CeO2 Nanowires Research Articles

A facile synthesis for hierarchical porous CeO2 nanobundles and their superior catalytic performance for CO oxidation

Porous CeO2 nanobundles with hierarchical nanoarchitecture show much better catalytic activities for CO oxidation compared to CeO2 nanorods, nanowires and nanoparticles.

A palladium-doped ceria@carbon core-sheath nanowire network: a promising catalyst support for alcohol electrooxidation reactions.

A novel palladium-doped ceria and carbon core-sheath nanowire network (Pd-CeO2@C CSNWN) is synthesized by a template-free and surfactant-free solvothermal process, followed by high temperature carbonization. This hierarchical network serves as a new class of catalyst support to enhance the activity and durability of noble metal catalysts for alcohol oxidation reactions. Its supported Pd nanoparticles, Pd/(Pd-CeO2@C CSNWN), exhibit >9 fold increase in activity toward the ethanol oxidation over the state-of-the-art Pd/C catalyst, which is the highest among the reported Pd systems. Moreover, stability tests show a virtually unchanged activity after 1000 cycles. The high activity is mainly attributed to the superior oxygen-species releasing capability of Pd-doped CeO2 nanowires by accelerating the removal of the poisoning intermediate. The unique interconnected one-dimensional core-sheath structure is revealed to facilitate immobilization of the metal catalysts, leading to the improved durability. This core-sheath nanowire network opens up a new strategy for catalyst performance optimization for next-generation fuel cells.

Glutamine-assisted synthesis of Cu-doped CeO2 nanowires with an improved low-temperature CO oxidation activity

Glutamine (GLN)-assisted Cu-doped CeO2 nanowires exhibit an outstanding performance for CO oxidation and can completely convert CO at 90 °C.

Template- and surfactant-free synthesis of ultrathin CeO2 nanowires in a mixed solvent and their superior adsorption capability for water treatment

Ultrathin CeO2 nanowires with a diameter of 5 nm and an aspect ratio of more than 100 can be prepared by a one-step refluxing approach in a mixed solvent composed of water and ethanol without using any templates or surfactants. The formation mechanism of the as-synthesized ultrathin nanowires has been investigated. The as-synthesized CeO2 nanowires with a high surface area of 125.31 m2 g-1 exhibited excellent wastewater treatment performance with high removal capacities towards organic dyes and heavy metal ions. In addition, the as-synthesized CeO2 nanowires can adsorb Congo red selectively from a mixed solution composed of several dyes. Successful access to high quality ultrathin nanowires will make it possible for their potential application in catalysis and other fields.

Green hydrothermal synthesis of CeO2 NWs–reduced graphene oxide hybrid with enhanced photocatalytic activity

In this study, CeO2 nanowires–reduced graphene oxide hybrids (CeO2 NWs–RGO) were synthesized by a green hydrothermal method using CeO2 NWs and graphene oxide (GO) as raw materials. During the process of reduction of GO, hydrothermal condition with supercritical water provides thermal and chemical factors to synthesize RGO. The photocatalytic experimental results show that the CeO2 NWs–RGO hybrids exhibit enhanced photocatalytic activity for degradation of Rhodamine B (RhB) under UV-light irradiation. It is found that the degree of photocatalytic activity enhancement strongly depends on the mass ratio of RGO in the hybrids, and the remarkable photocatalytic activity is 20 times that of pristine CeO2 NWs when the loading amount of RGO is 8.0 wt%. The enhancement of photocatalytic activity can be attributed to the excellently elevated absorption ability for the dye through π–π conjugation as well as the effective inhibition of the recombination of photogenerated electrons because of the electronic interaction between CeO2 NWs and RGO sheets.

Facile electrochemical synthesis of CeO2 hierarchical nanorods and nanowires with excellent photocatalytic activities

A simple, cost-effective and controllable electrochemical method has been developed to synthesize free-standing CeO2 hierarchical nanorods and nanowires.

