Meet the Cerium(IV) Phosphate Sisters: CeIV(OH)PO4 and CeIV2O(PO4)2

Yapryntsev A.D., Baranchikov A.E., Ivanov V.K.

The review summarizes the data on the chemical composition, crystal structure and functional properties of layered rare-earth hydroxides (LRHs), a new family of anion-exchangeable inorganic compounds. Comprehensive information is given on methods for the synthesis of LRHs including hydrothermal and hydrothermal-microwave treatment. Particular attention is paid to the methods of chemical design of hybrid functional materials based on LRHs. Prospects for fabrication of phosphors, heterogeneous catalysts and biomedical materials based on LRHs are analyzed. The bibliography includes 295 references.

Il’in E.G., Parshakov A.S., Yarzhemsky V.G., Ugolkova E.A., Goyeva L.V., Privalov V.I.

The first complexes of cerium tetrafluoride in solutions have been studied by 19F NMR and IR spectroscopy. The temperature dependence of the 19F NMR spectra has been explored, and conclusion has been made that dynamic equilibrium between the molecular adduct and singly charged ionic forms, including geometric isomers, exists in solution. The statistical probability for the formation of [CeF4(dmso)4] stereoisomers of square antiprism configuration has been calculated, and their assignment to possible stereoisomers have been made on the basis of relative intensities of the 19F NMR signals. Quantum-chemical calculations of the structure of one of the possible isomers have been performed for the [CeF4(dmso)4] molecular adduct, [CeF3(dmso)5]+ cation, and [CeF5(dmso)3]– anion to show their thermodynamic stability.

Steciuk G., Ghazisaeed S., Kiefer B., Plášil J.

The crystal structure of the U(iv)-phosphate mineral vyacheslavite has been solved from precession electron diffraction tomography (PEDT) data from the natural nano-crystal and further refined using density-functional theory (DFT) calculations. Vyacheslavite is orthorhombic, with the space group Cmca, with a ≈ 6.96 Å, b ≈ 9.07 Å and c ≈ 12.27 Å, V ≈ 775 Å3 (obtained from PEDT data at 100 K), Z = 8. Its structure is a complex heteropolyhedral framework consisting of sheets of UO7(OH) and PO4 polyhedra, running parallel to (001), interconnected by additional PO4 polyhedra. There is an (OH) group associated with the U(iv) polyhedron. The question of H2O presence within the small cavities of the framework has been addressed by the DFT calculations, which have proved that vyacheslavite does not contain any significant amount of H2O at room temperature.

Shekunova T.O., Istomin S.Y., Mironov A.V., Baranchikov A.E., Yapryntsev A.D., Galstyan A.A., Simonenko N.P., Gippius A.A., Zhurenko S.V., Shatalova T.B., Skogareva L.S., Ivanov V.K.

Hydrothermal crystallization pathways of amorphous ceric phosphate gels were found to be determined by the ammonia concentration in a reaction medium. This allows for highly selective hydrothermal synthesis of various finely crystalline ceric phosphates, including Ce(PO4)(HPO4)0.5(H2O)0.5, (NH4)2Ce(PO4)2(H2O), and previously unknown NH4Ce2(PO4)3. The structure of the latter compound was solved from powder X‐ray diffraction data. It appeared to be isostructural to ammonium thorium phosphate, NH4Th2(PO4)3; in this crystal structure, large channels (5.07 × 3.79 Å) located along the c‐axis are occupied by NH4+ ions.

Marsac R., Réal F., Banik N.L., Pédrot M., Pourret O., Vallet V.

