Thermodynamic properties of gaseous cerium phosphate studied by Knudsen effusion mass spectrometry

Gaseous CePO₂ has been identified by Knudsen effusion mass spectrometry during vaporization of CeO₂ and magnesium diphosphate from tungsten double, two‐temperature effusion cell. Structure and molecular parameters of gaseous cerium phosphate under study were determined using quantum chemical calculations. On the basis of equilibrium constants measured for gas‐phase reaction, standard formation enthalpy of CePO₂ was determined to be ?508 ± 41 kJ ? mol^?1 at the temperature 298 K.     

Nature of influence exerted by Na<Subscript>2</Subscript>SiF<Subscript>6</Subscript> on REE recovery from orthophosphoric acid solution in the course of CaSO<Subscript>4</Subscript>·0.5H<Subscript>2</Subscript>O crystallization

Chemical and X-ray phase analyses were used to study the influence exerted by Na₂SiF₆ on the isomorphic inclusion of cerium into the structure of CaSO₄?0.5H₂O precipitates formed from solutions of phosphoric acid hemihydrate (38 wt % P₂O₅). The poorly soluble suspensions of CaSO₄?0.5H₂O precipitates can serve as adsorbents for cerium compounds, with CaSO₄?0.5H₂O–NaCe(SO₄)₂?H₂O and CaSO₄?0.5H₂O–CePO₄?0.5H₂O solid solutions formed. The introduction of Na₂SiF₆ makes the sorption properties CaSO4?0.5H2O several times better because the Na₂SiF₆ phase is a source of sodium cations and creates the necessary Na: Ce ratio of 1: 1 for extracting cerium from the liquid phase into a precipitate in the form of a CaSO₄?0.5H₂O–[NaCe(SO₄)₂?H₂O + CePO₄?0.5H₂O] solid solution. Under the industrial conditions in which extraction phosphoric acid is manufactured, a similar isomorphous capture of rare-earth elements of the cerium group (La–Sm) may occur in joint precipitation of CaSO₄?0.5H₂O and Na₂SiF₆.     

The effect of cerium pre-treatment on the corrosion resistance of steel sheets

The steel samples have been coated with cerium layer by cathodic electrolytic deposition from the Ce(NO₃)₃·6H₂O solution in aqueous ethyleneglycol in the presence of hydrogen peroxide. The influence of the coating parameters (cathodic current density, pH, cerium concentration, hydrogen peroxide concentration, temperature, and treatment duration) on the surface properties; the optimum conditions of the formation of corrosion preventing coating have been elucidated. Hydrogen peroxide concentration and pH are the major factors influencing the deposition process. The corrosion resistance has been further enhanced after treatment with Na₃PO₄·12H₂O solution. The cerium-coated samples have been subsequently coated by cathodic electrostatic deposition from the colloidal solution of the paint. The coated materials have been subjected to mechanical testing (hardness, impact, cross cut, bending, and cupping tests), and their structure has been visualized by electron microscopy. The cerium coating has been found to improve the steel corrosion resistance by 15%.     

Novel water based cerium acetate precursor solution for the deposition of epitaxial cerium oxide films as HTSC buffers

A novel water based precursor solution using ethylenediaminetetraacetic acid (H₄EDTA) as a complexant and acetic acid and ethylenediamine (EDA) as additional components to obtain CeO₂ buffer layers on Ni (5%W) tapes is described in detail. The influence of complexation behavior in the formation of transparent and homogenous sols and gels by the combination of cerium acetate, acetic acid and H₄EDTA has been studied. The optimal growth conditions for cerium oxide were Ar-5% H₂ gas processing atmosphere, solution concentration levels of 0.2–0.4 M, a dwell time of 60 min at 900 °C and 5–30 min at 1,050 °C. X-ray diffraction, SEM, spectroscopic ellipsometry and pole figures were used to characterize the CeO₂ films. Highly textured CeO₂ layers were obtained.     

