Lanthanide Cations Research Articles

Solution and solid state structures of lanthanides(III) and uranyl(II) complexes of tripodal tris(2-pyridyl)-containing ligand on Ph3P(O) platform

Reaction of tris[2-(2′-pyridylmethoxy)phenyl]phosphine oxide (L) with f-element nitrates resulted in 1:1 complexes. The isolated complexes of ligand L with La(III), Eu(III), Tb(III), and U(VI) nitrates, and with La(III) chloride were studied in the solid state and solution by IR, Raman, and NMR spectroscopy, X-ray analysis, and also DFT calculations. Composition and structure of the complexes vary with lanthanide cation radius. According to the data of elemental analysis, vibrational spectroscopy, and X-ray diffraction, the ligand is coordinated in tridentate mode in crystalline La(III) and solid Eu(III) complexes: [Ln(OPO,N,Oeth-L)(H2O)(O,O-NO3)3], and in monodentate mode in crystalline complex [Tb(OPO-L)(H2O)2(O,O-NO3)3]. Nitrogen atoms of pyridine fragments of the ligand not involved in coordination produce intra- and intermolecular H-bonds with coordinated water molecules in the second coordination sphere of Ln(III). According to IR, NMR spectrometry, and DFT calculations, the structure of coordination polyhedron of the main species of Ln(III) complexes in acetonitrile solutions is retained including coordination of one of pyridine fragments in the second coordination sphere: [Ln{OPO,N,(N*),Oeth-L}(H2O)(O,O-NO3)3] and [Tb{OPO,(N*)-L}(H2O)2(O,O-NO3)3], where Ln = La, Eu, and N* is the nitrogen atom of pyridine fragment producing intramolecular H-bond with coordinated water molecule. According IR and Raman spectroscopy, ligand L is coordinated in bidentate mode in solid complex [UO2(OPO,N-L)(O,O-NO3)], and uncoordinated nitrogen atoms remain free. Solution structure of uranyl complex is labile and depends on solvent nature. Equilibria of complex species with variable coordination of nitrate ions, ligand L, and with probable involvement of water take place in CD3CN and CDCl3 solutions. Photophysical properties of the prepared Eu(III) and Tb(III) complexes were studied. The preliminary assessment of extraction properties of compound L was made. Stability of studied compounds in acetonitrile solutions was examined, and the structure of one of protolysis product of Eu(III) complex, [Eu(LH)(H2O)(NO3)4], was established by micro-IR and X-ray analysis.

Supercharged fluorescent proteins detect lanthanides via direct antennae signaling

A sustainable operation for harvesting metals in the lanthanide series is needed to meet the rising demand for rare earth elements across diverse global industries. However, existing methods are limited in their capacity for detection and capture at environmentally and industrially relevant lanthanide concentrations. Supercharged fluorescent proteins have solvent-exposed, negatively charged residues that potentially create multiple direct chelation pockets for free lanthanide cations. Here, we demonstrate that negatively supercharged proteins can bind and quantitatively report concentrations of lanthanides via an underutilized lanthanide-to-chromophore pathway of energy transfer. The top-performing sensors detect lanthanides in the micromolar to millimolar range and remain unperturbed by environmentally significant concentrations of competing metals. As a demonstration of the versatility and adaptability of this energy transfer method, we show proximity and signal transmission between the lanthanides and a supramolecular assembly of supercharged proteins, paving the way for the detection of lanthanides via programmable protein oligomers and materials.

Elucidating Polyphosphate Anion Binding to Lanthanide Complexes Using EXAFS and Pulsed EPR Spectroscopy.