The prediction of cerium (Ce) aqueous speciation is relevant in many research fields. Indeed, Ce compounds are used for many industrial applications, which may require the control of Ce aqueous chemistry for their synthesis. The aquatic geochemistry of Ce is also of interest. Due to its growing industrial use and its release into the environment, Ce is now considered as an emerging contaminant. Cerium is also used as a proxy of (paleo)redox conditions due to the Ce(iv)/Ce(iii) redox transition. Finally, Ce(iv) is often presented as a relevant analogue of tetravalent actinides (An(iv)). In the present study, quantum chemical calculations were conducted to highlight the similarities between the structures of Ce(iv) and tetravalent actinide (An(iv); An = Th, Pa, U, Np, Pu) aqua-ions, especially Pu(iv). The current knowledge of An(iv) hydrolysis, solubility and colloid formation in water was briefly reviewed but important discrepancies were observed in the available data for Ce(iv). Therefore, new estimations of the hydrolysis constants of Ce(iv) and the solubility of Ce(iv)-(hydr)oxides are proposed, by analogy with Pu(iv). By plotting pH-Eh (Pourbaix) diagrams, we showed that the pH values corresponding to the onset of Ce(iv) species formation (i.e. Ce(iv)-(hydr)oxide or dissolved Ce(iv)) agreed with various experimental results. Although further experimental studies are required to obtain a more accurate thermodynamic database, the present work might yet help to predict more accurately the Ce chemical behavior in aqueous solution.

Skogareva L.S., Shekunova T.O., Baranchikov A.E., Yapryntsev A.D., Sadovnikov A.A., Ryumin M.A., Minaeva N.A., Ivanov V.K.

It has been proposed to conduct the synthesis of cerium(III) orthophosphates by reacting cerium(IV) compounds with hydrogen peroxide in the presence of concentrated orthophosphoric acid at ambient temperature. It has been shown that the reaction of H2O2 with CeO2 suspensions in H3PO4 medium produces CePO4 · xH2O (rhabdophane structure), while that with CeO2 solutions in concentrated H3PO4 results in CePO4 (monazite structure).

Plakhova T.V., Romanchuk A.Y., Yakunin S.N., Dumas T., Demir S., Wang S., Minasian S.G., Shuh D.K., Tyliszczak T., Shiryaev A.A., Egorov A.V., Ivanov V.K., Kalmykov S.N.

Ultrafine 5 nm ceria isotropic nanoparticles were prepared using the rapid chemical precipitation approach from cerium(III) nitrate and ammonium hydroxide aqueous solutions. The as-prepared nanoparticles were shown to contain predominantly Ce(IV) species. The solubility of nanocrystalline CeO2 at several pH values was determined using ICP-MS and radioactive tracer methods. Phase composition of the ceria samples remained unchanged upon partial dissolution, while the shape of the particles changed dramatically, yielding nanorods under neutral pH conditions. According to X-ray absorption spectroscopy investigation of the supernatant, Ce(III) was the main cerium species in solution at pH < 4. Based on the results obtained, a reductive dissolution model was used for data interpretation. According to this model, the solubility product for ceria nanoparticles was determined to be log Ksp = −59.3 ± 0.3 in 0.01 M NaClO4. Taken together, our results show that the pH dependence of ceria anti- and pro-oxidant activit...

Bevara S., Achary S.N., Patwe S.J., Sinha A.K., Tyagi A.K.

In this manuscript we report crystal structure of a new complex binary phosphate K2Ce(4+)(PO4)2 in K2O-P2O5-CeO2 system prepared by solid state reaction at moderate temperature conditions. The prepared material was characterized by powder X-ray diffraction using lab source and synchrotron radiation as well as thermal analyses, Raman scattering, FTIR, and X-ray photoelectron spectroscopic studies. The crystal structure of the compound has been determined from powder XRD data by ab initio structure solution in direct space followed by Rietveld refinements. K2Ce(PO4)2 crystallizes in a monoclinic (P21/n) lattice with unit cell parameters: a = 9.1060(4), b = 10.8160(5), c = 7.6263(4) Å, β = 111.155(2)°, V = 700.50(6) Å(3). The unit cell contains two distinguishable PO4 tetrahedra and one CeO8 distorted square anti-prism. Raman spectroscopy confirmed the presence of isolated PO4(3-) groups in the structure. These PO4 tetrahedra are connected to one CeO8 polyhedra by sharing one edge and three other CeO8 polyhedra by sharing corners to form the three dimensional structure and empty channels parallel to a-axis. The channels are occupied by two crystallographically distinguishable K(+) ions which maintain the charge neutrality. Contrast to the earlier reported composition K4Ce2P4O15, this study revealed the composition in actual is K4Ce2P4O16 with Ce in 4+ oxidation state and is also supported by X-ray photoelectron spectroscopic and X-ray absorption near edge structure studies. Differential scanning calorimetric studies revealed a structural transition around 525 °C which reverts on cooling with a large thermal hysteresis. At higher temperature it undergoes a loss of oxygen atom and subsequently loss of phosphorus as P2O5. These thermal effects are also supported by in situ high temperature XRD studies. Finally the crystal chemistry of complex phosphates with tetravalent cations is also discussed.

