Nanocrystalline Ce Research Articles

Nanocrystalline Ce(OH)4-based materials: ruthenium selective adsorbent for highly alkaline radioactive liquid waste

Abstract Cerium hydroxide, Ce(OH)4 (Ce), has been synthesised and assessed as a Ru-selective adsorbent for treating alkaline radioactive liquid waste. Infrared spectroscopy, thermal analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy investigations confirmed the successful formation of nanocrystalline Ce from Ce(NO3)3·6H2O. Selective removal of 106Ru from the ion-exchange effluent of intermediate-level liquid waste (ILW) by Ce was assessed using a high-pure germanium (HPGe) gamma-ray spectrometer. The calculated average distribution coefficient (k D) was ∼200 mL/g. The percentage removal of 106Ru using Ce by varying time, [106Ru] and [Ce] was calculated. The adsorption of 106Ru on Ce follows pseudo-second-order and Freundlich isotherms. The calculated Q max was 93,584 Bq/g. Accelerated leaching studies of the Ru-laden Ce cement product were carried out and found suitable for transport and disposal. Further, Ce-Polyether sulphone (Ce-PES) and Ce-Chitosan (CeC) composites were prepared and assessed for their Ru-uptake capacity for engineering scale application.

Enhanced magnetic properties and anisotropy in hot-deformed Ce–Fe–B magnets by suppressing CeFe2 phase with Ga addition

Nanocrystalline Ce–Fe–B alloys exhibit potential utilization for low-cost permanent magnets, however, the preparation of anisotropic magnets with satisfactory magnetic properties remains a challenge. CeFe2 Laves phase with high melting point that forms in the Ce-rich Ce–Fe–B magnets has been considered as the reason to be detrimental to its hot-working process and magnetic performance. Herein, we report the significant effects of adding Ga to nanocrystalline melt-spun Ce17Fe78-xB6Gax alloys on suppressing the CeFe2 phase and enhancing coercivity. The x = 2.0 alloy is identified as the optimal precursor for preparing anisotropic hot-deformed magnet due to its lower CeFe2 phase content (5.7 wt.%), considerably less than that of the ternary Ce–Fe–B alloy (17.6 wt.%). The congruent alignment and platelet-shaped grain characteristics are obtained in the Ga-added hot-deformed magnet, indicating an enhanced anisotropy that results in an improved remanence from 4.2 kGs to 5.9 kGs. The development of such texture can be ascribed to the reduced amount of CeFe2 phase, allowing the formation of Ce-rich grain boundary (GB) phase, which is necessary to induce grain alignment during hot deformation process. Two types of Ga-containing GB phases are found in the Ga-added magnet, namely typical Ce-rich/Fe-lean GB phase and Ce6Fe13Ga phase. The uniformly distributed Ce-rich GB phases surrounding the main grains helps to magnetic isolate the Ce2Fe14B grains and thus enhance the coercivity, as verified by detailed microstructural characterizations combined with micromagnetic simulation. The work offers a potential way to realize anisotropy in Ce–Fe–B magnets and inspires further exploration of high abundance Ce-based magnets.

Room temperature aqueous synthesis of Ce(IV)-MOFs with UiO-66 architecture and their photocatalytic decarboxylative oxygenation of arylacetic acids

Cerium(IV)-based metal-organic frameworks (MOFs) have gained a growing attention in both scientific and industrial spheres due to their unique potential in fields such as redox catalysis and photocatalysis. However, the synthetic pathways of Ce(IV)-MOFs are still extremely dominated by the conventional solvothermal conditions. Meanwhile, the research on photocatalysis of Ce(IV)-MOFs is still in its infancy, more experimental evidence is highly desirable to accelerate the development of this field. Here we present an innovative, widespread, green and sustainable synthetic route for nanocrystalline Ce(IV)-MOFs with the UiO-66 structure. Seven Ce-UiO-66-MOFs were successfully prepared at room temperature using water as the sole solvent in the presence of sodium acetate (NaAc). Furthermore, the photocatalytic activities of these Ce(IV)-MOFs for decarboxylative oxygenation of 4-fluorophenylacetic acid to give corresponding C–O bond-forming products 4-fluorobenzaldehyde and 4-fluorobenzyl alcohol under blue light-emitting diodes (LEDs) irradiation and air were studied. Control experiments revealed that Ce-UiO-66-BDC exhibited the optimized catalytic efficiency among these Ce(IV)-MOFs, and can be applied to various arylacetic acids.