Reversible anion binding to lanthanide complexes in aqueous solution has emerged as an effective method for anion sensing. Through careful design of the organic ligand, luminescent lanthanide complexes capable of binding biologically relevant anions in a bidentate or monodentate manner can be realized. While single-crystal X-ray diffraction analyses and NMR spectroscopy have revealed the structural geometry of several host-guest complexes, the challenge remains in designing preorganized lanthanide receptors with enhanced anion selectivity for broader applications in diagnostics and bioimaging. To address this challenge, innovative and complementary methods to investigate host-anion binding geometry are becoming increasingly important. Herein, we demonstrate the combined use of Eu L3-edge extended X-ray absorption fine structure (EXAFS) and electron paramagnetic resonance (EPR) spectroscopy to elucidate the binding of nucleoside phosphates (ATP, ADP, and AMP) to a cationic lanthanide complex. We establish that ATP unequivocally binds the lanthanide center in a bidentate manner in water, while ADP adopts both bidentate and monodentate modes, and AMP binds in a monodentate manner. This interdisciplinary approach provides deeper insight into lanthanide host-guest chemistry in solution, laying the groundwork for designing emissive probes that undergo specific anion-induced structural changes and elicit desired optical responses upon binding.

Smaller rare-earth cation and mixed valent Mn incorporation as a dual strategy to enhance ferrimagnetic ordering temperatures in A-site ordered quadruple perovskites, LnCu3Mn1+xTi3-xO12 (Ln = La, Nd; x = 0, 0.3).

High-TC ferro-/ferrimagnetic quadruple perovskites constitute an important class of oxides that has garnered a lot of research attention in recent times, but their synthesis is commonly achieved under high-pressure conditions. Thus, the development of high-TC quadruple perovskites that can be synthesized under ambient pressure can be a key to the above problem. Herein, we report ambient pressure synthesis of a series of new A-site ordered quadruple perovskites, LnCu3Mn1+xTi3-xO12 (Ln = La, Nd; x = 0, 0.3), by coupled aliovalent-cation manipulation in CaCu3Ti4O12. The effect of smaller lanthanide Nd incorporation in place of La has been investigated. Furthermore, 30% mixed valency of Mn per Mn3+ has been introduced in place of Ti4+ following similar strategies adopted to achieve giant magnetoresistive manganites La0.7A0.3MnO3 (A = Ca, Sr, Ba) from LaMnO3. Mn is present in the 3+ state for x = 0 and in a mixed valent state (3+ and 4+) for x = 0.3, whereas Cu exists in the 2+ state in all the compounds. While LaCu3MnTi3O12 and LaCu3Mn1.3Ti2.7O12 show the onset of ferrimagnetic order at ∼60 and 110 K, respectively, the corresponding Nd analogs, NdCu3MnTi3O12 and NdCu3Mn1.3Ti2.7O12, exhibit enhanced TC's of ∼80 and 140 K, respectively. This work reveals an effective strategy of mixed-valent Mn incorporation in the B-sublattice and smaller rare-earth cation incorporation to achieve higher ferrimagnetic ordering temperatures in quadruple perovskites.

High-pressure behavior of high-entropy A2B2O7 pyrochlore

A single high-entropy pyrochlore-type compound (A2B2O7) was successfully synthesized, incorporating 8 different rare-earth cations at the A site and 2 different metal cations at the B site in equiatomic amounts [(8A1/8)2(2B1/2)2O7]. Powders with a nominal composition of (La1/8Sm1/8Nd1/8Pr1/8Y1/8Gd1/8Dy1/8Yb1/8)2(Hf1/2Zr1/2)2O7 were fabricated by glycine nitrate procedure (GNP). The GNP process yielded powders with low crystallinity and after subsequent calcination, a well crystalline ceramic powders were formed. The phase evolution was initially analyzed using X-ray diffraction (XRD). In situ high-pressure X-ray diffraction was employed to investigate the structural stability and high-pressure behavior of the A2B2O7 pyrochlore up to 25.8 GPa. Theoretical investigations of the high-entropy pyrochlore systems were performed and showed good agreement with the experimentally obtained results.

