CeO2 nanocrystals: Seed-mediated synthesis and size control

This work reports on seed-mediated synthesis and size control of monodispersed CeO₂ nanoparticles. CeO₂ nanoparticles of mean size smaller than 2 nm were first prepared by a simple mixing of aqueous solution of cerium (IV) sulfate and ammonia solution at ambient conditions. Using these as-prepared fine particles as the tiny seeds, tunable sizes of CeO₂ nanoparticles were achieved via a facile hydrothermal treatment. All samples were characterized by X-ray diffraction (XRD), infrared (IR) spectroscopy, UV-vis spectroscopy, and thermogravimetric analysis (TGA). It is shown that in comparison with other inorganic cerium salts such as cerium (III) nitrates, cerium (IV) sulfate appears more suitable for forming CeO₂ nanoparticles at room temperature. Sulfate groups are strongly thermodynamically adsorbed on CeO₂ nanoparticle surfaces. The formation mechanism, surface hydration and sulfation characteristics of the resulting CeO₂ nanoparticles are also discussed.     

Microwave-assisted synthesis of ceria nanoparticles

Nanocrystalline ceria (CeO₂) particles have been successfully prepared by microwave-assisted heating technique from an aqueous solution containing ammonium Ce(IV) nitrate and sodium hydroxide. Further thermal treatment of the as-prepared powder at 500 °C resulted in the formation of the well-crystallized CeO₂ nanoparticles with an average crystal size of about 8 nm, varying with the heating temperature. The as-prepared powder and the CeO₂ nanoparticles were examined using X-ray diffraction (XRD) and transmission electron microscope (TEM) techniques. It was found that the morphologies of the synthesized powder show from rod-like for the as-prepared sample to sphere-like for the heat-treated nanoparticles. Mechanism of CeO₂ nanocrystallite growth during annealing is primarily investigated.     

Dopant induced variations in microstructure and optical properties of CeO2 nanoparticles

Nanocrystalline CeO₂ particles doped in the range of 0-20% of Ca²⁺, La³⁺, and Zr⁴⁺ have been prepared from hydrothermal synthesis of nitrate solutions at 200 °C and the influences of the dopants on microstructure and optical properties of the nanoparticles have been investigated. The unit cell parameter is found to be modified by −0.39, +0.83 and +0.16% for doping of 20% Zr⁴⁺, La³⁺, and Ca²⁺, respectively. For each batch prepared, nanoparticles with a narrow size distribution of 5-15 nm have been obtained. A high-resolution transmission electron microscopy investigation reveals that these particles are single crystals mostly having hexagonal, square or circular two-dimensional projections. UV-visible spectra of doped powders exhibit shift of the absorption edge and absorption peak with respect to those of the undoped CeO₂ particles and has been attributed to compensation of Ce³⁺ and decreasing crystallite size as result of doping.     

Application of nanostructured Ca doped CeO2 for ultraviolet filtration

Calcium doped CeO₂ nanoparticles with doping concentrations between 0 and 50 mol% were synthesized by a co-precipitation method for ultraviolet filtration application. Below 20 mol% doping concentration, the samples were single-phase. From 30 mol%, CaCO₃ appears as a secondary phase. The calculated CeO₂ mean crystallite size was 9.3 nm for the pure and 5.7 nm for the 50 mol% Ca-doped sample. Between 250 and 330 nm, the absorbance increased for the 10, 30, and 40 mol% Ca-doped samples compared to the pure one. The band-gap was found to be 3.20 eV for the undoped, and between 3.36 and 3.51 eV for the doped samples. The blue shifts are attributed to the quantum confinement effect. X-ray photoelectron spectroscopy showed that the Ce³⁺ atomic concentration in the pure sample was higher than that of the 20 mol% Ca-doped sample.     

