Cerium Cations Research Articles

Electrocaloric effect and pyroelectric energy harvesting in diffuse ferroelectric Ba(Ti1-xCex)O3 ceramics

In the present work Ba(Ti1-xCex)O3 ceramics are prepared through a standard solid-state sintering process. Crystal structures, dielectric properties, ferroelectric properties and electrocaloric effects are exactly studied. Ce4+ ions cannot entirely enter the position of Ti4+, so some impure phases are generated. The diffusivity of phase transition is strengthened by substituting Ti4+ with Ce4+ cations. The maximal pyroelectric coefficient decreases, and the extent of corresponding temperature deviating from the dielectric peak temperature to higher temperature increases with increasing the content of cerium cations. The adiabatic temperature change and isothermal entropy change display the same tendency as that of the pyroelectric coefficient. The Ba(Ti0.9Ce0.1)O3 ceramic shows the largest adiabatic temperature change of 0.41 K and the largest isothermal entropy change of 0.45 J/(kg·K) among the ceramics. Accordingly, the adiabatic temperature change responsivity is 0.090 × 10−6 K·m/V, and the isothermal entropy change responsivity is 0.100 × 10−6 J·m/(kg·K·V). For individual composition, the absolute value of pyroelectric coefficient decreases with increasing the magnitude of applied electric field, and the temperature of maximal pyroelectric coefficient deviates from the dielectric peak temperature shifts to higher temperature. Ba(Ti0.9Ce0.1)O3 ceramics show the largest pyroelectric energy density of 0.14 J/cm3 among all compositions.

Adsorption mechanism of alkyl hydroxamic acid onto bastnäsite: Fundamental steps toward rational collector design for rare earth elements

Rare earth element (REE) production is limited in part by inefficient strategies for beneficiation. Hydroxamic acid ligands are promising reagents for the selective flotation of bastnäsite [(Ce,La)FCO3], a major REE ore mineral, but the mechanism and energetics of adsorption are not understood, interfering with the design of new, more efficient reagents. Here, the adsorption of octyl hydroxamic acid onto bastnäsite was measured using a combination of experimental and computational methods. In-situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy revealed changes in the hydroxamate functional group vibrational frequencies, corresponding to chelation with cerium cations at the bastnäsite surface. The results indicate a monodentate chemisorption mechanism at low surface loading that changes to bidentate chemisorption at higher concentrations. This interpretation is supported by molecular vibrational frequency shifts calculated using density functional theory (DFT), and orientation of the hydrocarbon chain measured by sum frequency generation (SFG) vibrational spectroscopy. The binding enthalpies of octyl hydroxamic acid interacting with La and Ce-bastnäsite surfaces were measured using isothermal titration calorimetry (ITC) revealing a stronger coordinating ability with bastnäsite than with a common gangue mineral, calcite (CaCO3). Because octyl hydroxamate favors monodentate adsorption at low surface coverages, the relative chelating strength of metal ions could be a poor predictor for selectivity under monolayer adsorption conditions. At higher surface loadings, where the bidentate mode of adsorption is active, selectivity is likely to be limited by increased flotation of gangue ores.

Effect of Pr on the electrical and chemical properties of cerium oxide prepared by combustion method

AbstractNanoparticles of Ce1−xPrxO2 (X: 0.6 and 0.8), were synthesized by the combustion method using citric acid as chelating and fuel agent. The X‐ray diffraction patterns and Rietveld refinements confirm that samples shown as a single phase in a cubic fluorite structure, with an increase in the lattice parameter as a function of Pr concentration. The crystallite size domains obtained by the Scherrer formula, confirm values around 10 and 37 nm. The scanning electron microscopy images, show that the solids are composed of dense heterogeneous aggregates. The X‐ray photoelectron spectroscopy, reveals that oxides are composed of cerium and praseodymium cations in oxidation states 4+ and 3+ respectively. The TPR‐H2 profiles indicate that cerium and praseodymium cations present in the obtained systems are completely reduced to Ce3+ and Pr3+ at temperatures above 790°C. The impedance spectroscopy data at room temperature showed that the conduction processes for the two systems take place at the grain boundaries. The Ce0.2Pr0.8O2 system offer lower resistance, due to the high amount of Pr3+ ions inserted in the structure and the high amount of oxygen vacancies formed in the synthesis process.