Polaron-assisted dielectric relaxation processes in donor-doped BaTiO3-based ceramics

Ceramic samples based on the Ba1-xGdxTiO3 system, where x = 0.001, 0.002, 0.003, 0.004 and 0.005, were prepared via the Pechini’s chemical synthesis route. Structural properties, analyzed from X-ray diffraction and Rietveld refinement, revealed the formation of the pure ABO3 perovskite structure with tetragonal symmetry (P4mm) for all the studied compositions. Doping with Gd3+ promoted a reduction in the unit-cell volume, confirming the preferential substitution of the rare-earth cation at the A-site. The dielectric properties have been analyzed over a wide temperature and frequency range, revealing a significant contribution of the conduction mechanisms in the dielectric response of the studied ceramics. In fact, by using the Davidson-Cole formalism, the observed electrical behavior was found to be associated with relaxation processes related to intrinsic defects mobility promoted by a thermally-activated polaronic mechanism. The obtained values of the activation energy for the relaxation processes, estimated from the Arrhenius’ law for the mean relaxation time, revealed a decrease from 0.29 up to 0.21 eV as the Gd-doping concentration increases, which suggests the conduction process to be associated with the polaronic effects due to the coexistence of Ti4+ and Ti3+ ions in the structure. Analysis from the conductivity formalism, by using the Jonscher’s universal power-law, confirmed the polaron-type conduction mechanism for the dielectric dispersion, as suggested by the dielectric analysis, being the nature of the hopping mechanism governed by small polaron hopping (SPH) charge transport in the studied Ba1–xGdxTiO3 ceramics.

Strategy to optimize the broadband near-infrared emission based on Eu2+-doped sulfureted garnet phosphors toward emerging spectroscopy applications

Eu2+-doped near-infrared (NIR) emitting phosphors, known for their high efficiency, broadband emission and spectral tunability, have gained much attention. However, achieving efficient NIR emission based on Eu2+ remains a challenge due to the co-existence of Eu3+, especially in materials (i.e. garnets and apatites) containing trivalent lanthanide cations. In this study, a Eu2+ doped sulfureted NIR-emitting garnet phosphor Ca3(Sc, Eu)2Si3(O, S)12: Eu2+ is successfully designed and synthesized. Notably, a strategy for regulating the initial valence state of dopants is proposed by using prepared EuS instead of the conventional Eu2O3 as raw material, enhancing the NIR emission by 135 %. Moreover, a sulfuration strategy is further introduced to enhance the NIR-emitting intensity and internal quantum efficiency by 192 % and 167.8 %, and to improve thermal stability by 154 % at 120 °C. The luminescence origin of the unusual broadband NIR emission is re-examined through chemical unit co-substitution strategy by introducing [Al3+Hf4+] to replace [Sc3+Si4+] ion pairs. Meanwhile, the spectral regulation and the performance optimization mechanism are systematically discussed. Finally, a green light pumped NIR LED device with a photoelectric efficiency of 9.43 %@100 mA and output power of 22.74 mW@100 mA is fabricated, showing remarkable potential in nondestructive testing and biomedical imaging applications.

Tuning the Spin Transition and Carrier Type in Rare-Earth Cobaltates via Compositional Complexity.

There is growing interest in material candidates with properties that can be engineered beyond traditional design limits. Compositionally complex oxides (CCO), often called high entropy oxides, are excellent candidates, wherein a lattice site shares more than four cations, forming single-phase solid solutions with unique properties. However, the nature of compositional complexity in dictating properties remains unclear, with characteristics that are difficult to calculate from first principles. Here, compositional complexity is demonstrated as a tunable parameter in a spin-transition oxide semiconductor La1- x(Nd, Sm, Gd, Y)x/4CoO3, by varying the population x of rare earth cations over 0.00≤ x≤ 0.80. Across the series, increasing complexity is revealed to systematically improve crystallinity, increase the amount of electron versus hole carriers, and tune the spin transition temperature and on-off ratio. At high a population (x = 0.8), Seebeck measurements indicate a crossover from hole-majority to electron-majority conduction without the introduction of conventional electron donors, and tunable complexity is proposed as new method to dope semiconductors. First principles calculations combined with angle resolved photoemission reveal an unconventional doping mechanism of lattice distortions leading to asymmetric hole localization over electrons. Thus, tunable complexity is demonstrated as a facile knob to improve crystallinity, tune electronic transitions, and to dope semiconductors beyond traditional means.