Underpotential surface reduction of mesoporous CeO<Subscript>2</Subscript> nanoparticle films

The formation of variable-thickness CeO₂ nanoparticle mesoporous films from a colloidal nanoparticle solution (approximately 1–3-nm-diameter CeO₂) is demonstrated using a layer-by-layer deposition process with small organic binder molecules such as cyclohexanehexacarboxylate and phytate. Film growth is characterised by scanning and transmission electron microscopies, X-ray scattering and quartz crystal microbalance techniques. The surface electrochemistry of CeO₂ films before and after calcination at 500 °C in air is investigated. A well-defined Ce(IV/III) redox process confined to the oxide surface is observed. Beyond a threshold potential, a new phosphate phase, presumably CePO₄, is formed during electrochemical reduction of CeO₂ in aqueous phosphate buffer solution. The voltammetric signal is sensitive to (1) thermal pre-treatment, (2) film thickness, (3) phosphate concentration and (4) pH. The reversible ‘underpotential reduction’ of CeO₂ is demonstrated at potentials positive of the threshold. A transition occurs from the reversible ‘underpotential region’ in which no phosphate phase is formed to the irreversible ‘overpotential region’ in which the formation of the cerium(III) phosphate phase is observed. The experimental results are rationalised based on surface reactivity and nucleation effects.     

A Detailed Insight into the Effects of Morphologies of Cerium Oxide on Fenton-like Reactions for Different Applications

As an exceptional Fenton-like reagent, cerium oxide (CeO₂) finds applications in biomedical science and organic pollutants treatment. The Fenton-like reaction catalyzed by CeO₂ typically encompasses two distinct processes: one resembling the classical Fenton reaction, wherein cerium (Ce³⁺) triggers the decomposition of hydrogen peroxide (H₂O₂) to yield reactive oxygen species (ROS), and the other involves the complexation of H₂O₂ on the Ce³⁺ surface, leading to the formation of peroxides. However, the influence of diverse CeO₂ morphologies on these two reaction pathways has not been comprehensively explored. In this study, CeO₂ exhibiting three typical morphologies, rods, cubes, and spheres, were prepared. The generation of ROS and peroxides was evaluated using the 3,3,5,5-tetramethylbenzidine (TMB) oxidation reaction and the reduction current of H₂O₂, respectively. Moreover, the impacts of pH variations and CeO₂/H₂O₂ concentrations on the production and conversion of these two reaction products were investigated. To corroborate the distinctions between the resultant products and their applicability, apoptosis assays and acid orange 7 (AO7) degradation analyses were performed. Notably, CeO₂ rods exhibited the highest proportion of Ce³⁺, predominantly engaging in complexation with H₂O₂ to foster peroxide formation, thereby facilitating the robust degradation of AO7. However, the generated peroxides appeared to occupy Ce³⁺ sites, thereby impeding the H₂O₂ decomposition process. Conversely, Ce³⁺ species on the surface of CeO₂ cubes were primarily involved in H₂O₂ decomposition, leading to heightened ROS production, and thus showcasing substantial potential for damaging A549 tumor cells. It is worth noting that the ability of these Ce³⁺ species to form peroxides through complexation with H₂O₂ was comparatively reduced. In summation, this study sheds light on the intricate interplay between distinct CeO₂ morphologies and their divergent impacts on Fenton-like reactions. These findings expand our comprehension of the influences on its reactivity of CeO₂ morphologies and open new insights for applications in diverse domains, from organic dye degradation to tumor therapy.     

A Study of the Solubility of Hydrated Orthophosphates of Yttrium,Lanthanum, Cerium,and Neodymium in Sulfuric-Phosphoric Acid Solutions at 20°C

The solubility of YPO₄ · 2H₂O, LaPO₄ · 1.5H₂O, CePO₄ · 1.5H₂O, and NdPO₄ · H₂O 10–60 wt % in sulfuric-phosphoric acid solutions containing 10–60 wt % H₂SO₄ and 13.8–41.4 H₃PO₄ was studied.     

