Synthesis Of CeO2 Research Articles

Microstructural characterization and equibiaxial flexural strength of CeO2 and Ti-doped CeO2

In this study, the synthesis of CeO2 and titanium dioxide (TiO2) doped CeO2 (TDC) monoliths are investigated, and their fracture strength is assessed using an equibiaxial flexure testing technique at room temperature. Pellets were synthesized using conventional powder processing and sintering methods to produce the desired characteristics. The TiO2 dopant concentration was optimized at 0.1 wt % TiO2 to obtain dense, solid-solution pellets with an enhanced grain microstructure. A ball-on-ring fixture was used to obtain the TRS and Weibull parameters of over 30 pellets for CeO2 and 0.1 wt % TDC to compare fracture behavior. The TRS of CeO2 pellets ranged from 88 to 160 MPa and the TRS of 0.1 wt % TDC pellets ranged from 102 to 171 MPa, both being consistent with published values. Weibull parameters, such as characteristic strength and Weibull modulus, were extracted as 129 MPa and 8.5 for CeO2 and 150 MPa and 9.3 for 0.1 wt % TDC, respectively. Although Hertzian contact damage was observed on compressive surfaces, failure initiation occurred on the tensile surfaces of both types of samples. Fracture surface analysis for CeO2 indicated a predominantly intergranular fracture while 0.1 wt % TDC had a predominantly transgranular fracture mode. The TRS of 0.1 wt % TDC resulted in increased Weibull parameters when compared to CeO2, indicating sample chemistry and microstructure impact mechanical behavior for these samples.

Improvement of the photocatalytic activity of CeO2 on the degradation of chlorophenolic compounds obtained by solution combustion synthesis (SCS). Effect of urea as fuel

This work presents a detailed study to determine the optimal urea content in the synthesis of CeO2 by the solution combustion method and thus obtain the highest photocatalytic activity in the degradation of phenolic compounds. Four CeO2 with different molar ratios urea:Ce(IV) = 0:1, 2:1, 4:1, and 7:1 were synthesized. The synthesized oxides were evaluated in the photocatalytic degradation of 3-chlorophenol, 4-chlorophenol, and 2,4-dichlorophenol using UV light. The synthesized materials were characterized by XRD, Raman spectroscopy, UV–Vis diffuse reflectance spectroscopy, FTIR spectroscopy, N2 physisorption, scanning electron microscopy, transmission electron microscopy and photoluminescence spectroscopy. Raman characterization showed that using urea as fuel favors the formation of oxygen vacancies, increasing up to the urea:Ce(IV) = 4:1 ratio. Photoluminescence studies indicated a decrease on the recombination of photogenerated charges when the oxides are synthesized with urea. The CeO2 synthesized without urea showed 26.6% degradation of 3-chlorophenol, which increased up to 73.6% when it was synthesized with urea. The photocatalytic activity improved mainly due to a higher content of oxygen vacancies and lower recombination of the photogenerated charges. The synthesis method used led to the formation of CeO2 with improved physicochemical properties, so its implementation in the synthesis of other metal oxides and the use of other fuel agents is of great interest for its investigation.

Dual applicability of ceria and silica nanospheres (CeO2@SiO2 NSs) assembled with pencil graphite electrode to sense ascorbic acid, extended with their antibacterial property

Ascorbic acid (AA), being core vitamin, prompts collagen protein growth that maintains our skin, bones, joint lining’s, teeth, gums, blood vessels and even ligament. Initially, synthesis of CeO2 and SiO2 nanoparticles and their nano-spheric composite (CeO2@SiO2NSs) materials through solvothermal and sol–gel routes was achieved. These nanospheres were defensibly characterized through appropriate characterization techniques. Pencil graphite electrode or PGE was modified by drop coating and electrochemically investigated for analytical and real samples with AA detection in phosphate buffer saline. CeO2@SiO2NSs/PGE electrode showed high sensitivity (167.5 μA/mM.cm2) and low LOD (70.18 µM) for AA. The modified electrode revealed good linear range, high stability, specificity and performed well for real samples’ AA detection. CeO2@SiO2 NSs also effectively inhibited multiple bacteria with and without solar irradiation. Overall, the NSs, due to their unique physical, chemical and optical properties offered path towards advance sensing and antibacterial material as well.