Lanthanide (Sm, Dy) Complexes with the 9,10-Phenanthrenediimine Redox-Active Ligand: Synthesis and Structures

The complex formation of the redox-active ligand bis(N, N’-2,6-diisopropylphenyl)-9,10-phenanthrenediimine (DippPDI) with alkaline metal (Li, K) and lanthanide (Sm, Dy) cations is studied. The reduction of DippPDI with an alkaline metal excess affords the dianionic form of the ligand (DippPDA2–), which crystallizes with the potassium cation as the coordination polymer [K2(DippPDA)(Thf)3] (Thf is tetrahydrofuran, THF). The reaction of equimolar amounts of the lithium salt with the dianionic form of the ligand and neutral diimine affords the lithium complex with the radical-anion form (DippPSI•–) crystallized as [Li(DippPSI)(Thf)2]. The samarium(III) complex [SmCp*(DippPDA)(Тhf)] (I) is formed by the reduction ofDippPDI with samarocene [Sm (Thf)2] (Cp* is pentamethylcyclopentadienide): both the samarium(II) cation and Cp*– anion are oxidized in the reaction.DippPDI does not react with similar ytterbocene. The dysprosium(III) complexes are synthesized by the ion exchange reactions between DyI3(Thf)3.5 and potassium or lithium salt with theDippPDA2-dianion. Similar complexes [Dy(DippPDA)I(Thf)2] (IIThf) and [Dy(DippPDA)I(Thf)(Et2O)] () are formed in the reactions with the potassium salt depending on the solvent used: a THF-hexane or a diethyl ether-n-hexane mixture, respectively. The coordination of the dysprosium cation by the π system of the conjugated fragment of the NCCN ligand is observed in IIThf, whereas in this coordination is absent. The reaction with Li2(DippPDA) affords the binary complex salt [Li(Тhf)3(Et2O)][DyI2(DippPDA)(Тhf)] (III, crystallization from a THF-Et2O mixture). The crystallization from THF gives the [Li(Тhf)4][DyI2(DippPDA)(Thf)] salt (III') containing the same anion as III. The structures of all new complexes are studied by X-ray diffraction (XRD, CIF files CCDC nos. 2260307–2260313).

How Bulk Versus Surface Chemistry Affects the Surface Reconstruction of Perovskite Nickelates and Their Activation By Fe Impurities

Whether surface reconstruction of LaNiO3 and the related Ruddlesden-Popper oxide La2NiO4 occurs during the oxygen evolution reaction has only recently emerged as a topic of rigorous study despite the implications this would have for its activity and stability at scales from the three-electrode cell to electrolyzer stacks. Correlation of structure to reconstruction propensity is much needed, but not well-understood. Building off of our work suggesting that these oxides do electrochemically reconstruct to the thermodynamically stable, amorphous, Fe impurity-sensitive, nickel hydroxide, we extend our observations to materials doped with alternative rare earth and alkaline earth metal cations at the La-site. First, we find that undoped La2NiO4 has a higher tendency to reconstruct, forming almost twice as much Ni(OH)2 for a given electrochemical treatment as LaNiO3 which we attribute to differences in Ni valence state between the two materials. This leads to a higher current density when exposed to Fe impurities by formation of more NiFeOxHy, the highest activity catalyst for OER known. Yet, the intrinsic activity of the Fe sites formed are equivalent within experimental error suggesting a convergence in surface composition despite different bulk composition. We find this reconstruction also occurs for doped materials, extending the library of materials expected to have dynamic surfaces during OER. Further, we use XPS coupled with argon ion sputtering to connect differences in reconstruction extent to the bulk and surface composition, with particular emphasis on the valence state of nickel as a possible descriptor.

