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Suitability of Raman Spectroscopy for Assessing Anisotropic Strain in Thin Films of Doped Ceria
摘要： A protocol for characterizing relaxation of anisotropic strain in thin films of 10 mol% Eu- or Sm-doped ceria is described. The method is based on comparison of Raman spectra and X-ray diffraction patterns from substrate-supported films, displaying in-plane compressive strain (initial state), with analogous data from 2 mm diameter self-supported films (i.e., membranes), prepared by partial substrate removal (final state). These membranes are found to be relaxed, i.e., approximately unstrained, but with increased unit cell volume. The effective (i.e., 2-state) Grüneisen parameter of the F2g Raman active mode for these films is calculated to be 0.4 ± 0.1, which is ≈30% of the literature value for the corresponding ceramics under isostatic pressure. On this basis, it is found that the observed red-shift of the F2g mode frequency following isothermal strain relaxation of the doped ceria thin films cannot be determined solely by the increase in average unit cell volume. The study presented here may shed light on the suitability of Raman spectroscopy as a technique for characterizing strain in lanthanide-doped ceria thin films.
关键词： doped ceria,Raman spectroscopy,Grüneisen parameter,anelastic relaxation
更新于2025-09-23 15:23:52
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Structural and Optical Properties of CeO2 Nanoparticles Synthesized by Modified Polymer Complex Method
摘要： Ceria nanoparticles (Ceria-NPs) were synthesized using a modified polymer complex method and their structural and optical properties were evaluated. The solids were heated at 550 °C and characterized using Raman, UV–Vis absorption, diffuse reflectance, X-ray photoelectron and photoluminescence spectroscopies, X-ray diffraction (XRD) and scanning and transmission electron microscopy. The primary particles obtained presented a size of ~ 10 nm. The XRD indicated that CeO2 was the only crystalline phase. From the UV–Vis and diffuse reflectance spectra, energy values of 3.8 eV and 3.4 eV were obtained, values that can be associated with band—band electronic transitions and/or with those that involve ionized states located within the gap caused by defects and isolated atoms of Ce3+. Photoluminescence spectra reiterated the existence of localized states in the gap. Raman spectra revealed the existence of peroxide (O2^2-) and superoxide (O2^-) over the surface of the ceria-NPs. The XPS results indicated that the concentrations of Ce3+ and Ce4+ were ～ 20.5% and ～79.5% respectively, and that the stoichiometry of oxygen was 1.9 per atom of Ce. The results obtained from the characterization of CeO2-NPs synthesized make it as promising material for environmental remediation, biomedicine, gas sensing and optoelectronic applications.
关键词： Modified polymer complex,Structural properties,Ceria-NPs,Optical properties,Synthesis
更新于2025-09-23 15:23:52
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Preparation and photocatalytic performance of Cu-doped CeO <sub/>2</sub> by citrate combustion method
摘要： Cu-doped cerium oxides were successfully prepared by nitrate combustion method. The crysatlline phase evolution, micro morphology and photocatalytic performance of the products are systematically studied by XRD, SEM/EDX and degradation rate of methylene blue. The results show that at relative low temperature (<600°C), 20 mol% copper can be dissolved into CeO2 fluorite type cubic structure, however, at high temperature of 700°C, CuO phase desolution from CeO2 solid solution is detected by XRD, and confirmed by DTA for 5% Cu-doped sample. The as prepared photocatalysts show agglomeration of ultra fine particles with porous structure. Degradation results of methylene blue indicate that better photocatalytic performance is obtained for 5% Cu-doped CeO2 under the stimulated visible light than UV light irradiation (both 254 nm and 365 nm), even the power of former is half of the later. The loss of photocatalytic activity for higher doping samples (>5% Cu) is believed to be the serious agglomeration of the particles and desolution of CuO from CeO2 solid solution.
关键词： doping,citrate combustion method,copper,photocatalytic,Ceria
更新于2025-09-23 15:23:52
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High efficiency solar chemical-looping methane reforming with ceria in a fixed-bed reactor
摘要： High ef?ciency solar chemical-looping methane reforming is demonstrated in a prototype reactor operated in a high-?ux solar simulator. The reactor includes six tube assemblies, which each comprise a ?xed-bed of ceria particles and a gas-phase heat recuperator. The cycle was accomplished by alternating the ?ow to one tube assembly between CH4 and CO2. In the initial series of experiments, temperature, CH4 concentration, reduction ?ow rate, and cycle duration were varied to minimize carbon accumulation and maximize ef?ciency. In the second set of tests, the reactor was operated at optimized conditions for ten cycles at 1228 and 1274 K. Higher temperature favors better performance. At 1274 K, CH4 conversion is 0.36, H2 selectivity is 0.90, CO selectivity is 0.82, CO2 conversion is 0.69, and the energetic upgrade factor is 1.10. Heat recovery effectiveness is over 95%. Solar-to-fuel ef?ciency is 7% and the thermal ef?ciency is 25%. Projected solar-to-fuel and thermal ef?ciencies are 31 and 67% for the full-scale reactor and 56 and 85% for a commercial reactor with lower thermal losses. The demonstrated ef?ciencies are the highest reported to-date for this process. The projected scaled-up ef?ciencies suggest solar chemical-looping methane reforming could be a competitive approach for production of solar fuels.
