Control of particle size and shape of precursors for ceria using ammonium carbonate as a precipitant

Spherical nanocrystalline precursors of ceria (CeO₂) and CeO₂ powder with different size distributions were prepared by a reflux method using cerium nitrate hexahydrate (CN) as the cerium source and ammonium carbonate (AC) as the precipitant. The crystalline phases of the synthesized CeO₂ precursors were identified as orthorhombic Ce₂O(CO₃)₂·H₂O and hexagonal CeCO₃OH. The particle size and shape could be easily controlled by the CN concentration and the ratio of [AC]/[CN]. The CeO₂ precursors were calcined at 400-700 °C to obtain CeO₂. The particle size distribution and morphology of the synthesized CeO₂ powders were unaffected by the calcination. The specific surface area of the CeO₂ powders was increased by the release of CO₂ and H₂O during the calcination. The calcination temperature is an important factor for the preparation of CeO₂ powder with a high surface area.     

Synthesis and sintering behaviour in CeO2-ZrO2 ceramics

The co-precipitation method has been employed to prepare CeO₂-ZrO₂ ceramics. The application of a wet chemical method is expected to yield highly sinterable material at lower sintering temperatures. The characteristics of the synthesized powders are evaluated with respect to the particle size distribution, calcination step, and the degree of agglomeration. The sintering behaviour of the prepared powder is studied at various temperatures to obtain different phase distributions and grain sizes. The amount of the monoclinic phase in the as-sintered specimen is decreased with increasing CeO₂ contents in CeO₂-ZrO₂. 13.7 mol% CeO₂ is sufficient to achieve a tetragonal phase in the CeO₂-ZrO₂ system. In addition, Y₂O₃ and MgO dopants in CeO₂-ZrO₃ reduce the grain size and result in a fully tetragonal phase for the 10 mol% CeO₂ matrix.     

Synthesis of porous Mg-doped CeO2 powders via self-propagating high-temperature synthesis route

The aim of this study was synthesis of Mg-doped porous cerium oxide powder by self-propagating high-temperature synthesis reaction of Mg-xCeO₂-O₂ system. Results indicated that doping Mg in the CeO₂ crystal structure increased its lattice parameter slightly, and shifted the Ce-O band in the FTIR spectra from 490 to 574 cm⁻¹. Moreover, the EDS results revealed the distribution of Mg in the CeO₂ microstructure. There were a high volume fraction of interconnected macro-pores in the microstructure of cerium oxide after the synthesis process. Increase in the x-value from 0.05 to 0.25 mol decreased the mean size and volume fraction of pores from 2.4 to 1 µm and 50 to 30 vol%, respectively. In addition, the BET surface area of porous CeO₂ varied between 0.3 and 1.57 m²/g. Finally, it was inferred that the SHS technique can be introduced as a rapid and novel method for synthesis of Mg-doped porous CeO₂ powders.     

Synthesis, microstructure and mechanical properties of ceria stabilized tetragonal zirconia prepared by spray drying technique

Ceria stabilized zirconia powders with ceria concentration varying from 6 to 16 mol% were synthesized using spray drying technique. Powders were characterized for their particle size distribution and specific surface area. The dense sintered ceramics fabricated using these powders were characterized for their microstructure, crystallite size and phase composition. The flexural strength, fracture toughness and microhardness of sintered ceramics were measured. High fracture toughness and flexural strength were obtained for sintered bodies with 12 mol% of CeO₂. Flexural strength and fracture toughness were dependent on CeO₂ concentration, crystallite size and phase composition of sintered bodies. Correlation of data has indicated that the transformable tetragonal phase is the key factor in controlling the fracture toughness and strength of ceramics. It has been demonstrated that the synthesis method is effective to prepare nanocrystalline tetragonal ceria stabilized zirconia powders with improved mechanical properties. Ce-ZrO₂ with 20 wt% alumina was also prepared with flexural strength, 1200 MPa and fracture toughness, 9.2 MPa√m.     

