Ceria

Cerium oxide (CeO2) has been prepared as a ceramic dielectric resonator by a conventional solid-state ceramic route. The sintered CeO2 has a high dielectric quality factor (Q×f), Q value of 10 000 at 6 GHz with a relative permittivity (ε′) of 23, and temperature coefficient of resonant frequency (τf of -53 ppm/°C. The Q value increases to 20 000 at 6 GHz when the CeO2 is doped with 1 mol% CaCO3. Higher levels of CaCO3 doping lowers the Q and ε′ values and simultaneously decreases τf. TiO2 doping decreases τf and slightly increases ε′, but deceases the Q value. The Q value of pure CeO2 increases to 105 000 at a frequency of 5.58 GHz when it is cooled to 30 K, whereas Q ≈ 85 000 at 5.48 GHz for 1-mol%-CaCO3-doped CeO2 at 30 K.

Design and development of highly active and durable oxygen reduction reaction (ORR) catalyst to replace Pt-and Pt-based materials are present challenges in fuel cell research including direct methanol fuel cells (DMFC). The methanol crossover and its subsequent oxidation at the cathode is another unwanted issue that reduces the efficiency of DMFC. Herein we report cobalt-doped ceria (Co-CeO 2) as a promising electrocatalyst with competent ORR kinetics mainly through a four-electron reduction pathway, and it surpasses Pt/C by a great margin in terms of stability and methanol tolerance. The Co-CeO 2 nanoparticles of diameter 4−7 nm were uniformly grown on reduced graphene oxide (rGO) by a facile single-step hydrothermal process. The as-synthesized Co-CeO 2 nanoparticles/rGO nanocomposites are further demonstrated as active energy storage materials in supercapacitors, underscoring the importance of the studied materials in renewable energy industries.

We report the first ever robocast (additive manufacturing/3D printing) sintered ceria scaffolds, and explore their use for the production of renewable fuels via solar thermochemical fuel production (STFP, water and carbon dioxide splitting using concentrated solar energy). CeO2 catalyst scaffolds were fabricated as 50 mm diameter discs (struts and voids ∼500 μm), sintered at 1450 °C, with specific surface area of 1.58 m2 g−1. These scaffolds have hierarchical porosity, consisting of the macroporous scaffold structure combined with nanoscale porosity within the ceria struts, with mesopores <75 Å and an average pore size of ∼4 nm, and microporosity <2 nm with a microporous surface area of 0.29 m2 g−1. The ceria grains were ≤500 nm in diameter after sintering. STFP testing was carried out via thermogravimetric analysis (TGA) with reduction between 1050–1400 °C under argon, and oxidation at 1050 °C with 50% CO2, gave rapid CO production during oxidation, with high peak CO production rates (0.436 μmol g−1 s−1, 0.586 ml g−1 min−1), for total CO yield of 78 μmol g−1 (1.747 ml g−1). 90% CO was obtained after just 10 min of oxidation, comparing well to reticulated ceria foams, this CO production rate being an order of magnitude greater than that for ceria powders when tested at similar temperatures.

Species-specific differences in the toxicity of manufactured nanoparticles (MNPs) have been reported, but the underlying mechanisms are unknown. We previously found that CeO2 NPs inhibited root elongation of head lettuce, whereas no toxic effect was observed on other plants (such as wheat, cucumber and radish). In this study, interactions between Lactuca plants and three types of CeO2 NPs (lab-synthesized 7 and 25nm CeO2 NPs, and a commercial CeO2 NPs) were investigated. It was found that CeO2 NPs were toxic to three kinds of Lactuca genus plants and different CeO2 NPs showed different degrees of toxicity. The results of X-ray absorption near edge fine structure indicate that small parts of CeO2 NPs were transformed from Ce(IV) to Ce(III) in roots of the plants that were treated with CeO2 NPs during the seed germination stage. But the high sensitivity of Lactuca plants to the released Ce3þ ions caused the species-specific phytotoxicity of CeO2 NPs. Differences in sizes and zeta potentials among three types of CeO2 NPs resulted in their different degrees of biotransformation which accounted for the discrepancy in the toxicity to Lactuca plants. This study is among the few, and may indeed the first, that addresses the relation between the physicochemical properties of nanoparticles and its species-specific phytotoxicity.

