Aqueous Solutions Of Cerium Nitrate Research Articles

MAINTAINING STABLE NANODISPERSED CERIUM OXIDE FOR HEAT TRANSFER PROCESSES

The introduction of heat carriers progressive types causes the productivity of heat exchange systems to increase. One of the challenges in thermal applied applications is the search for heat carriers that will provide revolutionary indicators of thermal conductivity and stability over time, thereby increasing the order of the heat transfer processes efficiency magnitude. The paper describes the creation of stable colloidal solutions using cerium oxide and organic stabilizers to provide better heat exchange performance compared to true solutions. Cerium oxide colloids were obtained by precipitation of the oxide from an aqueous solution of cerium nitrate with an aqueous ammonia solution in the presence of a polymer under vigorous stirring at room temperature. A number of cerium oxide nanosized dispersions, stabilized with polyvinylpyrrolidone, with a particle size of 1–10 nm were obtained. The content of CeO2 in the obtained dispersions was 1.72.10–3, 5.15.10–3, 8.6.10–3, 1.21.10–2, 1.72.10–2 % at a polymer content of 1.10–3 mol/l, the pH of the dispersions was 8–9. Electron microscopic images of the obtained nanodispersions showed a colloidal particles narrow distribution and cerium oxide nanoparticles in size. Colloidal particles are macromolecular tangles of polyvinylpyrrolidone with oxide nanoparticles strung in them. A volume of 20–50 nm organic matrix contains 10–40 particles of 1–10 nm cerium oxide. The particle size distributions of the dispersions established by the photon-correlation spectroscopy method have two areas of maxima for each sample. The first maximum for the dispersions of all investigated concentrations refers to particles with a diameter of 5–6 nm, which, in our opinion, are particles of cerium oxide, both in polymer beads and probably free from the stabilizer. Another maximum, depending on the sample, is observed at 30–70 nm or 100–300 nm, and relates to colloidal particles of PVP with cerium oxide encapsulated particles. The static stability of the cerium oxide obtained nanodispersions with polyvinylpyrolidone for two years under standard conditions is comparable to the true polymer solution. It is proposed by the method of UV spectroscopy to control the reproducibility of the obtaining materials technology. Tests of the thermal conductivity of the obtained 1.72.10–3 % stable cerium oxide nanodispersion were performed at 50 °C relative to distilled water with a thermal conductivity coefficient of 0.65 W/(m·deg). We found an increase in the coefficient for nanodispersions by 4–6 %, which is a significant value for dilute solutions. Ref. 15, Fig. 4 .

CHARACTERIZATION OF CeO2 DOPED MgAl2O4 PREPARED BY THE CHELATING AGENTS-ASSISTED IMPREGNATION METHOD

MgAl2O4 spinel employed as support of reforming catalysts was doped by CeO2. The samples were prepared by wet impregnation from aqueous solutions of cerium nitrate, with and without chelating agents. The chelating agents used were ethylenediamine-tetraacetic acid (EDTA), nitrilotriacetic acid (NTA) and citric acid (CA) at different pH of impregnation. The solids were characterized by TG, XRD, SBET, TPR, SEM-EDX and CO2-TPD. Nanoparticles of CeO2 between 5 and 6.8 nm were obtained by the thermal decomposition in air at 600 °C. The surface cerium reduction occurred in a wide temperature range of 450° to 670 °C. The use of citric acid at pH= 8 led to the lowest crystallite size of CeO2 and the lowest interaction with the spinel. The H2 consumption and extent of CeO2-support interaction did not show a clear dependence with the CeO2 crystallite sizes. The use of chelating agents in the impregnation step did not modify the total basicity. Slight changes in the strength of weak basic sites were observed.

Photoluminescent properties of spider silk coated with Eu-doped nanoceria

Spider dragline silk was coated with pure as well as Eu-doped ceria nanopowders at the room temperature. The treatment was done by immersion of the spider silk mesh into aqueous solutions of cerium nitrate (Ce(NO3)3) and ammonium hydroxide (NH4OH). Depending on the relationship between Ce3+ ion and ammonium hydroxide concentration, coated fibers exhibited a different thickness. Obtained materials were studied by means of FESEM. It was found that ceria nanoparticles of average size of 3 nm were coated along spider thread. X-ray diffraction (XRD) and selected-area electron diffraction (SAED) confirmed crystal nature of nanoparticle coating of spider silk. By using Williamson-Hall plots, crystallite size and strain were estimated. EDS measurement confirmed the presence of Eu in spider-Eu-doped ceria composite, and according to FTIR analysis, the interaction between CeO2 and spider silk was proposed. The morphology of obtained composite was observed by TEM. The photoluminescence emission spectra of spider silk coated with Eu-doped ceria were measured with two different excitations of 385 and 466 nm. The two-photon excited auto-fluorescence of spider silk coated with Eu-doped ceria was detected using a nonlinear laser scanning microscope. Obtained composite has a potential as a fluorescent labeling material in diverse applications.

