Tetravalent Metal Research Articles

Tetravalent metals modulated Zn-based layered double hydroxides and their mixed metal oxides for catalytic depolymerization of carbonyl-coordinating plastic waste

Plastic waste generation has become a global issue and presents a significant challenge concerning degradability in the environment. This poses a serious threat and adverse impact on the health of living creature and the environment ecosystem. The up-/re-cycling of plastic waste through catalytic depolymerization is becoming a sustainable way to reduce economic concerns about production and serious environmental impacts. Here, in the present study an effort has been made for the development of catalysts for efficient recycling of carbonyl group containing polymer waste [Polyethylene terephthalate (PET) and polycarbonate (PC)]. The sequential preparation of ZnMIV- and ZnAlMIV- LDHs (layered double hydroxides) (MIV= Zr and Ti) and their respective mixed metal oxide (MMOs) based catalytic materials, has been carried out by one-pot co-precipitation and calcination methods. The structural parameters were examined through the various characterisation techniques including XRD, FTIR, TEM, SEM, and EDS. The layered structure, high crystalline nature and hexagonal 2D-sheet/flakes like morphology with average particle size ranging from ~14 to 51nm [for LDHs] and ~6 to 21nm [for MMOs] were observed. Depolymerization of PET and PC using LDHs/MMOs catalyst in ethylene glycols (EG) produced bis(2-hydroxyethyl terephthalate) (BHET) and bisphenol A (BPA) monomers as main products, respectively. The catalyst quantity, concentration of solvent, recyclability of catalysts, reaction duration, and crystallization time have also been further investigated for better yield during catalytic glycolysis. The isolated monomers were further characterized by using melting point, mass spectroscopy, 1H-NMR, 13C-NMR and FTIR analysis. The order of catalytic activities of prepared samples as ZnTi-LDH˃ ZnAlTi-LDH ˃ ZnTi-MMO˃ ZnAlZr-LDH˃ ZnAlTi-MMO˃ ZnZr-LDH in PET depolymerization while in case of PC, the order as ZnTi-LDH˃ ZnAlTi-LDH ˃ ZnZr-LDH˃ ZnAlZr-LDH˃ ZnZr-MMO˃ ZnAlZr-MMO˃ ZnTi-MMO˃ ZnAlTi-MMO were observed. LDH samples showed higher catalytic conversion than their respective MMOs during PET and PC depolymerization into monomers BHET and BPA with % yield of ~76-83% and ~81-89%, respectively. ZnTi-LDH shows high catalytic efficacy in depolymerization of PET and PC with yield of (~82%) BHET monomer and (89%) BPA. This catalyst displayed good recyclability more than eight cycles during this catalytic glycolysis study.

Thermal and photochemical degradation of CsGeI3 and CsGeBr3: XPS and optical studies

The toxicity of complex lead halides significantly limits the commercialization and practical application of perovskite solar cells. In recent days, lead-free complex lead halides with a perovskite structure have become increasingly popular, among which germanium systems are the least studied. Here we present for the first time a systematic study of the thermal and photochemical stability of perovskite thin films of CsGeI3 and CsGeBr3. The measurements of optical absorbance and X-ray photoelectron spectra (XPS) of core levels and valence bands of Ge-based halide perovskites after light soaking and heat stress were thoroughly performed. It has been found the effect of thermal and photochemical degradation of Ge perovskites which is accompanied by reduction of I:Ge and Br:Ge ratios and appearance of tetravalent metal species fixed in XPS Ge 2p and Ge 3d spectra. The XPS O 1s measurements of irradiated and annealed Ge-based perovskites and their comparison with spectra of GeO2 have shown that formation of Ge4+-species is not due to metal oxidation but owing to defect-mediated hole-doping. While the Ge2+→Ge4+ process lowers the thermal and photochemical stability of Ge-based perovskites and limits their use in photovoltaics, the temperature induced hole doping is favorable for thermoelectric applications.

Effect of branching in the alkyl chain of diglycolamide on the sequestration of tetravalent actinides: solvent extraction and theoretical studies.

