As-synthesized CeO2 Research Articles

Synthesis of CeO2 Porous Nanospheres with Tunable Pore and Particle Sizes and Their Adsorption to Methyl Orange

The catalytic performance of ceria oxide (CeO[Formula: see text] was greatly influenced by the materials’ structure and surface area. In this paper, CeO2 porous nanospheres (PNS) with tunable pore and sphere sizes were synthesized by a solvothermal method using diethylene glycol as reaction media. All the as-synthesized CeO2 PNS presented good adsorption capacity for methyl orange, which makes them potential application in waste water treatment conveniently and economically. The control over the sphere and pore sizes of CeO2 PNS was achieved by regulating the volume of water bubble in the reaction system, which supplied limited room for the assembling of preformed CeO2 small nano-precursors.

Structural, morphological and optical properties of shuttle-like CeO2 synthesized by a facile hydrothermal method

In this study, the shuttle-like CeO2 particles were synthesized by hydrothermal method and characterized by X-ray diffraction (XRD), TG, scanning electron microscopy (SEM), Photoluminescence (PL), UV–vis and Raman analyses. The cubic fluorite structure and average particle size of ceria were confirmed by XRD. Initially differential thermal analysis and thermal gravimetric were used to analyze the reaction process and chemical mechanism, which suggested a crystallization temperature of the as-synthesized CeO2 powder at 600 °C. The reaction time and the reaction concentration of the solution were systematically investigated. It is found that the reaction time and the reaction concentration are key parameters for controlling the final morphology. Mixed oxidation states (Ce4+ and Ce3+) were detected in the samples, confirmed using X-ray photo-electron spectroscopy (XPS) and Raman. It has been proven that oxygen vacancies and Ce3+ ions exist at the grain surface and at the grain boundaries. The appearance of emission peaks and the visible luminescence peaks can be attributed to the oxygen related defects. The existence of Ce3+ ions and oxygen defects existing in shuttle-like CeO2 samples can lead to the formation of some localized band gap states, which is possibly responsible for the red shifting of band gap.

Effect of NaOH on morphologies and photocatalytic activities of CeO2 synthesized by microwave-assisted hydrothermal method

This research reports the successful synthesis of CeO2 nanorods as a photocatalyst in a solution containing different content of NaOH by the microwave-assisted hydrothermal method. The phase, morphologies and photocatalytic properties of the as-synthesized CeO2 samples were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible spectroscopy. The XRD patterns of products certified that the as-synthesized CeO2 samples were pure cubic CeO2 phase. TEM images revealed the presence of as-synthesized uniform CeO2 nanorods using 20ml NaOH solution. The influence of NaOH solution on the photocatalytic properties of as-synthesized CeO2 samples was investigated through degradation of methyl orange (MO) as a model dye. Over 95% photodegradation of MO was degraded by the CeO2 nanorods within 120min under UV light irradiation.

Synthesis, characterization and thermal stability of CeO2 stabilized ZrO2 ultra fine nanoparticles via a sol-gel route

CeO2 stabilized ZrO2 ultra fine nanoparticles were successfully synthesized via a simple and effective sol-gel synthetic approach by using zirconylchloride octahydrate, cerium nitrate hexahydrate, and citric acid as starting materials. A series of techniques, including X-ray diffraction (XRD), thermogravimetry (TG), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and N2-sorption analysis, were used to characterize the structure and morphology of the as-prepared samples. XRD studies indicate that the as-synthesized sample is of well crystallized tetragonal phase of CeO2 stabilized ZrO2 with high purity. TEM images show that the as-synthesized sample is composed of a large number of fine dispersive nanoparticles with an average size about 10 nm. The as-synthesized tetragonal CeO2 stabilized ZrO2 sample was heated at different temperatures in order to evaluate its thermal stability. The exprimental results reveal that the as-synthesized tetragonal CeO2 stabilized ZrO2 sample exhibits excellent stability without the occurrence of phase transformation.

Redox enzyme-mimicking activities of CeO2 nanostructures: Intrinsic influence of exposed facets.