Synthesis of CeO2 and CeO2/C Using Powdered Cellulose and Powdered Cellulose–Sucrose as a Template

Synthesis of CeO2 and CeO2/C Using Powdered Cellulose and Powdered Cellulose–Sucrose as a Template

Synthesis of CeO2 and CeO2/C Using Powdered Cellulose and Powdered Cellulose–Sucrose as a Template

CeO2 nanooxide has been synthesized from cerium(III) nitrate using powdered cellulose (PC) and its mixture with sucrose as templates. The removal of templates from composites (PC–Ce(NO3)3 and PC–sucrose–Ce(NO3)3) has been carried out in two ways: via direct burning-out of PC (PC–sucrose) in an air flow and via burning-out of the carbonizate after template pyrolysis. Using UV and IR spectroscopy, X-ray powder diffraction (XRD), and electron microscopy, the influence of the template composition and the method of its removal on the physicochemical characteristics of CeO2 nanoparticles has been studied. A carbon–oxide material CeO2/C has been synthesized by pyrolysis of PC–Ce(NO3)3 and PC–sucrose–Ce(NO3)3 composites. It has been established that the pyrolysis of PC–Ce(NO3)3 and PC–sucrose–Ce(NO3)3 leads to the formation, in the carbonizate, of CeO2 (cerianite) nanoparticles with sizes of 3–4 and 1–2.5 nm, respectively. The average diameter of nanoparticles (according to XRD data) is 3.8 and 2.3 nm. CeO2/C synthesized from the PC–sucrose–Ce(NO3)3 composite contains cerium(III) oxide. All CeO2 nanoparticles in the carbon matrix have a hydroxyl–hydrate cover. The burning of the organic or carbon matrix of the composites leads, regardless of the template used and synthesis conditions, to the formation of CeO2 (cerianite) nanoparticles with the same average diameter of 25 ± 1 nm (according to XRD data), containing an admixture of the Ce(III) phase and having a hydroxyl–hydrate cover. Carbon is present in the material in trace amounts (≤0.15 wt %). The size scatter of CeO2 nanoparticles produced by burning out PC from the PC–Ce(NO3)3 composite is 15–30 nm. In those cases when the organic component from PC–sucrose–Ce(NO3)3 is subjected to burning or the pyrolysis stage of both composites is included in the synthesis process, the appearance of a fraction of larger CeO2 particles (50–60 nm) is observed. The correctness of the obtained data has been confirmed in the course of the model process of hydrogen peroxide decomposition.

Syngas production by methane tri-reforming: Effect of Ni/CeO2 synthesis method on oxygen vacancies and coke formation

The CH4 tri-reforming process can contribute to mitigating CO2 emissions and enables the formation of syngas with different H2/CO ratios. Ni catalysts supported on CeO2 were synthesized by hydrothermal and ionothermal methods and were applied in methane tri-reforming reactions with GHSV of 48,000 mL/g.h, at atmospheric pressure and temperature of 800 °C. The catalytic activity in the tri-reforming reaction was enhanced by changing the morphological properties of the catalyst by appropriate selection of the amount of ionic liquid used in the synthesis procedure. Changing the composition resulted in methane conversion increasing from 60 % to 95 % and carbon dioxide conversion increasing from 40 % to 55 %. Increased Ni dispersion was related to the oxygen vacancies on the Ni-Ce surface, which created interfacial active sites. The results of XANES combined with XPS revealed that a partial reduction of Ni species contributed to high hydrogen yields, due to the distribution of active sites over the catalyst surface. These sites remained active during 5 h, demonstrating the positive effect of the ionic liquid used in the CeO2 synthesis. In addition, post-reaction characterization results showed Ni re-oxidation on the ceria support produced without ionic liquid.

Morphology Modulated Photocatalytic Activity of CeO2 Nanostructures for Selective Oxidation of Biobased Alpha‐Pinene to Oxygenates