Alginate hydrogel microbeads incorporated with Ag nanoparticles obtained by electrochemical method

An innovative method was developed for production of alginate hydrogel microbeads incorporated with silver nanoparticles (AgNPs) based on electrochemical synthesis followed by electrostatic extrusion. AgNPs were synthesized galvanostatically at different values of AgNO₃ concentration in the initial solution (0.5–3.9 mM), current density (5–50 mA cm⁻²), and implementation time (0.5–10 min). Increase in all of these parameters increased the concentration of AgNPs in alginate solution and was confirmed by TEM analysis and UV–vis spectroscopy. Cyclic voltammetry studies and Fourier transform infrared spectroscopy proved the alginate to be a good capping agent for the electrochemical synthesis of silver nanoparticles, due to coordination bonding between hydroxyl and ether groups, as well as ring oxygen atoms in uronic acid residues of alginate molecules, and Ag nanoparticles. Ag/alginate colloid solution was used for production of uniform hydrogel microbeads (with diameter of 487.75 ± 16.5 μm) by electrostatic extrusion technique. UV–vis spectroscopy confirmed retention and entrapment of AgNPs in microbeads during the production process. Alginate microbeads incorporated with AgNPs are attractive as biocompatible carriers and/or efficient donors of AgNPs as active components especially for potential biomedical applications, which was demonstrated by the antibacterial activity against Staphylococcus aureus.     

Preparation and characterization of CeO2 highly dispersed on activated carbon

A new material constituted by cerium dioxide highly dispersed on activated carbon (CeO₂/AC) was prepared by an impregnation method using cerium(III) nitrate as CeO₂ precursor. In order to evaluate the degree of ceria dispersion on the carbon support, CeO₂/AC was characterized by a number of techniques: thermogravimetry coupled with a mass spectrometer (TG-MS), N₂ adsorption at 77 K, temperature-programmed desorption (TPD), temperature-programmed reduction (TPR) and transmission electron microscopy (TEM). The analysis of the decomposition process under inert atmosphere indicated that cerium nitrate decomposes at 440-460 K, with the evolution of NO. Furthermore, this process produces an additional oxidation of the carbon surface (with evolution of N₂O) and the subsequent onset of new oxygen surface groups, detected by means of temperature-programmed desorption. The ceria deposition process takes place with a decrease in the N₂ adsorption capacity of the starting carbon support, and the analysis of the pore size distribution showed that the majority of ceria particles are situated at the most internal part of the carbon porosity. The temperature-programmed reduction profile of CeO₂/AC was very different to that shown by unsupported CeO₂, with only one continuous reduction process at low temperatures (800-900 K). Finally, TEM pictures gave direct evidence that ceria is highly dispersed on the carbon surface, with a narrow CeO₂ particle distribution centred around 3 nm.     

Synthesis and conductivity of cerium oxide nanoparticles

Cerium oxide (CeO₂) nanoparticles have been synthesized through composite-hydroxide-mediated approach. The X-ray powder diffraction (XRD) measurement proved that the pure cubic CeO₂ could be obtained at a low temperature region (170-220 °C). The particle size, micrograph morphology and microstructure were investigated by transmission electron microscope (TEM) and environmental scanning electron microscope (ESEM). The conductivity of as-synthesized CeO₂ was measured by a standard four-probe method. The conductivity of CeO₂ increases slightly with the increase of temperature. And the conductivity increases rapidly to 0.02418 s cm^− 1 at 830 °C. The product is a potential material for intermediate temperature solid oxide fuel cells (ITSOFC).     

Synthesis of barium titanate nanoparticles via a novel electrochemical route

An electrochemical route from Ti metal plate in KOH and Ba(OH)₂ electrolyte at room temperature is first established for the synthesis of BaTiO₃ nanoparticles. Anodic sparks play a key role, and KOH concentration is one of the most significant factors which affect the appearance of anodic sparks in this method. XRD patterns show that the powder obtained in our study is a pure perovskite phase BaTiO₃ with a cubic structure, whose size and morphology are subsequently studied by TEM. The mean diameter of the particles is 13.8 nm and the standard deviation (S.D.) fitted is 6.26 nm. It is also found that the mean size of the obtained nanoparticles increase from 13.8 nm to 168.0 nm, when 60 vol.% absolute ethanol is replaced by distilled water as the solvent of the electrolyte.     