In this study, magnesia stabilized zirconia based nanocrystalline ceramics were produced through a polymer precursor route using gadolinium and boron. The powders were characterized during the various steps by structural and morphological techniques (FT-IR, XRD, and SEM). XRD results proved that a tetragonal phase is predominant for all samples with varying magnesium contents and no monoclinic zirconia solid solution appears. The crystallite sizes of the samples were calculated using Scherrer equation. The smallest crystallite size was obtained for the sample containing Zr/Mg/Ce/Gd/B ratio of 82/0/10/8/0. The lattice parameters were calculated for cubic, tetragonal, hexagonal, and orthorhombic structures. SEM results show all the samples have spherical grains. The average grain diameters were calculated for all the samples. The smallest average grain diameter was obtained for the sample containing Zr/Mg/Ce/Gd/B ratio of 82/0/10/8/0.

Atomic scale computer simulations, validated with experimental data, are used to uncover the factors responsible for defect-induced chemical expansion observed in non-stoichiometric oxides, exemplified by CeO2 and ZrO2. It is found that chemical expansion is the result of two competing processes: the formation of a vacancy (leading to a lattice contraction primarily due to electrostatic interactions) and the cation radius change (leading to a lattice expansion primarily due to steric effects). The chemical expansion coefficient is modeled as the summation of two terms that are proportional to the cation and oxygen radius change. This model introduces an empirical parameter, the vacancy radius, which can be reliably predicted from computer simulations, as well as from experimental data. This model is used to predict material compositions that minimize chemical expansion in fluorite structured solid oxide fuel cell electrolyte materials under typical operating conditions.

A 3.7% Rh/CeO 2 catalyst was prepared by wet impregnation of a low-surface-area ceria (23 m 2 g −1) with an aqueous solution of rhodium nitrate. This catalyst was reduced in a flow of H 2 at temperatures T R ranging from 200 to 1000 • C. The number of reduced centres of ceria in Rh/CeO 2 catalysts was measured by in situ reoxidation of these centres at T OX by pulses of water according to the following reaction: Reduced centre + H 2 O → Oxidised centre + H 2. The amount of hydrogen, Q H , evolved in the reaction allows us to calculate the number of reduced centres of the support since the noble metal would not be oxidised. Q H remains relatively small for T R not exceeding 500 • C, then increases rapidly to reach a pseudo-plateau at about 850 • C. At 900–1000 • C, the oxide composition would be close to CeO 1.75. Contrasting with the effect of T R , relatively small variations are recorded with T OX for a catalyst reduced at 850 • C: a maximum value of Q H is reached for T OX close to 850 • C, but 74% of this maximum yield in H 2 is already obtained when the reaction with steam is carried out at 100 • C. Oxidation by steam was also carried out on a catalyst prereduced in deuterium. It was shown that the hydrogen formed comes from the decomposition of water (H 2) and not from the storage of deuterium in the support during the reduction stage. In situ characterisation by XRD showed that there is a deep perturbation of the cubic structure at 850 • C, followed by a reduction of CeO 2 into Ce 2 O 3 (hexagonal) at higher temperatures (900–1000 • C). A treatment in water restores the cubic structure of CeO 2. The support having been previously reduced at 900 • C, there is virtually no sintering of the ceria crystallites upon these high-temperature treatments in hydrogen and steam.

The defect structure and ionic diffusion processes within the anion-deficient, fluorite structured system Ce1−xYxO2−x/2 have been investigated at high temperatures (873 K – 1073 K) as a function of dopant concentration, x, using a combination of neutron diffraction studies, impedance spectroscopy measurements of the ionic conductivity and molecular dynamics (MD) simulations using interionic potentials developed from ab initio calculations. Particular attention is paid to the short-range ion-ion correlations, with no strong evidence that the anion vacancies prefer, at high temperature, to reside in the vicinity of either cationic species. However, the vacancy-vacancy interactions play a more important role, with preferential ordering of vacancy pairs along the 111 directions, driven by their strong repulsion at closer distances, becoming dominant at high values of x. This effect explains the presence of a maximum in the ionic conductivity in the intermediate temperature range (873 K – 1073 K) as a function of increasing x. The wider implications of these conclusions for understanding the structure-property relationships within anion-deficient fluorite structured oxides are briefly discussed, with reference to complementary studies of yttria and/or scandiaium doped zirconia Zr1−xYxO2−x/2 and Zr1−xScxO2−x/2 published previously.