Effect of 20 mol % gadolinium doping on oxide ion conductivity of ceria as electrolyte for intermediate temperature solid oxide fuel cells

The gadolinium-doped ceria is investigated as electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to its oxide ion conductivity. The doping of Gd3+ to Ce4+ can introduce a small strain in the lattice thereby improved conductivity with low activation energy is expected. The 20 mol. % gadolinium doped ceria (Ce0.8Gd0.2O2−δ) nanocrystalline powder is prepared here by citrate - complexation method. The XRD, Rietveld refinement, FTIR, UV-Visible, FESEM/EDX, and a c - impedance techniques are used to characterize this sample. The oxide ion conductivity is determined between 523 − 1023 K. The Ce0.8Gd0.2O2−δ shows highest oxide ion conductivity of 6.79 × 10−3 S cm−1 and 1.11 × 10−2 S cm−1 at 973 K and 1023 K, respectively. The Ce0.8Gd0.2O2−δ showed lower activation energies of 1.09, 0.70, and 0.88 eV for grain, grain boundary, and total conduction, respectively. Thus, the nano crystalline Ce0.8Gd0.2O2−δ is proposed as potential electrolyte for IT-SOFCs.

Synthesis, structure and ionic conductivity of nanocrystalline Ce1−xLaxO2−δ as an electrolyte for intermediate temperature solid oxide fuel cells

La-doped CeO2 nanoparticles of composition Ce1−xLaxO2−δ (0 ≤ x ≤ 0.1) have been studied here as prospective electrolytes for intermediate temperature solid oxide fuel cells (IT-SOFCs). They were synthesized by auto-combustion method and the powder samples were calcined at 700 °C to get ultrafine nanocrystalline particles. They were characterized by XRD, Raman, FTIR, XPS, DRS, FESEM/EDX, particle size analyzer and ac-impedance techniques. Ionic conductivity was measured from 350 − 750 °C. The Ce0.90La0.1O2−δ (0.1 LDC) and Ce0.95La0.05O2−δ (0.05 LDC) showed a maximum conductivity of 8.89 × 10−3 and 8.32 × 10−3 S cm−1 at 700 °C, respectively. The σt of 0.1 LDC = 1.01 × 10−2 S cm−1 at 750 °C. The activation energy of 0.1 LDC and 0.05 LDC was found to be 0.70 eV and 0.87 eV, respectively. These values are higher than those reported for La-doped CeO2 in literature. The SOFC performance with 0.05 LDC as electrolyte showed open circuit voltage of 0.81 V and maximum power density of 41 mW cm−2 at 650 °C using hydrogen as fuel.

Enhanced red emission of glycothermally synthesized Ce:YAG nanophosphors via Mn2+ addition

Mn2+ was shown to be incorporated as a co-dopant in glycothermally synthesized Ce:YAG-based nanophosphors to enhance the red component of the emission spectrum. Structural characterization showed a preferential inclusion of Mn2+ in the Y site. AlIV/AlVI ratios were found to decrease from 0.25 in Ce:YAG nanophosphors to 0.11 with the addition of Mn2+, indicating a ∼10x increase in octahedral Al sites over bulk Ce:YAG, particularly on the particle surface. Luminescence of Mn2+ at 594 nm, indicating octahedral Al site occupation was also observed, likely due to the high doping concentration of Mn2+. Strategies to improve the luminescence of Mn2+ included adding Si4+ in the form of tetraethyl orthosilicate (TEOS) for charge compensation and the addition of an intrinsic shell layer to enhance the local crystal field. XPS confirmed no change of Mn2+ valence after reaction, indicating Mn (II) acetate to be a precursor compatible with the glycothermal method for the synthesis of Ce:YAG-based nanophosphors. 3 mol% Mn2+ was found to be a suitable doping concentration, with quenching observed at 5%. Addition of an intrinsic shell layer greatly improved the optical characteristics of the Mn2+ emission, and the photoluminescence quantum yield (PLQY) increased from 44% to 73%. Fluorescence lifetimes of nanocrystalline Ce:YAG and Mn2+ containing samples dropped from 101.1 ns to 90.7 ns, respectively, indicating the presence of a non-radiative energy transfer mechanism from Ce to Mn2+.

