Nanostructured Cerium Oxide Research Articles

Ultra-thin cerium oxide nanostructures through a facile aqueous synthetic strategy

In this work, synthesis of ultra-thin 2D CeO2 nanoribbons is reported for the first time along with rod-shaped nanostructures via a surfactant free aqueous method. CeO2 nanoribbons of length >100nm have been synthesised through a mild reaction route involving ammonia precipitation and subsequent heating and ageing at 0°C. 2D nanostructures are proposed to be formed as a result of self-assembly of CeO2 molecules. The ribbons exhibited amorphous X-ray diffraction pattern and TEM showed a ribbon like morphology with crystal facets of ∼0.33nm spacing corresponding to (111) plane of CeO2. HR-TEM confirmed that the nanorods are enclosed by {111} planes and have preferentially grown in {110} direction. The surface area of the powder containing majority nanorods is 82m2/g and their average pore size is ∼3nm. The nanostructures exhibited optical band gaps dominated by the regular quantum confinement effect as well as presence of defects.

Defect Engineering in Cubic Cerium Oxide Nanostructures for Catalytic Oxidation

Traditional nanostructured design of cerium oxide catalysts typically focuses on their shape, size, and elemental composition. We report a different approach to enhance the catalytic activity of cerium oxide nanostructures through engineering high density of oxygen vacancy defects in these catalysts without dopants. The defect engineering was accomplished by a low pressure thermal activation process that exploits the nanosize effect of decreased oxygen storage capacity in nanostructured cerium oxides.

Corrosion Resistance and Durability of Superhydrophobic Surface Formed on Magnesium Alloy Coated with Nanostructured Cerium Oxide Film and Fluoroalkylsilane Molecules in Corrosive NaCl Aqueous Solution

The corrosion resistant performance and durability of the superhydrophobic surface on magnesium alloy coated with nanostructured cerium oxide film and fluoroalkylsilane molecules in corrosive NaCl aqueous solution were investigated using electrochemical and contact angle measurements. The durability of the superhydrophobic surface in corrosive 5 wt% NaCl aqueous solution was elucidated. The corrosion resistant performance of the superhydrophobic surface formed on magnesium alloy was estimated by electrochemical impedance spectroscopy (EIS) measurements. The EIS measurements and appropriate equivalent circuit models revealed that the superhydrophobic surface considerably improved the corrosion resistant performance of magnesium alloy AZ31. American Society for Testing and Materials (ASTM) standard D 3359-02 cross cut tape test was performed to investigate the adhesion of the superhydrophobic film to the magnesium alloy surface. The corrosion formation mechanism of the superhydrophobic surface formed on the magnesium alloy was also proposed.

Ozonation of model organic compounds catalysed by nanostructured cerium oxides

Cerium oxides prepared by the precipitation method and hydrothermal synthesis, with distinct morphologies and particle size, were tested as catalysts in the ozonation of selected organic compounds. Oxalic acid, aniline and a reactive dye were used as representative of organic pollutants. In the case of oxalic acid, an increase in the catalytic activity with the increase of the percentage of Ce(III) on the surface was observed. Both single and catalytic ozonation allowed the total removal of aniline after 30min of reaction; the cerium oxide prepared by the precipitation method was the best catalyst for promoting the mineralization of aniline solutions. TOC removals close to 100% were obtained in all cases when cerium oxides were used as catalysts in the ozonation of the reactive dye tested.

Electronic sensors built on nanostructured cerium oxide films

The influence of the technical parameters of nanostructured CeO x film production on electronic, structural, optical, and photoelectronic characteristics has been studied for their practical application as the active element of various microelectronic sensors—such as high-performance photoresistors, MOS-photodiodes for bioluminescence registration, ion-selective field-effect transistor (ISFETs), and MOS-varactors indicating pH changing as a result of biochemical processes. X-ray photoelectron spectroscopy analysis (XPS) has shown that the ratio of Ce3+ and Ce4+ ions in CeO x films has changed, depending on the technological regime and, first and foremost, on the temperature of the substrate, which results in an changing of the fundamental gap width. The correlation between these alterations and the optical and photoelectric characteristics has been determined. On the basis of highly sensitive photo photoreceivers and living organisms (daphnia and bioluminescence bacteria), a portative electron bioluminescent metric complex has been created to determine the overall water toxicity caused by mycotoxin patulin, biphentrin, and chlorpyrifos. The minimal sensitivity threshold for patulin is 0.1 mg/l after a 2 h experiment and 0.01 mg/l after 6 and 24 h experiments; for biphentrin, it is 0.01 mg/l after a 3 h experiment and 0.0001 mg/l after a 24 h experiment. It is shown that applying nanocrystalline films of cerium oxide CeO x as the dielectric of MOS structures increases the sensitivity and stability of these sensors due to the high density of the surface of sensitive centers of CeO x (to 1020 m−2), the high values of dielectric permeability (ɛ = 26) and the band-gap width (3.6 eV), and low values of leakage currents. The results of ISFET and MOS varactor application with nanocrystalline CeO x film for the creation of immune and enzymatic biosensors have been demonstrated. The sensitivity threshold of an enzymatic sensor based on choline esterase to organophosphorous pesticides is 10−9 M, and for ions of heavy metals it is 10−7 M. The pH sensitivity of ISFET is 58 mV/pH, which is close to the maximal possible sensitivity for the semiconductor-dielectric-solution structure (the so-called Nernst sensitivity is 59 mV/pH).