Boosting Polyethylene Hydrogenolysis Performance of Ru-CeO2 Catalysts by Finely Regulating the Ru Sizes

Hydrogenolysis is an effective method for converting polyolefins into high-value chemicals. For the supported catalysts commonly used, the size of active metals is of great importance. In this study, it is discovered that the activity of CeO₂-supported Ru single atom, nanocluster, and nanoparticle catalysts shows a volcanic trend in low-density polyethylene (LDPE) hydrogenolysis. Compared with CeO₂ supported Ru single atoms and nanoparticles, CeO₂-supported Ru nanoclusters possess the highest conversion efficiency, as well as the best selectivity toward liquid alkanes. Through comprehensive investigations, the metal-support interactions (MSI) and hydrogen spillover effect are revealed as the two key factors in the reaction. On the one hand, the MSI is strongly related to the Ru surface states and the more electronegative Ru centers are beneficial to the activation of C H and C C bonds. On the other hand, the hydrogen spillover capability directly affects the affinity of catalysts and active H atoms, and increasing this affinity is advantageous to the hydrogenation of alkane species. Decreasing the Ru sizes can promote the MSI, but it can also reduce the hydrogen spillover effect. Therefore, only when the two effects achieve a balance, as is the case in CeO₂-supported Ru nanoclusters, can the hydrogenolysis activity be promoted to the optimal value.     

Synthesis and luminescence of Sr2CeO4 fine particles

Fine particles of a blue emission phosphor Sr₂CeO₄ have been synthesized using a chemical co-precipitation technique, and the textual and luminescent properties were compared with the one synthesized by the conventional solid-state reaction method. Particle size and distribution of the Sr₂CeO₄ fine powder prepared by the co-precipitation process were smaller and narrower than those obtained by the samples prepared from the conventional one. The emission intensity of the fine particles was equal to that of the larger particles prepared from the solid-state reaction, on the contrary to the general tendency that emission intensity decrease with particle size reduction. Although no Ce³⁺ peaks were observed in EPR measurements, X-ray photoelectron spectra of the samples clearly elucidated the existence of Ce³⁺ only on the surface of Sr₂CeO₄.     

Synthesis of micron-sized porous CeO2SiO2 composite particles for ultraviolet absorption

Micron-sized porous composite particles composed of CeO₂ and SiO₂ nanoparticles were prepared for a UV absorption application by an aerosol spray-drying process from as-prepared CeO₂ nanoparticles, commercial SiO₂, and a polystyrene latex template. The morphology, structure crystallinity and pore size distribution of the as-prepared porous CeO₂SiO₂ composite particles were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Barrett-Joyner-Halenda (BJH) method, respectively. The porous CeO₂SiO₂ composite particles, with diameters of approximately 10 μm, showed a spherical morphology. As the contents of CeO₂ in the precursor was increased from 0.25 wt% to 1.5 wt%, we observed a change in the morphology of the composite particles from compactly packed porous particles to loosely packed porous particles. The as-prepared CeO₂SiO₂ composite particles were composed of meso- and macropores in the range of 3–200 nm. The effect of the CeO₂ content on the porous composite particles in terms of the UV absorption properties was also investigated by UV-visible spectroscopy. When the content of CeO₂ exceeded 0.75 wt% in the precursor, the particles showed higher UV absorption values compared to those of commercial TiO₂ nanoparticles. The as-prepared porous CeO₂SiO₂ composite particles can therefore be promising materials given their high UV absorption value.     

Effects of CeO2 coating uniformity on high temperature cycle life performance of LiMn2O4

CeO₂ is coated using different precipitants on the surface of LiMn₂O₄ in order to investigate the effect of CeO₂ coating uniformity on the cycle life performance at high temperature. CeO₂ is prepared by a precipitation method without the use of a surfactant. Ammonium carbonate or ammonium hydroxide is respectively used as a precipitant in order to control the morphology and particle size of CeO₂. More uniform coating layer composed of well dispersed CeO₂ nanoparticles is obtained with ammonium hydroxide while aggregation lead to non-uniform coating layer when ammonium carbonate is used. The CeO₂-coated LiMn₂O₄ shows better cyclability both at room temperature and 60 °C than the pristine sample but much higher capacity retention rate can be achieved by using ammonium hydroxide. The smaller particle size and uniform coating layer obtained using ammonium hydroxide appear to contribute to the better cycling performance.     