Ionic Conductivity of Ce0.91Ca0.09O2 as an Electrolyte for Intermediate Temperature Solid Oxide Fuel Cells

The search for new cost-effective electrolyte materials for IT-SOFC towards its mass scale commercialization has gained momentum in recent years. The Ca- doped ceria having composition Ce0.91Ca0.09O2 was prepared using the facile conventional solid-state method. The structural and electrical properties of low sintered ceramic samples have been characterized by X-ray diffraction (XRD), UV–VIS diffuse reflectance spectroscopy (DRS) and A.C. impedance technique respectively. The oxide ion conductivity was measured between the temperatures 573 K−973 K in air. The obtained results showed that total conductivity is mainly dependent on the grain boundary effect. The nanocrystalline Ce0.91Ca0.09O2 exhibited the high total ionic conductivity of 7.36  103 S cm1 at 973 K with a lower activation energy of 0.96 eV. The obtained results highlight the use of cost-effective dopant in ceria lattice to develop commercially viable electrolyte materials for IT-SOFC.

Microstructure Characterization and Magnetic Characteristics of Ce–Fe–B Based Spark Plasma Sintered Magnets

Nanocrystalline Ce–Fe–B based rare earth permanent magnets are prepared by spark plasma sintering (SPS) method using grounded ribbons as raw material. The phase compositions, microstructure, magnetic properties, intergranular magnetic interactions, recoil loops, and corrosion resistance of the magnets are investigated systemically. The relationship among sintering processes, microstructures, and magnetic characteristics are discussed in depth by mainly using transmission electron microscope (TEM) and Physical Property Measurement System (PPMS) techniques. It is demonstrated that the sintering temperature has a significant influence on the average grain size and width of coarse grain areas. The optimized magnetic properties of remanent magnetization $J_{r}= 0.37$ T, coercivity $H_{\mathrm {ci}} = 227$ kA/m, and maximum energy product $(BH)_{\mathrm {max}}= 16$ kJ/m3 are obtained at 650 °C under 50 MPa for 2 min. Their exchanging coupling interactions are quite weak compared with those of the counterpart alloys. The exchanged decoupled of soft magnetic materials and inhomogeneous magnetic anisotropy result in open and steep recoil loops. The electrochemical experiment results display that the corrosion resistance of the magnets is improved by sintering at high temperature. This paper plays a role in guiding the future research and development of nanocrystalline Ce–Fe–B based permanent magnetic materials.

CO Oxidation over Metal Oxide (La2O3, Fe2O3, PrO2, Sm2O3, and MnO2) Doped CuO-Based Catalysts Supported on Mesoporous Ce0.8Zr0.2O2 with Intensified Low-Temperature Activity

CuO-based catalysts are usually used for CO oxidation owing to their low cost and excellent catalytic activities. In this study, a series of metal oxide (La2O3, Fe2O3, PrO2, Sm2O3, and MnO2)-doped CuO-based catalysts with mesoporous Ce0.8Zr0.2O2 support were simply prepared by the incipient impregnation method and used directly as catalysts for CO catalytic oxidation. These mesoporous catalysts were systematically characterized by X-ray powder diffraction (XRD), N2 physisorption, transmission electron microscopy (TEM), energy-dispersed spectroscopy (EDS) mapping, X-ray photoelectron spectroscopy (XPS), and H2 temperature programmed reduction (H2-TPR). It was found that the CuO and the dopants were highly dispersed among the mesoporous framework via the incipient impregnation method, and the strong metal framework interaction had been formed. The effects of the types of the dopants and the loading amounts of the dopants on the low-temperature catalytic performances were carefully studied. It was concluded that doped transition metal oxides could regulate the oxygen mobility and reduction ability of catalysts, further improving the catalytic activity. It was also found that the high dispersion of rare earth metal oxides (PrO2, Sm2O3) was able to prevent the thermal sintering and aggregation of CuO-based catalysts during the process of calcination. In addition, their presence also evidently improved the reducibility and significantly reduced the particle size of the CuO active sites for CO oxidation. The results demonstrated that the 15CuO-3Fe2O3/M-Ce80Zr20 catalyst with 3 wt. % of Fe2O3 showed the best low-temperature catalytic activity toward CO oxidation. Overall, the present Fe2O3-doped CuO-based catalysts with mesoporous nanocrystalline Ce0.8Zr0.2O2 solid solution as support were considered a promising series of catalysts for low-temperature CO oxidation.