CeO2 nanoparticles (NPs) have been well demonstrated as an antioxidant in protecting against oxidative stress-induced cellular damages and a potential therapeutic agent for various diseases thanks to their redox enzyme-mimicking activities. The Ce3+/Ce4+ ratio and oxygen vacancies on the surface have been considered as the major originations responsible for the redox enzyme-mimicking activities of CeO2 NPs. Herein, CeO2 nanostructures (nanocubes and nanorods) exposed different facets were synthesized via a facile hydrothermal method. The characterizations by X-ray photoelectron spectroscopy, Raman spectroscopy, and UV-Vis spectroscopy show that the Ce3+/Ce4+ ratio and oxygen vacancy content on the surfaces of as-synthesized CeO2 nanostructures are nearly at the same levels. Meanwhile, the enzymatic activity measurements indicate that the redox enzyme-mimicking activities of as-synthesized CeO2 nanostructures are greatly dependent on their exposed facets. CeO2 nanocubes with exposed {100} facets exhibit a higher peroxidase but lower superoxide dismutase activity than those of the CeO2 nanorods with exposed {110} facets. Our results provide new insights into the redox enzyme-mimicking activities of CeO2 nanostructures, as well as the design and synthesis of inorganic nanomaterials-based artificial enzymes.

Template-free controlled hydrothermal synthesis for monodisperse flowerlike porous CeO2 microspheres and their superior catalytic reduction of NO with NH3

Monodisperse flowerlike porous CeO2 microspheres with the diameters of 2–5 μm composed of numerous nanosheets as the petals with variable thickness of 40–200 nm have been successfully synthesized via a facile hydrothermal technique. Various techniques have been applied to investigate the CeO2 nanostructures, including XRD, SEM, TEM, XPS, Raman spectra, PL spectra, BET, and in situ DRIFTS. The reaction temperature, reaction time, reaction solution, the amount of H2O2 and ethylenediamine were systematically investigated. It is found that the reaction temperature, reaction time, reaction solution, the amount of H2O2 and ethylenediamine are key parameters for controlling the final morphology. The flowerlike CeO2 microspheres have a cubic fluorite structure and there are Ce3+ ions and oxygen vacancies in surface of samples. The as-synthesized CeO2 samples showed enhanced optical properties with the decrease of reaction temperature. Furthermore, flowerlike CeO2 microspheres obtained at 120 °C for 48 h displayed a high surface area of 83.81 m2 g−1 and narrow pore size of 3.86 nm by N2 adsorption and desorption measurement. The outstanding catalytic performance for the flowerlike CeO2 microspheres can be attributed to the much larger surface areas, fancy morphology and the best redox behaviour of surface oxygen on the CeO2 surface.

Palladium catalyst supported on stair-like microstructural CeO2 provides enhanced activity and stability for low-concentration methane oxidation

Octahedral CeO2 microparticles possessing a stair-like microstructure comprising self-assembled nano-sized rectangular blocks were synthesized by a hydrothermal synthetic route. The samples were characterized by X-ray diffraction, scanning/transmission electron microscopy, and nitrogen adsorption/desorption techniques. The structural functions of the as-synthesized CeO2 as support for the Pd catalyst were investigated by the catalytic oxidation of low-concentration methane. The results showed that the unique stair-like structure of CeO2 improved the stability of the Pd catalyst for continuous conversion of low-concentration methane, which suggests that the as-synthesized CeO2 has potential application in the removal of low-concentration methane from ventilation air and other oxidations.

Synthesis of CeO2 nanosheets with a room temperature ionic liquid assisted method

CeO2 nanosheets were directly synthesized by a precipitation process with the aid of 1-butyl-3-methyl-imidazolium ionic liquids at room temperature. The anion species and the concentration of the room temperature ionic liquids (RTILs) have a great influence on the morphology of the resulting products. The as-prepared CeO2 is irregular and agglomerated seriously in the absence of RTILs, while it changes from nanocube to nanosheet with increasing the RTIL concentration or decreasing the polarity and hydrophilicity in the orders [Bmim]Cl > [Bmim]Br > [Bmim]BF4 > [Bmim]PF6. The CeO2 nanocubes have relatively uniform grain size distribution with size of 4.5–6.4 nm, and the nanosheets are assembled by a great deal of nanocrystalline whose length and width extend to hundreds of nanometers. The as-synthesized CeO2 exhibits an excellent removal capacity for the organic pollutant Congo red dye, indicating its potential use in practical wastewater treatment.