DGA (diglycolamide) ligands show a different extraction behavior of trivalent metal ions by changing the branching alkyl chain length as well as the branching at the methylene position. There are no studies of these factors on the extraction efficiency of these DGA derivatives for the extraction of tetravalent actinides. We have evaluated four different DGA derivatives for the extraction of Np, Pu, and Th from molecular diluents. The n-butyl derivative shows enhanced extraction efficiency and branching gives rise to a reduction in the extraction efficiency of tetravalent ions. The distribution ratios are higher in pure octanol than in a mixture of 30% octanol and 70% n-dodecane. This behavior is in marked difference to that of the extraction of trivalent ions where the addition of an alcohol generally decreases the distribution ratio of trivalent ions due to the ligand-modifier intercation, poor aggregation or micelle formation tendency of DGAs in polar solvents. This suggests that micelle-mediated extraction may not be the dominating factor for the extraction of tetravalent metal ions. Slope analysis suggests the involvement of only two DGA molecules in the extracted species suggesting no/poor possibility of micelle formation in the present system. The higher extraction in pure octanol may be due to a better solubility of the extracted complexes in this polar medium compared to the mixture of octanol and n-dodecane. The water and acid uptake, the back extraction, and the radiation stability of the solvent systems were also investigated. DFT studies were performed to get a better insight into the extraction and complexation of the different DGA solvent systems.

Expanding the Phase Space for Halide-Based Solid Electrolytes: Li-Mg-Zr-Cl Spinels.

Chloride-based solid electrolytes are intriguing materials owing to their high Li+ ionic conductivity and electrochemical compatibility with high-voltage oxide cathodes for all-solid-state lithium batteries. However, the leading examples of these materials are limited to trivalent metals (e.g., Sc, Y, and In), which are expensive and scarce. Here, we expand this materials family by replacing the trivalent metals with a mix of di- and tetra-valent metals (e.g., Mg2+ and Zr4+). We synthesize Li2Mg1/3Zr1/3Cl4 in the spinel crystal structure and compare its properties with the high-performing Li2Sc2/3Cl4 that has been reported previously. We find that Li2Mg1/3Zr1/3Cl4 has lower ionic conductivity (0.028 mS/cm at 30 °C) than the isostructural Li2Sc2/3Cl4 (1.6 mS/cm at 30 °C). We attribute this difference to a disordered arrangement of Mg2+ and Zr4+ in Li2Mg1/3Zr1/3Cl4, which may block Li+ migration pathways. However, we show that aliovalent substitution across the Li2-z Mg1-3z/2Zr z Cl4 series between Li2MgCl4 and Li2ZrCl6 can boost ionic conductivity with increasing Zr4+ content, presumably due to the introduction of Li+ vacancies. This work opens a new dimension for halide-based solid electrolytes, accelerating the development of low-cost solid-state batteries.

Ternary cesium(rubidium) tungstates: production and impedance spectroscopy

The work is aimed at the directed synthesis of new phases of tungstates containing mono-, tri-, and tetravalent metals, as well as the determination of their crystallographic, thermal, and electrophysical properties. The study used the method of solid-phase synthesis to obtain tungstate phases with composition MRA0.5(WO4)3 (M – singly, R – triply-, and A – tetra-charged elements) within the temperature range of 400–750 °С. Their crystallographic and thermal characteristics were determined. The synthesized ternary tungstates crystallizing in a hexagonal system were studied using differential scanning calorimetry. The technique revealed an increase in the melting temperatures of compounds with increasing ionic radius of the trivalent cation in the series CsRTi0.5(WO4)3 (R = Al, Cr, Ga, Fe, In). The same correlation is observed when switching from rubidium to cesium derivatives. The thermal stability of ternary titanium and hafnium tungstates was compared. The melting temperatures of RbRTi0.5(WO4)3 are about 20 °С higher than those of their hafnium counterparts. The dielectric characteristics of CsRTi0.5(WO4)3 (R = Fe, Cr) belonging to the ternary tungstate family were analyzed via impedance spectroscopy. The temperature and frequency dependences of the conductivity of ternary tungstates at different frequencies (1 Hz – 1 mHz), measured in heating and cooling modes, are characterized by a slight temperature hysteresis, reaching 10-2–10-3 S/cm in the high-temperature region at activation energy values of 0.4–0.5 eV. The impedance frequency spectra measured within the range of 1 Hz – 1 mHz at different temperatures confirm the ion-conducting properties of the sample, which allows the obtained phases to be considered promising solid electrolytes.