Microcomposites of zirconium phosphonates with a conducting polymer, polyaniline: Preparation, spectroscopic study and humidity sensing

The microcomposites of a conducting polymer, polyaniline, with four layered zirconium phosphonates, viz. 4-sulfophenylphosphonate, 2-sulfoethylphosphonate, 4-carboxyphenylphosphonate, carboxymethylphosphonate, were prepared and characterized by wide-angle X-ray diffraction and FTIR and Raman spectroscopies. Aniline hydrochloride was proved to intercalate the hosts containing sulfonic group. The intercalation was not observed with the carboxyl-containing phosphonates. Two methods of aniline oxidation, using peroxydisulfate anion, cerium(IV) or iron(III) cations as aniline oxidants, were tested. FTIR and Raman spectra suggest that the intercalated aniline does not polymerize. Polyaniline grows on phosphonates during surface polymerization rather than to be generated as a free polymer in the bulk of reaction mixture. Conductivity varied from 10−9 S cm−1 to 10−3 S cm−1 depending on the way of preparation and the type of the phosphonate filler. The conductivity response to the ambient humidity strongly depends on the filler and suggests the possibility to apply these materials in humidity sensors.

Epoxy-polyamide nanocomposite coating with graphene oxide as cerium nanocontainer generating effective dual active/barrier corrosion protection

An epoxy-polyamide composite coating with dual active/barrier corrosion protection capabilities was formulated using graphene oxide (GO) as a gallery for storage and targeted release of cerium cation inhibitors by an ion exchange mechanism on the steel corrosion sites. The successful adsorption of cerium cations over the GO nanosheets was detected via SEM, TGA and Raman spectroscopy. The role of Ce-GO in the barrier properties and active inhibition was evidenced through EIS assessment of polymeric coatings with and without an artificial scratch. SEM/EDS analysis of the scratch region indicated formation of a protective layer resulting from release of Ce component from the nanocontainer.

Sigma bond activation of deuterium mediated by atomic cerium cations: Experiment and theory

Reaction of ground-state Ce+ (5d24f1) with deuterium in a reaction cell at a pressure of 1.5–4.0 Torr and temperatures ranging from approximately 265–515 K is studied. Rate constants for formation of CeD2+ are acquired and vary from approximately 2.8 × 10−14 to 2.1 × 10−13 cm3/s. A negative temperature dependence is observed for the measured rate constants, indicating the reaction becomes less efficient as the temperature increases, consistent with an exothermic reaction. Electronic structure calculations were performed using density functional theory (DFT) at the PBE0 level to characterize all reactant and product species as well as to generate potential energy surfaces (PESs) for the insertion reaction. This combination of experimental and theoretical results suggest that Ce+ inserts into the deuterium sigma bond in an overall exothermic and barrierless process.

Enhanced epoxy coating based on cerium loaded Na-montmorillonite as active anti-corrosive nanoreservoirs for corrosion protection of mild steel: Synthesis, characterization, and electrochemical behavior

In this study, Na-montmorillonite (MMT) was intercalated with the cerium cations. The Ce3+ cations intercalated sodium montmorillonite (Ce-MMT) nanoreservoirs were incorporated into the epoxy coating. The active inhibitive performance of the synthesized nanoreservoirs and their effect on the protective behavior of the epoxy coating was investigated in the present study. For this purpose, field emission scanning electron microscopy, Fourier transformation infrared spectroscopy, inductively coupled plasma optical emission spectroscopy and X-ray diffraction analyses were employed to characterize the synthesized nanoreservoirs. Characterization results showed that the Ce3+ cations successfully intercalated into the MMT structure. The active anti-corrosion performance of the Ce-MMT was proved by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, open circuit potential, and salt spray tests. In the electrolyte phase, the obtained results showed that the corrosion resistance of the steel samples significantly improved in the presence of the Ce-MMT extract and the observed corrosion efficiency was about 93%. Also, the results of surface study confirmed the subsequent effect of the active nanoreservoirs on the chemical composition and surface morphology of the steel samples. In the coating phase, the result of the EIS and salt spray tests confirmed the enhanced inhibitive behavior of the epoxy coating in the presence of the Ce-MMT nanoreservoirs.

Quantum-Chemical Modeling of the First Coordination Sphere of the Metal Cation in Monazite

A model of minimum size clusters in orthophosphates has been suggested. In the case of monazite, the cluster includes a cerium(III) cation with nine oxygen atoms of the first coordination sphere, from seven neighboring phosphate anions. Its charge consists of the cation charge QM and the charges of the oxygen atoms QO =–1 a. u. The results of quantum-chemical simulation assume the possibility of the Ce(III) cation substitution with the Th(III), Th(IV) and U(IV) actinide cations. Substitution with thorium is favorable over that with uranium.

Structure-activity relationship of nanostructured ceria for the catalytic generation of hydroxyl radicals.