Phase equilibria in the partial system CePO4−NaPO3−Ce(PO3)3

The ternary system CePO₄?NaPO₃?Ce(PO₃)₃ was investigated by differential thermal analysis, powder X-ray diffraction and microscopy in reflected light. Two double phosphates, NaCeP₂O₇ and NaCe(PO₃)₄, occur in this system. Both NaCeP₂O₇ and NaCe(PO₃)₄ melt incongruently, at 800 and 865°C, respectively. Two systems, NaCeP₂O₇?NaCe(PO₃)₄ and CePO₄?NaCe(PO₃)₄, were found to occur in this region. Their phase diagrams are presented.     

Electrosynthesis of vanadophosphate by anodic oxidation of vanadium in phosphoric acid solutions

Anodic polarisation of vanadium has been studied in aqueous H₃PO₄ solutions. In all solutions, from 1 to 14 M H₃PO₄, vanadium oxidation occurred at +0.2 V/SCE. A passivation behaviour was observed. In all the cases, the polarisation curve showed a current peak followed by a current plateau. The peak current was dependent upon phosphoric acid concentration. It decreased with the increase of acid concentration. Current oscillations occurred for vanadium anode for lowest concentrated solutions. All the electrochemical observations agreed with the formation of an anodic electrodeposit of vanadophosphate. The yellowish product isolated after controlled potential oxidation has been identified to VOPO₄,2H₂O.     

Rare earth phosphate powders RePO4·nH2O (Re=La,Ce or Y) II. Thermal behavior

The thermal behavior, thermostructural and morphological changes, of rare earth phosphate powders RePO₄·nH₂O (Re=La, Ce or Y) was investigated up to 1500°C using high temperature X-ray diffraction, FT-infrared and Raman spectroscopies and thermogravimetry coupled with differential thermal analysis. The hydration water of the compounds was zeolitic (for Re=La or Ce) or coordinated (for Re=Y) and was associated with a divariant or a monovariant equilibrium of dehydration, respectively. The high temperature anhydrous monoclinic phase LaPO₄ or CePO₄ formed irreversibly at about 750°C after the total dehydration of the hexagonal hydrated structure while the dehydration of the monoclinic YPO₄·2H₂O phase began from about 190°C with its simultaneous decomposition into tetragonal YPO₄. A polytrioxophosphate secondary minor phase Re(PO₃)₃ resulting from adsorbed H₃PO₄ was formed at 950°C and decomposed at 1350°C. The particle morphology did not change with the temperature but grain coalescence occurred below 1000°C.     

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

Two new cerium(IV) phosphates were obtained: cerium(IV) hydroxidophosphate, Ce(OH)PO₄, and cerium(IV) oxidophosphate, Ce₂O(PO₄)₂, which were shown to complement the classes of isostructural compounds M(OH)PO₄ and R₂O(PO₄)₂, where M=Th, U and R=Th, U, Np, Zr. Ce₂O(PO₄)₂ oxidophosphate is formed by elimination of H₂O from the crystal structure of Ce(OH)PO₄ during its thermal decomposition. The structures of Ce(OH)PO₄ and Ce₂O(PO₄)₂ are related to each other with the same Cmce space group and similar unit cell parameters (a=6.9691(3) Å, b=9.0655(4) Å, c=12.2214(4) Å, V=772.13(8) ų, Z=8; a=7.0220(4) Å, b=8.9894(5) Å, c=12.544(1) Å, V=791.8(1) ų, Z=4, respectively).     

Ceria/vinylpyridine polymer nanocomposite: an ecofriendly catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones

The three-component condensation of aldehydes, β-ketoesters and urea has been carried out in water using ceria (cerium oxide, CeO₂) nanoparticles supported on poly(4vp-co-dvb) as a catalyst for the preparation of 3,4-dihydropyrimidin-2(1H)-ones in good yields. The catalyst was recovered easily and reused without loss of its activity.     