Insights into Carbon Dioxide Capture over Glycine‐Functionalized Metal–Organic Framework‐808 from DFT Calculations

AbstractMetal‐organic framework‐808 (MOF‐808), functionalized with amino acids, is a promising class of materials for carbon dioxide (CO2) capture. In this study, we employed density functional theory calculations to investigate the mechanism of CO2 capture by glycine‐functionalized MOF‐808 (MOF‐808‐Gly). MOF‐808 was treated with one, two, three, or four glycine molecules to investigate the effect of glycine functionalization. It is proposed that the capture reaction proceeds in a single step involving proton transfer and C−N bond formation. With increasing glycine loading, the reaction barriers decreased, whereas the observed rate increased. When considering the substitution of different tetravalent metal centers (Zr and Hf) on the MOF‐808 node, it is found that substituting these tetravalent metal centers does not affect the capture activity. The capture reaction under humid conditions was also studied by introducing explicit and implicit amounts of water. The presence of a water molecule led to reduced barriers and more stable capture product formation, indicating the enhanced performance of MOF‐808‐Gly in CO2 capture.

Sodium Cerium Phosphate, (Na,Ce)2Ce(PO4)2 ⋅ xH2O, with Mixed Cerium Oxidation States

AbstractA previously unknown double ceric sodium phosphate hydrate Na1.97Ce1.03(PO4)2 ⋅ xH2O containing both ceric and cerous cations was obtained by the hydrothermal treatment of amorphous ceric phosphate mixed with a sodium hydroxide aqueous solution. The presence of Ce3+ in the structure was proved by HERFD‐XANES and ESR spectroscopy. Iterative transformation factor analysis of HERFD‐XANES data allowed estimating the content of Ce3+ as 10 % of the total cerium. Water content of x=0.55 has been determined by thermogravimetric analysis combined with mass‐spectrometry data. The structure of the compound was solved from powder X‐ray diffraction data (S.G. P21/c a=6.9441(2) Å, b=11.6805(3) Å, c=9.3434(3) Å, β=111.6827(18)°). The new ceric sodium phosphate hydrate has a tunnel structure, where Ce3+ cations most likely partially occupy Na+ positions. The crystal structure of the novel compound has no direct analogues among the crystal structures of double tetravalent metal phosphates.

Studies on electromagnetic properties of lithium based ferrimagnetic spinel oxides prepared with different additives and microwave sintering

Soft ferrimagnetic spinel lithium based oxides were prepared with additives like V2O5 and Na2SiO3 and sintered with the efficient microwave sintering technique. Tetravalent metal ions substituents like Mn+4, Ti+4 were used to enhance the important properties like D. C. resistivity, saturation magnetization, permeability, hysteresis and dielectric behavior. The ferrites were sintered at different sintering temperatures viz., 900, 950 and 1000 °C for 10 min by microwave technique and by conventional technique at 1050 °C for 4h. X-ray diffraction (XRD) studied the structural behavior which confirmed the spinel characteristics, Scanning electron microscopy (SEM) and EDAX revealed the microstructural and elemental compositions respectively of the ferrites. The use of additives and the microwave sintering significantly influencing the microstructural behavior and subsequently on the electromagnetic properties could be observed. Studies of initial permeability and initial permeability loss found to remain nearly constant with change in frequency until at certain frequency they showed resonance behavior. The resonance frequency’s dependence on the microstructures of the ferrites could be observed. Temperature dependence behavior of the dielectric parameters and the B-H loop traced from torroidal samples of the ferrites were studied.