Synthesis and characterization of cubic δ–phase stabilized Bi2O3 electrolytes by triple rare earth cation doping for intermediate temperatures SOFCs

Face–centered cubic–Bi2O3 (δ–phase), a high–ion conductor, is an essential solid electrolyte option, particularly for low–low–temperature SOFC applications. It is widely accepted that δ–Bi2O3 exhibits higher conductivity than the YSZ electrolytes typically utilized in HT–SOFC units. The present study investigates the structural, thermal, surface, and conductivity characteristics of the Bi2O3 electrolytes co–doped with Tb–Sm–Gd rare earth. The XRD data indicate that, except composition 20Tb20Sm20Gd, all compositions are stabilized with the cubic δ–phase at room temperature. The estimated lattice constants additionally suggest lattice contraction, confirming that the partial cation substitutes between host Bi3+ and rare earth cations are successful. The DTA curves do not have any endothermic or exothermic peaks, indicating a possible phase transition. Arrhenius plots prove that DC conductivity decreases as the dopant ratio increases, implying a drop in polarization power. The highest conductivity is found to be 0.131 S/cm for the composition 10Tb10Sm10Gd.

Influence of Rare-Earth Doping Content and Type on Phase Transformation and Transport Properties in Highly Doped CeO2.

Rare-earth doped CeO2 materials find extensive application in high-temperature energy conversion devices such as solid oxide fuel cells and electrolyzers. However, understanding the complex relationship between structural and electrical properties, particularly concerning rare-earth ionic size and content, remains a subject of ongoing debate, with conflicting published results. In this study, we have conducted comprehensive long-range and local order structural characterization of Ce1-xLnxO2-x/2 samples (x ≤ 0.6; Ln = La, Nd, Sm, Gd, and Yb) using X-ray and neutron powder diffraction, Raman spectroscopy, and electron diffraction. The increase in the rare-earth dopant content leads to a progressive phase transformation from a disordered fluorite structure to a C-type ordered superstructure, accompanied by reduced ionic conductivity. Samples with low dopant content (x = 0.2) exhibit higher ionic conductivity in Gd3+ and Sm3+ series due to lower lattice cell distortion. Conversely, highly doped samples (x = 0.6) exhibit superior conductivity for larger rare-earth dopant cations. Thermogravimetric analysis confirms increased water uptake and proton conductivity with increasing dopant concentration, while the electronic conductivity remains relatively unaffected, resulting in reduced ionic transport numbers. These findings offer insights into the relationship between transport properties and defect-induced local distortions in rare-earth doped CeO2, suggesting the potential for developing new functional materials with mixed ionic oxide, proton, and electronic conductivity for high-temperature energy systems.

Role of the coupling of the electronic transitions on the order of the metal-to-insulator phase transition in nickelates

Rare-earth nickelates (chemical formula RNiO3, R being a rare-earth cation) display a temperature-dependent metal-to-insulator transition (MIT) together with a breathing distortion of the NiO6 octahedra units at a temperature ranging from 0 to 600 K depending on the size of the R cation. Their rich phase diagram is also characterized by a paramagnetic to antiferromagnetic transition that occurs at the same temperature as the MIT for R = Pr, Nd, while it arises at lower temperatures for all the other members of the series. In this work, we have investigated the order of the MIT in a portion of the phase diagram spanning from SmNiO3 to NdNiO3 by means of temperature dependent transport measurements and resonant elastic x-ray scattering performed on high quality epitaxial SmxNd1−xNiO3 solid solution thin films. Our results show that the order of the metal-to-insulator transition does not depend on whether or not the MIT is coupled with the magnetic transition.

Selective Liquid-Liquid Extraction of Thorium(IV) from Rare-Earth Element Mixtures.

One of the major challenges in processing rare-earth element (REE) materials arises from the large amounts of radioactive thorium (Th) that are often found within REE minerals, encouraging enhanced metal separation procedures. We report here a study aimed at developing improved systems for REE processing with the goal of efficient extraction of Th(IV) from acidic solution. A tripodal ligand, TRPN-CMPO-Ph, was prepared that utilizes carbamoylmethylphosphine oxide (CMPO) chelators tethered to a tris(3-aminopropyl)amine (TRPN) capping scaffold. The ligand and its metal complexes were characterized by using elemental analysis, NMR, Fourier transform infrared spectroscopy, mass spectrometry, and luminescence spectroscopy. Using a liquid-liquid metal extraction protocol, TRPN-CMPO-Ph selectively extracts Th(IV) at an efficiency of 79% from a mixture of Th(IV), UO22+, and all rare-earth metal cations (except promethium) dissolved in nitric acid into an organic solvent. Th(IV) extraction selectivity is maintained upon extraction from a mixture that approximates a typical monazite leach solution containing several relevant lanthanide ions, including two ions at higher concentration relative to Th(IV). Comparative studies with a tris(2-aminoethyl)amine (TREN)-capped derivative are presented and support the need for a larger TRPN capping scaffold in achieving Th(IV) extraction selectivity.