Voncken J.H.

This chapter discusses the chemical and physical properties of the lanthanides, some of which are in a certain way peculiar. It discusses the oxidation states of the REE, and the phenomenon called the lanthanide contraction (meaning that the atomic radius decreases with increasing atomic number in the series lanthanum–lutetium). It lists the isotopes known per element, and explains the radioactivity of promethium, the only element of the rare earths that has only radioactive isotopes and no stable isotopes. Magnetism and luminescence also are discussed.

Xu D., Zhang Y., Zhang D., Yang S.

In this paper, Gd(OH)3 microcrystals (MCs), with hierarchical dumbbell-like structures, were prepared via a one-step hydrothermal route using KOH as the alkaline source and ethylenediaminetetraacetic acid as the chelating reagent. XRD patterns and SEM images showed the typical hexagonal phase and the three-dimensional micro-dumbbell structure with an average length of 9 μm and diameter of 7 μm. The time dependent morphogenesis, the growth kinetic mechanism and the intrinsic electric field were exploited to demonstrate the formation mechanism of the Gd(OH)3 micro-dumbbell hierarchical architectures. Gd2O3 hierarchical MCs and their lanthanide-doped counterparts could also be obtained via heat treatment. Gd2O3:Yb3+/Er3+ hierarchical MCs exhibited relatively pure visible emission under near-infrared (980 nm) and violet (379.4 nm) excitation. Besides, NIR emission from Yb3+ 2F5/2 and Er3+ 4I13/2 was also found, which may be of particular interest for telecommunications applications. The possible energy transfer mechanisms were discussed. Moreover, Gd2O3 samples also have considerable magnetic mass susceptibility with a value of 1.321 × 10−4 emu g−1 Oe−1 by magnetic property studies. This work provides another path for preparing Gd2O3 hierarchical MCs.

Behrsing T., Deacon G.B., Junk P.C.

The chemistry of rare earths is fundamental to an understanding of the role of rare earths as corrosion inhibitors and to the preparation of effective rare earth-containing inhibitors. This chapter defines rare earth elements and their place in the Periodic Table, including electronic configurations, oxidation states and the lanthanoid contraction, their discovery, location and abundance, and their uses other than as corrosion inhibitors. A major section is devoted to the general chemistry of rare earths elements, oxides, hydroxides, salts and coordination compounds, and includes a discussion of their separation together with a brief account of their spectra and magnetic properties. A further section deals with rare earth carboxylate complexes as these are promising inhibitors. Their synthesis and structures are described together with attempts at modelling their behaviour on iron (steel) surfaces. Ongoing problems are also considered.

Lai Y., Chang Y., Wong T., Tai W., Chang W., Lii K.

A uranium(IV) phosphate, Na10U2P6O24, was synthesized under hydrothermal conditions at 570 °C and 160 MPa and structurally characterized by single-crystal X-ray diffraction. The valence state of uranium was established by UV-vis and U 4f X-ray photoelectron spectroscopy. The powder sample has a second-harmonic-generation signal, confirming the absence of a center of symmetry in the structure. The structure contains UO8 snub-disphenoidal polyhedra that are linked to monophosphate tetrahedra by vertex and edge sharing such that a three-dimensional framework with intersecting 12-sided circular and rectangular channels is formed. All 10 sodium sites are situated inside the channels and are fully occupied. This is the first uranium(IV) phosphate synthesized under high-temperature, high-pressure hydrothermal conditions. The isotypic cerium(IV) phosphate, Na10Ce2P6O24, was also synthesized under the same hydrothermal conditions. It is the first structurally characterized Ce(IV) phosphate with a P/Ce ratio of 3. Crystal data of Na10U2P6O24: orthorhombic, P212121 (No. 19), a = 6.9289(3) Å, b = 16.1850(7) Å, c = 18.7285(7) Å, V = 2100.3(2) Å(3), Z = 4, R1 = 0.0304, and wR2 = 0.0522. Crystal data of Na10Ce2P6O24: orthorhombic, P2(1)2(1)2(1) (No. 19), a = 6.9375(14) Å, b = 16.215(3) Å, c = 18.765(4) Å, V = 2111.0(7) Å(3), Z = 4, R1 = 0.0202, and wR2 = 0.0529.