Luminescence Properties of Europium-Doped Cerium Oxide Nanoparticles: Role of Vacancy and Oxidation States

Enhancing the optical emission of cerium oxide nanoparticles is essential for potential biomedical applications. In the present work, we report a simple chemical precipitation technique to synthesize europium-doped cerium oxide nanostructures to enhance the emission properties. Structural and optical properties showed an acute dependence on the concentration of oxygen ion vacancy and trivalent cerium, which, in turn, could be modified by dopant concentration and the annealing temperature. Results from X-ray photoelectron spectroscopy showed an increase in tetravalent cerium concentration to 85% on annealing at 900 degrees C. The concentration of oxygen ion vacancy increased from 1.7x10(20) cm(-3) to 4.1x10(20) cm(-3) with the increase in dopant concentration. Maximum emission at room temperature was obtained for 15 mol % Eu-doped ceria, which improved with annealing temperature. The role of oxygen ion vacancies and trivalent cerium in modifying the emission properties is discussed.

Hydrogen peroxide sensor based on horseradish peroxidase immobilized nanostructured cerium oxide film

Nanostructured cerium oxide (NanoCeO 2) film deposited onto indium-tin-oxide (ITO) glass substrate by solution casting has been used for immobilization of horseradish peroxidase (HRP) via physiosorption technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis and electrochemical techniques have been utilized for characterization of NanoCeO 2/ITO electrode and HRP/NanoCeO 2/ITO bioelectrode. The HRP/NanoCeO 2/ITO electrode exhibits value of the apparent Michaelis–Menten constant ( K m) as 2.21 μM, linear regression coefficient as 0.998 and linearity for hydrogen peroxide as 1.0–170 μM obtained using electrochemical response measurements. Besides this, HRP/NanoCeO 2/ITO bioelectrode can be used about 20 times and is stable for 5 weeks at 4 °C. The results of photo-response studies carried out on HRP/NanoCeO 2/ITO bioelectrode indicate reasonable agreement with those obtained using amperometric technique.

A nanostructured cerium oxide film-based immunosensor for mycotoxin detection

Rabbit-immunoglobulin antibodies (r-IgGs) and bovine serum albumin (BSA)have been immobilized onto sol–gel-derived nanostructured cerium oxide(nanoCeO2) film fabricated onto an indium–tin-oxide (ITO) coated glass plate to detect ochratoxin-A (OTA).Broad reflection planes obtained in x-ray diffraction (XRD) patterns reveal the formation ofCeO2 nanostructures. Electrochemical studies reveal thatnanoCeO2 particles provide an increased electroactive surface area for loading of r-IgGs with desired orientation,resulting in enhanced electron communication between r-IgGs and electrode. BSA/r-IgGs/nanoCeO2/ITO immunoelectrode exhibits improved characteristics such as linear range(0.5–6 ng dl−1), lowdetection limit (0.25 ng dl−1), fast response time (30 s) and high sensitivity(1.27 µA ng−1 dl−1 cm−2). The high value of the association constant(Ka,0.9 × 1011 l mol−1) indicates thehigh affinity of the BSA/r-IgGs/nanoCeO2/ITO immunoelectrode to OTA.