Formation and characterisation of CeO2 and Gd:CeO2 nanowires/rods for fuel cell applications

Ceria and gadolinium (Gd) doped ceria nanowires have been synthesised by hydrothermal technique with mild reaction conditions. The structure and morphology of as-prepared nanowires were studied by X-ray diffraction and field emission scanning electron microscopy (FE-SEM) techniques. The FE-SEM analysis revealed the formation of nanowires with an average diameter of 10–15 nm. Atomic force microscopy (AFM) analysis for the annealed samples confirms the existence of well defined nanorods of 120–150 nm diameter and 1–1.3 μm length. Fluorescence and diffuse reflectance spectroscopy techniques have been used to study the optical properties of the prepared nanowires. The observed red shift in the ultraviolet–visible absorption spectra confirmed the promoted electron–phonon interaction in CeO2 and Gd:CeO2 nanowires compared to bulk structures. The prepared nanowires/rods were thermally stable at up to 350 °C, as revealed by thermogravimetric analysis. The electrical properties were studied by cyclic voltammetry (CV) and impedance spectroscopy. The CV results demonstrated that Gd:CeO2 exhibited a higher electro-oxidation than CeO2 nanowires.

Dopant-Induced Modification of Active Site Structure and Surface Bonding Mode for High-Performance Nanocatalysts: CO Oxidation on Capping-free (110)-oriented CeO2:Ln (Ln = La–Lu) Nanowires

Active center engineering at atomic level is a grand challenge for catalyst design and optimization in many industrial catalytic processes. Exploring new strategies to delicately tailor the structures of active centers and bonding modes of surface reactive intermediates for nanocatalysts is crucial to high-efficiency nanocatalysis that bridges heterogeneous and homogeneous catalysis. Here we demonstrate a robust approach to tune the CO oxidation activity over CeO2 nanowires (NWs) through the modulation of the local structure and surface state around Ln(Ce)' defect centers by doping other lanthanides (Ln), based on the continuous variation of the ionic radius of lanthanide dopants caused by the lanthanide contraction. Homogeneously doped (110)-oriented CeO2:Ln NWs with no residual capping agents were synthesized by controlling the redox chemistry of Ce(III)/Ce(IV) in a mild hydrothermal process. The CO oxidation reactivity over CeO2:Ln NWs was dependent on the Ln dopants, and the reactivity reached the maximum in turnover rates over Nd-doped samples. On the basis of the results obtained from combined experimentations and density functional theory simulations, the decisive factors of the modulation effect along the lanthanide dopant series were deduced as surface oxygen release capability and the bonding configuration of the surface adsorbed species (i.e., carbonates and bicarbonates) formed during catalytic process, which resulted in the existence of an optimal doping effect from the lanthanide with moderate ionic radius.

The surfactant-assisted synthesis of CeO2 nanowires and their catalytic performance for CO oxidation

CeO 2 nanowires were synthesized via a facile synthesis method using PEO–PPO–PEO (P123) as the surfactant. Thermo gravimetric analysis and differential scanning calorimetry (TG–DSC), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), transmission election microscopy(TEM), selected election diffraction (SAED), energy-dispersive spectrometry (EDS), and Barrett–Joyner–Halenda (BJH), were employed to characterize the samples. The obtained CeO 2 nanowires have the diameters of 10–50 nm, the lengths of up to several micrometers, and some mesopores on the surface. CO conversion was used as a catalytic test reaction revealing that the activity of the nanowires was substantially higher than that of the commercial CeO 2 . The possible formation mechanism of the CeO 2 nanowires attributed to nanoparticles layer-by-layer assembly and the Ostwald ripening process. ► CeO 2 nanowires were synthesized using PEO–PPO–PEO as the surfactant. ► The formation mechanism attributed to self-assembly and the Ostwald ripening ► The surfactant, temperature and time were the major factors to form CeO 2 nanowires. ► CeO 2 nanowires show superior catalytic activity for CO oxidation.