Antioxidant novel activities of curcumin complexes with Mg(II), Ca(II), Cu(II), Cr(III) and Se(IV) metal ions: synthesis and spectral studies

Curcumin (Cur) metal complexes of Mg(II), Ca(II), Cu(II), Cr(III), and Se(IV) were prepared and characterized using elemental analysis, molar conductance, IR, UV-spectra, 1H NMR, SEM, TEM, and X-ray diffraction. The very low values of molar conductance confirm that Cl- ions are absent inside or outside the chelation sphere confirming their non-electrolytic nature, while for Cr(III) Cur is high compared to other curcumin complexes, confirming that Cl- ions are inside the complexation sphere. Based on IR and electronic spectra, the Cur C=O group in enol form chelated to Mg(II), Ca(II), Cu(II), Cr(III), and tetravalent metal (Se). The surface morphology of the curcumin chelates showed an increase in particle size and irregular grains shaped with an elongated morphology. Transmission electron microscopy revealed that the Cur chelates have spherical black spots like shape with a particle size of 72.21-88.75 nm, 34.89-57.33 nm, and 80.71-100 nm for Cu(II), Zn(II), and Se(IV) Cur respectively. X–ray powder diffraction patterns for Cu(II) Cur complexes showed particle size within 70-90 nm; the antioxidant activities of Cur and its metal complexes were assessed. Results showed that the Cur complexes with Cr, Mg, Ca, Cu, or Se showed potent antioxidant activities. Further studies could evaluate the potency of these complexes to elevate the antioxidant defense system and enhance body functions against degenerative diseases, such as aging, Alzheimer's disease, and viral diseases.
 KEY WORDS: Curcumin, Mg/Cur, Cu/Cur, Se/Cur, Electronic spectra, Antioxidant, Oxidative stress
 Bull. Chem. Soc. Ethiop. 2024, 38(2), 347-363. 
 DOI: https://dx.doi.org/10.4314/bcse.v38i2.6

Simultaneous adsorption of anionic and cationic species on UiO-66 and MIL-125 MOFs: Mechanisms & selectivity

Metal-organic frameworks (MOFs) have attractive properties, including regular pore structure, high specific surface area, tunable surface properties, and abundant active sites. Such properties have boosted their recent development in many fields, including water treatment. In this study, MOFs composed of tetravalent metals (Ti4+ and Zr4+) and dicarboxylate linker (terephthalate – BDC) were modified using surface functionalization and/or pore structure through defect engineering to enhance adsorption properties. It has been shown that the Ti-containing materials (MIL-125) show a greater affinity for cationic species, while the Zr-containing samples (UiO-66) have a higher affinity for anionic species. Surface charge and electrostatic interactions could account for such a difference in adsorption properties. Zeta potential measurements showed that MIL-125 has a more negative surface charge for both non-functionalized and amino-functionalized versions, which favors the interaction with cationic molecules. On the other hand, UiO-66 has a more positive surface, which facilitates interactions with anionic molecules. Within each MOF family, the non-functionalized structures emerged as the best-performing materials. Specifically, MIL-125(H) and UiO-66(H)_5eq, with 5eq denoting the amount of H2O added during synthesis, showed superior performance. Furthermore, by performing simultaneous adsorption experiments with anionic and cationic contaminants, it was found that the adsorption of the anionic dye acid orange 7 (AO7) onto the UiO-66 framework is primarily based on specific interactions between the sulfonic group (-SO3-) within the AO7 molecule and the inorganic core Zr6O4(OH)4 of UiO-66. The interaction between MIL-125 and the cationic dye methylene blue (MB) was found to be more delocalized, based on electrostatic and π-π interactions between the benzene domains. Finally, except for MIL-125(H), all the tested MOFs showed high stability in water and in the adsorption process. The higher stability of UiO-66 over MIL-125 materials can be attributed to steric effects and lower metal electronegativity. Compared to MIL-125(H), the higher stability of MIL-125(NH2) is probably related to the formation of intramolecular hydrogen bonds.