Industrial mass production of nanocrystalline Ce0.9Gd0.1O1.95 via a solid–liquid method using gluconic acid

Abstract To achieve industrial mass production, a simple and efficient solid–liquid method (SLM) was applied to synthesize nanocrystalline gadolinium-doped ceria (Ce 0.9 Gd 0.1 O 1.95 , GDC), using gluconic acid (GA) as a complexing agent and polyethylene glycol (PEG) as a surfactant. Unlike traditional wet-chemical methods, this method of forming metal-complex compounds does not involve heating processes, which are known to pose risks of fire and explosion. The substitution of GA for traditional citric acid (CA) reduces the corrosion of stainless-steel equipment. The effects of the varying amounts of GA and polymerization degrees of PEG were discussed. The physical properties of the precursors were characterized using thermogravimetry/differential thermal analysis (TG/DTA). The crystallinity and grain size of the GDC powders were analysed using X-ray diffractometry (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), and particle-size distribution (PSD) analyses. The results show that the GDC powder with additions of 20 wt% GA and 1 wt% PEG2000 that was sintered at 800 °C has a single phase with a particle size of around 40 nm; it is also homogenous and highly pure. In addition, the ionic conductivity of the GDC pellet that was sintered at 1450 °C for 5 h is 0.046 S/cm at 750 °C. These results indicate that this novel SLM is suitable for the mass synthesis of high-performance nanocrystalline Ce 0.9 Gd 0.1 O 1.95 powders.

Sintering kinetics of nanocrystalline Ce0.9Zr0.1O2 prepared by gel combustion method

The sintering process of nanometric Ce0.9Zr0.1O2 mixed oxides prepared by the amino acid–nitrate gel combustion method was analyzed by dilatometry using the constant heating rate (CHR) and stepwise isothermal dilatometry (SID) methods. The morphology of the mixed oxides was studied by scanning and transmission electron microscopies. The evolution of crystallite size with temperature was analyzed by time-resolved X-ray powder diffraction with synchrotron radiation. The sintering behavior resulted dependent on the morphology of the powders. Samples with nanometric crystallite size start to sinter even 500 K before than micrometric sample. We concluded that sintering process of nanometric Ce0.9Zr0.1O2 is controlled by grain-boundary diffusion for temperatures below 1373–1573 K, depending on the morphology of the sample. At high temperature, the grain-boundary and lattice diffusion become parallel controlling mechanism for sintering.

Facilely fabricating mesoporous nanocrystalline Ce–Zr solid solution supported CuO-based catalysts with advanced low-temperature activity toward CO oxidation

The synergistic effect between CuO and mesoporous Ce–Zr solid solution greatly enhanced the advanced low-temperature catalytic activity toward CO oxidation.

A novel Ce-MOF/PES mixed matrix membrane; synthesis, characterization and antifouling evaluation

A new polyethersulfone (PES) nanofiltration membrane, modified with nanocrystalline Ce(III) metal–organic framework (MOF), was produced via the phase inversion method and characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle and porosity measurements. The morphology and performance of these membranes were investigated in terms of pure water flux, water contact angle, fouling parameters and dye removal. Modified PES membranes showed an increase in the pure water flux relative to the bare membrane. The changes in sublayer and skin layer of modified membranes and also increased pore size and porosity is obvious from the SEM images of PES membranes porosity measurements. Moreover, the surface hydrophilicity of the MOF embedded membranes was improved due to the tendency of water to the membrane surface. The antifouling properties of the membranes were evaluated by powder milk solution and measuring the flux recovery ratio (FRR). The results revealed the modified membrane with 0.5wt.% of MOF nanoparticle (NPs) had the best antifouling property and also the highest porosity and water flux. Nanofiltration performance of membranes was appraised by probing of the retention of Direct Red 16. The result showed that all the modified membranes have a higher dye rejection capacity than the bare PES membrane.