Photocatalytic and magnetic properties of loosened ceria hollow microspheres synthesized by a single-step hydrothermal method

Loosened CeO2 hollow microspheres with 0.5–1 μm in diameter have been successfully synthesized by a single-step hydrothermal method using Ce(NO3)·6H2O as cerium, urea as precipitant, HNO3 as mineralizer, and polyvinyl pyrrolidone as complexant at 200 °C for different time periods. X-ray diffraction inferred that Ce(OH)CO3 was gradually transformed to CeO2 with increasing reaction time from 12 to 60 h, and no Ce(OH)CO3 was detected but CeO2 when the reaction time was 60 h. XPS and UV–Vis absorption spectra analysis indicated that the as-synthesized CeO2 contained a large number of Ce3+ in their surface. M–H curve for the loosened CeO2 hollow microspheres showed an excellent ferromagnetic behavior at room-temperature, which can be attributed to the presence of Ce3+ ions. The BET surface area of the catalyst was confirmed to be 83.83 m2 g−1 synthesized at 200 °C for 60 h. Correspondingly, its pore width distribution was 6.5 nm. The photocatalytic activities of the ceria were evaluated by the photodegradation of methyl orange under UV light irradiation. Not only the presence of Ce3+ ions, but the high surface area led to the excellent photocatalytic performance of the loosened CeO2 hollow microspheres.

One-step in situ synthesis of CeO₂ nanoparticles grown on reduced graphene oxide as an excellent fluorescent and photocatalyst material under sunlight irradiation.

CeO2 nanoparticles (NPs) with average particle size of ∼17 nm were grown on graphene sheets by simply mixing cerium chloride as the Ce precursor with graphene oxide (GO) in distilled water and the simultaneous reduction of GO to reduced graphene oxide (rGO), followed by a one-step hydrothermal treatment at 150 °C. A unique blue to green tuneable luminescence was observed as a function of the excitation wavelength. With this method, significant applications of rGO-CeO2 nanocomposites in many optical devices could be realized. The photocatalytic activity of the as-synthesized CeO2 and rGO-CeO2 nanocomposite was investigated by monitoring the degradation of methylene blue (MB) dye under direct sunlight irradiation. The rGO-CeO2 nanocomposite exhibited excellent photocatalytic activity compared to CeO2 NPs by degrading 90% of the MB dye in 10 min irradiation under sunlight. This property of rGO-CeO2 nanocomposites was ascribed to the significant suppression of the recombination rate of photo-generated electron-hole pairs due to charge transfer between rGO sheets and CeO2 NPs and the smaller optical band-gap in the rGO-CeO2 nanocomposite.

Hydrothermal synthesis of hexagonal CeO2 nanosheets and their room temperature ferromagnetism

Hexagonal CeO2 nanosheets of 40–50 nm in thickness and 300–400 nm in side-length have been successfully synthesized via controlling the morphology of CeCO3OH precursors by a facile hydrothermal technique using CeCl3·7H2O as cerium source, ammonium hydrogen carbonate as precipitants, and ethylenediamine as complexant. The reaction time and the amount of CeCl3·7H2O and ethylenediamine were systematically investigated. The as-synthesized hexagonal CeO2 nanosheets were examined by XRD, SEM, TEM, XPS, Raman scattering and magnetization measurements. It is found that the amount of CeCl3·7H2O and ethylenediamine are key parameters for controlling the final morphology. The hexagonal CeO2 nanosheets have a fluorite cubic structure and there are Ce3+ ions and oxygen vacancies in surface of samples. The synthesized CeO2 shows excellent room temperature optical properties. M–H curve exhibits excellent room-temperature ferromagnetism (RTFM) with saturation magnetization (Ms) of 3.02 × 10−2 emu/g, residual magnetization (Mr) of 0.68 × 10−2 emu/g and coercivity (Hc) of 210 Oe, which is likely attributed to the effects of the Ce3+ ions and oxygen vacancies.

