CeO2 Hollow Microspheres Research Articles

SYNTHESIS, CHARACTERIZATION OF CeO2@Ag HOLLOW SPHERES AND EVALUATION OF THEIR CATALYST ACTIVITY FOR THE REDUCTION OF 4-NP

A CeO2@Ag hollow spherical composite catalyst was synthesized with the template method. Firstly, a SiO2@CeO2 core-shell structure was synthesized using SiO2 spheres as the template, and then the SiO2 core was removed by etching to obtain hollow CeO2 spheres. The CeO2 hollow microspheres have a large specific surface area, which can effectively suppress the aggregation of Ag nanoparticles, leading to CeO2@Ag with a regular morphology and well dispersed Ag nanoparticles. There is a strong synergistic effect between CeO2 and Ag, which is beneficial to improving the catalytic performance. As a result, the CeO2@Ag hollow spherical composite catalyst can reduce 4-nitrophenol efficiently.

The mechanism on enhancing heat and mass transfer property for improving CH4 catalytic combustion performance of hollow CeO2 microspheres

In this work, hollow CeO2 microspheres were synthesized and the catalytic performance of lean-CH4 combustion and stability were conducted. The structure property of the hollow CeO2 microspheres was characterized for tentatively exploring the catalytic advancement of hollow CeO2 microspheres. Further, the heat and mass transfer property of hollow CeO2 microspheres was calculated to investigate the mechanism of reactants/products and heat transfer property on hollow structure. The hollow CeO2 microspheres show greater catalytic performance and long term stability than the solid CeO2. The numerical results indicate that the hollow structure could increase the heat and mass transfer property, which could improve the reaction rate in the light off stage, thermodynamic region and homogeneous reaction region of the methane combustion process. This work provides a sight for increasing the heat and mass transfer property of catalyst for heterogeneous catalysis reaction.

Intriguing MnOx Decorated CeO2 Hollow Microspheres with Abundant Interfaces and Phase Boundaries Toward Styrene Oxidation

Intriguing MnOx Decorated CeO2 Hollow Microspheres with Abundant Interfaces and Phase Boundaries Toward Styrene Oxidation

Synthesis of Fe-MOFs/h-CeO2 hollow micro-spheres and their highly efficient photocatalytic degradation of RhB

A series of Fe-MOFs/h-CeO2 composite photocatalysts were synthesized by a hydrothermal method using cerium oxide hollow microspheres as carriers, naphthalene dicarboxylic acid as an organic ligand, and iron as a metal center. The obtained samples were characterized by XRD, SEM, TEM, UV-Vis, XPS, and PL. It shows that the samples contained hollow CeO2 microspheres with a diameter of about 500 nm as the carrier, and the surface was a burr-like shell coated with Fe-MOFs about 100 nm. The bandgap of Fe-MOFs/h-CeO2 was reduced to 1.62 eV; the photocatalytic performance was tested via RhB degradation. The results indicate that the Fe-MOFs/h-CeO2 composites show enhanced photocatalytic activity, in contrast with CeO2 hollow microspheres. All of this can be attributed to the that the MOFs fabricated could not only improve the light adsorption through the outer shells and provide more active sites but also enhance charge carriers. It is expected that this study could provide helpful results for fabricating and exploration of composite catalysts with tunable photocatalytic performance.

Synthesis of CeO2 hollow microspheres with oxidase-like activity and their application in the catalytic degradation of p-nitrophenol

ABSTRACT CeO2 materials have received wide attention given their oxidase-like activity without the need for an unstable oxide substrate in the catalytic process. Nevertheless, their application and mechanism in the catalytic oxidation of refractory organic pollutants needs further study. Herein, CeO2 hollow microspheres (HMS) with an intrinsic oxidase-like activity were synthesised via a template-free hydrothermal method and their effectiveness in degrading p-nitrophenol(p-NP) was investigated. HMS showed a maximum p-NP degradation rate of 76.5% at a CeO2 dosage of 40 mg, 2 h reactive time, at 30°C and pH of 4.8 when the concentration of p-NP was 20 mg L−1. The catalytic activity of CeO2 HMS also exhibited good thermal stability and reusability. These results provide strong evidence that CeO2 HMS can be utilised as an oxidase mimetic for the efficient catalytic degradation of refractory organic pollutants. A possible mechanism for the degradation of p-NP is also discussed.

