.5) room-temperature ionic liquids (ILs) with –OSO3H functionalized cations are introduced. The strong acidity, easy synthesis, and better physical properties of these R–OSO3H ILs make them excellent alternatives to the well-known sulfonic acid (R–SO3H) ILs, especially in the domain of metal processing.
Co-reporter:David Dupont, Evelien Renders, Stijn Raiguel and Koen Binnemans
Chemical Communications 2016 - vol. 52(Issue 43) pp:NaN7035-7035
Publication Date(Web):2016/05/04
DOI:10.1039/C6CC02350A
Sulfamic acid (NH3–SO3) is an acidic zwitterion with many applications. N-Alkylated derivatives are introduced, which can be used as a new class of metal extractants R2NH–SO3 and as new super-acidic ionic liquids [R2NH–SO3H][Tf2N]. The synthesis, properties and novel applications of this versatile platform are discussed.
Co-reporter:David Dupont, Stijn Raiguel and Koen Binnemans
Chemical Communications 2015 - vol. 51(Issue 43) pp:NaN9009-9009
Publication Date(Web):2015/04/27
DOI:10.1039/C5CC02731D
New sulfonic acid functionalized ionic liquids (SAFILs) with bis(trifluoromethylsulfonyl)imide anions were synthesized. These ionic liquids are strong Brønsted acids and can solubilize metal oxides. Water-immiscible SAFILs were used as organic phases in solvent extraction studies.
Co-reporter:Daphne Depuydt, Liwang Liu, Christ Glorieux, Wim Dehaen and Koen Binnemans
Chemical Communications 2015 - vol. 51(Issue 75) pp:NaN14186-14186
Publication Date(Web):2015/07/31
DOI:10.1039/C5CC05649G
Ionic liquids with an ether-functionalised cation and the bis(2-ethylhexyl)phosphate anion show thermomorphic behaviour in water, with a lower critical solution temperature. These ionic liquids are useful for homogeneous liquid–liquid extraction of first-row (3d) transition metals.
Co-reporter:Bieke Onghena, Tomas Opsomer and Koen Binnemans
Chemical Communications 2015 - vol. 51(Issue 88) pp:NaN15935-15935
Publication Date(Web):2015/09/07
DOI:10.1039/C5CC06595J
A [P44414][Cl]–NaCl–H2O ionic liquid-based aqueous biphasic system shows promising results for the separation of cobalt(II) and nickel(II) by homogeneous liquid–liquid extraction. The extracting phase consists of a hydrophilic ionic liquid that is salted-out by sodium chloride, indicating that there is no need for using hydrophobic ionic liquids.
Co-reporter:Alok Rout and Koen Binnemans
Dalton Transactions 2015 - vol. 44(Issue 3) pp:NaN1387-1387
Publication Date(Web):2014/11/19
DOI:10.1039/C4DT02766C
Trivalent rare-earth ions were extracted from nitric acid medium by the neutral phosphine oxide extractant Cyanex 923 into ionic liquid phases containing the bis(trifluoromethylsulfonyl)imide anion. Five different cations were considered: 1-butyl-3-methylimidazolium, 1-decyl-3-methylimidazolium, methyltributylammonium, methyltrioctylammonium and trihexyl(tetradecyl)phosphonium. The extraction behavior of neodymium(III) was investigated as a function of various parameters: pH, extractant concentration, concentration of the neodymium(III) ion in the aqueous feed and concentration of the salting-out agent. The loading capacity of the ionic liquid phase was studied. The extraction efficiency increased with increasing pH of the aqueous feed solution. The extraction occurred for all ionic liquids via an ion-exchange mechanism and the extraction efficiency could be related to the solubility of the ionic liquid cation in the aqueous phase: high distribution ratios for hydrophilic cations and low ones for hydrophobic cations. Addition of nitrate ions to the aqueous phase resulted in an increase in extraction efficiency for ionic liquids with hydrophobic cations due to extraction of neutral complexes. Neodymium(III) could be stripped from the ionic liquid phase by 0.5–1.0 M nitric acid solutions and the extracting phase could be reused. The extractability of other rare earths present in the mixture was compared for the five ionic liquids.