Single-bubble sonoluminescence of itterbium(II or III) and thulium(II or III) chloride nanoparticles colloidal suspensions in dodecane

Colloidal suspensions of nanoparticles of di- and trivalent ytterbium and thulium chloride crystals in dodecane were prepared by ultrasonic dispersion. The average nanoparticle size in the suspensions was 20–35 nm. During single-bubble sonolysis with the bubble moving at the standing wave antinode, identical bands with a maximum at 550 nm appeared in the sonoluminescence spectra with spectral resolution Δλ = 15 nm for suspensions of both Yb(II) and Yb(III) salts. Bands with a maximum at 600 nm were found for suspensions of Tm(II) and Tm(III) salts. These sonoluminescence bands coincide with the photoluminescence bands of Yb(II) (550 nm) or Tm(II) (600 nm) salts, respectively. For suspensions of divalent lanthanide salts, these sonoluminescence bands appear when nanoparticles get into a moving bubble, because of collisional excitation of Yb(II) or Tm(II) in the bubble plasma, which periodically appears during acoustic oscillations: [Ln(II)]suspension → [Ln(II)]bubble → [Ln(II)]plasma → [Ln(II)*]plasma → Ln(II) + hνLn(II). The presence of analogous bands for suspensions of trivalent lanthanide salts is caused, in particular, by also their reduction in the plasma after they get into a bubble: [Ln(III)]suspension → [Ln(III)]bubble → [Ln(III)]plasma → [Ln(II), Ln(II)*]plasma → [Ln(II)*]plasma → Ln(II) + hνLn(II). The reduction of lanthanide ions in the bubble plasma is not limited to the reaction Ln(III) → Ln(II), Ln(II)*, but can proceed further giving singly charged lanthanide cations and lanthanide atoms: Ln(II) → Ln(I), Ln(I)* → Ln(0), Ln(0)*. The single-bubble sonoluminescence spectra with Δλ = 1.5 nm for a suspension of Yb(III) salt showed characteristic lines of Yb(I) and Yb(0). These characteristic lines and bands for ytterbium and thulium atoms and ions are suitable for sonoluminescent spectroscopic analysis, that is, identification and quantification of ions in solutions and suspensions and determination of electronic temperature in bubble plasma.

A Common Bottleneck for Metal Oxidation by Molecular Oxygen Across Size Regimes: Kinetics of Atomic Lanthanide Cations (La+-Lu+) with O2.

Kinetics of the lanthanide cations (Ln+ = La+-Lu+ excluding Pm+) reacting with molecular oxygen were measured in a selected-ion flow tube apparatus from 300 to 600 K. Where exothermic, these reactions occur efficiently, producing LnO+ + O. The reactions display positive temperature dependences consistent with Arrhenius equation behavior and show small activation energies (0-2 kJ mol-1) that are strongly correlated to promotion energies of the Ln+ atoms. Reanalysis of literature data on neutral Ln + O2 reactions show a similar correlation with slightly larger activation energies (0-10 kJ mol-1). The data are explained by a common mechanism controlling oxidation by molecular oxygen in these systems, as well as in gas-phase reactions of transition metal and posttransition metal cluster anions, neutral clusters deposited on surfaces, and for oxygen incident on metal surfaces. It is posited that across these systems, the height of an early barrier along the reaction coordinate is predictable based on knowledge of the electronic states of the reactants and may be used to either promote or inhibit oxygen activation.