AbstractThe effective Ce3+/Ce4+ redox and oxygen mobility of CeO2 induced by tunable nanostructure morphology has attracted a great interest in photocatalytic organic synthesis. Herein, we report on the microwave‐assisted synthesis of CeO2 with nanoparticles (NPs), nanorods (NRs) and nanocubes (NCs) morphologies. The optical‐electronic properties of the nanostructure CeO2 catalysts varied relatively with the respective morphologies. Ce‐NPs catalyst showed a significant blue shift while a red shift was observed for Ce‐NCs and a slight blue shift for Ce‐NRs. The Ce‐NRs and Ce‐NPs showed high charge recombination suppression, which was due to the formation of surface defects associated with dislocations, steps and oxygen vacancies (Vo) as elucidated from the photolumiscence, X‐ray photoelectron spectroscopy and electron paramagnetic resonance results. The surface oxygen defects populated with reactive superoxide oxygens of Ce‐NRs and its high surface showed better photocatalytic activity for oxidation of alpha‐pinene to pinene oxide, verbenol and verbenone as major products. A pinene conversion of 33.6 % to pinene oxide with the selectivity of 54.3 % was achieved with Ce‐NRs. The effective photocatalytic activity of the Ce‐NRs was attributed to its enhanced efficient charge recombination suppression and oxygen vacancies. Ce‐NRs catalyst was recyclable without any significant loss of its initial photoactivity.

Synthesis of CeO2 as promising adsorbent for the management of free-DNA harboring antibiotic resistance genes from tap-water

The free-deoxyribonucleic acid (free-DNA) cassette harboring antibiotic resistance gene in drinking water has been linked with impaired public health. To prevent the problem of antibiotic resistance, we have synthesized a CeO2 adsorbent that exhibit highly positive character in a wide pH range, via the simple self-propagation combustion protocol, for the removal of free-DNA harboring antibiotic resistance genes. Molecular characterization of the extracted genes showed that the sizes for E. coli and inherent gyrB genes are 147 and 460 bp with a purity between 19 and 2.0. The XRD, SEM, TEM, and PZC results of the as-synthesized CeO2 showed an agglomerate of pure cubic-faced centered material and highly crystalline, with a net charge at pH 6.2. Experimental results revealed that the reaction proceeded via pseudo-first-order kinetic, and it is governed by electrostatic attraction. The free-DNA solution pH, electrolyte, and competing ions impacted on the adsorption process. Further experimental results showed that the as-synthesized CeO2 adsorbent has the potential to be used for the removal of free-DNA harboring ARGs from tap-water even under oxic conditions.

Synthesis of CeO2@S Composite as Cathode Material for in Lithium-Sulfur Batteries

Synthesis of CeO2@S Composite as Cathode Material for in Lithium-Sulfur Batteries

Development of RuO2/CeO2 heterostructure as an efficient OER electrocatalyst for alkaline water splitting

Here, the synthesis of RuO2 loaded CeO2 with varying amount of Ru loading with enhanced amount of Ce3+ and surface area, through synthesis of CeO2 using cerium ammonium carbonate complex as procure followed by Ru loading by impregnation and calcination at 300 °C, is presented. Corresponding characterizations by XRD, SEM, TEM, XPS of all the samples reveal the formation of highly crystalline mesoporous CeO2 nanoparticles with uniformly dispersed RuO2 particles on the CeO2 surface having approximately 45% Ce3+. All the samples were utilized as oxygen evolution reaction (OER) catalyst for electrocatalytic H2 generation through water electrolysis. Electrocatalytic experiments reveal that synthesized 1 wt% RuO2 loaded CeO2 (1-RuO2/CeO2) showed superior OER activity. A quite low over-potential of 350 mV is required to attain a current density of 10 mA/cm2 (ɳ10), with a Tafel slope of 74 mVdec−1 for OER in 1 M KOH solution. The synthesized 1-RuO2/CeO2 electrocatalyst also exhibited superior long term stability in basic medium and redox atmosphere.

Understanding CeO2‐Based Nanostructures through Advanced Electron Microscopy in 2D and 3D

AbstractEngineering morphology and size of CeO2‐based nanostructures on a (sub)nanometer scale will greatly influence their performance; this is because of their high oxygen storage capacity and unique redox properties, which allow faster switching of the oxidation state between Ce4+ and Ce3+. Although tremendous research has been carried out on the shape‐controlled synthesis of CeO2, the characterization of these nanostructures at the atomic scale remains a major challenge and the origin of debate. The rapid developments of aberration‐corrected transmission electron microscopy (AC‐TEM) have pushed the resolution below 1 Å, both in TEM and in scanning transmission electron microscopy (STEM) mode. At present, not only morphology and structure, but also composition and electronic structure can be analyzed at an atomic scale, even in 3D. This review summarizes recent significant achievements using TEM/STEM and associated spectroscopic techniques to study CeO2‐based nanostructures and related catalytic phenomena. Recent results have shed light on the understanding of the different mechanisms. The potential and limitations, including future needs of various techniques, are discussed with recommendations to facilitate further developments of new and highly efficient CeO2‐based nanostructures.