An Electrocatalyst for a Hydrogen Evolution Reaction in an Alkaline Medium: Three‐Dimensional Graphene Supported CeO2 Hollow Microspheres

Transition metal oxides (TMO) are promising candidates for low‐cost and high‐efficiency catalysts for the hydrogen evolution reaction (HER). However, the low conductivity and severe agglomeration of catalyst particles hinder their practical application. Herein, we report an effective HER electrocatalyst of 3D‐rGO‐CeO2 with three‐dimensional reduced graphene oxide (3D‐rGO) decorated with CeO2 hollow microspheres through a hydrothermal self‐assembly approach. It is shown that the CeO2 hollow microspheres with an average size of ca. 680 nm are uniformly encapsulated within the porous structure of 3D‐rGO. Compared with bare CeO2 hollow microspheres, the 3D‐rGO‐CeO2 composite exhibits remarkably enhanced electrocatalytic activity for HER with a relatively low onset overpotential of 192 mV, a smaller overpotential of 0.34 V at the current density of 10 mA cm–2, and a modest Tafel slope of 112.8 mV decade–1 in a 1 m KOH solution. The enhanced performance of 3D‐rGO‐CeO2 can be ascribed to the introduction of 3D rGO in the composite, which provides a highly conductive network for rapid charge‐carrier transmission, and rich porous structures for the easy access of the electrolyte to the catalyst during the HER process.

Highly Efficient Au Nanocatalysts for Heterogeneous Continuous-Flow Reactions Using Hollow CeO2 Microspheres as a Functional Skeleton

Hollow Au/CeO2 as a highly efficient and stable heterogeneous catalyst is successfully used for a continuous-flow reaction. The hollow CeO2 microspheres with thicknesses of 21 nm as functional supports can greatly improve the catalytic activity and stability of the Au nanoparticles. The catalytic activity of hollow Au/CeO2 catalysts is 4.5 times higher than the Au catalysts without the hollow structure under the same reaction conditions for the reduction of 4-nitrophenol. Meanwhile, the hollow structure also accelerates the mass transfer of reactant for the continuous-flow system. A high turnover number of 65.7 mol h–1 molAu–1 is yielded for hollow Au/CeO2 catalysts at a flow rate of 250 mL h–1 with remarkable stability for a continuous-flow 4-nitrophenol reduction reaction. The present continuous-flow system exhibits a huge potential for the automation treatment of pollutant 4-nitrophenol.

Yeast-template synthesized Fe-doped cerium oxide hollow microspheres for visible photodegradation of acid orange 7

Fe-doped cerium oxide (CeO2) hollow microspheres were successfully synthesized by a simple co-precipitation route using yeast asa bio-template and nitrate as the oxide precursor. The products were characterized by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, N2 adsorption–desorption isotherms and UV–Vis diffuse reflectance spectroscopy. It was found that the products had a well-defined ellipsoidal morphology and the size of the hollow microspheres was about 1.5–2.5μm. The formation mechanism of Fe-doped CeO2 hollow microspheres was proposed and discussed as well. The photocatalytic test results showed that the Fe-doped CeO2 hollow microspheres exhibited a higher photocatalytic activity in the degradation of acid orange 7 (AO7) aqueous solutions containing H2O2 under visible irradiation compared with CeO2 hollow microspheres and Fe-doped CeO2 nanoparticles, which was attributed to their more oxygen vacancies, higher specific surface area and lower band gap. The degradation rate of the Fe-doped CeO2 hollow microspheres was found to be 93% after 80min and the degradation reaction followed pseudo-first-order kinetics.