Water splitting by solar energy-driven two-step thermochemical cycles is a promising approach for large-scale production of renewable fuels (e.g. hydrogen). The key challenge is developing materials capable of withstanding the harsh environmental conditions and to ensure high reliability in use, particularly in terms of redox kinetics and better activity at low operation temperatures. In this work, we demonstrate that cork-templated ceria can significantly enhance the hydrogen production performance under solar irradiation heating. Three types of ceria morphologies were synthesised and investigated in two-step thermochemical redox cycles, namely ceria granules (ecoceramics) prepared from cork templates based on either a green water-based or an acetone solvent-based approach, as well as ceria foams replicated from polyurethane templates. These materials were cycled in a high-temperature indirectly-irradiated solar tubular reactor, heated via concentrated solar light, using a temperature-swing process. Samples were typically thermally reduced at 1400–1450 °C and subsequently re-oxidised with H2O between 950–1150 °C. The green synthesis ceria granules had up to 25% and 32% higher average H2 production yields than the acetone-based ecoceramics and replicated ceria foams, respectively. On average, H2 production rates for cork-templated ceria granules (1.3 ± 0.2 mL min−1 g−1) were up to ∼60% higher than for ceria foams (0.8 ± 0.3 mL min−1 g−1), indicating that the morphology of this three-dimensionally ordered macroporous (3-DOM) CeO2 improves the reaction kinetics. This is attributed to the smaller mean cell size of the cork-derived ecoceramic (25 μm) compared to that of the replicated ceria foam (575 μm), suggesting that their semi-closed wall cells enhanced reaction rates. The increase in reduction temperature from 1400 to 1450 °C resulted in the highest H2 production rate (1.6 mL min−1 g−1) reported so far for 3-DOM ceria. Neither loss in redox performance nor change in grain morphology was observed from the first to the last cycle. These findings show that cork-like structural features are key to engineering efficient materials for enhanced solar thermochemical fuel production.

FREE DOWNLOAD FROM: https://authors.elsevier.com/c/1XGfx7tB8766Tc              This work addresses the solar-driven thermochemical production of CO and O2 from two-step CO2-splitting cycles, using both ceria granules prepared from cork templates (CG) and ceria foams from polyurethane templates (CF). These materials were cycled in a high-temperature indirectly-irradiated solar tubular reactor using a temperature-swing process. Samples were typically reduced at 1400 °C using concentrated solar power as a heating source and subsequently oxidised with CO2 between 1000–1200 °C. On average, CO production yields for CG were two times higher than for CF, indicating that the morphology of this three-dimensionally ordered macroporous (3-DOM) CeO2 improves the reaction kinetics. Their performance stability was demonstrated by conducting 11 cycles under solar irradiation conditions. Slightly increasing the reduction temperature strongly enhanced the reduction extent, and thus the CO production yield (reaching about 0.2 mmol g−1 after reduction at 1450 °C in inert gas), while decreasing the oxidation temperature mainly improved the CO production rate (up to 1.43 μmol s−1 g−1 at 1000 °C). Characterisation of the 3-DOM structure, by means of XRD and SEM, provided insights into the reactivity behaviour of the developed materials. The pre-sintered ceria granules retained their structure after cycling. The fact that the mean cell size of CG is smaller (at least one order of magnitude) than that of CF suggests that its exposed surfaces enhanced reaction rates by a factor of two. Moreover, the maximum fuel production rate of CG was roughly three times greater than that reported previously for a ceria reticulated porous foam with dual-scale porosity.

We have applied the bond valence method to cerium oxides to determine the oxidation states of the Ce ion at the various site symmetries of the crystals. The crystals studied include cerium dioxide and the two sesquioxides along with some selected intermediate phases which are crystallographically well characterized. Our results indicate that cerium dioxide has a mixed-valence ground state with an f-electron population on the Ce site of 0.27 while both the A- and C-sesquioxides have a nearly pure f^1 configuration. The Ce sites in most of the intermediate oxides have non-integral valences. Furthermore, many of these valences are different from the values predicted from a naive consideration of the stoichiometric valence of the compound.