CeO2 Nanowires Aqueous γ-Radiation Dosimeter for Low Dose Sensitively Detecting

In radiation accident, detecting the accurate radiation rapidly is very important for rescuing wounded persons and dealing with the emergency. In the past decades, aqueous chemical dosimeter was widely used in the dose monitoring of radiation. However, each chemical dosimeter has a dose detection limit, for example, ×10 7 Gy for Frick dosimeter and 1000 Gy for FBX (ferrous sulphate- benzoic acid-xylenol orange) one. Those chemical dosimeters are not suitable for monitoring of dose less than 1000 Gy. In this work, CeO2 nanowires were synthesized by a hydrothermal method for developing a new low dose aqueous -radiation dosimeter. The researching results showed that the aqueous CeO2 nanowire dosimeter exhibited high sensitivity to -radiation of less than 1000 Gy dose and a good linear response in dose range from 20 Gy to 500 Gy. The radiation response mechanism of the CeO2 nanowires aqueous - radiation dosimeter is given as well. Furthermore, the effect of the initial CeO2 concentration on absorption varying rate of the CeO2 nanowires aqueous -radiation dosimeter was also investigated. The results indicated that absorption varying rate increased with the CeO2 concentration decreasing. In a lower concentration of 0.05 mg/ml, the relative absorption variation rate of CeO2 nanowires aqueous reached more than 83% under 28 Gy. A radical scavenger (ethanol) was added in the CeO2 nanowires aqueous to researching impact of radicals on the reaction of the CeO2 nanowires with -ray. There was almost no change of the absorption observed after ethanol adding, indicating the radicals produced from water radiolysis were closely relevant to the reaction of the CeO2 nanowires with -ray. The CeO2 nanowires dosimeter may be used as a highly sensitive, cost-effective dosimeter in ultra-low dose environment, which can help fireman detecting the radiation rapidly in radiation accident emergency rescue.

CeO2 nanowires with high aspect ratio and excellent catalytic activity for selective oxidation of styrene by molecular oxygen

CeO2 is a most promising oxidation catalyst and its superior oxidation performance is highly dependent on the extent of its Ce4+/Ce3+ redox cycle, shape, surface area and surface structure. Herein, a simple, efficient and aqueous solution based hydrothermal synthetic route for uniform CeO2 nanowires (NWs), with high aspect ratio and surface area, using an aqueous solution of cerium ammonium carbonate complex as precursor and poly(ethylene glycol) (PEG) as structure directing agent, is described. Cobalt incorporated CeO2 NW (Co–CeO2) were also synthesized by impregnation followed by calcination. Structural and morphological characterization by XRD, SEM and TEM showed that synthesized CeO2 NWs are of cubic fluorite crystal structure, with approximately 7 ± 2 nm width and several micrometers in length, bundled, grown through the (110) surface keeping the active (100) surface exposed. XPS and TPD analysis revealed the presence of both Ce3+ and Ce4+ with higher amount of Ce3+ as well as Co2+ and Co3+ species. The amount of PEG is crucial for the synthesis of uniform CeO2 wires and other varying shapes. A probable formation mechanism of wires through the (110) surface is proposed. Synthesized CeO2 shapes were employed as catalyst for selective oxidation of styrene to styrene oxide using molecular oxygen as oxidant. Shape selective catalytic studies revealed that the synthesized Co–CeO2 NWs showed excellent catalytic activity. Kinetic study revealed that the oxidation reaction followed the Langmuir–Hinshelwood model. The synthesized CeO2 NW catalysts are recyclable with no significant loss in catalytic activity in subsequent cycles.

Mesoporous CeO2 nanowires as recycled photocatalysts

Mesoporous CeO2 nanowires (NWs) were synthesized through a facile hydrothermal process by using triblock copolymer F127 as the template. XRD analysis confirmed the cubic phase of the synthesized CeO2 NWs. High-yield one-dimensional NWs with accessible mesopores could be observed from SEM and TEM images, and the surface area of the material was confirmed to be 273 m2 g−1 with pore width distribution of 6.9–13.8 nm. The mesoporous CeO2 NWs could be used as efficient photocatalysts for organic dye degradation under UV light irradiation, which was superior compared with commercial photocatalyst P-25 and commercial CeO2 powders. The NW structure facilitates the recovery of catalyst by sedimentation, leading to the impressive reusability of these mesoporous CeO2 NWs.