Synthesis of size tuneable cadmium sulphide nanoparticles from a single source precursor using ammonia as the solvent

Size tuneable cadmium sulphide nanoparticles of a few nanometres in size were prepared by thermolysis of a single source precursor of cadmium xanthates with variable carbon chain length (Cd(ROCS₂)₂, where R denotes -C₂H₅, -C₄H₉, -C₈H₁₇ and -C₁₂H₂₅, respectively) in an ammonia solution. The particle size, morphology and crystallinity of these nanoparticles were characterized using X-ray powder diffractometry, transmission electron microscopy, and nitrogen adsorption/desorption techniques. The results show that hexagonal CdS nanoparticles can be produced by thermolysis of cadmium alkyl xanthate in an ammonia solution at a temperature as low as 100 °C. The size of CdS particles (between 5.60 nm and 3.71 nm) decreases with increasing length of carbon chain in the precursor, as further confirmed by UV-visible and fluorescence spectrophotometric measurements. The size tuning mechanism of CdS from cadmium alkyl xanthate is also discussed.     

New route to prepare nanocrystalline TiO2 and its reaction mechanism

Titanium oxide nanoparticles are prepared by electrochemical dissolution of pure titanium in a mixed acetylacetone and ethanol solution followed by direct sol-gel process of the electrolyte. Infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and TEM have been used to investigate the structure of precursor and nanocrystalline TiO₂. Characterization of the electrochemical product reveals that Ti(OEt)_m(acac)_n was formed by anodic dissolution of titanium in a mixed acetylacetone and ethanol solution. Infrared experiments show that hydrolysis of Ti(OEt)_m(acac)_n precursor removes first OEt groups, the chelating acac groups are still observed in the gel and can only be removed upon heating to 473 K. This study also shows that nanocrystalline TiO₂ prepared by this route has a textural and thermal stability with size distribution of 5-20 nm.     

Magnetic properties and photoabsorption of the Mn-doped CeO2 nanorods

Mn-doped CeO₂ nanorods have been prepared from CeO₂ particles through a facile composite-hydroxide-mediated (CHM) approach. The analysis from X-ray photoelectron spectroscopy indicates that the manganese doped in CeO₂ exists as Mn²⁺. The magnetic measurement of the Mn-doped CeO₂ nanorods exhibits an enhanced ferromagnetic property at room temperature with a remanence magnetization (Mr) of 1.36 × 10⁻³ emu/g and coercivity (Hc) of 22 Oe. Comparative UV-visible spectra reveal the shift of the absorption peak of the CeO₂ from ultraviolet region to visible light region after being doped with Mn. The room temperature ferromagnetic properties and light absorption of the Mn-doped CeO₂ nanorods would have potential applications in photocatalysis and building of photovoltaic devices.     

Silicon dioxide coating of CeO2 nanoparticles by solid state reaction at room temperature

The synthesis of SiO₂ coated CeO₂ nanoparticles by humid solid state reaction at room temperature is described. Transmission electron microscope results show that CeO₂ particles were coated with a layer of SiO₂. Binding energy of Ce 3d_5/2 was shifted from 883.8 to 882.8 eV after coating in the XPS Ce 3d spectra. This confirms the chemical bond formation between SiO₃²⁻ and Ce⁴⁺. Because the surface photovoltage property of CeO₂ nanoparticles that were used as core materials in the experiment approaches to that of CeO₂ macroparticles, peak P2 (electron transition from O 2p on surface to Ce 4f) disappeared in the surface photovoltage spectrum of CeO₂ nanoparticles. Also, the effect of SiO₂ on the electron transition from O 2p to Ce 4f results in the lowering of surface photovoltage response intensity of P1 peak (electron transition from O 2p in bulk to Ce 4f).     