Reactive oxygen species (ROS) are powerful oxidants generated in both biological systems and natural environments. Though enzyme-mimic activity and Fenton-like reactions have been postulated to explain how ceria nanoparticles and ROS are involved in the catalytic decomposition of hydrogen peroxide (H2O2), the corresponding reaction kinetics for this reaction have not yet been completely resolved. Here we present our investigation of the structure-activity relationship of ceria nanostructures for the generation of hydroxyl radicals through the catalytic decomposition of H2O2. Different nanostructured ceria including nanorods (NR), nanocubes (NC), and nanooctahedra (NO), together with commercial ceria, were examined to elucidate the relationship between the morphology and reaction kinetics. The initial relative production rates of hydroxyl radicals over different ceria nanostructures were determined using fluorescence measurements and were applied to obtain the apparent activation energy for their intrinsic activity comparisons. The activity trend of the order: ceria NR > ceria NC > ceria NO > commercial ceria was observed. This trend was rationalized and assessed using activity descriptive factors including the intensity ratio of Raman bands of vibration modes due to atomic defects, the percentage of surface Ce3+ content, and the average coordination number of oxygen anions surrounding each cerium cation in the ceria samples.

Cerium ion promotes the osteoclastogenesis through the induction of reactive oxygen species

Cerium and cerium containing materials have been drawing increasing attentions in industrial and biomedical applications in recent decades. The increased applications of cerium have also increased the risk of human body exposed to cerium ions. Due to its similar ionic radius to calcium(II), cerium(III) have found mainly deposited in the skeletal system. However, the effects of cerium(III) on the bone metabolism homeostasis remain poorly understood. In the present study, the effect of cerium(III) on the osteoclastogenesis which plays a pivotal role in bone metabolism homeostasis was investigated. Cerium(III) could enhance the expression and activity of NADPH oxidase1 (Nox1) leading to the elevation of intracellular reactive oxygen species (ROS) level. The augmentation of ROS level activated the RANKL dependent osteoclasts differentiation pathways resulted in the promotion of osteoclastogenesis, while anions associated with cerium(III) cation have no effects on the differentiation of osteoclasts. The cerium(III) activated osteoclasts exhibited enhanced bone resorption capability. These results provided fundamental information for understanding the potential effects of cerium(III) on the metabolism homeostasis of skeletal system which is of great reference value for future biomedical applications of cerium salts.

Corrosion Protection of AA2024-T3 by Cerium Malate and Cerium Malate-Doped Sol–Gel Coatings

Cerium malate (CeMal) was tested as a corrosion inhibitor for AA2024-T3 in this work. Corrosion inhibition on bare AA2024-T3 indicated that the inhibiting effect was a result of the synergistic effect of cerium cations and maleic anions. The corrosion of AA2024-T3 was stagnated by greatly reducing the corrosion current when CeMal was present in NaCl solutions. CeMal was adsorbed on the surface of AA2024-T3 forming a protective film in the initial stage. Then, cerium cations transformed to cerium oxide/hydroxides, precipitating on the cathode sites to inhibit the further corrosion. The electrochemical impedance spectra results of the sol–gel coatings proved that CeMal was an effective corrosion inhibitor in the sol–gel coatings to provide corrosion protection for AA2024-T3.

In situ oxidation and reduction of cerium dioxide nanoparticles studied by scanning transmission electron microscopy

Cerium dioxide nanocubes and truncated octahedra were reduced and oxidized in the scanning transmission electron microscope. The reduction process was stimulated by the electron beam and oxidation was supported by background gases in the microscope environment. High-angle annular dark field imaging is sensitive to local lattice distortions that arise as oxygen vacancies are created and cerium cations reduce enabling high spatial resolution characterization of this process with temporal resolution on the order of seconds. Such measurements enable us to differentiate and infer that the observed behavior between the nanocubes and truncated octahedra may be due to the difference in crystallographic termination of surfaces. In situ measurements taken with different partial pressures of oxygen reveal the cerium oxidation state and the dose rate threshold for the onset of beam reduction are influenced by the environment. Increasing oxygen partial pressure reduces the Ce3+ content and decreases susceptibility to electron beam driven reduction.

Progress in the extraction and separation of rare earths and related metals with novel extractants: A review

Rare earths (REs) play a key role in high-tech fields and the associated thorium is a vital element for nuclear energy. However, to be used in high-tech industry or nuclear energy, these elements must first be recovered from the deposits and purified. As solvent extraction is the main technology for the recovery and purification of the metals, the review mainly presents our recent works on the extraction and separation of tetravalent cerium cation by neutral α-aminophosphonates, the individual rare earth separation by α-aminophosphonic acids, and the continuous preparation of high-purity thorium. The extraction and separation of some other metals are also discussed.