Ion coordination in aqueous solutions of cerium nitrate from X-ray diffraction data

Aqueous solutions of cerium nitrate were studied by X-ray diffraction over a wide concentration range under standard conditions. The presence of prepeaks on experimental X-ray diffraction intensity curves can be explained by the long-range order of ions. With a decrease in the concentration of cerium nitrate, the pseudoperiodic distribution of composite cation-anion complexes changes to an even interionic distribution in the water network of a solvent, which is reflected by the intensity curves. The experimental radial distribution functions were calculated and interpreted.

Enhanced optical properties of heterostructured ZnO/CeO2 nanocomposite fabricated by one-pot hydrothermal method: Fluorescence and ultraviolet absorption and visible light transparency

Many researchers investigated the properties of either discrete metal oxide CeO2 or ZnO materials. However, less attention has been paid to the various nanostructure and performances of CeO2 and ZnO nanocomposite up to now. In this paper, a facile and low cost one-pot hydrothermal synthesis method has been adopted to obtained directly precursors of CeCO3OH and Zn5(CO3)2(OH)6 with different Ce atom molar ratios to Zn, which are transformed into their corresponding metal oxide to form the ZnO/CeO2 heterostructure nanocomposites (HSNCs) by pyrolysis. The heterostructure is composed of ZnO and CeO2 monocrystals, simultaneously, CeO2 monocrystals are well dispersed on the surface of ZnO monocrystal for cosmetics. Bing dependent on the analysis results of XRD and TEM for the obtained precursors before and after pyrolysis, the formation mechanism of HSNCs was proposed. To the best of our knowledge, the paper first reported heterostructured ZnO/CeO2 nanocomposite grown in one-pot mixed aqueous solution of cerium nitrate, zinc acetate and urea without other extra surfactant. Additionally, the influence of various Ce/Zn molar ratios on the heterostructure, fluorescence emission and UV–visible absorption properties of HSNCs was investigated in detail. ZnO/CeO2 HSNCs display higher fluorescence emission with the increasing Ce/Zn molar ratio. Meanwhile, the larger Ce/Zn molar ratio of ZnO/CeO2 HSNCs, the stronger transparency in the visible light region and the weaker UV absorption. The results are due to the fact that the band gap of ZnO/CeO2 HSNCs will decrease from 3.25 to 3.08eV when Ce/Zn atom molar ratio is increased from 0 to 0.08. By the comprehensive analysis on the optical performances of HSNCs with the different Ce/Zn atom molar ratios, ZnO/CeO2-0.04 HSNCs could become UV absorber materials and transparent material in the visible region. ZnO/CeO2-0.04 HSNCs with the UV-filtering and Vis-transparent properties is appropriate for personal-care cosmetics.

Catalytic Combustion of Toluene on Pd/CeO<SUB>2</SUB>–TiO<SUB>2</SUB> Catalysts

Pd/TiO2 and Pd/CeO2 were reported to be very active to destruct toluene. Combination of TiO2 and CeO2 is an interesting candidate to achieve a catalyst with higher activity. In this study, a series of Pd/CeO2-TiO2 catalysts with various Pd loadings were prepared. CeO2-TiO2 was prepared by impregnation of aqueous solution of cerium nitrate into TiO2 support. It was then calcined at 400 degrees C. Pd was loaded by incipient-wetness impregnation method. The Pd loadings in all samples were fixed at 0.5 wt.%. The catalysts were characterized by powder X-ray diffraction, transmission electron microscopy, high resolution transmission electron microscopy, temperature-programmed reduction of hydrogen, and X-ray photoelectron spectroscopy. The catalysts were tested for total oxidation of toluene. The feed concentration of toluene was 8.564 g/m3 (2085 ppm), with GHSV = 10,000 h(-1). Pd particle sizes were 3-5 nm and well-dispersed on the support. CeO2 on TiO2 was easier to reduce than the bulk CeO2, therefore it could enhance the activity of VOC destruction. Pd/CeO2-TiO2 was more active than Pd/CeO2 and Pd/TiO2. Pd/CeO2-TiO2 with Ce/Ti ratio of 2/8 was very active for toluene destruction, due to its lower oxygen reduction temperature of ceria and higher concentration of Pd(0).

Correlations between electrochemical mechanisms and growth of ceria based coatings onto nickel substrates

Cathodic electrosynthesis of cerium-containing films onto model Ni and both raw and aluminized nickel-based superalloy was investigated from concentrated aqueous solutions of cerium nitrate at room temperature. The correlations between the electrochemical features and the microstructure of the resulting layers were established. Polarization curves revealed that transient deposition stages were the most critical as both composition and surface condition of the substrate strongly influenced the nucleation and growth processes and the final morphology of the coatings. SEM/EDS analyses showed that the films initially developed in a homogeneous manner onto raw substrates whereas nuclei grew mainly onto grain boundaries of aluminized samples before covering the grains. Quick growth kinetics led to oxygen defective deposits composed of a mixture of hydrated cerium oxide/hydroxide incorporating carbonates and trapped nitrates due to incomplete reactions.