2-(Pyridin-2-yl)quinazolin-4(3H)-one derivatives as new ligands for lanthanide(iii) cations

2-(Pyridin-2-yl)quinazolin-4(3H)-one derivatives as new ligands for lanthanide(iii) cations

U(V) Stabilization via Aliovalent Incorporation of Ln(III) into Oxo-salt Framework.

Pentavalent uranium compounds are key components of uranium's redox chemistry and play important roles in environmental transport. Despite this, well-characterized U(V) compounds are scarce primarily because of their instability with respect to disproportionation to U(IV) and U(VI). In this work, we provide an alternate route to incorporation of U(V) into a crystalline lattice where different oxidation states of uranium can be stabilized through the incorporation of secondary cations with different sizes and charges. We show that iriginite-based crystalline layers allow for systematically replacing U(VI) with U(V) through aliovalent substitution of 2+ alkaline-earth or 3+ rare-earth cations as dopant ions under high-temperature conditions, specifically Ca(UVIO2)W4O14 and Ln(UVO2)W4O14 (Ln=Nd, Sm, Eu, Gd, Yb). Evidence for the existence of U(V) and U(VI) is supported by single-crystal X-ray diffraction, high energy resolution X-ray absorption near edge structure, X-ray photoelectron spectroscopy, and optical absorption spectroscopy. In contrast with other reported U(V) materials, the U(V) single crystals obtained using this route are relatively large (several centimeters) and easily reproducible, and thus provide a substantial improvement in the facile synthesis and stabilization of U(V).

Rare earth elements recovery and mechanisms from coal fly ash by column leaching using citric acid

Rare earth elements (REEs) play an irreplaceable role in supporting the advancement of the global economy and technology, but their limited supply drives researchers to devise effective strategies for the recovery of REEs from alternative sources, including coal fly ash (CFA). In this work, a new column leaching method using citric acid as the lixiviant was proposed to enhance the recovery of REEs from CFA at room temperature. The mechanism of column leaching was investigated based on sample properties, leaching results, and the adsorption characteristics and complexation of citric acid. REEs in the CFA were found to be hosted into the amorphous aluminosilicate matrix in the form of oxides and fluorides using SEM-EDS. Compared to the maximum recovery of total REEs (TREEs, < 30 %) in the conventional agitation leaching tests, the recovery of TREEs in the column leaching tests increased significantly to 64.8 %, while the leaching rate of impurities (Al, Ti, and Fe) was less than 13.7 %. Results of the Zeta potential measurements showed that the citric acid and rare earth cations were adsorbed on the surface of CFA particles. These adsorption phenomena may make REEs bind to the CFA surface, thereby resulting in low leaching recoveries of REEs. Rare earth-citrate complexes in the lixivium were isolated by antisolvent precipitation, demonstrating that rare earth cations can be complexed by citrate. During the column leaching process, the leached rare earth ions were complexed with citrate and then carried away with the flowing liquid phase, which improved the recovery of REEs.

Tailoring Co site reactivity via Sr and Ni doping in LaCoO3 for enhanced water splitting performance

Perovskite oxides (ABO3) featuring rare-earth cations in the A-site and first-row transition-metal cations in the B-site, have emerged as promising catalytic materials for addressing the slow kinetics of the water splitting reaction. In this study, we synthesized La1-xSrxCo1-yNiyO3 using the solution combustion synthesis method and conducted a comprehensive investigation into the structural, surface, and electronic properties of the resulting materials. The strategic doping of Sr in La sites and Ni in Co sites has notably enhanced the kinetics and effectiveness of both the oxygen evolution reaction at the anode and the hydrogen evolution reaction at the cathode, leading to an overall improvement in water splitting efficiency over La1-xSrxCo1-yNiyO3. Detailed mechanistic studies have revealed the crucial role of high covalency and surface oxygen vacancies, tailored through aliovalent doping, in enhancing the catalytic activity of the oxygen evolution reaction in La1-xSrxCo1-yNiyO3. This research serves as a pioneering effort to establish a correlation between electronic and surface properties and to elucidate the mechanistic aspects of water splitting over perovskite materials.