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.

Preparation of novel CeMo(x) hollow microspheres for low-temperature SCR removal of NOx with NH3

A series of novel Mo doped CeO2 hollow microspheres have been successfully synthesized using carbon microspheres as templates, which were characterized by XRD, SEM, TEM, BET and used to remove NOx upon NH3-SCR at lower temperature.

Facile fabrication of CeO2 hollow microspheres with yeast as bio-templates

CeO2 hollow microspheres were prepared through a facile method by using yeast cells as bio-templates. The yeast provided a solid frame for the deposition of cerium hydroxide to form the hybrid Ce(OH)3@yeast precursor. The resulting CeO2 hollow microspheres were obtained by calcining the precursor. The products were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), fourier transform infrared spectroscopy (FTIR), N2 adsorption/desorption analysis, X-ray photoelectron spectrum (XPS) and H2 temperature programmed reduction (H2-TPR). It was found that the products fully retained the morphology of the yeast cells and the size of the hollow microspheres was about 1.5–2 μm. The catalytic test results showed that the as-obtained hollow CeO2 microspheres possessed a higher catalytic activity in CO oxidation than the commercial CeO2, which attributed to their higher surface area, hollow structure and superior reducibility. This study provided a promising route for the preparation of a variety of other inorganic hollow microspheres.

One-pot Synthesis of Hollow Microspheres of Cerium Oxide and Their Application in Electrochemical Sensors

Abstract Monodisperse hollow cerium oxide (CeO2) microspheres were successfully synthesized by a convenient one-pot preparative method. It was found that the morphology of the hollow CeO2 microspheres was sensing to reaction conditions. A possible mechanism for the formation of hollow CeO2 microspheres was discussed. Moreover, we investigated the electrochemical properties of the resultant hollow CeO2 microspheres by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It was found that the electrochemical sensors based on hollow CeO2 microspheres exhibited high electrochemical response.

CO sensor based on thick films of 3D hierarchical CeO2 architectures

Hollow CeO2 microspheres, having 3D architectures on their surface, were prepared by a microwave-assisted coprecipitation method. By this method, ceric ammonium nitrate was diluted in formic acid. The application of microwave irradiation produced the precipitation of a white powder, with the simultaneous emission of NO2. At low temperature, cerium formate was formed; whereas from 400°C, CeO2 with cubic crystal structure was identified. The morphology of the samples calcined from 170 to 600°C was of hollow microspheres, with size between 1.5 and 10μm. Their surface displayed unique 3D architectures, which consisted of ramifications formed by the assembly of nanograins and nanoporous. Microwave irradiation played a key role in the formation of 3D hollow architectures. The effect of the concentration of ceric ammonium nitrate on the particle morphology was also investigated. Thick films were prepared by depositing a suspension of the CeO2 powder on alumina substrates. The electrical characterization in gases was performed in alternating current (AC). The films exhibited a reliable and quantitative detection of carbon monoxide from 250°C. The effect of the applied frequency and the operating temperature was analyzed.

Multi-shelled CeO2 hollow microspheres as superior photocatalysts for water oxidation

A general self-templating method is introduced to construct triple-shelled CeO₂ hollow microspheres, which are composed of tiny CeO₂ nanoparticles. When the triple-shelled CeO₂ hollow microspheres are used as photocatalysts for direct water oxidation with AgNO₃ as the electron scavenger, excellent activity and enhanced stability for O₂ evolution are achieved, in contrast with commercial CeO₂ nanoparticles, single-shelled CeO₂ hollow microspheres and double-shelled CeO₂ hollow microspheres. Such an outstanding performance is attributed to the unique properties of the triple-shelled CeO₂ hollow microspheres including more efficient multiple reflections of the incident light by the inner shells, the larger surface area and more active sites for improving separation of electron-hole pairs, and the more curved surfaces unfavorable for deposition of in situ generated Ag nanoparticles.