Sonochemical Synthesis of Lanthanide Ions Doped CeF3 Nanoparticles: Potential Materials for Solid State Lighting Devices

Nanocrystalline CeF3 and CeF3 doped with Dy3+, Tb3+ and Eu3+ ions have been successfully synthesized via a mild ultrasound assisted route from an aqueous solution of cerium nitrate and potassium borofluoride. The nanoparticles obtained were characterized extensively by techniques like powder X-ray diffraction, transmission electron microscopy and selected area electron diffraction. Their luminescence properties have also been studied. The nanoparticles showed characteristic emission of respective dopants (Dy3+ and Tb3+) when excited at the 4f --> 5d transition of Ce3+. The chromaticity coordinates for these samples were calculated and it was observed that the CeF3 co doped with Dy3+ and Tb3+ gave an emission very close to white light.

Continuous synthesis of organic–inorganic hybridized cubic nanoassemblies of octahedral cerium oxide nanocrystals and hexanedioic acid

We synthesized cubic nanoassemblies of octahedral CeO(2) nanocrystals by simply heating an aqueous solution of cerium nitrate (Ce(NO(3))(3)) in the presence of hexanedioic acid (HOOC(CH(2))(4)COOH) in a lab-scale plug-flow reactor. It was concluded that the octahedral shape of the primary CeO(2) nanocrystals plausibly leads to octa-coordination of the primary nanocrystals, thus enabling controlled assembly to form a cubic structure.

Fabrication of Mesoporous Cerium Dioxide Films by Cathodic Electrodeposition

Mesoporous cerium dioxide (Ceria, CeO2) thin films have been successfully electrodeposited onto ITO-coated glass substrates from an aqueous solution of cerium nitrate using CTAB (Cetyltrimethylammonium Bromide) as a templating agent. The synthesized films underwent detailed characterizations. The crystallinity of synthesized CeO2 film was confirmed by XRD analysis and HR-TEM analysis, and surface morphology was investigated by SEM analysis. The presence of mesoporosity in fabricated films was confirmed by TEM and small angle X-ray analysis. As-synthesized film was observed from XRD analysis and HR-TEM image to have well-crystallized structure of cubic phase CeO2. Transmission electron microscopy and small angle X-ray analysis revealed the presence of uniform mesoporosity with a well-ordered lamellar phase in the CeO2 films electrodeposited with CTAB templating.

Morphological Control and Luminescent Properties of CeF3 Nanocrystals

The nanocrystals of CeF3 with the hexagonal structure and different morphologies such as the disk, the rod, and the dot have been successfully synthesized via a mild ultrasound assisted route from an aqueous solution of cerium nitrate and different fluorine sources (KBF4, NaF, NH4F). The use of different fluorine sources has a remarkable effect on the morphology of the final product. The luminescence and UV−vis absorption properties of CeF3 nanocrystals with different morphologies have been investigated. Compared with other shape nanocrystals, the luminescence intensity of the disklike nanocrystals is obviously enhanced. It is suggested that the function-improved materials could be obtained by tailoring the shape of the CeF3 nanocrystals.

Ce-containing Mordenites: Synthesis, structure and reactivity towards NO and CO gases

Aqueous solutions of cerium nitrate of increasing concentrations (2.5, 5 and 7.5 wt.% Ce) have been contacted with the components forming Mordenite zeolite; during forming the gel under hydrothermal conditions, for allowing the accessibility of Ce ions to proceed into compensating positions in Mordenite structure. These materials were characterized by the methods of FTIR, XRD, N 2 adsorption and UV–vis diffuse reflectance spectroscopy. The interaction of NO and CO adsorptions; at room temperature, on thermally pre-treated (300 °C, 10 −5 Torr, 3 h) as well as pre-reduced (50 Torr, 500 °C, 1 h) samples were studied by in situ Fourier transform infrared spectroscopy. XRD and FTIR results indicate that the Ce atoms are mostly present in internal surfaces in Mordenites for 2.5 and 5CeMOR samples whereas for 7.5CeMOR, a decrease in diffusion of Ce to be in compensating positions is perceived; as conceived from lowering the lattice volume, pointing to the presence of discrete amounts of CeO 2 (582 cm −1) and cerium silicate (Si–O–Ce; 797 cm −1) species. All the samples indicate intra-crystalline mesopores as depicted from V l– t plots particularly the 7.5CeMOR sample that showed the highest wide-pore volume (0.073 cm 3/g), lowest pore radius (21 Å) and thus, revealed the highest S BET between all samples (363 m 2/g). UV–vis characterization of 7.5CeMOR sample shows octahedral Ce species (345, 360 and 390 nm) in small clusters inside zeolite channels and most probably originated from cerium silicates having different coordination with NaMOR along with discrete amounts of CeO 2 (420 nm) species. CO readily adsorbs on the Ce 3+ sites of the pre-reduced 7.5CeMOR catalyst, rather than those on Ce 4+, to display minor amounts of carboxylate and dominant amounts of monodentate carbonate that were amenable to decompose to produce CO 2 gas (2335 cm −1). On the other hand, the in situ interaction of nitric oxide (NO) gas on the 7.5CeMOR catalyst led to the formation of a series of nitrosyl species: N 2O (2240 cm −1), NO (1908 cm −1), N 2O 3 (1880 cm −1) and (NO) 2s,as (1844, 1734–1720 cm −1). Such nitrosyl complexes were favorably formed on Ce 3+ in 7.5CeMOR those exchanged Na ones.