关键词： Reforming,Redox cycle,Solar thermochemical,Chemical-looping,Metal oxide,Ceria
更新于2025-09-23 15:22:29
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Heat transfer model of a 50 kW solar receiver-reactor for thermochemical redox cycling using cerium dioxide
摘要： This work reports on the development of a transient heat transfer model of a solar receiver-reactor designed for thermochemical redox cycling by temperature and pressure swing of pure cerium dioxide in the form of a reticulated porous ceramic (RPC). In the first, endothermal, step the cerium dioxide RPC is directly heated with concentrated solar radiation to 1500 °C while under vacuum pressure of less than 10 mbar, thereby releasing oxygen from its crystal lattice. In the subsequent, exothermic, step the reactor is re-pressurized with carbon dioxide as it cools, and at temperatures below 1000 °C the partially reduced cerium dioxide is re-oxidized with a flow of carbon dioxide. To analyze the performance of the solar reactor and to gain insight into improved design and operational conditions, a transient heat transfer model of the solar reactor for a solar radiative input power of 50 kW during the reduction step was developed and implemented in ANSYS CFX. The numerical model couples the incoming concentrated solar radiation using Monte-Carlo ray tracing, incorporates the reduction chemistry by assuming thermodynamic equilibrium, and accounts for internal radiation heat transfer inside the porous ceria by applying effective heat transfer properties. The model was experimentally validated using data acquired in a high-flux solar simulator, where temperature evolution and oxygen production results from model and experiment agreed well. The numerical results indicate the prominent influence of solar radiative input power, where increasing it substantially reduces reduction time of the cerium dioxide structure. Consequently, the model predicts a solar-to-fuel energy conversion efficiency of > 6% at a solar radiative power input of 50 kW; efficiency > 10% can be obtained provided the RPC macro porosity is substantially increased and better volumetric absorption and uniform heating is achieved. Managing the ceria surface temperature during reduction to avoid sublimation is a critical design consideration for direct absorption solar receiver-reactors.
关键词： design optimization,reactor modelling,ceria,thermochemical cycles,solar energy,reticulated porous ceramic
更新于2025-09-23 15:19:57
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Reduced graphene oxide@ceria nanocomposite-coated polymer microspheres as a highly active photocatalyst
摘要： Herein we report a facile two-step synthetic strategy for fabricating the ternary polystyrene/reduced graphene oxide/ceria (PS/RGO@CeO2) nanocomposite particles for the first time through the self-assembly of the RGO on the surface of PS microsphere (PS/RGO) and then the attachment of CeO2 nanoparticles (NPs) onto the as-prepared PS/RGO nanocomposite particles. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis have been employed to characterize the morphology and composition of the as-prepared samples. The size and mass loading of resulting CeO2 NPs on the PS/RGO nanocomposite particles are easily tunable. Furthermore, the photocatalytic performance of as-prepared ternary nanocomposite particles towards the degradation of methylene blue is investigated. Notably, the PS/RGO@CeO2 nanocomposite particles have high photocatalytic activity due to the synergistic effect between the CeO2 NPs and RGO in such a unique structure, and moreover, they also exhibit high stability in a recyclable manner. Therefore, it can be expected that our ternary nanocomposite particles are an attractive photocatalyst candidate for various photocatalytic applications.