The stability of the electrode/electrolyte interface is a critical issue in solid-oxide cells working at high temperatures, affecting their durability. In this paper, we investigate the solid-state chemical mechanisms that occur at the interface between two electrolytes (Ce0.8Sm0.2O2, SDC, and BaCe0.9Y0.1O3, BCY) and a cathode material (La0.8Sr0.2MnO3, LSM) after prolonged thermal treatments. Following our previous work on the subject, we used X-ray microspectroscopy, a technique that probes the interface with submicrometric resolution combining microanalytical information with the chemical and structural information coming from space-resolved X-ray absorption spectroscopy. In LSM/BCY, the concentration profiles show striking reactive phenomena at the interface with a variety of micrometer-sized secondary phases: in particular, X-ray absorption spectra reveal at least three different chemical states for manganese (from +3 to +6). Also in LSM/SDC, a couple previously reported as chemically stable, we found...

Naturally occurring and sustainable materials can be used as a template to create biomimetic/biomorphic ceramics, known as Ecoceramics (environmentally conscious ceramics). In this work, cork was chosen as template to produce novel ceria (CeO2) ecoceramics, for applications in water splitting for H2 production via direct concentrated solar thermochemical fuel production (TCFP). The cork powder was pyrolised at 900 °C and the resulting carbon skeleton was infiltrated with an aqueous CeO2 precursor, and then heated at 1000 °C for 2 h to produce the ecoceramic. The cellular structure of the cork was maintained, with hexagonal cell dimensions of 20-30 μm in diameter, but the grains were nanoscale at ≤100 nm. XRD data confirmed that CeO2 was the only crystalline phase obtained. An important feature was that, while the rectangular side walls were maintained to hold the three-dimensionally ordered macroporous (3DOM) cellular cork structure, the rear hexagonal walls were pierced repeatedly through the structure, unlike in the original cork structure, which will allow gasses such as H2 to permeate well into the structure, greatly increasing the reactive area available for catalysis. The next step will be to test the capabilities of both the regular, porous 3DOM structure and the nanoscale grains for thermochemical water splitting to produce hydrogen under direct concentrated solar energy.

In this work, we demonstrate the mechanism by which electronic charge localization increases the chemical expansion coefficient in two model systems, CeO2-δ and BaCeO3-δ. Using Density Functional Theory calculations, we predict that this coefficient is increased by more than 70% when charge is fully localized, consistent with the observation that materials with smaller degree of charge localization have smaller chemical expansion coefficients. This finding has important consequences for devising materials with smaller chemical expansion coefficients and for the reliability of the widely-used Shannon’s ionic radii.

Two synthesis strategies for obtaining ceria-silica mesoporous carriers for drug delivery applications were explored. Core-shell and MCM-CeO2 composite materials were obtained by coating ceria nanoparticles with mesoporous silica and by one-step approach, respectively. Doxycycline was adsorbed onto the ceria-silica and MCM-41 silica carriers and the resulting hybrid samples and the inorganic supports were characterized by smalland wide-angle XRD, N2 adsorptiondesorption isotherms, FT-IR spectroscopy, and scanning electron microscopy. In vitro doxycycline release profiles were determined in phosphate buffer solution, pH 5.5, by UV-VIS spectroscopy. The MCM-CeO2 composite containing 10% ceria nanoparticles exhibited the slowest antibiotic release rate, being the best doxycycline delivery support.

Different lanthanide (Ln)-doped cerium oxides (Ce0.5Ln0.5O1.75, where Ln: Gd, La, Pr, Nd, Sm) were loaded with Cu (20 wt. %) and used as catalysts for the oxidation of ethyl acetate (EtOAc), a common volatile organic compound (VOC). For comparison, both Cu-free (Ce-Ln) and supported Cu (Cu/Ce-Ln) samples were characterized by N₂ adsorption at -196 °C, scanning/transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and temperature programmed reduction in H₂. The following activity sequence, in terms of EtOAc conversion, was found for bare supports: CeO₂ ≈ Ce0.5Pr0.5O1.75 &gt; Ce0.5Sm0.5O1.75 &gt; Ce0.5Gd0.5O1.75 &gt; Ce0.5Nd0.5O1.75 &gt; Ce0.5La0.5O1.75. Cu addition improved the catalytic performance, without affecting the activity order. The best catalytic performance was obtained for Cu/CeO₂ and Cu/Ce0.5Pr0.5O1.75 samples, both achieving complete EtOAc conversion below ca. 290 °C. A strong correlation was revealed...