Solvothermal synthesis of N-doped CeO2 microspheres with visible light-driven photocatalytic activity

N-doped CeO2 microspheres were fabricated by a one-step low temperature (180°C) solvothermal route from Ce(NO3)3·6H2O, HNO3, and ethanol, utilizing HNO3 as the nitrogen source. The structure, composition, BET specific surface area and optical properties of N-doped CeO2 sample were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, wavelength dispersive X-ray fluorescence, field emission scanning electron microscopy, N2 adsorption–desorption isotherms, and UV–vis diffuse reflectance spectroscopy. The photocatalytic results demonstrated that as-synthesized N-doped CeO2 microspheres possessed much higher photocatalytic activity than that of pure CeO2 in the photocatalytic activity of aqueous rhodamine 6G under visible light (λ>420nm) irradiation. Moreover, the photocatalytic results indicated that the as-synthesized N-doped CeO2 was a kind of promising photocatalyst in remediation of water polluted by some chemically stable azo dyes under visible light irradiation.

The effect of CO-doped on the room-temperature ferromagnetism of CeO2 nanorods

Abstract Co-doped CeO2 nanorods of 10–20 nm in diameter and 200–600 nm or more in length have been synthesized by a simple co-precipitation method. The results of XRD and SADE analysis indicate that the as-synthesized CeO2 samples have the fluorite structure. X-ray photoelectron spectroscopy and Raman spectra show that Ce4+ and Ce3+ ions coexist at the surface of non-doped CeO2 nanorods. The magnetic measurements indicated that Co-doped CeO2 nanorods exhibit stronger ferromagnetism at room temperature, and while increasing the amount of Co ions, the ferromagnetism increase more, which can be associated with the presence of Ce3+ and Co2+.

Design of 3-Dimensionally Self-Assembled CeO2 Nanocube as a Breakthrough Catalyst for Efficient Alkylarene Oxidation in Water

This paper reports preparation of CeO2 nanocrystals by using oleic acid as a surfactant. A strong coordinating property of oleic acid toward (100) planes of the nanocrystals facilitated three-dimensional (3D) assembly via oriented attachment of the nanocrystal building blocks to form (100) surface exposed porous cubic ceria by sharing {111} facets. As-synthesized materials were characterized by HRTEM, SEM, XRD, FTIR, Raman spectroscopy, and BET surface area analyzer. 3D morphology was established by STEM-HAADF technique and dark-field TEM. As-synthesized CeO2 nanocubes showed breakthrough in catalytic performance, enabling quantitative pX conversion and absolute selectivity in terephthalic acid (>99%). The presence of higher concentrations of oxygen vacancies (1.42 × 1021 cm–3), owing to preferred exposed surfaces and lower individual crystallites size (6 nm), and larger surface area and pore size have been reasoned for high catalytic effectiveness. The catalyst recyclability experiments showed only 6% activity loss in TA yield in the fourth cycles.

Synthesis of CeO2 nanoparticles using flame-assisted spray pyrolysis and solid state diffusion routes

The stable and crystalline phase of pure nanostructured CeO2 was directly synthesized by flame-assisted spray pyrolysis and solid state diffusion route. Different characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible (UV-Vis), and thermo gravimetric analysis (TGA) were employed to examine the structural, morphological, optical, and thermal properties of the final product. Similarly, the comparative carbon dioxide (CO2)-sensing response of as-synthesized CeO2 nanoparticles by both routes was also reported. The CeO2 nanoparticles synthesized by solid state diffusion method exhibit good sensitivity (3.38 %) at room temperature, low operating temperature (398 K), fast response time (32 s), and recovery time (36 s) along with good stability.

A facile polyol-mediated approach to tunable CeO2 microcrystals and their photocatalytic activity

An efficient solvothermal method was developed to prepare CeO2 microcrystals with different shapes using a polyol–ethanol mixed solvent as the reaction medium. The as-synthesized product was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and UV–vis diffuse reflectance spectroscopy (DRS). It was found that different kinds or amounts of polyols and the concentration of oleic acid have significant impacts on the well-defined CeO2 microcrystals. The as-synthesized CeO2 microcrystals displayed different optical absorption properties and different photocatalytic performances for the degradation of Rhodamine B (RhB) under UV and visible light irradiation, which was used to model sunlight.