Microfluidic synthesis of metal oxide nanoparticles via the nonaqueous method

Microfluidic synthesis allows for a good control of the particle formation conditions while minimizing the consumption of material. In this study, we exploited these advantages for the nonaqueous synthesis of TiO2, ZnO and CeO2 nanoparticles in a closed micro droplet reactor which resulted in well-defined particle structures. Monodisperse droplets are generated in amicrofluidic flow-focusing area and subsequently transported to a reaction zone allowing synthesis temperatures of up to 200 °C. In addition, we showed that a continuous particle generation process using solid precursor species can be realized without channel clogging. We present different microfluidic designs with reaction zones consisting either of a long meandering channel or a short expansion channel to realize the different reaction times required for the respective model systems. Interestingly, we found that at elevated temperatures, the reaction mixture diffuses into the surrounding continuous phase fluid which leads to a shrinkage of the droplets, forcing eventually the assembly of highly spherical aggregate structures. Depending on the different model systems, we obtained nanospheres of about 100 nm from the CeO2 synthesis and microspheres up to 17 µm in size from the TiO2 synthesis. In contrast, ZnO syntheses at milder temperatures were conducted without any droplet shrinkage which resulted in randomly shaped aggregates of 150 nm that self-assembled in the droplet micro reactor. Thus, a versatile synthesis technique is presented that can be applied for various metal oxides over a broad range of reaction parameters, as a promising approach for the controlled production of high quality nanoparticles.

Design and synthesis of CeO2 nanowire/MnO2 nanosheet heterogeneous structure for enhanced catalytic properties

A novel CeO2 nanowires/MnO2 nanosheets heterogeneous structure was successfully synthesized by a facile hydrothermal method and its carbon monoxide (CO) catalytic properties were studied. Amorphous MnO2 nanosheets were firstly formed on the surface of CeO2 nanowires to establish a core-shell structure mediated by interfacial redox process which was further transformed to δ-MnO2 through post heat treatment. Compared with as-prepared CeO2 nanowires, CeO2 nanowires/MnO2 nanosheets heterogeneous architecture showed improved catalytic performance because of the strong synergistic interaction between CeO2 and MnO2 at the interface. Moreover, the formation of δ-MnO2 further enhanced the catalytic properties by achieving more defective structures through a slight Mn doping. The catalytic activities can be further enhanced by core-shell compositional optimization. Thus, designing heterogeneous junction was an attractive approach for improving the catalytic properties of CeO2 based nanomaterials.

Sintering of Ce, Sm, and Pr Oxide Nanorods

Synthesis of CeO2, Pr2O3, and Sm2O3 nanorods and their sintering have been investigated. In a strongly alkaline medium, nanorods of CeO2, Pr2O3, and Sm2O3 were prepared from trivalent salts of rare earths (Ce, Pr, Sm) via precipitation synthesis. Nanorods were formed by nanocrystallites of fibrous structure, which were produced by the mechanism of self‐arrangement of hexagonal particles of Re(III) hydroxides. The subsequent transformation of hydroxide into oxide proceeded via self‐preservation of the rod‐like structure. In CeO2, the fibrous structure was noncohesive during thermal treatment at temperature of 500°C and higher. Regardless of the shape of the CeO2 particles (spherical versus rod‐like), sintered ceramic was formed by equiaxial grains. The cohesion of the fibrous structure of Pr and Sm oxides was higher than in CeO2. The rod‐like shape of the particles of Pr and Sm oxides was (partially) preserved during sintering.

Synthesis of Nanostructured Catalytic Materials from Microemulsions

Since the 1980s [1,2], colloidal systems such as microemulsions (ME) have been widely investigated, especially for the synthesis of nanomaterials for various applications.[...]