Solar thermochemical conversion of H2O and captured CO2 is considered for the production of high-value solar fuels and CO2 valorization, using nonstoichiometric oxygen-exchange redox materials. This work aims to compare the thermochemical cycle performance of different ceria structures, including biomimetic cork-templated ceria (CTCe), ceria foams (CeF), and ceria bulk fiber boards (CeFB), to study the effect of the morphology on fuel production from two-step H2O and CO2 splitting via solar redox cycling. The considered materials underwent thermochemical cycles in a directly irradiated solar reactor under various operating conditions. Typically, a thermal reduction at 1400 °C under Ar at atmospheric pressure, using concentrated solar energy, was carried out followed by an oxidation step with H2O or CO2 between 800 and 1050 °C. The comparison of the fuel production rate and yield from the reactive materials highlighted the importance of the material thermal stability during cycling. CTCe and CeF showed good O2 and fuel production stability over repeated cycles, while CeFB exhibited a decrease of the production because of sintering and thermal gradient due to its low thermal conductivity. Biomimetic CTCe showed a higher fuel production rate compared to the other investigated materials, explained by the favorable microstructure of the cork-based ceramic. The morphology obtained from the cork structure led to the improvement of the redox activity, demonstrating the relevance of studying this material for thermochemical H2O and CO2 splitting cycles. In addition, the impact of the operating conditions was investigated. A decrease of the starting oxidation temperature, an increase of the CO2 molar fraction (lower CO/CO2 ratio), or a high total gas flow rate favoring gas product dilution had a beneficial impact on the CO (or H2) production rate.

Two synthesis strategies for obtaining ceria-silica mesoporous carriers for drug delivery applications were explored. Core-shell and MCM-CeO2 composite materials were obtained by coating ceria nanoparticles with mesoporous silica and by one-step approach, respectively. Doxycycline was adsorbed onto the ceria-silica and MCM-41 silica carriers and the resulting hybrid samples and the inorganic supports were characterized by smalland wide-angle XRD, N2 adsorptiondesorption isotherms, FT-IR spectroscopy, and scanning electron microscopy. In vitro doxycycline release profiles were determined in phosphate buffer solution, pH 5.5, by UV-VIS spectroscopy. The MCM-CeO2 composite containing 10% ceria nanoparticles exhibited the slowest antibiotic release rate, being the best doxycycline delivery support.

The chemical compatibility between electrolytes and electrodes is an extremely important aspect governing the overall impedance of solid-oxide cells. Because these devices work at elevated temperatures, they are especially prone to cation interdiffusion between the cell components, possibly resulting in secondary insulating phases. In this work, we applied X-ray microspectroscopy to study the interface between a samarium-doped ceria (SDC) electrolyte and lanthanum ferrite cathodes (La0.4Sr0.6Fe0.8Cu0.2O3 (LSFCu); La0.9Sr0.1Fe0.85Co0.15O3 (LSCF)), at a submicrometric level. This technique allows to combine the information about the diffusion profiles of cations on the scale of several micrometers, together with the chemical information coming from space-resolved X-ray absorption spectroscopy. In SDC-LSCF bilayers, we find that the prolonged thermal treatments at 1150 °C bring about the segregation of samarium and iron in micrometer-sized perovskite domains. In both SDC-LSCF and SDC-L...

The increasing chances of manufactured nanoparticles (NPs) being released into the environment highlight the importance of understanding their interactions with plants, which are the basis of ecosystems. In this study, the phytotoxicity of CeO2 NPs on asparagus lettuce was assessed. Lettuce seeds were treated with CeO2 NPs in a plant agar medium at a wide range of concentrations (0–2000 mg L−1) for 5 days. At high concentrations (≥500 mg L−1), CeO2 NPs altered the activity of superoxide dismutase (SOD), induced lipid peroxidation and cell membrane damage, and inhibited the root growth. The results of X-ray absorption near edge fine structure (XANES) indicate that part of the CeO2 NPs were transformed from Ce(IV) to Ce(III) in the roots. The released Ce3+ may account for the phytotoxicity of CeO2 NPs.