Preparation and characterization of CeO2 highly dispersed on activated carbon

A new material constituted by cerium dioxide highly dispersed on activated carbon (CeO₂/AC) was prepared by an impregnation method using cerium(III) nitrate as CeO₂ precursor. In order to evaluate the degree of ceria dispersion on the carbon support, CeO₂/AC was characterized by a number of techniques: thermogravimetry coupled with a mass spectrometer (TG-MS), N₂ adsorption at 77 K, temperature-programmed desorption (TPD), temperature-programmed reduction (TPR) and transmission electron microscopy (TEM). The analysis of the decomposition process under inert atmosphere indicated that cerium nitrate decomposes at 440-460 K, with the evolution of NO. Furthermore, this process produces an additional oxidation of the carbon surface (with evolution of N₂O) and the subsequent onset of new oxygen surface groups, detected by means of temperature-programmed desorption. The ceria deposition process takes place with a decrease in the N₂ adsorption capacity of the starting carbon support, and the analysis of the pore size distribution showed that the majority of ceria particles are situated at the most internal part of the carbon porosity. The temperature-programmed reduction profile of CeO₂/AC was very different to that shown by unsupported CeO₂, with only one continuous reduction process at low temperatures (800-900 K). Finally, TEM pictures gave direct evidence that ceria is highly dispersed on the carbon surface, with a narrow CeO₂ particle distribution centred around 3 nm.     

CuO/CeO2 catalysts prepared with different cerium supports for CO oxidation at low temperature

The activity of a catalyst depends on the nature of its support, its active site, and its preparation method. This study aimed to employ various types of CeO₂ supports such as commercial CeO₂ and self-prepared CeO₂ for the preparation of copper catalysts. The CuO/CeO₂ catalysts were prepared using the polyol process and impregnation method. The catalysts were characterized using Brunauer–Emmett–Teller analysis, scanning electron microscopy, and X-ray analysis, and their catalytic activity for CO removal was evaluated in a microcatalytic reactor. The experimental results showed that the catalytic activity of the CuO/CeO₂ catalysts with different calcination temperatures decreased in the following order: 500 °C > 300 °C > 700 °C. Compared to the impregnation method, the polyol process generated well-dispersed metal particles over the support and showed higher CO removal efficiency with low activation energy. Compared to CuO/CeO₂ catalysts with commercial CeO₂, those with CeO₂ that was self-prepared by pyrolysis had a large pore volume and good crystal structure of CeO₂ and showed good performance. The catalytic activity for CO removal was in the following order: CuO/CeO₂-P (pyrolysis) > CuO/CeO₂-C (commercial) > CuO/CeO₂-D (deposition precipitation). CuO/CeO₂-P catalysts showed good activity even at low temperature. The CuO/CeO₂-P(300)-P-120 min catalyst was found to possess the good CO removal rate when the oxygen content was 6%, CO concentration was 500 ppm, catalyst weighed 1.0 g, pollutant gas velocity was 500 mL min⁻¹, SV was 3.7 × 10⁴ h⁻¹, and reaction temperature was 150 °C.     