Optimization of a highly active nano-sized Pt/CeO2 catalyst via Ce(OH)CO3 for the water-gas shift reaction

Crystalline cerium hydroxy carbonate (CHC: Ce(OH)CO3) was prepared by a novel precipitation/digestion method at room temperature in air. The nano-sized CeO2 supports were obtained by the thermal decomposition of CHC and the Pt/CeO2 catalysts were prepared by an incipient wetness impregnation method. The pre-calcination temperature and aging time were optimized to obtain a highly active Pt/CeO2 catalyst for the water gas shift reaction (WGS). The Pt/CeO2 catalyst exhibited the highest CO conversion (82%) and the lowest activation energy (55 kJ/mol) at a very high gas hourly space velocity (GHSV) of 45,515 h−1 when the optimized synthesis parameter (pre-calcined temperature = 400 °C and aging time = 4 h) was used in the synthesis of CeO2. This is mainly due to the high BET surface area, nano-sized CeO2, and intimate interaction between Pt and CeO2.

Synthesis of CeO2 by thermal decomposition of oxalate and kinetics of thermal decomposition of precursor

CeO2 was synthesized by calcining Ce2(C2O4)3·8H2O above 673 K in air. The precursor and its calcined products were characterized using thermogravimetry and differential scanning calorimetry, Fourier transform infrared spectra, X-ray powder diffraction, scanning electron microscopy, and UV–Vis absorption spectroscopy. The result showed that cubic CeO2 was obtained when the precursor was calcined above 673 K in air for 2 h. The UV–Vis absorption spectroscopy studies showed that superfine CeO2 behaved as an excellent UV-shielding material. The thermal decomposition of the precursor in air experienced two steps, which are: first, the dehydration of eight crystal water molecules, then the decomposition of Ce2(C2O4)3 into cubic CeO2. The values of the activation energies associated with the thermal decomposition of Ce2(C2O4)3·8H2O were determined based on the Starink equation.

Synthesis of CeO2 and CeZrO2 mixed oxide nanostructured catalysts for the iso-syntheses reaction

The different CeO2 oxides and mixed oxide CeZrO2 showed nanosized structures and morphologies in particular distinct structural and surface properties. These catalysts were effective in the iso-synthesis reaction. The flowerlike CeO2 (F) and the mixed oxide (CeZrO2) showed the highest selectivity toward isobutene and isobutene and low methane formation. The turnover frequency (TOF) related to the total basicity and total acid sites are equal for all catalysts within a factor less than 2 and did not change with the oxygen lattice capacity (OSC), which confirms that the reaction is structure insensitive. The selectivity of total hydrocarbon and of CO2 are independent of the basic sites. However, the selectivity of total iso-C4 exhibits a linear relationship with the basic sites. The mixed oxide (CeZrO2) presented the strongest basic sites and thus the highest selectivity to iso-C4. Significant is the influence of Lewis acid sites on the selectivity of isobutene increasing and isobutane decreasing both linearly with Lewis acid sites. The ratio isobutene/isobutane presented a linear relationship with the Lewis acid sites which are directly related to OSC capacity of reducible oxides.

Synthesis of CeO2 or α–Mn2O3 nanoparticles via sol–gel process and their optical properties

Nanocrystalline cubic fluorite/bixbyite CeO2 or α–Mn2O3 has been successfully synthesized by using methanol as a solvent via sol–gel method calcined at 400 °C. The obtained products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), UV–vis absorption and Photoluminescence (PL) spectroscopy. TEM reveals that the as-synthesized ultra-fine samples consist of elliptical/spherical and sheet-like morphology of crystalline particles of 8/30 nm, which are weakly aggregated. Optical absorbance spectra reveal that the absorption of ceria in the UV region originates from the charge- transfer transition between the O2− (2p) and Ce4+ (4f) orbit in CeO2. However, α–Mn2O3 nanostructures with nearly pure band gap emission should be of importance for their applications as UV emitters.

Synthesis of CeO2 and Y2O3-Doped CeO2 Composite Fibers by Electrospinning

Electrospinning was employed to produce homogeneous inorganic-organic composite fibers from alcohol solutions containing polyvinyl butyral (PVB) and precursor of yttrium and cerium ions. Upon heat treatment, ceria and yttria-doped ceria fibers were obtained. The fibers retained the original morphology observed in the as-spun composition. X-ray diffraction was used to identify the crystalline phases of the final products. Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and BET analysis were employed to study the ceramic-phase formation and the morphological evolution of the fibers. Thus, uniform ceria and yttria-doped ceria fibers several micrometers long of high-phase purity were produced. The CeO2 and the CeO2 with Y2O3 fibers presented average diameters that ranged from 0.8 to 1.7 µm, and the distribution of specific surface ranged from 24 to 127 m2/g after heat treatment at 1000°C.