Self‐Assembly of Cerium Oxide Nanostructures in Ice Molds

The formation of nanorods, driven by the physicochemical phenomena during the freezing and after the aging of frozen ceria nanoparticle suspensions, is reported. During freezing of a dilute aqueous solution of CeO2 nanocrystals, some nuclei remain in solution while others are trapped inside micro- and nanometer voids formed within the growing ice front. Over time (2-3 weeks) the particles trapped within the nanometer-wide voids in the ice combine by an oriented attachment process to form ceria nanorods. The experimental observations are consistent with molecular dynamics simulations of particle aggregation in constrained environments. These observations suggest a possible strategy for the templated formation of nanostructures through self-assembly by exploiting natural phenomena, such as voids formed during freezing of water. This research suggests a very simple, green chemical route to guide the formation of one- and three-dimensional self-assembled nanostructures.

Sol-gel derived nanostructured cerium oxide film for glucose sensor

Sol-gel derived nanostructured cerium oxide (CeO2) film deposited on gold (Au) electrode has been utilized for physisorption of glucose oxidase (GOx). X-ray diffraction, atomic force microscopy, UV-visible spectroscopy, and electrochemical techniques have been used to characterize sol-gel derived CeO2∕Au electrode and GOx∕CeO2∕Au bioelectrode. The response characteristics of the glucose bioelectrode (GOx∕CeO2∕Au) indicate linearity, detection limit and shelf-life as 50–400mg∕dL, 12.0μM, and 12weeks, respectively. The value of apparent Michaelis–Menten constant (Km) of GOx∕CeO2∕Au bioelectrode has been found to be 13.55μM.

Sol–gel derived nanoporous cerium oxide film for application to cholesterol biosensor

Cholesterol oxidase (ChOx) has been immobilized onto sol–gel derived nano-structured cerium oxide (NS-CeO 2) film deposited on indium-tin-oxide (ITO) coated glass substrate. Phase identification of sol–gel NS-CeO 2 film carried out using X-ray diffraction (XRD) yields reflection peak at 29.4° corresponding to (1 1 1) plane with oriented crystallite (34 nm) along c-axis normal to the substrate. Electrochemical studies reveal that NS-CeO 2 provides electroactive surface for the loading of ChOx and enhances electron transfer rate in the ChOx/NS-CeO 2/ITO bioelectrode. The low value of Michaelis–Menten constant ( K m) obtained as 2.08 mM indicates enhanced ChOx affinity to cholesterol. The observed results show application of sol–gel derived NS-CeO 2 for biosensing without any functionalization.

Nanostructured CeO2 Powders by XPS

Two different synthetic routes were used to synthesize three nanostructured cerium (IV) oxide powders: Two samples were obtained by precipitation from a basic solution of cerium nitrate and treated at 523 and 923 K, respectively, the third one was prepared by a microwave-assisted heating hydrolysis method and treated at 523 K. Compared with the first method, microwave synthesis has the advantage of very short reaction times and produces small particles with a narrower particle size distribution. All of these advantages can be attributed to the fast and homogeneous microwave heating which gives rise to a rapid and more simultaneous nucleation and ready dissolution of the gel. The present work focuses on the XPS analysis: The influence of the heat treatment and the preparation procedure on the surface properties are deeply investigated. Besides the wide scan spectrum, detailed spectra for the Ce 3d, Ce 4d, O 1s, and C 1s regions and related data are presented and discussed.

열화학적 방법에 의한 산소센서용 세리아 나노분말 합성

The nanostructured cerium oxide powders were synthesized by spray thermal decomposition process for the use as the raw materials of resistive oxygen sensor. The synthesis routes consisted of 1) spray drying of water based organic solution made from cerium nitrate hydrate () and 2) heat treatment of spray dried precursor powders at in air atmosphere to remove the volatile components and identically to oxidize the cerium component. The produced powders have shown the loose structure agglomerated with extremely fine cerium oxide particles with about 15 nm and very high specific surface area (). The oxygen sensitivity, n ( and the response time, measured at in the sample sintered at , were about 0.25 and 3 seconds, respectively, which had much higher performances than those known in micron or sized sensors.

Properties and Reactivity of Nanostructured CeO2 Powders: Comparison among Two Synthesis Procedures

Three nanostructured cerium(IV) oxide powders were synthesized by two different synthetic routes: two samples were obtained by precipitation from a basic solution of cerium nitrate and treated at ...