Co-reporter:Marc Steichen, Neil R. Brooks, Luc Van Meervelt, Jan Fransaer and Koen Binnemans
Dalton Transactions 2014 - vol. 43(Issue 32) pp:NaN12341-12341
Publication Date(Web):2014/06/16
DOI:10.1039/C4DT00182F
New homoleptic and heteroleptic zinc(II)-containing liquid metal salts with N-alkylimidazole (AlkIm) ligands and bis(trifluoromethylsulfonyl)imide (Tf2N−) anions are described. The general formulae of the complexes are [Zn(AlkIm)6][Tf2N]2 and [Zn(AlkIm)6−x(AlkIm′)x][Tf2N]2. Single-crystal X-ray diffraction revealed that, in the solid state, the cations consist of octahedral zinc(II) centres. The heteroleptic complexes contain two different N-alkylimidazole ligands. The melting points of the liquid metal salts are below or slightly above room temperature. The dependence of the melting points, viscosity and crystal structure on the alkyl chain length of the N-alkylimidazole ligand for the homoleptic complexes and on the ratio of the two N-alkylimidazole ligands AlkIm and AlkIm′ for the heteroleptic compounds is discussed. The possibility of incongruent melting and the presence of a mixture of the four-coordinate zinc(II) centre and neutral ligands is discussed. The new zinc(II)-containing liquid metal salts have been used as non-aqueous electrolytes for electrodeposition of zinc. A highly reversible deposition–stripping behaviour was found. Zinc electroplating was possible at very high current densities of more than −200 mA cm−2 in unstirred solutions. Compact and highly crystalline zinc deposits were obtained.
Co-reporter:Murugan Ganapathi, Svetlana V. Eliseeva, Neil R. Brooks, Dimitri Soccol, Jan Fransaer and Koen Binnemans
Journal of Materials Chemistry A 2012 - vol. 22(Issue 12) pp:
Publication Date(Web):
DOI:10.1039/C2JM13925A
Co-reporter:Sil Wellens, Ben Thijs, Claudia Möller and Koen Binnemans
Physical Chemistry Chemical Physics 2013 - vol. 15(Issue 24) pp:NaN9669-9669
Publication Date(Web):2013/04/12
DOI:10.1039/C3CP50819F
The proof-of-principle for the separation of metals by solvent extraction using two mutually immiscible ionic liquids is given. Cobalt was extracted from the ionic liquid 1-ethyl-3-methylimidazolium chloride to the ionic liquid trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate. A distribution ratio of 44 was obtained. Cobalt could be selectively separated from nickel, with a separation factor of 207. The extraction mechanism was elucidated using UV-VIS absorption measurements. The mutual solubility between the two ionic liquids was determined by 1H NMR. Processing steps such as washing, stripping and regeneration of the ionic liquid phases are discussed.
Co-reporter:Evert Vanecht, Koen Binnemans, Jin Won Seo, Linda Stappers and Jan Fransaer
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 30) pp:NaN13571-13571
Publication Date(Web):2011/06/15
DOI:10.1039/C1CP20552H
The growth of gold nanoparticles (NPs) synthesized by sputter deposition on an ionic liquid surface is studied in situ in the bulk phase of the ionic liquids (ILs) 1-butyl-3-methylimidazolium dicyanamide [C1C4Im][N(CN)2], 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [C1C4Im][Tf2N], 1-butyl-3-methylimidazolium tetrafluoroborate [C1C4Im][BF4], 1-butyl-3-methylimidazolium hexafluorophosphate [C1C4Im][PF6] and 1-butyl-3-methylimidazolium triflate [C1C4Im][TfO]. It is found that primary nanoparticles with a diameter smaller than 2.5 nm are present in the sample immediately after sputtering. Growth of these primary particles proceeds after the end of the sputtering process and stops when the nanoparticles reach a certain size. Depending on the viscosity of the ionic liquid this growth process can proceed several hours to several days. The growth speed is fastest for the least viscous ionic liquid and follows the trend [C1C4Im][N(CN)2] > [C1C4Im][Tf2N] > [C1C4Im][TfO] > [C1C4Im][BF4] > [C1C4Im][PF6]. It is also found that a higher concentration of sputtered gold results in faster growth of the gold nanoparticles. A discussion on the growth mechanism of sputtered gold NPs is included.