Momma K., Ikeda T., Belik A.A., Izumi F.

A computer program, Dysnomia, for the maximum-entropy method (MEM) has been tested for the evaluation and advancement of MEM-based pattern fitting (MPF). Dysnomia is a successor to PRIMA, which was the only program integrated with RIETAN-FP for MPF. Two types of MEM algorithms, i.e., 0th-order single-pixel approximation and a variant of the Cambridge algorithm, were implemented in Dysnomia in combination with a linear combination of the “generalized F constraints” and arbitrary weighting factors for them. Dysnomia excels PRIMA in computation speed, memory efficiency, and scalability owing to parallel processing and automatic switching of discrete Fourier transform and fast Fourier transform depending on sizes of grids and observed reflections. These features of Dysnomia were evaluated for MPF analyses from X-ray powder diffraction data of three different types of compounds: taurine, Cu2CO3(OH)2 (malachite), and Sr9In(PO4)7. Reliability indices in MPF analyses proved to have been improved by using multiple F constraints and weighting factors based on lattice-plane spacings, d, in comparison with those obtained with PRIMA.

Lundgren G.

The crystal structures of some oxide and hydroxide sulphates or chromates of tetravalent metal ions have been investigated by X-ray methods. The results show that the crystals contain polynuclear complexes, either infinite or finite. The following types of infinite complexes occur in the crystals: 1 chains [Me (OH2)2+]n in Th(OH)2CrO4H2O, Th(OH)2SO4, and U(OH)2SO4 2 chains [MeO2+]n (type I) in TiOSO4H2O 3 chains [MeO2+]n (type II) in CeOSO4H2O 4 two-dimensional, net-like complexes in zirconium chromates. Finite complexes, [Me6O4(OH)4]12+, are formed in the crystals of U6O4(OH)4(SO4)6 and Ce6O4(OH)4(SO4)6. In VOSO4(H2O)5, the metal ions do not seem to be joined by oxide or hydroxide bridges, but form mononuclear V-O6 octahedra.

McIntyre L.J., Jackson L.K., Fogg A.M.

A class of anion exchangeable layered hydroxides incorporating the smaller lanthanides within the layers has been synthesized via a hydrothermal route. These materials have the composition Ln2(OH)5NO3·xH2O (Ln = Y, Gd−Lu; x ≈ 1.5) and the potential to combine the properties of the lanthanides with the flexibility of intercalation hosts. Powder XRD data suggest that the crystallinity of the Gd phase is lower than that of the other materials, and reactions with the larger lanthanides lead to the formation of other phases, indicating a limiting cationic radius for these materials. The anion exchange capacity of these materials has been shown by facile reactions with a range of organic carboxylate and sulfonate anions, leading to the complete replacement of the nitrate anion.

Plakhova T.V., Vyshegorodtseva M.A., Seregina I.F., Svetogorov R.D., Trigub A.L., Kozlov D.A., Egorov A.V., Shaulskaya M.D., Tsymbarenko D.M., Romanchuk A.Y., Ivanov V.K., Kalmykov S.N.

Baranchikov A.E., Kozlova T.O., Istomin S.Y., Mironov A.V., Vasilchikova T.M., Gippius A.A., Plakhova T.V., Vasilyeva D.N., Ivanov V.K.

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.

Kozlova T.O., Khvorostinin E.Y., Rodionova A.A., Vasilyeva D.N., Baranchikov A.E., Ivanov V.K.