关键词： polystyrene microsphere,ceria nanoparticle,reduced graphene oxide,nanocomposite particle,catalysis
更新于2025-09-19 17:15:36
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Synergy of the catalytic activation on Ni and the CeO <sub/>2</sub> –TiO <sub/>2</sub> /Ce <sub/>2</sub> Ti <sub/>2</sub> O <sub/>7</sub> stoichiometric redox cycle for dramatically enhanced solar fuel production
摘要： Solar thermochemical approaches to CO2 and H2O splitting have emerged as an attractive pathway to solar fuel production. However, efficiently producing solar fuel with high redox kinetics and yields at lower temperature remains a major challenge. In this study, Ni promoted ceria–titanium oxide (CeO2–TiO2) redox catalysts were developed for highly effective thermochemical CO2 and H2O splitting as well as partial oxidation of CH4 at 900 1C. Unprecedented CO and H2 production rates and productivities of about 10–140 and 5–50 times higher than the current state-of-the-art solar thermochemical carbon dioxide splitting and water splitting processes were achieved with simultaneous close to complete CH4 conversions and high selectivities towards syngas. The underlying mechanism for the exceptional reaction performance was investigated by combined experimental characterization and density functional theory (DFT) calculations. It is revealed that the metallic Ni and the Ni/oxide interface manifest catalytic activity for both CH4 activation and CO2 or H2O dissociation, whereas CeO2–TiO2 enhances the lattice oxygen transport via the CeO2–TiO2/Ce2Ti2O7 stoichiometric redox cycle for CH4 partial oxidation and the subsequent CO2 or H2O splitting promoted by catalytically active Ni. Such findings substantiate the significance of the synergy between the reactant activation by catalytic sites and the stoichiometric redox chemistry governing oxygen ion transport, paving the way for designing prospective materials for sustainable solar fuel production.
关键词： thermochemical CO2 splitting,solar fuel production,density functional theory,Ni promoted ceria–titanium oxide,thermochemical H2O splitting,methane partial oxidation,redox catalysts
更新于2025-09-19 17:15:36
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Flash Sintering Samaria-Doped Ceria–Carbon Nanotube Composites
摘要： Composite ceramic green pellets were prepared by attrition milling a mixture of (CeO2)0.8(Sm2O3)0.2 (samaria-doped ceria, SDC) ceramic powder and carbon nanotubes (CNTs), followed by uniaxial and isostatic pressing. The pellets were sintered inside a dilatometer by applying AC electric fields at 850 °C and limiting the electric current to 1 A, achieving 20.2% final shrinkage. The SDC samples reached 13.3% shrinkage under the same conditions. Higher average grain sizes were measured in specimens flash sintered with CNTs. Impedance spectroscopy analyses show that the specimens flash sintered with addition of CNTs have higher electrical conductivity. Higher delivered Joule heating at the interfaces due to the presence of the electronic conductors (CNTs) are proposed as the main reason for that improvement of the electrical behavior.
关键词： flash sintering,solid electrolytes,carbon nanotubes,impedance spectroscopy,samaria-doped ceria
更新于2025-09-19 17:15:36
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Elaboration of microporous CeO2 thin layers having nanocrystallites network controlled by Pluronic P123: Impact of key experimental parameters
摘要： Microporous ceria thin ?lms having nanocrystallites network were synthesized by evaporation-induced self-assembly process, using P123 amphiphilic copolymer as structure-directing agent. The impact of key experimental parameters, i.e., the sol ageing, the relative humidity (RH), the thermal treatment, on the thin layer elaboration were investigated. The results show that the organization of the nanoparticles is possible for a sol ageing time lower than 16 days and that the size of the mesophase within the thin layer increases with the relative humidity ?xed during the ?lm deposition. Finally, an increase of the thermal treatment temperature from 300 to 1000 °C leads to the formation of ?uorite-like dioxide material coupled with a loss of nanocrystallites organization and porosity due to the increase of the size of the crystallites. This loss of nanocrystallites organization is more drastic in the direction perpendicular to the surface and less pronounced along the surface. Thus, a compromise between the crystallization and the preservation of the porosity needs to be found.
关键词： relative humidity,P123 amphiphilic copolymer,evaporation-induced self-assembly,nanocrystallites network,thin films,thermal treatment,Microporous ceria,sol ageing
更新于2025-09-16 10:30:52
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The Crystallization Mechanism of the Octahedron-Like Ce <sub/>1-x</sub> Yb <sub/>x</sub> O <sub/>2-x/2</sub> and Ce <sub/>1-x</sub> Lu <sub/>x</sub> O <sub/>2-x/2</sub> Ceria-Based Mixed Oxide.
摘要： The crystal growth process of the octahedron-like Ce0.95(Yb or Lu)0.05O1.975 was studied by the various techniques. It has been found that the oriented attachment mechanism plays the main role during the crystal growth process. The detailed examination of the crystallite growth process was possible thanks to phosphates-addition as a thin film on the oxide surface. The octahedron-like, iso-oriented crystals are built of the small octahedral mixed oxides crystals via the oriented attachment process. The mechanism of the crystal growth of the pure ceria is probably the same but the there is no thin film of the cerium phosphate on the ceria crystals surface.
关键词： nanocrystalline materials,crystal growth,mixed oxides,Ceria
更新于2025-09-10 09:29:36