An Insight into Halide Solid-State Electrolytes: Progress and Modification Strategies

Tremendous studies have been engaged in exploring the application of solid-state electrolytes (SSEs) as it provides opportunities for next-generation batteries with excellent safety and high energy density. Among the existing SSEs, newly developed halide SSEs have become a hot spot owing to their high ionic conductivity up to 1 mS cm −1 and their stability against high-voltage cathode. As a result, halide SSEs have been shown to be promising candidates for all-solid-state lithium batteries (ASSLBs). Here, we review the progress of halide SSEs and available modification strategies of halide SSE-based batteries. First, halide SSEs are divided into four different categories, including halide SSEs with divalent metal, trivalent metal, tetravalent metal, and non-metal central elements, to overview their progress in the studies of their ionic conductivity, crystal structure, conductive mechanism, and electrochemical properties. Then, based on their existing drawbacks, three sorts of modification strategies, classified as chemical doping, interfacial modification, and composite electrolytes, along with their impacts on halide SSE-based batteries, are summarized. Finally, some perspectives toward halide SSE research are put forward, which will help promote the development of halide SSE-based batteries.

Theoretical study of fructose adsorption and conversion to trioses on metal-organic frameworks.

The conversion of chemically modified biomass into more valuable chemicals has recently gained significant attention from industry. In this study, we investigate the adsorption of fructose and its conversion into two trioses, glyceraldehyde (GLA) and dihydroxyacetone (DHA), on metal-organic frameworks using density functional theory calculations. The reaction mechanism proceeds through two main steps: first, the opening of the fructose ring; second, the retro-aldol fragmentation, which is favored over intramolecular hydrogen shifts. The substitution of a tetravalent metal in the metal-organic framework leads to different adsorption strengths in the order Hf-NU-1000 > Zr-NU-1000 > Ti-NU-1000. The catalytic activities of Hf-NU-1000 and Zr-NU-1000 are found to be similar. Both are more active than Ti-NU1000, corresponding to their relative Lewis acidity. It was found that functionalization of the organic linkers of the Hf-NU-1000 MOF does not improve its catalytic activity. The catalytic activity follows the order Hf-MOF-808 > Hf-NU-1000 > Hf-UIO-66 when based on either the overall activation energy or the turnover frequency (TOF).

Structure and size of complete hydration shells of metal ions and inorganic anions in aqueous solution.

The structures of nine hydrated metal ions in aqueous solution have been redetermined by large angle X-ray scattering to obtain experimental data of better quality than those reported 40-50 years ago. Accurate M-OI and M-(OI-H)⋯OII distances and M-OI(H)⋯OII bond angles are reported for the hydrated magnesium(II), aluminium(III), manganese(II), iron(II), iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) ions; the subscripts I and II denote oxygen atoms in the first and second hydration sphere, respectively. Reported structures of hydrated metal ions in aqueous solution are summarized and evaluated with emphasis on a possible relationship between M-OI-OII bond angles and bonding character. Metal ions with high charge density have M-OI-OII bond angles close to 120°, indicative of a mainly electrostatic interaction with the oxygen atom in the water molecule in the first hydration shell. Metal ions forming bonds with a significant covalent contribution, as e.g. mercury(II) and tin(II), have M-OI-OII bond angles close to 109.5°. This implies that they bind to one of the free electron pairs in the water molecule. Comparison of M-O bond distances of hydrated metal ions in the solid state with one hydration shell, and in aqueous solution with in most cases at least two hydration shells, shows no significant differences. On the other hand, the X-O bond distance in hydrated oxoanions increases by ca. 0.02 Å in aqueous solution in comparison with the corresponding X-O distance in the solid state. A linear correlation is observed between volume, calculated from the van der Waals radius of the hydrated ion, and the ionic diffusion coefficient in aqueous solution. This correlation strongly indicates that monovalent metal ions, except lithium and silver(I), and singly-charged monovalent oxoanions have a single hydration shell. Divalent metal ions, bismuth(III) and the lanthanoid(III) and actinoid(III) ions have two hydration shells. Trivalent transition and tetravalent metal ions have two full hydration shells and portion of a third one. Doubly charged oxoanions have one well-defined hydration shell and an ill-defined second one.