The sorption properties of amorphous cerium(IV) hydrogen phosphate and crystalline phases NH4Ce2(PO4)3, (NH4)2Ce(PO4)2·H2O, and Ce(OH)PO4 towards the 243Am(III), 232Th(IV), 237Np(V), and 233, 238U(VI) radionuclides were studied in aqueous media at pH 1, 4, 7, and 10 for 24 h. The highest degree of sorption (up to 100%) was found for amorphous cerium(IV) hydrogen phosphate. The pH dependences of radionuclide sorption for crystalline compounds were shown to be similar to one another: the highest sorption was observed at pH 7 (up to 100% for 243Am(III)), while the lowest values were observed for pH 10 and 1. An exception was provided by 237Np(V), the sorption of which was close to zero in the pH range of 1–7 and reached 60% at pH 10. Keeping amorphous and crystalline cerium(IV) phosphates in acid medium leads to quantitative desorption of all of the tested radionuclides within the first 5 h.

Kozlova T.O., Khvorostinin E.Y., Rodionova A.A., Vasilyeva D.N., Baranchikov A.E., Ivanov V.K.

The sorption properties of amorphous cerium(IV) hydrogen phosphate and crystalline phases NH4Ce2(PO4)3, (NH4)2Ce(PO4)2·H2O, and Ce(OH)PO4 towards the 243Am(III), 232Th(IV), 237Np(V), and 233, 238U(VI) radionuclides were studied in aqueous media at pH 1, 4, 7, and 10 for 24 h. The highest degree of sorption (up to 100%) was found for amorphous cerium(IV) hydrogen phosphate. The pH dependences of radionuclide sorption for crystalline compounds were shown to be similar to one another: the highest sorption was observed at pH 7 (up to 100% for 243Am(III)), while the lowest values were observed for pH 10 and 1. An exception was provided by 237Np(V), the sorption of which was close to zero in the pH range of 1–7 and reached 60% at pH 10. Keeping amorphous and crystalline cerium(IV) phosphates in acid medium leads to quantitative desorption of all of the tested radionuclides within the first 5 h.

Tronev I.V., Sheichenko E.D., Razvorotneva L.S., Trufanova E.A., Minakova P.V., Kozlova T.O., Baranchikov A.E., Ivanov V.K.

The possibility of preparation of crystalline double cerium(IV) phosphates (NH4)2Ce(PO4)2⋅H2O and NH4Ce2(PO4)3 under the conditions of microwave-assisted hydrothermal synthesis has been analyzed. It has been shown that these phosphates in a single-phase state can be obtained in the temperature range of 130–190°С with a synthesis duration of ≥5 min, while the phase composition of the synthesis products is determined by the molar ratio of ammonia and phosphoric acid in the reaction mixture. Short-term (5 min) low-temperature (130°С) hydrothermal synthesis under microwave heating leads to the preparation of (NH4)2Ce(PO4)2⋅H2O and NH4Ce2(PO4)3 with a particle size of ~70 and ~200 nm, respectively. At higher temperatures and treatment times (190°C and 24 h), the particle size of these phases increases to ~200 and ~500 nm, respectively. For the first time, the value of the optical band gap for (NH4)2Ce(PO4)2⋅H2O was determined to be 2.8 and 3.1 eV for indirect and direct transitions, respectively.

Tronev I.V., Sheichenko E.D., Razvorotneva L.S., Trufanova E.A., Minakova P.V., Kozlova T.O., Baranchikov A.E., Ivanov V.K.

The possibility of preparation of crystalline double cerium(IV) phosphates (NH4)2Ce(PO4)2⋅H2O and NH4Ce2(PO4)3 under the conditions of microwave-assisted hydrothermal synthesis has been analyzed. It has been shown that these phosphates in a single-phase state can be obtained in the temperature range of 130–190°С with a synthesis duration of ≥5 min, while the phase composition of the synthesis products is determined by the molar ratio of ammonia and phosphoric acid in the reaction mixture. Short-term (5 min) low-temperature (130°С) hydrothermal synthesis under microwave heating leads to the preparation of (NH4)2Ce(PO4)2⋅H2O and NH4Ce2(PO4)3 with a particle size of ~70 and ~200 nm, respectively. At higher temperatures and treatment times (190°C and 24 h), the particle size of these phases increases to ~200 and ~500 nm, respectively. For the first time, the value of the optical band gap for (NH4)2Ce(PO4)2⋅H2O was determined to be 2.8 and 3.1 eV for indirect and direct transitions, respectively.