Electrospinning of CeO2-ZnO composite nanofibers and their photocatalytic property

CeO₂-ZnO composite nanofibers were fabricated via the electrospinning technique using zinc acetate and cerium nitrate as the precursors, poly(vinylpyrrolidone) as the fiber template, and 2:1(v/v) ethanol/water mixtures as the co-solvent, followed by thermal treatment at 600 °C for 3 h. Various characterization methods were employed to investigate the morphologies and structures of the nanofibers. The calcined composite nanofibers showed a continuous line feature with an average diameter of 46 nm composed of 15 ± 3 nm CeO₂ and ZnO nanoparticles. Photocatalytic activity experiments showed that the Rhodamine B was almost completely decomposed when it was catalyzed by CeO₂-ZnO nanofibers within 3 h, while only 17.4% and 82.3% were decomposed under catalysis by CeO₂ and ZnO nanofibers respectively. Such CeO₂-ZnO composite nanofibers could have potential applications in the treatment of organic-polluted water.     

Hydroxy propyl cellulose capped silver nanoparticles produced by simple dialysis process

Silver (Ag) nanoparticles (∼6 nm) were synthesized using a novel dialysis process. Silver nitrate was used as a starting precursor, ethylene glycol as solvent and hydroxy propyl cellulose (HPC) introduced as a capping agent. Different batches of reaction mixtures were prepared with different concentrations of silver nitrate (AgNO₃). After the reduction and aging, these solutions were subjected to ultra-violet visible spectroscopy (UVS). Optimized solution, containing 250 mg AgNO₃ revealed strong plasmon resonance peak at ∼410 nm in the spectrum indicating good colloidal state of Ag nanoparticles in the diluted solution. The optimized solution was subjected to dialysis process to remove any unreacted solvent. UVS of the optimized solution after dialysis showed the plasmon resonance peak shifting to ∼440 nm indicating the reduction of Ag ions into zero-valent Ag. This solution was dried at 80 °C and the resultant HPC capped Ag (HPC/Ag) nanoparticles were studied using transmission electron microscopy (TEM) for their particle size and morphology. The particle size distribution (PSD) analysis of these nanoparticles showed skewed distribution plot with particle size ranging from 3 to 18 nm. The nanoparticles were characterized for phase composition using X-ray diffractrometry (XRD) and Fourier transform infrared spectroscopy (FT-IR).     

Size-controlled synthesis, microstructure and magnetic properties of Ni nanoparticles

Ni nanoparticles with different mean diameters of 15-83 nm were synthesized by solution reduction process. The size of Ni nanoparticles can be controlled by varying the concentration of NiCl₂·6H₂O and synthesis temperature. The samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). Results show that the synthesized particles are single-phased Ni with a face-centered cubic crystal structure. Magnetic measurements indicate that Ni nanoparticles are ferromagnetic. The lattice constants and coercivities of the samples are size-dependent.     

Hydrothermal fabrication of various morphological α-Fe2O3 nanoparticles modified by surfactants

Two kinds of various morphological α-Fe₂O₃ nanoparticles modified by anionic surfactant (sodium dodecylsulfonate, SDS) and cationic surfactant (hexadecyipyridinium chloride, HPC), respectively, have been synthesized via hydrothermal method, using simple inorganic salt (NH₄)₃Fe(C₂O₄)₃ and alkali NaOH as starting precursors. Meanwhile, α-Fe₂O₃ nanoparticles without surfactant are also fabricated under the same conditions for comparison. The resultant products were characterized by means of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron micrograph (TEM) combined with electron diffraction (ED) and magnetization measurements. It is interesting that the obtained α-Fe₂O₃ nanoparticles without surfactant are polyhedral with average particle size of 90 ± 35 nm; while the obtained α-Fe₂O₃ nanoparticles modified by SDS are ellipsoidal with mean particle size of major axis: ca. 420 nm; minor axis: ca. 205 nm and those modified by HPC are spherical with mean particle size of ca. 185 nm observed from TEM. In addition, magnetic hysteresis measurements reveal that the α-Fe₂O₃ nanoparticles modified by two surfactants show enhancement in coercivity (H_c) and the remanent magnetization (M_r) compared with those of the obtained α-Fe₂O₃ nanoparticles without surfactant at room temperature. The experimental results suggest that the surfactants not only significantly influence the size and shape of the particles, but also their magnetic properties.     