New Structure Type among Octahydrated Rare‐Earth Sulfates, β‐Ce2(SO4)3·8H2O,and a new Ce2(SO4)3·4H2O Polymorph

Syntheses, crystal structures and thermal behavior of two new hydrated cerium(III) sulfates are reported, Ce₂(SO₄)₃·4H₂O ( I ) and β‐Ce₂(SO₄)₃·8H₂O ( II ), both forming three‐dimensional networks. Compound I crystallizes in the space group P2₁/n. There are two non‐equivalent cerium atoms in the structure of I , one nine‐ and one ten‐fold coordinated to oxygen atoms. The cerium polyhedra are edge sharing, forming helically propagating chains, held together by sulfate groups. The structure is compact, all the sulfate groups are edge‐sharing with cerium polyhedra and one third of the oxygen atoms, belonging to sulfate groups, are in the S–Oμ₃–Ce₂ bonding mode. Compound II constitutes a new structure type among the octahydrated rare‐earth sulfates which belongs to the space group Pn. Each cerium atom is in contact with nine oxygen atoms, these belong to four water molecules, three corner sharing and one edge sharing sulfate groups. The crystal structure is built up by layers of [Ce(H₂O)₄(SO₄)]_nⁿ⁺ held together by doubly edge sharing sulfate groups. The dehydration of II is a three step process, forming Ce₂(SO₄)₃·5H₂O, Ce₂(SO₄)₃·4H₂O and Ce₂(SO₄)₃, respectively. During the oxidative decomposition of the anhydrous form, Ce₂(SO₄)₃, into the final product CeO₂, small amount of CeO(SO₄) as an intermediate species was detected.     

Preparation of Ammonium Cerium Phosphate via Low-heating Solid State Reaction and Its Catalysis for Benzyl Acetate Synthesis

Ammonium cerium phosphate was prepared with (NH₄)₃PO₄·3H₂O and Ce(SO₄)₂·4H₂O as raw materials and PEG‐400 as surfactant via a solid state reaction at low‐heating temperature. The characterization result of XRD indicates that the molecular formula of the product was (NH₄)₂Ce(PO₄)₂·H₂O. The synthesis of benzyl acetate was carried out with H₂SO₄/ammonium cerium phosphate as catalyst, and uniform experimental design as well as data mining technology was applied to the experiments, in which the effect of the reaction time, the molar ratio of acid to alcohol and the amount of catalyst on the conversion yield of acetic acid were studied. When benzalcohol was 0.10 mol, under the optimal reaction conditions, i.e. reaction time of 174 min, 2.02 of molar ratio of acid to alcohol and 0.5 g of catalyst, the esterification rate of acetic acid was 97.9%. The ammonium cerium phosphate had potential for industry application since it not only was feasible and simple in synthesis technics, but also had good catalysis activity for the synthesis of benzyl acetate.     

Characteristics of oxygen exchange in phosphoric acid

The oxygen exchange between phosphoric acid and water at various temperatures and concentrations has been investigated in the presence and absence of K₂HPO₄. The minimum rate of exchange is observed for a solution concentration of 2–2.5 mole/l. It has been shown that in concentrated solutions of phosphoric acid the formation of H₄PO ₄ ⁺ is possible, and the true rate constant of the acid-catalytic conversion and the basicity constant of H₃PO₄ has been calculated. It has been found that in a solution where the mobility of the oxygen atom towards the anion increases, the value of the limiting current on the anodic dissolution of copper diminishes.     

Ce(H2O)(PO4)3/2(H3O)1/2(H2O)1/2, a second entry in the structural chemistry of cerium(IV) phosphates

A cerium(IV) phosphate has been prepared using precipitation methods and its structure has been solved by single crystal X-ray diffraction (R₁ = 0.0292 for 3092 reflections with I>2σ(I) and wR₂ = 0.0540). Ce(H₂O)(PO₄)_3/2(H₃O)_1/2(H₂O)_1/2 crystallises in the monoclinic space group C2/c (a = 15.7058(17) Å, b = 9.6261(9) Å, c = 10.1632(4) Å, ß = 121.623(7)°, and V = 1308.4 (2) Å³). Its structure is based on a negatively charged 3D framework, made of cerium atoms connected by PO₄ tetrahedra. There are two types of PO₄ units; one shares only corners with the cerium coordination polyhedra while the other one shares edges and corners. This structure also includes hydronium cations, to balance the framework charge, and water molecules. One special feature of this 3D framework is the formation of interconnected tunnels which extend along the c axis and contain the hydronium cations and the water molecules. This open framework and the presence of cationic species in the tunnels are in perfect agreement with the previously reported ion exchange properties.     