Simultaneous NO Reduction and Hg0 Oxidation over La0.8Ce0.2MnO3 Perovskite Catalysts at Low Temperature

La1–xAxMn1–yByO3 (A = Ca, Sr and Ce, B = Cu, Co and Fe, x = 0/0.2, y = 0/0.2) perovskite catalysts were employed for simultaneous NO and Hg0 removal. The perovskite structure is beneficial for low temperature catalysis. The substitution of A-site cations with cerium (Ce) cations significantly improved the catalytic activity of perovskite catalyst. 90% NO conversion and 98% Hg0 oxidation was attained using La0.8Ce0.2MnO3 catalyst at 200 °C. Hg0 oxidation posed negligible effect on NO reduction. Compared to the N2 plus 4% O2 atmosphere, Hg0 oxidation was significantly facilitated by selective catalytic reduction atmosphere. The enhancement in Hg0 oxidation was probably attributed to NO2 originated from NO. Furthermore, a possible reaction mechanism was proposed, in which surface oxygen, Mn4+ and Ce4+ contributed to NO and Hg0 removal. Such knowledge provides useful information for the development of effective and economical NO and Hg0 removal technology for coal-fired power plants.

The Effect of Chromium Oxide on the Conductivity of Ce0.9Gd0.1O2, a Solid-Oxide Fuel Cell Electrolyte

To study the effect of chromium oxide on the electric properties of Ce0.9Gd0.1O2, a solid-oxide fuel cell electrolyte, two approaches were used: (a) the studying of electrochemical properties of the Ce0.9Gd0.1O2- electrolyte after the spontaneous adsorption of chromium-containing molecules from a gas phase and (b) the analyzing of transport properties of the Ce0.9Gd0.1O2-based chromium-containing compositions obtained by the mixing of solid-oxide electrolyte with chromium(III) oxide. It was found that the chromium reduction at the electrolyte surface dominates when chromium is adsorbed from gas phase. Both approaches allow concluding that the chromium presence in Ce0.9Gd0.1O2 deteriorates the electrolyte transport properties at temperatures above 735°С. This is caused by the chromium incorporation into the electrolyte’s fluorite structure, as well as surface microheterogeneity induced by the chromium presence at the Ce0.9Gd0.1O2 surface and the cerium and gadolinium cation redistribution between the grains’ bulk and surface. At intermediate temperatures (below 735°С) the electric conductivity of the Ce0.9Gd0.1O2-based chromium-containing composition exceeds that of the initial solid-oxide electrolyte, which can be due to changes in transport properties of the chromium-containing phases formed at the Ce0.9Gd0.1O2 surface and grain boundaries.

Phase Formation in Al2O3–ZrO2–CeO2 Nanopowders Modified with Calcium Cations

We have studied phase formation in calcium-modified Al2O3–ZrO2–CeO2 nanopowders during sol–gel synthesis. The results demonstrate that heat treatment of the nanopowders first leads to the formation of a zirconium dioxide-based solid solution stabilized with cerium cations. Raising the heat treatment temperature helps the crystallization of corundum, a stable phase of aluminum oxide, to reach completion. In the temperature range 1400–1550°C, we observe the formation of a second aluminum-containing phase: calcium cerium hexaaluminate consisting of long prismatic grains.

CHARGE TRANSPORT FEATURES IN THE COMPOSITE ANODES OF SOLID OXIDE FUEL CELLS: MICROSTRUCTURAL AND IN-SITU RAMAN SPECTROSCOPY ANALYSES

In this work, we carry out the high-resolution electron microscopy of microstructure of grains boundaries of anion and electronic conductors in composite Ni/YSZ anodes before and after study of the current–voltage characteristics of model SOFCs. We propose a mechanism of 2-stage reaction of hydrogen oxidation occurring in the vicinity of triplephase boundary of Ni/YSZ SOFC anodes. On the first stage, metallic nickel is oxidized to nickel oxide by oxygen anion coming from the solid electrolyte membrane. On the second one, hydrogen reduces nickel oxide to metallic nickel, and water is formed. Decrease of the Ni grains size in the vicinity of contact with anion conductor grains is shown to be the result of NiO nano-grains appearance and their consequent reduction to metallic Ni during SOFC operation. High-resolution electron microscopy analysis demonstrates the significant changes in microstructure of grains boundaries of anion and electronic conductors in composite Ni/YSZ anodes after application of load current to SOFC. Nano-sized NiO grains appear in near-boundary regions of Ni grains after current tests. Orientation alignment between YSZ and nano-sized NiO lattices is unambiguous evidence of epitaxial growth of nickel oxide at YSZ surface as on a substrate that is possible only as a result of oxygen anion transport from anion conductor YSZ to the metal surface during current passage through the solid oxide fuel cell. We study the chemical transformations in the electrochemical reaction zone in SOFC composite electrodes depending on the current density passing the SOFC by new “in-situ” Raman spectroscopy technique. Increase of the current passing is shown to lead to growth in the intensity of Raman peak connected with symmetric oscillations of CeO 2 group. We connect this result with the change of the cerium cations charge state from Ce 3+ to Ce 4+ and consider this to be direct proof of the charge transfer in composite anode via oxygen anion transfer.