Graphene oxide (GO) doped CeO2 as potential enhancer of methyl orange degradation

In this article, a simple method for the synthesis of Graphene Oxide-Cerium oxide (GO/CeO₂) is carried out. The prepared sample was characterized in detail, such as scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman, Brunauer-Emmett-Teller technology N₂ adsorption-desorption analysis (BET), photoluminescence (PL) and UV-visible diffuse reflectance spectroscopy (DRS). It was indicated that GO was successfully incorporated into CeO₂. The photocatalytic mechanism of GO/CeO₂ was also explained. The MO solution catalyzed by CeO₂ and GO/CeO₂ was analyzed by a UV-visible spectrometer. The efficiency of GO/CeO₂ degrading methyl orange (MO) is improved from 50% to 87% compared to pure CeO₂ under the visible light. GO/CeO₂ exhibited better photocatalytic performance than CeO₂, which indicated GO doping improved the photocatalytic capacity of the CeO₂ catalyst. It may have potential applications in addressing environmental wastewater.     

Optimization of a nanoparticle ball milling process parameters using the response surface method

Nanocrystalline TiO₂-CeO₂ powders were synthesized from their TiO₂ and CeO₂ oxides using mechanical ball milling process. The response surface method is applied to identify optimal parameters for the synthesis of TiO₂-CeO₂ photocatalyst. Analysis of variance and main effect plot are used to determine the significant parameters and set the optimal level for each parameter. Regression analysis showed good agreement of experimental data with the second-order polynomial model with a coefficients of determination: R²?=?0.991, R²_Adj.?=?0.940 and R²_Pred.?=?0.983. Under optimal experimental conditions of TiO₂:CeO₂ weight percentage ratio 71:29, milling speed 200?rpm, and milling time 115?min the highest photodegradation efficiency was achieved. On the basis of the above statistical analysis, it was found that the band gap energy of TiO₂-CeO₂ nanoparticles decreases with the increase of the milling speed and milling time with constant TiO₂:CeO₂ weight percentage ratio. Obtained results suggest that mechanical ball milling process is a rapid, efficient and low energy consumption method to synthesize TiO₂-CeO₂ photocatalyst.     

Enhanced microwave absorption performance of nitrogen-doped porous carbon dodecahedrons composite embedded with ceric dioxide

CeO₂/Co/C dodecahedrons composites with excellent microwave absorption performance were synthesized by using a hydrothermal method. ZIF-67/CeO₂ was first prepared by introducing CeO₂ into the precursor of ZIF-67 and then CeO₂/Co/C composite was obtained after heat treatment. Impedance matching of the samples could be well adjusted by controlling the content of CeO₂. Unique dodecahedral structure for more interfacial reflection and cerium dioxide oxygen vacancies enhance microwave absorption performance. Specifically, the CeO₂/Co/C exhibited a minimum reflection loss of ?68.83 dB is observed at 5.92 GHz, while the thickness was 3.69 mm. The introduction of CeO₂ effectively enhanced the impedance matching of the materials and improved the microwave absorption performance. Therefore, this CeO₂/Co/C composite is a promising microwave absorber material with high performance.     

Optical,morphological, electrical properties of ZnO-TiO2-SnO2/CeO2 semiconducting ternary nanocomposite

Low dielectric constant and low dielectric loss with moderate wide bandgap, novel semiconducting metal oxide composites are useful materials for applying optoelectronic, microwave dielectric ceramics. A less dielectric constant is required for wireless communication to reduce the cross pairing between conductors and also for fast signal transmission. In the present study, the structural, optical, and dielectric properties of ternary ZnO - TiO₂ added with SnO₂/CeO₂ semiconducting nanocomposite materials were investigated and synthesized by the solid-state gelation method. The samples were sintered at a temperature of 450 ⁰C. The X-ray diffraction patterns of composites revealed the existence of TiO₂ anatase phase, SnO_2, and CeO₂. The average crystallite size at d₁₀₁ was measured using the Scherer method, ranging from 6.18 nm to 9.13 nm. The overall crystallite size was calculated using the Size-strain plot method, and it is in the range of 14.8 nm to 17.16 nm. The surface morphology of all samples appears uniform in size and spherical shape. The average particle size of grains was 35 nm. The absorbance properties studied by UV–Visible spectroscopy and bandwidth were 2.6 eV calculated using Tauc’s plot method, and it reveals the formation of new energy levels. The dielectric properties of pellet dimensions of 1 mm thickness and 10 mm diameter, measured from the LCR meter, are indicated at 1 kHz frequency. The most significant dielectric constant (ε_r) and lowest loss tangent (Tan δ) are 53.89 and 0.25 for pure ZnO - TiO₂, and the lowest dielectric constant (ε_r) and less loss tangent (Tan δ) are 9.69 and 0.38 for 1 wt% CeO₂ doped to ZnO - TiO₂. The conductivity of the composite is in the range of 10^-7 S/cm. With additive concentration to ZnO - TiO₂, both SnO₂ and CeO₂ are equally potential and modifies the parameters due to the similar bandgaps and more oxygen availability.     