Experimental and theoretical investigations were performed to investigate the effect of water on optical properties of nanoceria as a function of Ce 3+ concentration. Theoretical studies based on density functional plane-wave calculations reveal that the indirect optical transitions in bare ceria nanoparticles are red-shifted with an increase in the concentration of Ce 3+. However, ceria nano-particles model with adsorbed water molecules show a blue shift in the indirect optical spectra under identical conditions. Direct optical transitions are almost independent of Ce 3+ concentration but show a pronounced blue shift in the aqueous environment relative to the bare nanoparticles. The theoretical study is consistent with our experimental observation in difference of shift behaviour in bare and aqueous suspended ceria nanoparticles. This change from red-to blue-shift in indirect optical transitions is associated with the polarization effect of water molecules on f-electron states.

Two synthesis strategies for obtaining ceria-silica mesoporous carriers for drug delivery applications were explored. Core-shell and MCM-CeO2 composite materials were obtained by coating ceria nanoparticles with mesoporous silica and by one-step approach, respectively. Doxycycline was adsorbed onto the ceria-silica and MCM-41 silica carriers and the resulting hybrid samples and the inorganic supports were characterized by small- and wide-angle XRD, N2 adsorptiondesorption
isotherms, FT-IR spectroscopy, and scanning electron microscopy. In vitro doxycycline release profiles were determined in phosphate buffer solution, pH 5.5, by UV-VIS spectroscopy. The MCM-CeO2 composite containing 10% ceria
nanoparticles exhibited the slowest antibiotic release rate, being the best doxycycline delivery support.

Ag@CeO2 nanocomposites were synthesized by a biogenic and green approach using electrochemically active biofilms (EABs) as a reducing tool. The as-synthesized Ag@CeO2 nanocomposites were characterized and used in antimicrobial, visible light photocatalytic and photoelectrode studies. The Ag@CeO2 nanocomposites showed effective and efficient bactericidal activities and survival test against Escherichia coli O157:H7, and Pseudomonas aeruginosa. The as-synthesized Ag@CeO2 nanocomposites also exhibited enhanced visible light photocatalytic degradation of 4-nitrophenol and methylene blue than pure CeO2. A photocatalytic investigation showed that the Ag@CeO2 nanocomposites possessed excellent visible light photocatalytic activities compared to pure CeO2. Electrochemical impedance spectroscopy and photocurrent measurements showed that the as-synthesized Ag@CeO2 nanocomposites exhibited excellent and enhanced responses to visible light irradiation. These results suggest that the AgNPs anchored at CeO2 induced visible light photoactivity by decreasing the recombination of photogenerated electrons and holes, and extending the response of pure CeO2 to visible light. Overall, as-synthesized Ag@CeO2 nanocomposites are smart materials that can be used for a range of applications, such as antimicrobial activity, visible light photocatalysis and photoelectrode.

Europium-doped ceria (EDC, Ce0.9Eu0.1O2−δ)/alkaline carbonate (LNC, (Li,Na)2CO3) composite ceramics prepared through a one-step citrate-based route were analyzed by powder X-ray diffraction, infrared and laser Raman spectroscopies as well as scanning and transmission electron microscopy. The electrochemical behavior of the electrolyte material was studied by impedance spectroscopy in air, CO2 and N2 + H2 (90/10 vol%, respectively) gas mixtures, in the temperature range 300–600 °C. The sub micrometric and even nanosized ceramic particles appeared as merged inside the mixed carbonates, with modest grain to grain necking. The EDC/LNC composite electrolytes showed a conductivity of 0.27 S cm−1 at 600 °C in air, amongst the best ever reported, exceeding the usual requirements for fuel cell applications.

Pure phase and europium doped ceria nanocrystals have been synthesized by a single step simple solvothermal process. Different spectroscopic, diffractive and microscopic techniques were used to determine the morphology, size, crystal structure and phase of all the samples. Electron energy loss spectroscopy (EELS) for elemental mapping confirmed that good solid solutions were formed and that the particles had a homogeneous distribution of europium. The defect chemistry was more complex than might be expected with the incorporation of each Eu3+ ion resulting in the production of an anion vacancy since the doping results in charge compensating (i.e. for Eu3+) anion vacancies as well as vacancies due to oxygen removal from the crystallite surface. Variations in nanoparticles dimension and lattice parameters were measured as a function of dopant concentrations and their variations explained. The band gap of the samples could be tailored by the doping. The doped samples were found to be luminescent due to the substitution of Ce4+ ions in the cubic symmetric lattice by the dopant ions. The thermal stability of the fluorescence properties was also investigated.