Kozlova T.O., Vasil’eva D.N., Kozlov D.A., Teplonogova M.A., Birichevskaya K.V., Baranchikov A.E., Gavrikov A.V., Ivanov V.K.

Sarkar S., Sarkar S., Patra A.K.

Boat-, cuboid-, and dumbbell-shaped hierarchical morphology of cerium (IV) hydroxidophosphate materials were synthesized by simple hydrothermal method. Nature of base in the reaction medium had a significant impact on morphogical tuning of the materials.

Golubenko D.V., Manin A.D., Wang Y., Xu T., Yaroslavtsev A.B.

Recently, the selectivity of ion-exchange membranes and its control have been the subject of numerous fundamental and applied studies. This paper reports an enhanced monovalent anion selectivity of hybrid membrane based on the FujiFilm® Type I anion-exchange membrane and in situ synthesized cerium phosphate (CeP) with a gradient distribution over the membrane thickness. The Cl/SO 4 -selectivity coefficient ( P(Cl/SO 4 ) ) of hybrid membranes reached 6.2. The effect of modification on the Cl/SO 4 selectivity passed through a minimum as the total concentration of the external solution increased from 0.04 M to 1 M. For low concentration electrolytes, Cl/SO 4 -selectivity improving was attributed to partial neutralization of positive fixed charges by negative fixed charges of cerium phosphate, which causes an effective decrease of ion-exchange capacity and reduction of electrostatic selectivity factor favouring sulfate transport; for high concentration electrolytes, to the formation of narrow transport channel between the surface of the inorganic nanoparticle and the pore wall, which causes a decrease of sulfate transport due to the size sieving effect. The hybrid membranes and cerium phosphate were characterized using ATR FTIR and 31 P MAS NMR spectroscopy, XRD analysis and scanning electron microscopy with EDX microanalysis. • Monovalent ion selectivity of AEMs was improved by cerium phosphate modification. • Up to a 55% increase in the Cl/SO4-selectivity coefficient was observed. • Selectivity improvement depends on the external electrolyte concentration. • It is assumed that a change in the separation mechanism causes this dependence.

Kozlova T.O., Baranchikov A.E., Ivanov V.K.

The review analyzes the data on the composition, structure, and properties of amorphous and crystalline cerium(IV) orthophosphates published between 1882 and 2020. The review includes information on Ce(IV) complexation in aqueous solutions, formation conditions and characteristics of amorphous inorganic and organo-inorganic cerium(IV) hydrogen orthophosphates, and structural diversity of crystalline cerium(IV) orthophosphates. Formation conditions and structure of the closest chemical analogs of cerium(IV) orthophosphates, Group IV metal and actinide (thorium and uranium) orthophosphates, have been compared for the first time; the comparison provided a basis to assess the possibilities to prepare isostructural cerium(IV) compounds unknown to date.

Kozlova T.O., Baranchikov A.E., Birichevskaya K.V., Kozlov D.A., Simonenko N.P., Gavrikov A.V., Teplonogova M.A., Ivanov V.K.

Cerium(IV) hydrogen phosphate Ce(PO4)(HPO4)0.5(H2O)0.5 has been prepared by hydrothermal treatment of gels obtained by hydrolysis of cerium-containing phosphoric acid solutions. The obtained compound and the products of its heating in a wide temperature range have been analyzed by X-ray powder diffraction analysis, IR spectroscopy, mass spectrometry of gaseous thermolysis products, and scanning electron microscopy. Thermal decomposition of the compound at temperature up to 1200°С has been refined. In particular, it has been shown that crystalline cerium(III) phosphate (CePO4) forms upon heating of Ce(PO4)(HPO4)0.5(H2O)0.5 in air even at 600°C.