Microstructure and corrosion resistance of Ni-based alloy laser coatings with nanosize CeO2 addition

Micron-size Ni-base alloy (NBA) powders were mixed with both 1.5 wt.% (hereinafter %) micron-size CeO₂ (m-CeO₂) and also 1.5% and 3.0% nano-size CeO₂ (n- CeO₂) powders. These mixtures were coated on low-carbon steel (Q235) by 2.0 kW CO₂ laser cladding. The effects on the microstructures, phases and electrochemical corrosion of the coatings upon the addition of m- and n- CeO₂ powders to NBA (m- and n- CeO₂ /NBA) have been investigated. The results showed that a smooth coating was prepared under suitable processing parameters (P= 2.0 kW, V= 180 mm min^{- 1}) by adding 1.5% n- CeO₂. In addition to the primary phases of γ-Ni, Cr₂₃C₆ and Ni₃B in the Ni-base alloy coating, CeNi₃ was formed in Ni-base alloy coatings with both n- CeO₂ and m-CeO₂ particles, and CeNi₅ appeared in the coating upon decreasing the size of CeO₂ particles. Well-developed dendrites were observed in the Ni-base alloy coating; directional dendrites grew at the interface in the coating upon the addition of m-CeO₂, whereas fine and multioriented dendrites grew upon decreasing the size of CeO₂ particles to the nanoscale. Actinomorphic dendrites and compact equiaxed dendrites grew from the interface to near the surface upon increasing the content of n- CeO₂ from 1.5 to 3.0%. In strongly acidic HNO₃ solution, the severe corrosion of dendrites occurred and there were many corrosion pits in the Ni-base alloy coating; intercrystalline corrosion also has a dominant role upon the addition of m-CeO₂, whereas uniform corrosion occurs in the coating as the size of CeO₂ particles is decreased to nanoscale.     

Enhanced optical properties of heterostructured ZnO/CeO2 nanocomposite fabricated by one-pot hydrothermal method: Fluorescence and ultraviolet absorption and visible light transparency

Many researchers investigated the properties of either discrete metal oxide CeO₂ or ZnO materials. However, less attention has been paid to the various nanostructure and performances of CeO₂ and ZnO nanocomposite up to now. In this paper, a facile and low cost one-pot hydrothermal synthesis method has been adopted to obtained directly precursors of CeCO₃OH and Zn₅(CO₃)₂(OH)₆ with different Ce atom molar ratios to Zn, which are transformed into their corresponding metal oxide to form the ZnO/CeO₂ heterostructure nanocomposites (HSNCs) by pyrolysis. The heterostructure is composed of ZnO and CeO₂ monocrystals, simultaneously, CeO₂ monocrystals are well dispersed on the surface of ZnO monocrystal for cosmetics. Bing dependent on the analysis results of XRD and TEM for the obtained precursors before and after pyrolysis, the formation mechanism of HSNCs was proposed. To the best of our knowledge, the paper first reported heterostructured ZnO/CeO₂ nanocomposite grown in one-pot mixed aqueous solution of cerium nitrate, zinc acetate and urea without other extra surfactant. Additionally, the influence of various Ce/Zn molar ratios on the heterostructure, fluorescence emission and UV–visible absorption properties of HSNCs was investigated in detail. ZnO/CeO₂ HSNCs display higher fluorescence emission with the increasing Ce/Zn molar ratio. Meanwhile, the larger Ce/Zn molar ratio of ZnO/CeO₂ HSNCs, the stronger transparency in the visible light region and the weaker UV absorption. The results are due to the fact that the band gap of ZnO/CeO₂ HSNCs will decrease from 3.25 to 3.08 eV when Ce/Zn atom molar ratio is increased from 0 to 0.08. By the comprehensive analysis on the optical performances of HSNCs with the different Ce/Zn atom molar ratios, ZnO/CeO₂-0.04 HSNCs could become UV absorber materials and transparent material in the visible region. ZnO/CeO₂-0.04 HSNCs with the UV-filtering and Vis-transparent properties is appropriate for personal-care cosmetics.     