Corrosion protective ability of electrodeposited ceria layers

It has been ascertained that the electrochemically deposited thin films of cerium oxides, containing mainly CeO₂ and also some insignificant amount of Ce₂O₃, are acting as an effective cathodic coating, leading to restoration of the passive state of the studied stainless steel (OC 404) samples. This effect is associated with a strong shifting of the stationary corrosion potential of the steel in positive direction, moving over from potentials characteristic of corrosion in active state to potentials falling within the zone of passivity. In this respect, another basic purpose of the investigations was the elucidation of the mechanism of action of the cerium oxide film and in particular collecting experimental evidence for the supposition about the occurrence of an efficient depolarization reaction of CeO₂ reduction (resulting in a state of passivity—improved ability of self-passivation) instead of hydrogen depolarization reaction. For this purpose, we considered also the decrease in the surface concentration of ceria in the passive layer under the conditions of the actual corrosion process (self-dissolution) of the stainless steel by means of XPS, SEM, ICP-AES, and gravimetric analyses. A decrease in the surface concentration of CeO₂ (Ce⁴⁺) has been observed, which is known to be chemically inert in acidic media. The obtained results prove the occurrence of an effective cathodic process of Ce⁴⁺ (CeO₂) reduction into Ce³⁺ (soluble in acids Ce₂O₃ ) in the superficial oxide film.     

一维双链镉(Ⅱ)配合物[Cd(C5H5N)CH2C(OH)(PO3)(PO3H)·3H2O]n的合成与晶体结构

A new cadmium complex [Cd(C₅H₅N)CH₂C(OH)(PO₃)(PO₃H)·3H₂O]_n((C₅H₄N)CH₂C(OH)(PO₃H₂)₂=1-hydroxy-2-(2-pyridyl)ethylidene-1,1-diphosphonate acid) has been synthesized under hydrothermal conditions. Single crystal structure determination reveals that the compound has a ladder-like chain structure in which the edge-shared {CdO₆} octahedra are linked by {CPO₃} tetrahedra through corner-sharing. The chains of {Cd(C₅H₅N)CH₂C(OH)(PO₃)(PO₃H)}_n are linked by inter-chain hydrogen bonds, forming a supramolecular layer. CCDC: 722396.     

Synthesis and characterization of new strontium 4-carboxyphenylphosphonates

Several new strontium 4-carboxyphenylphosphonates, i.e., two modifications of Sr(HOOCC₆H₄PO₃H)₂, SrH(OOCC₆H₄PO₃)·H₂O, Sr₃(OOCC₆H₄PO₃)₂·4H₂O and Sr₃(OOCC₆H₄PO₃)₂·5.7H₂O were prepared and characterized by elemental analysis, thermogravimetry, X-ray powder diffraction and infrared spectroscopy. It was found that the compositions of these compounds depend on the acidity of the reaction medium. In addition, the presented compounds are interconvertible in dependence on pH. The position of the acid hydrogen atom in SrH(OOCC₆H₄PO₃)·H₂O was determined from the IR spectra of the studied compounds.The structure of the β modification of Sr(HOOCC₆H₄PO₃H)₂ was solved from its X-ray powder diffraction pattern using an ab initio method (the FOX program) with subsequent Rietveld refinement in the FULLPROF program. The compound is monoclinic, with the space group P2₁/c (No. 14), a=49.88(2), b=7.867(2), c=5.602(3) Å, β=128.68(2)°, and Z=4. It has a one-dimensional structure with an inorganic part built of SrO₈ distorted tetragonal antiprisms.     

Synthesis of CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> hydrosols via peptization at room temperature

A procedure is developed for the synthesis of concentrated CeO₂-ZrO₂ hydrosols based on the peptization of a precipitate obtained by the hydrolysis of a cerium nitrate-zirconium oxynitrate mixture. The time intervals and optimum [H⁺]/[Me ⁿ⁺] molar ratios giving rise the formation of CeO₂-ZrO₂ hydrosols stable to aggregation with a narrow particle size distribution are established. The size, shape, density, and phase composition of the hydrosol particles are determined.