Oxygen vacancy and Ce3+ ion dependent magnetism of monocrystal CeO2 nanopoles synthesized by a facile hydrothermal method

Monocrystal CeO2 nanopoles of 15–25nm in diameter and 300–900nm or more in length were synthesized within 100h using hydrothermal method with CeCl3·7H2O as cerium source, NaOH as mineralizer, and ethylenediamine as complexant. The results of XRD and SADE analysis indicate that the as-synthesized CeO2 samples have the fluorite structure. The band gaps of CeO2 samples are 0.08–0.38eV smaller than that of bulk CeO2. X-ray photoelectron spectroscopy shows that the concentration of Ce3+ is higher than 20% for CeO2 samples. All the as-synthesized CeO2 samples exhibit the room temperature ferromagnetism (RTFM), and the saturation magnetization (Ms) gradually increases with the increase of Eg up to 2.92eV and then decreases with Eg increasing more. The highest Ms of 0.167emu/g is obtained from the CeO2 nanopoles synthesized within 100h. The RTFM mechanism of CeO2 nanopoles has been proposed which can be mainly attributed to the influence of oxygen vacancies and Ce3+ ions.

Hydrothermal synthesis of monocrystalline CeO2 nanopoles and their room temperature ferromagnetism

CeO2 nanopoles have been successfully synthesized by a hydrothermal method using CeCl3·7H2O as cerium, NaOH as mineralizer, and ethylenediamine as complexant. X-ray diffraction (XRD) and selective area electron diffraction (SAED) infered that the as-synthesized CeO2 nanopoles exhibited a fluorite cubic structure and monocrystalline phase. Scanning electron microscope (SEM) and transmission electron microscope (TEM) showed that CeO2 have pole-like nanostructures. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy reflected the existence of the oxygen vacancies and Ce3+ ions in the CeO2 nanopoles. Magnetization measurements exhibited room temperature ferromagnetism (RTFM) with saturation magnetization (Ms) of 0.167emu/g, and coercivity (HC) of 165Oe, which is likely associated with Ce3+ ions and oxygen vacancies in the CeO2 nanopoles.

Hydrothermal Biotemplated Synthesis of Biomorphic Porous CeO2 and Their Catalytic Performance

Biomorphic porous CeO2 powder was synthesized by the hydrothermal method using stems of clover as biotemplates. Thermogravimetric and differential thermal analysis, X-ray diffraction, N2 adsorption–desorption, field emission scanning electron microscopy and Fourier transfer infrared spectroscopy were applied to characterize the samples. The oxygen storage/release capacity (OSC) and catalytic oxidation performance of the biomorphic porous CeO2 for acid magenta were also investigated. Results show that the as-synthesized CeO2 powders exhibit a cubic phase and have porous structures with pore size ranging from several to dozens of micrometers. The results of N2 adsorption–desorption measurement suggest that the biomorphic CeO2 contains a large number of mesopores on the surface of CeO2 framework; and, the pore diameter is from 15–35 nm. The OSC value of the biomorphic porous CeO2 is 174.6 μmol O2/g ceria, which is two-times higher than powdered CeO2. After catalytic oxidation for 300-min by the biomorphic porous CeO2, the decolorizing rate of acid magenta is close to 95 %, which is higher than for powdered CeO2 (64 %).

Facile fabrication of porous hollow CeO2 microspheres using polystyrene spheres as templates

Porous hollow CeO2 microspheres were fabricated using negative-charged PS microspheres as templates by a facile method. The hollow CeO2 microspheres were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and N2 adsorption–desorption. The results showed that the as-synthesized hollow CeO2 microspheres are well monodisperse and uniform in size. The porous shells of hollow microspheres are relatively rough and composed of tiny nanoparticles. The external diameter, internal diameter, and shell thickness of hollow CeO2 microspheres are about 190, 160, and 15 nm, respectively. A possible mechanism for the formation of hollow CeO2 spheres was also discussed.