In this study, neodymia doped poly(vinyl) alcohol/zirconium–cerium acetate (PVA/Zr-Ce) nanofibers were prepared using the electrospinning technique, and then calcined at 800°C for 2 hours. For this purpose, PVA/Zr-Ce polymer solutions doped with different concentrations of neodymia were prepared using electrospinning technique, and then calcined and sintered at 800°C for 2 hours. The effect of neodymia doping was investigated in terms of solution properties, morphological changes and thermal characteristics. The fibers were characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and scanning electron microscope (SEM). The measurements showed that the conductivity, pH, viscosity, and surface tension of the hybrid polymer solutions have decreased with increasing Nd acetate content. The FT-IR spectra of the fibers were in good accordance with the literature. The average crystal size values for calcined and sintered samples which were obtained from precursor solutions were calculated. XRD analysis showed that the crystallite size was decreased with increasing Nd content. This result is verified by the calculation of the total areas of the peaks appeared in the XRD spectra. The very sharp and high intense peaks found in the diffraction patterns revealed the crystalline nature of the product. Moreover, the SEM micrograph of the fibers showed that the average fiber diameters decreased with increasing Nd content.

OPEN ACCESS - FREE ONLINE at https://doi.org/10.3389/fchem.2019.00601 : This review explores the advances in the synthesis of ceria materials with specific morphologies or porous macro-and microstructures for the solar-driven production of carbon monoxide (CO) from carbon dioxide (CO 2). As the demand for renewable energy and fuels continues to grow, there is a great deal of interest in solar thermochemical fuel production (STFP), with the use of concentrated solar light to power the splitting of carbon dioxide. This can be achieved in a two-step cycle, involving the reduction of CeO 2 at high temperatures, followed by oxidation at lower temperatures with CO 2 , splitting it to produce CO, driven by concentrated solar radiation obtained with concentrating solar technologies (CST) to provide the high reaction temperatures of typically up to 1,500 • C. Since cerium oxide was first explored as a solar-driven redox material in 2006, and to specifically split CO 2 in 2010, there has been an increasing interest in this material. The solar-to-fuel conversion efficiency is influenced by the material composition itself, but also by the material morphology that mostly determines the available surface area for solid/gas reactions (the material oxidation mechanism is mainly governed by surface reaction). The diffusion length and specific surface area affect, respectively, the reduction and oxidation steps. They both depend on the reactive material morphology that also substantially affects the reaction kinetics and heat and mass transport in the material. Accordingly, the main relevant options for materials shaping are summarized. We explore the effects of microstructure and porosity, and the exploitation of designed structures such as fibers, 3-DOM (three-dimensionally ordered macroporous) materials, reticulated and replicated foams, and the new area of biomimetic/biomorphous porous ceria redox materials produced from natural and sustainable templates such as wood or cork, also known as ecoceramics.

Strong shock wave interactions with ceramic material ceria (CeO 2) in presence of O 2 and N 2 gases were investigated using free piston driven shock tube (FPST). FPST is used to heat the test gas to very high temperature of about 6800–7700 K (estimated) at pressure of about 6.8–7.2 MPa for short duration (2–4 ms) behind the reflected shock wave. Ceria is subjected to super heating and cooling at the rate of about 10 6 K/s. Characterization of CeO 2 sample was done before and after exposure to shock heated test gases (O 2 and N 2). The surface composition, crystal structure, electronic structure and surface morphology of CeO 2 ceramic were examined using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). Results obtained from the experimental investigations show that CeO 2 can withstand high pressure accompanied by thermal shock without changing its crystal structure. Reducible CeO 2 releases lattice oxygen making it possible to shift between reduced and oxidized states upon the interaction with shock heated gas. Due to such reaction mechanism, CeO 2 ceramic undergoes nitrogen doping with decrease in lattice parameter. Investigations reveal that CeO 2 retains its crystal structure during strong shock interaction, even at elevated pressure.