Co-reporter:Alok Rout, Justyna Kotlarska, Wim Dehaen and Koen Binnemans
Physical Chemistry Chemical Physics 2013 - vol. 15(Issue 39) pp:NaN16541-16541
Publication Date(Web):2013/07/24
DOI:10.1039/C3CP52218K
The ionic liquids 1-hexyl-3-methylimidazolium bis(2-ethylhexyl)phosphate, [C6mim][DEHP], 1-hexyl-1-methylpyrrolidinium bis(2-ethylhexyl)phosphate, [C6mpyr][DEHP], and tetrabutylammonium bis(2-ethylhexyl)phosphate, [N4444][DEHP], were prepared and characterized using 1H and 13C NMR spectroscopy. The extraction behavior of neodymium(III) from nitrate medium by these ionic liquids, diluted with the room temperature ionic liquids 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C6mim][NTf2], 1-hexyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [C6mpyr][NTf2], and tributylmethylammonium bis(trifluoromethylsulfonyl)imide, [N1444][NTf2], was studied. The distribution ratio of neodymium(III) was measured as a function of various parameters, such as pH, concentration of the ionic liquid extractant, nature of diluents, concentration of ionic liquid cations and nitrate anions in the aqueous phase. The extraction behavior was compared with that obtained for a solution of the molecular extractant bis(2-ethylhexyl)phosphoric acid (DEHPA) in an ionic liquid diluent. The extraction of neodymium(III) in the ionic liquids [C6mim][DEHP] and [C6mpyr][DEHP] showed markedly different extraction properties in comparison with that of the quaternary ammonium analogue [N4444][DEHP], especially concerning the pH dependence of the extraction process. These results show that the extraction process can be tuned by the selection of the ionic liquid cation. The extraction experiments also included the trivalent rare-earth ions lanthanum(III), cerium(III), praseodymium(III), ytterbium(III) and yttrium(III). Studies of the stripping behavior and the reusability of the ionic liquids were carried out, which indicate that the ionic liquids can be reused with no loss in activity.
Co-reporter:Alok Rout and Koen Binnemans
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 23) pp:NaN16045-16045
Publication Date(Web):2016/05/24
DOI:10.1039/C6CP02301K
The ionic liquid trihexyl(tetradecyl)phosphonium thiocyanate has been used for the extraction of the transition metal ions Co(II), Ni(II), Zn(II), and the rare-earth ions La(III), Sm(III) and Eu(III) from aqueous solutions containing nitrate or chloride salts. The transition metal ions showed a high affinity for the ionic liquid phase and were efficiently extracted, while the extraction efficiency of the rare-earth ions was low. This difference in extraction behavior enabled separation of the pairs Co(II)/Sm(III), Ni(II)/La(III) and Zn(II)/Eu(III). These separations are relevant for the recycling of rare earths and transition metals from samarium cobalt permanent magnets, nickel metal hydride batteries and lamp phosphors, respectively. The extraction of metal ions from a chloride or nitrate solution with a thiocyanate ionic liquid is an example of “split-anion extraction”, where different anions are present in the aqueous and ionic liquid phase. Close to 100% loading was possible for Co(II) and Zn(II) up to a concentration of 40 g L−1 of the transition metal salt in the initial aqueous feed solution, whereas the extraction efficiency for Ni(II) gradually decreased with increase in the initial feed concentration. Stripping of Co(II), Zn(II) and Ni(II) from the loaded ionic liquid phase was possible by a 15 wt% NH3 solution. The ionic liquid could reused after extraction and stripping.
Co-reporter:Koen Binnemans
Journal of Materials Chemistry A 2009 - vol. 19(Issue 4) pp:NaN453-453
Publication Date(Web):2008/10/09
DOI:10.1039/B811373D
Recent progress in the design of low-melting liquid-crystalline metal complexes (metallomesogens) has facilitated the study of the photophysical properties of these compounds in the mesophase. Luminescence in the liquid crystal state has been observed for metallomesogens incorporating lanthanide(III), gold(I), silver(I), copper(I) or zinc(II) ions. An alternative approach to liquid-crystalline metal-containing systems is doping a metal complex in a liquid-crystal host. A fascinating property of these materials is the ability to observe linearly polarized emission.