Size Distribution of Gold Nanoparticles Used by Small Angle X-ray Scattering

ABSTRACT

The size distribution of gold nanoparticles was estimated based on the scattering intensity data obtained from small angle X-ray scattering (SAXS) and compared with the result of micrographs by transmission electron microscopy. The slope of the Guinier plot was used to estimate the mean size assuming a narrow particle size distribution. When the size distribution is narrow, the mean size can be easily obtained from slope of a Guinier plot of scattering data within 10% error. Additionally, assuming a lognormal size distribution, the size distribution and the mean size can be calculated using the experimental SAXS data in the fitting analysis. The histogram method, which utilizes the coefficient matrix of scattering intensity, was also applied to the estimation of the size distribution, and this method could be useful for a rough estimate of the size distribution.     

Synthesis of nano-ceria powder of high thermal stability

A new method is studied for preparing nano-ceria by acid leaching MgO from CeO₂−MgO mixed powder made by calcining a gel. The MgO in the mixed powder can be leached completely with acetic acid solution at room temperature, but the CeO₂ remains unaffected. The surface area (Sg) of the resulting CeO₂ increases with Mg/Ce ratio, but approaches constant after the ratio is larger than a given value which is higher for the higher gel calcining temperature. When Mg/Ce is 8 (molar ratio) and the calcining temperature is 1253 K, the Sg of the resulting ceria remains 25.1 m²/g even after annealed at 1253 K for 4 h. In comparison with the conventional methods, CeO₂ from the new method shows higher surface area and higher thermal stability.     

The effect of rare earth CeO2 on microstructure and properties of in situ TiC/Al–Si composite

In this work, CeO₂ is investigated as an additive for in situ preparation of TiC/Al–Si composite using exothermal dispersion (XD)+casting technology. Experimental results show that CeO₂ at high temperature exhibits the same function as Ce, which is a kind of good modificator. When 0.5 wt.% CeO₂ additive is added, the microstructure of eutectic silicon is significantly changed (the size is greatly reduced). Meanwhile, the amount of TiC particles is increased and the size is reduced. Compared with the composite without added CeO₂, the hardness value (HB) value, tensile strength and tensile elongation are greatly increased. However, under dry sliding friction test, weight loss of the composite is not significantly changed.     

Daylight photocatalysis performance of biomorphic CeO2 hollow fibers prepared with lens cleaning paper as biotemplate

Hierarchical, biomorphic CeO₂ hollow fibers with mesoporous tube walls have been fabricated using lens cleaning paper as biotemplates. After sintered at 550 °C in air, the cellulosic fibers of paper were converted into micro-tubes composing of CeO₂ crystallites with grain size about 8 nm. The photocatalytic activity of the CeO₂ fibers was evaluated by photodegradation efficiency of methylene blue in aqueous solution under daylight irradiation. The characterized results show that the CeO₂ fibers faithfully replicated micro-fibrous structure derived from original template and possessed dramatic enhanced photocatalytic activity compared with bulk CeO₂. This simple biotemplate method provides a cost-effective and eco-friendly route to obtain high performance photocatalysts.