Compositional Analysis of Metal(IV) Phosphate and Phosphonate Materials—Pitfalls and Best Practices

Metal(IV) phosphate and phosphonates materials have increasingly found their applications in water purification, heterogeneous catalysis, drug delivery, and proton-exchange membrane fuel cells. The strong linkage between tetravalent metal cations and phosphate/phosphonate groups offers a unique bottom-up design platform, resulting in chemically stable inorganics or hybrids. Task-specific physiochemical functionalities could be deposited by modifying the phosphate/phosphonate groups before the material synthesis. The high reactivity between the metal centre and the phosphorus-containing linker, on the other hand, often leads to obtaining unordered materials (amorphous solids or coordination polymers). The chemical composition of the prepared materials is a key parameter in guiding the synthetic approach and in governing their performances. This narrative review focuses on critically summarising the traditional and advanced analytical methods for probing the composition of these materials. The reader is introduced to and guided on the advances and restrictions of different analysis techniques when probing metal(IV) phosphates/phosphonates. Both solution-based and solid-state spectroscopic techniques are covered with a focus on understanding the quantity and the linkage status of the phosphorus-containing moieties. These techniques include atomic spectroscopy, mass spectroscopy, nuclear magnetic resonance spectroscopy, X-ray-based methods, and neutron activation analysis.

Theoretical insights into poly(ethylene terephthalate) glycolysis catalyzed by acid-base pairs in Zn-supported MOF-808 metal-organic framework

We study the polyethylene terephthalate (PET) glycolysis catalyzed by the Zn-supported MOF-808, employing density functional theory. A PET dimer connected with C − O linkages is modeled as a representative PET active region. Two reaction pathways are identified: concerted and stepwise. With the Zn Lewis acid and the terminal hydroxo Lewis base at the Zr node contribution, the stepwise pathway shows lower activation barriers, making it the preferred route. We consider the MOF-808 node influence, which stabilizes species along the reaction coordinates, especially transition states. We compare catalytic activity of different tetravalent metal centers of MOF-808, finding Zn-Hf-MOF808 ≥ Zn-Zr-MOF808 > Zn-Ti-MOF808.

Structure analysis and luminescence properties of red-emitting iodide scintillators with potassium-hexachloroplatinate(IV) type structure

Halide compounds with chemical formula A2MX6 (A: alkali metal or Tl, M: tetravalent metal, X: halogen) have previously been reported as intrinsic scintillators. However, some application fields e.g., utilizing waveguides, require novel scintillators with emission wavelengths longer than that of Cs2HfI6 as bright and red/infrared scintillators. Thus, in this study, cation-substituted Cs2HfI6 crystals (Rb2HfI6, K2HfI6, Cs2ZrI6, Rb2ZrI6, and K2ZrI6) were grown using the vertical Bridgman method, and their crystal structures were analyzed via single-crystal X-ray diffraction. The crystal structures of Cs2HfI6 and Cs2ZrI6 were determined to be cubic (space group: Fm3̅m), Rb2HfI6 and Rb2ZrI6 were tetragonal (space group: P4/mnc), and K2HfI6 and K2ZrI6 were monoclinic (space group P21/c). In addition, the emission spectra of Rb2HfI6, K2HfI6, Rb2ZrI6, and K2ZrI6 showed that their peaks exhibited a 25 nm red-shift in comparison with that of Cs2HfI6, whereas those of Cs2ZrI6 did not. For A2MI6 compounds, the emission was effectively determined by A-site cation substitution. Moreover, the pulse-height spectra were successfully measured for A2HfI6. The scintillation light outputs of Cs2HfI6, Rb2HfI6, and K2HfI6 were estimated to be approximately 60,000, 40,000, and 33,000 photons/MeV, respectively.

A Cationic Octanuclear Zirconium Peroxide Ring with Unusual Thermal Stability.

Studies about the reaction of ZrIV ions with peroxides and the properties of the resulting zirconium peroxide clusters are significant for understanding zirconium chemistry in the nuclear fuel cycle and the advancement of less explored Group IV metal oxo clusters. Herein, an octanuclear zirconium peroxide cluster, designated as Zr8, was synthesized and characterized by using multiple techniques. Crystallographic analysis revealed that Zr8 has a ringlike structure and unusual positive charges, while tetravalent metal oxo clusters are mostly neutral. In situ variable-temperature Raman spectra indicated that Zr8 has unexpected thermal stability, which may be related to the strong interaction between ZrIV ions and peroxide groups. Small-angle X-ray scattering data showed that Zr8 self-assembled in the reactant solution prior to crystallization. In short, Zr8 expands the limited family of zirconium peroxide clusters and enriches the properties of metal peroxides.