Optical and mechanical performance of nanostructured cerium oxides for applications in optical devices

Nanostructured CeO2−x films have been grown by electron beam evaporation (EBE) and ion beam assisted deposition (IBAD). The CeO2−x consists of grains with size 9–28 nm and nanoscale voids enhancing the surface and quantum-size effects. We investigate the sizedependent electronic properties of nanostructured CeO2−x films and we establish relations between them and the film structure, composition and morphology. We investigate how the structure and morphology variations affect the absolute values of the dielectric function at the UV-Vis and IR spectral regions. The nature of the fundamental gap Eg of CeO2−x is also considered. In addition we study in detail the light absorption mechanisms in the UV spectral regions and we correlate them with the reported band structures of the pure CeO2 and Ce2O3. We also employ nanoindentation testing to compare the mechanical response of CeO2−x films grown by EBE and IBAD. Correlations between the mechanical properties of the films and the growth parameters have been made providing the possibility of tailoring films with good mechanical performance for optical device applications.

Dielectric properties and electronic transitions of porous and nanostructured cerium oxide films

Cerium dioxide (CeO2) exhibits exceptional electronic properties such as optical transparency and high refractive index (n) and high dc dielectric constant (k). Therefore, it is an attractive material for ultra-thin gate oxide in CMOS technology, where high-k dielectrics are required. We study the electronic properties of nanostructured and porous cerium oxide (CeOx) films, 110–500nm thick, grown on Si by electron beam evaporation (EBE) and ion beam assisted deposition (IBAD). The film microstructure and morphology (grain size, porosity, defect concentration, surface and interface roughness) are controlled by varying the process parameters appropriately. They have been studied by high-resolution and transmission electron microscopy (HRTEM). The optical properties have been studied by spectroscopic ellipsometry (SE) and k was determined by capacitance measurements. We have found that the values of k and n (1.6–2.5 depending on porosity) are affected by the electronic transitions, which are strongly correlated with the microstructure and morphology of the films. We investigate how the microstructure and morphology variations affect the absolute values of the dc dielectric constant and of the dielectric function at the UV-Vis and IR spectral regions. In addition, we investigate the very important role of the defects, which have the form of grain boundaries, trivalent Ce3+ and O vacancies. As a result we were able to tailor n and k of CeOx films controlling their porosity and defect density.

Enhanced catalytic activity of nanostructured cerium oxide films

We study the catalytic activity and structure, density and morphology of nanostructured ceria (CeO 2− x , 0.15<x<0.05, grain size 4–28 nm) films using X-ray diffraction (XRD) and reflectivity (XRR). The voids content of the films was determined by XRR and was found to vary between 7% and 40%. The catalytic efficiency of the films is investigated using temperature programmed reaction (TPR) and monitoring the oxidation products. The TPR results are correlated with the density and grain size of the CeO 2− x films and show that smaller grain size may reduce the activation temperature of C combustion as low as ∼200 °C.

Nanostructured Cerium Oxide “Ecocatalysts”

Catalysts based on cerium oxide are now used as effective oxidation systems in numerous environmental applications. Cerium oxide was introduced into the catalysis field relatively recently, in 1976, and not as a catalyst initially. Rather, it was chosen as the key oxygen-storage component of the three-way catalyst (TWC) used in automotive exhausts. Accordingly, ceria is used to extend the air/fuel ratio window in the exhaust gas, releasing or accepting oxygen, respectively, under fuel-rich or fuellean conditions, so that the noble metal catalyst operates at the desirable stoichiometric air/fuel ratio, at which it effectively converts all three gaseous pollutants—CO, hydrocarbons, and NO—to innocuous products. A solid solution of cerium and zirconium oxides is used in today's catalytic converters because of its higher oxygen-storage capacity (OSC) compared with pure ceria. In the years that followed the introduction of ceria into the catalytic converter, many additional merits of cerium oxide were realized, first as an active catalytic component of the TWC and subsequently as a catalyst and sorbent in various industrial applications. A review article by Trovarelli on ceria-based catalysts is a good recent compilation.

Nanostructured ceria-based catalysts for oxydehydrogenation of ethane with CO2

Nanostructured cerium oxides, pure or doped with CaO, prepared from amorphous acetate precursors obtained by the freeze drying method, exhibit high surface areas and are active and selective catalysts for the oxydehydrogenation of ethane (ODE) using CO2as an oxidant. The incorporation of Ca into a solid solution in the ceria framework reduces the activity but improves markedly the selectivity to ethene and the efficiency of CO2. Under reaction conditions, the pure ceria was stable even at 1023 K, while the surface area of the Ca-containing sample decreased markedly. This change was accompanied by a drastic increase in the selectivity to ethene, allowing to obtain yields of ethene up to 22% with 91% selectivity.

ChemInform Abstract: Nanostructured Cerium Oxide: Preparation and Properties of Weakly‐Agglomerated Powders.

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