Nanoparticles of La0.8Ca0.2Fe0.8Ni0.2O3−δ perovskite for solid oxide fuel cell application

Polycrystalline samples of La_0.8Ca_0.2Fe_0.8Ni_0.2O_3−δ (LCFN) with perovskite type structure have been prepared by combustion, freeze drying, citrate-gel process and liquid mix method. The analysis of X-ray powder diffraction indicated that the samples were single phase and crystallized in an orthorhombic (space group, Pnma no. 62) structure.Transmission electron microscopy (TEM) analysis on the synthesized powder at 600 °C by liquid mix method showed clusters of 150 nm formed by nanoparticles of 20 nm. Electrochemical performance of LCFN cathodes, which are used for intermediate temperature solid oxide fuel cells, were investigated. The polarization resistance was studied using two different electrolytes: Y-doped zirconia (YSZ) and Sm-doped ceria (SDC). The dc four-probe measurement exhibits a total electrical conductivity, over 100 S cm⁻¹ at T ≥ 600 °C, pointing out that strontium can be substituted for the cheaper calcium cation without destroying the electrochemical properties. Experimental results indicate that nanoparticles have more advantages in terms of smaller particle size and better electrochemical performance.     

Corrosion behaviour of sol–gel coatings doped with cerium salts on 2024-T3 aluminum alloy

The corrosion behaviour of the sol–gel coatings doped with cerium chloride or cerium nitrate on 2024-T3 aluminum alloy was investigated by using electrochemical impedance spectroscopy (EIS) and immersion tests. The sol–gel matrix was obtained through hydrolysis, condensation of 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetramethoxysilane (TMOS), using diethylentriamine as curing agent. The results indicated that cerium nitrate with concentration of 1 × 10⁻³ mol L⁻¹ in the silane solution was excellent on self-healing for the sol–gel coating, while cerium chloride had no obvious effect. This result suggested that the introduction of Cl⁻ promoted the under-film pitting of 2024-T3 substrate. It was found that Ce(OH)₃ and Ce(OH)₂²⁺ simultaneously existed in the silane solution by X-ray diffraction (XRD) analysis. Ce(OH)₂²⁺ transformed to CeO₂ due to high-temperature curing of sol–gel matrix demonstrated by X-ray photoelectron spectroscopy (XPS) analysis. Therefore, it can be considered that Ce(OH)₃ and CeO₂ played inhibition roles in the corrosion process of the sol–gel coatings.     

Study of local environment of Ag in Ag/CeO2 catalyst by EXAFS

The combustion synthesized Ag/CeO₂ catalysts have been characterized by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy at the Ag K-edge. It has been found that Ag⁺ like species is present in 1% Ag/CeO₂ catalyst, whereas mostly Ag metal clusters are found in 3% Ag/CeO₂. The analysis of EXAFS spectra indicates that about one oxygen atom is coordinated to Ag central atom at a distance of 2.19 Å in 1% Ag/CeO₂ catalyst along with eight coordinated AgAg bond at 2.86 Å. The AgO bond is absent in 3% Ag/CeO₂.     

The synthesis and optical property of solid-state-prepared YAG:Ce phosphor by a spray-drying method

Ce³⁺-activated yttrium aluminum garnet (Y₃Al₅O₁₂:Ce, YAG:Ce) powder as luminescent phosphor was synthesized by the solid-state reaction method. The phase identification, microstructure and photoluminescent properties of the products were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), absorption spectrum and photoluminescence (PL) analysis. Spherical phosphor particle is considered better than irregular-shaped particle to improve PL property and application, so this phosphor was granulated into a sphere-like shape by a spray-drying device. After calcinating at 1500 °C for 0, 4, and 8 h, the product was identified as YAG and CeO₂ phases. The CeO₂ phase content is decreased by increasing the calcination time or decreasing the Ce³⁺ doping content. The product showed higher emission intensity resulted from more Ce³⁺ content and larger grain size. The product with CeO₂ was found to have lower emission intensity. This paper presents the crystal structures of Rietveld refinement results of powder XRD data.