Ion-pairing extraction and their reaction modeling of anionic M-Cl species with cationic NTAamide(C6) extractant and comparison with density functional theory calculations

Solvent extraction is conducted using a total of 20 di-, tri-, and tetravalent metals, revealing high stability constants with Cl− and the N,N,N′,N′,N″,N″-hexahexyl-nitrilotriacetamide (NTAamide(C6)) extractant. The metals used here may behave as anions at high Cl− concentrations, and NTAamide(C6), which contains a tertiary N atom, is protonated under acidic conditions. Most of the metal ions in this study display higher distribution ratios (D(M)) from HCl than those from HNO3, although NO3− hardly forms metal-complexes, and exhibit 1:1 stoichiometries with NTAamide, based on the slopes of acid and metal extraction. The high D(M) may be due to ion-pair extraction based on the combination of cationic extractants and anionic metal-chloride ions. Following the experimental results, the association constants and distribution coefficients of the group 12 elements are calculated via ion-pair extraction modeling using density functional theory calculations, and the simulations of D yield calculated values with the same trend as that of the measured values. In the future, it will be possible to calculate the distribution ratio precisely by considering the size effect in the exosphere of metal and chloride ions and the HSAB rule.

Nucleation & growth of α-Ti(HPO4)2·H2O single-crystal and its structure determination from X-ray single–crystal data

α-titanium phosphate phase [α-Ti(HPO4)2·H2O; abbreviated as α-TiP] is a nanolayered metal phosphate with several industrial and recent biotechnological applications related to their nanolayered morphology and ion exchange capabilities. Structural wise, α-TiP is a tetravalent metal phosphate that tends to crystallize into microcrystalline powder. Here we report that the crystallization of single α-TiP crystals with suitable dimensions (>50 μm) for single-crystal X-ray diffraction could be effectuated using a prolonged hydrothermal treatment of a metallic titanium alloy (Ti–6Al–4V) in a highly concentrated phosphoric acid aqueous solution. Accordingly, the single-crystal X-ray diffraction analysis revealed the crystalline structure in a monoclinic space group, P21/c, with a = 8.6288(5) Å, b = 5.00546(17) Å, c = 19.1468(11) Å, and β = 127.555(9)°. Although the space group is the same crystallographic space group that was previously reported from the microcrystalline powder relying on powder X-ray diffraction (PXRD) and neutron powder diffraction, the obtained unit cell volume is slightly larger. Bulk of the obtained crystals were also subjected to detailed analyses using polarization optical microscopy (POM), scanning electron microscopy combined with energy dispersive X-ray microanalysis (SEM-EDX), Fourier transform Infrared Spectroscopy (FTIR) and thermal analysis (TG/SDTA). The single crystals are hexagonally shaped and exhibit the exact titanium to phosphorus ratio expected for α-TiP. The bulk sample PXRD pattern resembles perfectly that reported for the α-TiP polycrystalline powder with clearly sharper peaks. TGA-SDTA analysis revealed the expected thermal behaviour for α-TiP phase and demonstrated their higher thermal stability when compared to the polycrystalline powder.

Crystalline versus Amorphous: High-Performance Hafnium Phosphonate Framework for the Separation of Uranium and Transuranium Elements.

Metal phosphonate frameworks (MPFs) consisting of tetravalent metal ions and aryl-phosphonate ligands feature a large affinity for actinides and excellent stabilities in harsh aqueous environments. However, it remains elusive how the crystallinity of MPFs influences their performance in actinide separation. To this end, we prepared a new category of porous, ultrastable MPF with different crystallinities for uranyl and transuranium separation. The results demonstrated that crystalline MPF was generally a better adsorbent for uranyl than the amorphous counterpart and ranked as the top-performing one for uranyl and plutonium in strong acidic solutions. A plausible uranyl sequestration mechanism was unveiled by using powder X-ray diffraction in tandem with vibrational spectroscopy, thermogravimetry, and elemental analysis.