In this study, a new method to synthesize neodymium doped ceria ceramic nanopowders by the electrospinning of the hybrid polymers solution of their composite precursor was put forward. Calcined and sintered nanopowders were characterized by FT-IR, XRD, BET, SEM, and AFM techniques. According to the XRD analysis, the obtained powders are single phase and independent of the dopant concentration in the range investigated. The crystallite sizes were calculated using Scherrer equation. Moreover, lattice parameters, dislocation densities and microstrain values were calculated. BET results show that the increase of the neodymium doped content decrease the surface area of the composite powders, confirming the highly ordered micro and mesostructure. SEM and AFM results show that the samples have spherical grains. According to the surface roughness measurements, the increase in the amount of neodymium and the decrease in the amount of cerium decreased the surface roughness.

In this study, a new method to synthesize neodymium doped ceria ceramic nanopowders by the electrospinning of the hybrid polymers solution of their composite precursor was put forward. Calcined and sintered nanopowders were characterized by FT-IR, XRD, BET, SEM, and AFM techniques. According to the XRD analysis, the obtained powders are single phase and independent of the dopant concentration in the range investigated. The crystallite sizes were calculated using Scherrer equation. Moreover, lattice parameters, dislocation densities and microstrain values were calculated. BET results show that the increase of the neodymium doped content decrease the surface area of the composite powders, confirming the highly ordered micro and mesostructure. SEM and AFM results show that the samples have spherical grains. According to the surface roughness measurements, the increase in the amount of neodymium and the decrease in the amount of cerium decreased the surface roughness.

Doping in ceria (CeO2) nanoparticles with europium (Eu) of varying concentrations (0, 0.1, 0.5, …, 50 atom%) is studied using complementary experimental techniques and novel observations were made during the investigation. The immediate observable effect was a distinct reduction in particle sizes with increasing Eu concentration attributed to the relaxation of strain introduced due to the replacement of Ce4+ ions by Eu3+ ions of larger radius. However, this general trend was reversed in the doping concentration range of 0.1–1 atom% due to the reduction of Ce4+ to Ce3+ and the formation of anion vacancies. Quantum confinement effects became evident with the increase of band gap energy when the particle sizes reduced below 7–8 nm. Positron annihilation studies indicated the presence of vacancy type defects in the form of vacancy clusters within the nanoparticles. Some positron annihilation was also seen on the surface of crystallites as a result of diffusion of thermalized positrons b...

Different lanthanide (Ln)-doped cerium oxides (Ce0.5Ln0.5O1.75, where Ln: Gd, La, Pr, Nd, Sm) were loaded with Cu (20 wt. %) and used as catalysts for the oxidation of ethyl acetate (EtOAc), a common volatile organic compound (VOC). For comparison, both Cu-free (Ce-Ln) and supported Cu (Cu/Ce-Ln) samples were characterized by N₂ adsorption at -196 °C, scanning/transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and temperature programmed reduction in H₂. The following activity sequence, in terms of EtOAc conversion, was found for bare supports: CeO₂ ≈ Ce0.5Pr0.5O1.75 &gt; Ce0.5Sm0.5O1.75 &gt; Ce0.5Gd0.5O1.75 &gt; Ce0.5Nd0.5O1.75 &gt; Ce0.5La0.5O1.75. Cu addition improved the catalytic performance, without affecting the activity order. The best catalytic performance was obtained for Cu/CeO₂ and Cu/Ce0.5Pr0.5O1.75 samples, both achieving complete EtOAc conversion below ca. 290 °C. A strong correlation was revealed...

In this study, magnesia stabilized zirconia based nanocrystalline ceramics were produced through a polymer precursor route using gadolinium and boron. The powders were characterized during the various steps by structural and morphological techniques (FT-IR, XRD, and SEM). XRD results proved that a tetragonal phase is predominant for all samples with varying magnesium contents and no monoclinic zirconia solid solution appears. The crystallite sizes of the samples were calculated using Scherrer equation. The smallest crystallite size was obtained for the sample containing Zr/Mg/Ce/Gd/B ratio of 82/0/10/8/0. The lattice parameters were calculated for cubic, tetragonal, hexagonal, and orthorhombic structures. SEM results show all the samples have spherical grains. The average grain diameters were calculated for all the samples. The smallest average grain diameter was obtained for the sample containing Zr/Mg/Ce/Gd/B ratio of 82/0/10/8/0.