The magnetic properties and domain structures of nanocrystalline Ce–Fe–B magnets with enhanced maximum energy products

Optimizing of alloy composition and heat-treatment for rapidly solidified Ce–Fe–B magnets can lead nanocrystalline products with enhanced magnetic properties. In this work, the magnetic properties and domain structures of the nanocrystalline Ce[Formula: see text]Fe[Formula: see text]Co1Zr[Formula: see text]B6 have been investigated. The results show that hard Ce2Fe[Formula: see text]B magnetic phase and paramagnetic CeFe2 phase are crystallized for the heat treated alloys, while the volume fraction and grain size of Ce2Fe[Formula: see text]B and CeFe2 phases change significantly with the increase of annealing temperature. The enhanced coercivity H[Formula: see text] of 6.32 kOe and maximum energy products (BH)[Formula: see text] of 5.52 MGOe have been observed for the Ce[Formula: see text]Fe[Formula: see text]Co1Zr[Formula: see text]B6 ribbons at the optimal annealing temperature of 520[Formula: see text]C and 580[Formula: see text]C, respectively. Meanwhile, the magnetization reversal behaviors and the nucleation field of the annealed sample were discussed in detail. The domain structures analysis provides more information on the characteristic of the domain width W as well as the exchange interactions.

Defects and oxygen vacancies tailored structural and optical properties in CeO2 nanoparticles doped with Sm3+ cation

In this study, the correlation between the concentration of dopant ions and oxygen vacancy defect of Sm-doped CeO2 Nano-particles (NPs) were investigated systematically by X-ray diffraction (XRD), Ultraviolet–visible-Near Infrared spectroscopy (UV–Vis–NIR) and Surface-enhanced Raman spectroscopy (SERS). The nano-crystalline Ce1−xSmxO2 (x = 0.00, 0.02, 0.04, 0.06, 0.08 and 0.10) samples were synthesized using co-precipitation chemical route. The XRD measurements revealed that Sm3+ ions are successfully incorporated at the Ce4+ ion sites in the face centered cubic (fcc) lattice of CeO2 NPs. The high-resolution transmission electron microscopy (HRTEM) and Selected area electron diffraction (SEAD) patterns were analyzed to study the surface morphology, crystallinity, atomic structure of the samples. The average particle size calculated with TEM images was obtained in the range of 5–8 nm for Ce1−xSmxO2 samples for all the doping concentrations. The UV–Vis–NIR spectroscopy and Surface-enhanced Raman Spectroscopy were analyzed to investigate the optical properties and defect structure in these NPs. The UV–Vis–NIR spectroscopy measurements revealed that due to aggregation of particles the optical band gap energy was varied with fluencies of Sm3+ ions as well as due to particle size variations of NPs. Peak asymmetry and broadening of Raman active mode further ascribed the presence of oxygen vacancy (whether extrinsic or intrinsic), which were varied with the fluencies of Sm3+ ions in CeO2 NPs. This paper presented a systematic study on the fluencies of Sm doping in CeO2 nano-particle lattice to understand the role of vacancies, intrinsic and extrinsic oxygen vacancies and their effect on tailoring the structural and optical properties of doped CeO2 nano-particles for various applications like luminescent materials, oxygen transportation, catalysts, ultraviolet fuel cells, corrosion prevention etc.