Highly effective inhibition of mild steel corrosion in 3.5% NaCl solution by green Nettle leaves extract and synergistic effect of eco-friendly cerium nitrate additive: Experimental, MD simulation and QM investigations

The synergistic effects of eco-friendly cerium nitrate additive on the corrosion inhibition performance of green Nettle leaves extract were investigated on mild steel in 3.5% NaCl solution by electrochemical, surface characterization and theoretical molecular dynamics (MD) simulations and quantum mechanics (QM) methods. The effect of Nettle leaves extract: cerium nitrate ratio on the mild steel corrosion inhibition was studied. The electrochemical impedance spectroscopy (EIS) and polarization tests were applied to examine the corrosion inhibition properties. In addition, the adsorption process and the synergistic effects between Nettle leaves extract and cerium cations were theoretically evaluated by using MD simulations and QM computations based on density functional theory (DFT) approach. Surface characterization techniques namely field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were employed for studying the surface morphology and composition of the film deposited. The experimental results revealed that combination of Nettle leaves extract and cerium nitrate with ratio of 400ppm:400ppm resulted in the highest corrosion inhibition efficiency (about 95%) and a thick and nanostructure organic/inorganic film formation on mild steel based on the organic compounds of Nettle leaves extract, i.e., hystamine, serotonin and quercetin, and the cerium cations, namely histamine-Ce3+, serotonin-Ce3+ and quercetin-Ce3+. The mixture of Nettle leaves extract and cerium cations acted as a mixed type inhibitor with dominant effect on the anodic reactions restriction. Furthermore, the computational results obtained from MD simulations demonstrated the adsorption ability of organic-inorganic inhibitors onto steel substrate, implying their inhibition effects in agreement with experimental observations.

Structural Role of Cerium Oxide in Lead Silicate Glasses and Glass Ceramics

Silicate glasses and glass ceramics in the system CeO2-PbO-SiO2 have been studied as a function of the structure factors R and K. The latter two factors are defined as: R = (CeO2 + PbO)/SiO2 and K = (SiO2/CeO2) molar ratios. In this glass, PbO is fixed at 50 mol% and CeO2 increases at the expense of SiO2. NMR investigations have revealed that increasing R which is accompanied with decreasing K leads to reasonable decrease in the shielding of silicon atoms. The chemical shift (δ) showed an increasing behavior due to increasing non-bridging oxygen atoms (NBO) in silicate network. It is evidenced that NBO in cerium free glass is much lower than that of glasses containing CeO2. Increasing R is clearly leading to higher chemical shift and higher NBO. This reflects that CeO2 has an effective structural role, since it would be consumed in all cases as an intermediate oxide. The main portions from CeO2 and PbO inter as glass modifiers which are consumed to form NBO atoms. A limited portion of CeO2 acts as glass former which consumed to form tetrahedral cerium containing NBO due to modification by PbO as a modifier oxide. Increasing R = [(CeO2 + PbO)/SiO2] from 1 to 2.34 leads to a frequent increase of NBO in the average glass network. FTIR spectroscopy of the glasses showed a clear shift of the main absorbance peak toward the low wavenumber with increasing R which confirms the increasing silicate units containing NBO atoms. XRD of the investigated materials revealed the presence of some nanostructures from cerium silicate crystalline phases. Formation of separated phases containing micro clusters is found to depend on NBO concentration, since NBO can facilitate process of phase separation. Majority of modifier are consumed to form NBO in the glass network and the rest are aggregated or separated to form silicate phase riches with cerium cations. In such case, some of silicon atoms are electrically compensated with both Pb and Ce cations.

Modified hierarchical birnessite-type manganese oxide nanomaterials for CO catalytic oxidation

Hierarchical birnessite-type manganese oxide catalysts modified by transition metal (cobalt, cerium, copper, and nickel) cations were synthesized via a facile hydrothermal reaction.