Formaldehyde-assisted hydrothermal synthesis of one-dimensional CeO2 and their morphology-dependent properties

CeO2 nanobelts, nanorods and nanowires have been synthesized by a formaldehyde-assisted hydrothermal system. It is found that the morphologies of these one-dimensional (1D) CeO2 nanomaterials are dependent on the components of the corresponding precursors, which is achieved to control the reaction degree of Cannizzaro disproportionation tuned by Na/Ce molar ratio, hydrothermal temperature and type of strong alkali. The characterization results indicate that the morphologies of 1D CeO2 nanomaterials are closely correlated to their structural features, such as lattice cell parameters, specific surface area and pore volume. These 1D nanomaterials show excellent morphology-dependent optical absorption and catalytic performance. From nanowires, nanorods to nanobelts, the visible absorption gradually decreases along with the increasing of band gap values, whereas the catalytic activity of CO oxidation increases along with lattice cell expansion. This synthetic route using formaldehyde may open a new insight into fabricating one-dimentional rare earth oxides with different morphologies and extending their potential applications.

Electrospun cerium nitrate/polymer composite fibres: synthesis, characterization and fibre-division model

Cerium (III) nitrate/poly(vinylpyrrolidone) (Ce(NO3)3/PVP) composite fibres have been prepared by electrospinning. After calcining the composite fibres in air at 500 °C, CeO2 nanowires were obtained. The characterizations of the as-spun composite fibres and resultant nanowires have been carried out by a scanning electron microscope (SEM), an infrared spectrometer, an x-ray diffractometer and a fluorescence spectrophotometer. Interestingly, some unusual ribbon-like or twin fibres were observed besides the common fibres with circular or elliptic cross sections. We developed a fibre-division model resulting from Coulomb repulsion and solvent vaporization to interpret the formation of the ribbons or twin fibres, which has been confirmed by the SEM studies. Our results also indicate that the formation of the ribbons or twin fibres is less dependent on operation voltage and work distance.

Hydrothermal synthesis and photoluminescence behavior of CeO2 nanowires with the aid of surfactant PVP

Well-crystalline CeO2 nanowires were prepared via a surfactant-assisted hydrothermal process. Reaction temperature and reaction time were changed for the determination of optimal synthesis parameters. The as-obtained products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and field emission scanning electron microscopy (FESEM). The results show that single crystal CeO2 nanowires with high yield and good uniformity can be obtained hydrothermally at 180°C for 12 h with the aid of 2.0 g surfactant (polyvinyl pyrrolidone, PVP). The role of PVP was then discussed and a possible growth mechanism was proposed. Moreover, room temperature photoluminescence (PL) spectra were obtained for these CeO2 nanowires, which are believed to be related to the abundant defects in these nanostructures.

Supercritical CO2-facilitating large-scale synthesis of CeO2 nanowires and their application for solvent-free selective hydrogenation of nitroarenes

Ceria nanowires were synthesized on a large scale by a simple, efficient, and environmentally benign strategy using supercritical (SC) CO2 expanded ethanol as reaction medium. Morphological characterization by SEM and TEM showed that most of the nanowires were bundles composed of individuals oriented parallel to each other throughout the whole length of the nanowires. Statistical data from AFM measurements showed that approximately 10% ceria nanowires (bundles/individuals) were ultrafine ones with diameters less than 5 nm. The effects of precursor concentration, reaction time and CO2 pressure on the formation of nanowires were studied, and it was found that SC CO2 played a key role in the evolution of the nanowires. As such, a possible formation mechanism for the as-prepared nanowires was provided. Moreover, the synthesis strategy was proved to be applicable to other rare earth oxide (La2O3, Eu2O3) nanowire preparation. Additionally, we successfully decorated ceria nanowires with ultrafine Pt nanoparticles via a sonication-facilitating deposition method. The as-prepared Pt-CeO2 showed superior catalytic activity and good selectivity for the solvent-free hydrogenation of nitrobenene and o-chloronitrobenzene.

A surfactant and template-free route for synthesizing ceria nanocrystals with tunable morphologies

Nanosized crystalline ceria (CeO2) is synthesized through a surfactant- and template-free solution precipitation-hydrothermal method. We report that pure CeO2 nanocrystals with shapes consisting of nanospheres, nanowires, and nanorods can be obtained simply by varying the anionic composition or the type of counter ion, such as chloride, nitrate and phosphate in solution before the hydrothermal treatment. The shape-controlling effect of these anions is explained by the selective interaction of these ions with specific facets of CeO2, leading to the growth of CeO2 nanocrystals with varying morphologies. Unlike techniques that require the use of organic and inorganic additives or templates, the new methodology represents a simple yet effective means to fabricate CeO2 nanowires or nanoparticles with the potential to be further tuned to provide a morphologically controllable route for tailoring and designing CeO2 nanomaterials for a wide variety of applications.