The crystal structure of compositionally homogeneous mixed ceria-zirconia oxides by high resolution X-ray and neutron diffraction methods

AbstractThe real/atomic structure of single phase homogeneous nanocrystalline Ce0.5Zr0.5O2±δoxides prepared by a modified Pechini route and Ni-loaded catalysts of methane dry reforming on their bases was studied by a combination of neutron diffraction, synchrotron X-ray diffraction, total X-ray scattering and X-ray absorption spectroscopy. The effects of sintering temperature and pretreatment in H2were elucidated. The structure of the mixed oxides corresponds to a tetragonal space group indicating a homogeneous distribution of Ce and Zr cations in the lattice. A pronounced disordering of the oxygen sublattice was revealed by neutron diffraction, supposedly due to incorporation of water into the structure when in contact with air promoted by the generation of anion vacancies in the lattice after reduction or calcination at high temperatures. However, such disordering has not resulted in any occupation of the oxygen interstitial positions in the bulk of the nanodomains.

Synthesis of nanocrystalline Ce0.95Mn0.05O2 solid solution powders as support for nickel catalyst in dry reforming reaction

For the preparation of the Ce0.95Mn0.05O2 solid solution as a catalyst support, the co-precipitation, sol-gel and hydrothermal methods were applied and the 10wt.%Ni/Ce0.95Mn0.05O2 catalysts were synthesized by the wet impregnation method on the prepared supports. The physicochemical characteristics of the samples were determined by the X-ray diffraction (XRD), BET surface area, scanning electron microscopy (SEM), temperature programmed reduction and oxidation (TPR and TPO) analyses. The results revealed that the carrier prepared by the co-precipitation method showed higher potential as a catalyst carrier. The investigation of the influence of the nickel content over the carrier prepared by the co-precipitation method showed that the 10wt.% Ni was the optimum content to prepare a catalyst with acceptable catalytic performance in dry reforming reaction. The catalysts with higher percentage of nickel exhibited a higher degree of deactivation due to severe carbon deposition.

Preparation of nanocrystalline Ce1−xSmx(Fe,Co)11Ti by melt spinning and mechanical alloying

Permanent magnetic materials based on Ce(Fe, Co)12−xTix with the ThMn12 structure are promising candidates for replacing NdFeB magnets. Its intrinsic magnetic properties are not far below the values of Nd2Fe14B, and the high amount of Fe and the fact that Ce is much more abundant and less expensive than Nd encourages the reasonable interest in these compounds. Nanocrystalline magnetic material of the composition Ce1−xSmxFe11−yCoyTi (x=0−1 and y=0; 1.95) has been produced by both melt spinning and mechanical alloying. Alloys containing only Ce as rare earth element (x=0) show coercivities below 77kA/m, while for x=1 Hc,J values up to 392kA/m are reached. Coercivity shows rather an exponential than a linear dependence on the gradual substitution of Ce by Sm.

Structure and photoluminescence properties of Ce0.5Zr0.5O2:Eu3+ nanoparticles synthesized by hydrothermal method

Eu3+-doped Ce0.5Zr0.5O2 nanocrystals were prepared by a hydrothermal method. The structural and optical properties of the samples were characterized by X-ray diffraction, Raman scattering and photoluminescence spectra. No luminescence was observed for Ce0.5Zr0.5O2, while Ce0.5Zr0.5O2:Eu3+ nanoparticles as-prepared and calcined at 400 °C showed emission due to Eu3+. The emission spectrum of the Eu3+ site shows that the total intensity decreases with increasing concentration of Eu3+ from 1 to 10% in Ce0.5Zr0.5O2. The broad band in the excitation spectrum of calcined Ce0.5Zr0.5O2:Eu3+ originates from the charge transfer (CT) transition. The local distortion and the asymmetry factor around the Eu3+ centers were discussed with the Raman and photoluminescence spectra. The present study provides both knowledge expected to lead to novel nanocrystal phosphor materials and a useful measure for analyzing the catalytic properties of nanocrystalline Ce0.5Zr0.5O2.

Ceria-zirconia Mixed Oxide Prepared through a Microwave-assisted Synthesis for CO2 Sensing in Low Power Work Function Sensors

In this work the sensitivity towards CO2 of pure ceria, zirconia and a Ce-Zr mixed oxide were tested in a Kelvin Probe setup. The nanocrystalline powders were obtained by microwave-assisted synthesis. A high work function response in humid air was observed for all compositions, the mixed oxide exhibiting the best sensing characteristics. Based on the results presented here, we propose nanocrystalline Ce0.8Zr0.2O2 as a CO2 sensitive layer for work function based gas sensors.