Uniform Eu3+:CeO2 hollow microspheres formation mechanism and optical performance

The novel Eu3+:CeO2 hollow microspheres are successfully fabricated by a facile and green route, employing the colloidal carbon spheres as sacrificial templates. In the coating process, the large amount of hydrophilic functional groups are beneficial to the adsorption of Ce3+, Eu3+ and OH− to form the initial amorphous precursors on the surfaces of the carbon spheres. When heat-treated at appropriate temperature, the carbon spheres in the cores are burned away, while the precursors in the shell crystallize to the Eu3+:CeO2, forming a hollow structure. The Eu3+ ions occupy the Ce sites in the CeO2 lattice, and yield intense red emissions under 340nm excitation. This material of hollow microspheres may find potential applications in the field of color display.

Biogenic synthesis and catalysis of porous CeO2 hollow microspheres

Porous CeO2 hollow microspheres were successfully prepared through a facile process by using the rape pollen as the biotemplate. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), the N2 adsorption and desorption, X-ray diffraction (XRD), UV-vis diffuse reflectance spectra, and hydrogen temperature-programmed reduction (H2-TPR) were used for their characterization. The results showed that the obtained materials exhibited the same morphology as that of the pollen template, with a diameter of ca. 10 μm, and the surface was evenly covered with a special network-like structure with mesh size of about 0.3 μm, and the Brunauer-Emmett-Teller (BET) surface area was measured to be 156 m2/g. The detailed property investigation inferred that the product exhibited better photocatalytic activity in acid fuchsine decolorization under daylight because of higher surface area, smaller crystallite size and higher oxygen capacity.

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.

Mesoporous CeO2 Hollow Spheres Prepared by Ostwald Ripening and Their Environmental Applications

In the original article,1 an important paper2 that reported the synthesis of single/multiwall hollow CeO2 microspheres by a hydrothermal method was inadvertently not cited. Although that method is similar to ours, there are variations in the amounts of reactants, reaction temperature, and template usage, which result in different size and shape of the spheres. We apologise for the oversight of that paper. The Authors

Bubble template synthesis of hollow CeO2 microspheres through a solvothermal approach

The authors present a solvothermal process to fabricate hollow CeO2 microspheres. Polyvinyl pyrrolidone is employed as polymer surfactant to assist the forming process of hollow structured microspheres in the solution. The as-prepared samples are characterised through X-ray diffraction, transmission electron microscopy and scanning electron microscopy, and the catalytic activity is investigated through measuring the conversion of CO to CO2 over the catalysts.

Facile One-Step Synthesis of Double-Shelled CeO2 Hollow Spheres and Their Optical and Catalytic Properties

Abstract Double-shelled CeO2 hollow microspheres (4–5 µm) were synthesized through a facile one-step hydrothermal treatment of Ce(NO3)3·6H2O in the presence of citric acid and hexamethylenetetramine (HMTA), and scanning and transmission electron microscopies demonstrated the samples are hollow spheres with litchi-like surfaces. The assembly of the hollow spheres was contributed to coordination effect of additives employed in the reaction system and the ripening growth in the process. Meanwhile, two other spherical structures including polyhedron-constituted and porous microspheres assembled with nanocrystals were also synthesized by varying the experimental parameters in the synthetic route. The UV–vis spectroscopic investigation demonstrated that the absorption edge of the three samples was blue shifted accordingly with their constituted primary crystallite sizes. In addition, investigation showed that the catalytic activities for CO oxidation of the three spheres types were considerably higher than those of commercial CeO2 powders, and their activities were in the order of porous > litchi-like double-shelled hollow > polyhedron-constituted, consistent with their BET surface area of 33, 22, and 10 m2 g−1. Specially, the litchi-like double-shelled hollow spheres showed much better catalytic properties per unit weight catalyst.