Anomalous Electrical Conductivity of Nanosheaves of CeO2

CeO2 is a functional oxide known to conduct oxygen ions at elevated temperatures. Enhancement of the ionic conductivity can lead to its application as an electrolyte for solid oxide fuel cells that can operate at low temperatures. We report here a one-dimensional CeO2 nanostructure with a novel sheaflike morphology which exhibits the oxygen-ionic conductivity distinctively higher than that of conventional CeO2 electrolyte. The oxygen nonstoichiometry in the CeO2 nanowires constituting the sheaf was determined by electron energy loss spectroscopy (EELS) and was found to be very small. We thus attribute this anomalously high ionic conductivity to enhanced oxygen-ion mobility at the interfaces between CeO2 nanowires in the sheaf rather than to increased charge-carrier concentration which is often responsible for enhanced ionic conductivity in nanostructured ionic conductors.

Facile Synthesis under Near-Atmospheric Conditions and Physicochemical Properties of Hairy CeO2 Nanocrystallines

Treating freshly prepared cerous hydroxide with hydrogen peroxide (H2O2) under ambient conditions provides a facile and efficient way for converting CeO2 nanoparticles (∼22 nm, 37 m2/g) into nanowires of fine diameters (down to ∼5 nm) and outstanding specific surface areas (∼184 m2/g). The CeO2 nanomaterials were examined by XRD, BET, FT-IR, TG, HR-TEM, Raman scattering, and UV−vis absorption spectroscopy. The results show that the nanowires are single crystalline and of high purity and low defect (oxygen vacancy) concentration and are growing perpendicular to {220} planes. The CeO2 nanowires show indirect and direct band gaps of ∼2.37 and 2.91 eV, respectively, which are both ∼0.15 eV lower than those observed from the nanoparticle form (∼22 nm) for the respective interband transitions. The CeO2 nanowires were proposed to grow via a dissolution−reprecipitation mechanism, with an unstable Ce(OH)3O·OH hyperoxide intermediate as the template.

Facile synthesis of ceria rhombic microplates

Interest in the fabrication of inorganic particles with controlled size and shape is driven by their potential unique and tunable physical properties and the desire to engineer advanced bulk materials from microor nano-scale building blocks [1, 2]. CeO2 is a technologically important rare earth material because of its wide applications as fast ion conductors, oxygen storage capacitors, catalysts, UV blockers, polishing materials, and optical displays [3–7]. Both single crystal and polycrystalline ceria microor nano-structures with different shapes, such as nanopolyhedra [8], nanocubes [9], nanospheres [10], nanorods/nanowires [11–16], coreshell nanowires [17], nanotubes [18, 19], and triangular microplates [20] have been synthesized by us and other research groups in recent years. It is found that the properties and applications of microor nano-materials are related to their morphologies and sizes. For example, Guo et al. [20] synthesized CeO2 triangular microplates by a thermal decomposition–oxidation process using Ce(OH)CO3 microplates as the precursor, and suggested that these materials with triangular structures could find potential applications in multiple fields as catalysts, storage hydrogen devices, and optically or electrically functional host materials. Zhong et al. [21] reported that the flowerlike micro-ceria can be used as not only an effective sorbent for the removal of pollutants in water treatment but also as an excellent support for gold nanoparticles to remove CO by catalytic oxidation, demonstrating a promising potential in environmental remediation. Sun et al. [22] reported that the monodisperse flowerlike ceria microspheres can be used as a support for catalysts with various purposes. Previous reports show that micro-ceria with the special morphology has a potential application in various fields. However, few studies have been reported on the fabrication of CeO2 rhombic microplates. Recently, we synthesized CeO2 nanoplates, nanorods, and nanotubes using CTAB as a surfactant under a low-temperature hydrothermal condition [23], and we also developed a facile template-free liquid precipitation method to synthesize CeO2 nanorods, nanotubes, nanowires, and nanocubes [24]. Herein, we first report a simple surfactant-assisted method to synthesize CeO2 rhombic microplates.