Preparation and Characterization of Fibrous Cerium Oxide Templated from Activated Carbon Fibers

AbstractHigh surface area cerium oxide has been prepared using a carbon templating method. Impregnation of a highly mesoporous activated carbon (Darco KB-B) with an aqueous solution of cerium nitrate, followed by carbon burn off, afforded ceria with surface area of up to 148 m2/g. According to thermogravimetric studies, ceria formation proceeds via decomposition of cerium nitrate at ca. 410 K; oxidation of the carbon template commences at the same temperature, being facilitated by the release of NO2 from the Ce compound. Use of activated carbon fibers (ACFs) as template was found to provide a simple route to fibrous cerium oxide. The lower surface areas (3 - 59 m2/g) of the resulting ceria fibers reflect the largely microporous nature of the ACFs; evidently the Ce nitrate solution is unable to penetrate their micropores. Consequently, the surface area of the ceria product is found to increase with increasing mesoporosity of the ACF template. Electron microscopy reveals that the ceria fibers are composed of highly crystalline primary particles of 5-10 nm diameter; further, the fibers display a number of interesting morphological features at the macro- and nano-scales.

Preparation of mesoporous activated carbon fiber by steam activation in the presence of cerium oxide and its adsorption of Congo red and Vitamin B12 from solution

Activated carbons are widely used in separation and purification processing, and as catalysis supports [1, 2]. Activated carbon fibers (ACFs) as a new type of activated carbon have an excellent adsorptive property due to large specific surface area, pore volume, and uniform microporosity. Generally, the micropore in ACF cannot meet some special demands, such as adsorption of bulky molecules from solution and catalyst supports for macromolecule reaction [3]. So, it is desired to increase the mesopore and macropore content in ACF and exploit its new applications. Polymer additives or catalyst was added to the carbon source and carbonized to obtain mesoporous carbon fiber; but it was difficult to eliminate the catalyst from the mesoporous carbon fiber matrix [4–6]. The transition metal and rare earth metal compounds can promote the development of mesopores in activated carbon [7–9]. The activation reaction takes place in the immediate vicinity of metal/oxide particles, leading to the formation of mesopores and macrospores by pitting holes into the carbon matrix [10]. Potassium hydrate can promote the mesopore development, but it needs higher loading amount if the post-treatment is complex. Yttrium acetylacetonate [Y(acac)3] was added to the precursor of carbon and used as catalyst to increase the mesopore content of ACF, but the cost was high [11]. Cerium oxide showed certain activity due to its role in the oxidization–reduction cycle [12] and it could promote the mesopore development in activated carbon with scatter pore size distribution due to the original property of activated carbon [13]. In the current work, cerium nitrate was selected to investigate its catalytic effect on the mesopore development of commercial ACF with steam activation. The commercial ACF was first impregnated with the aqueous solution of cerium nitrate. The loadings of cerium nitrate on the basis of activated carbon were 2.0 wt%. The samples were then dried at 110 ◦C for

Ceria nanoparticles: Size, size distribution, and shape

Nanocrystalline ceria particles have been prepared by mixing aqueous solutions of cerium nitrate and hexamethylenetetramine at room temperature. The smallest size of nanoparticles synthesized is 2 nm. For each batch prepared, a narrow size distribution is found with a standard deviation less than ±15%. A transmission electron microscopy (TEM) investigation shows that these particles are single crystals having either an octahedral shape with eight {111} surfaces, or with an additional {200} surface-truncated octahedral shape. In-situ ultraviolet-visible light absorption has been performed to measure the absorption edge and to monitor the growth of nanoparticles. The results from light absorption correlate well with those of the TEM images, providing an in-situ method to measure the particle size during synthesis.

Growth and Optical Properties of NaY(WO4)2:Eu Crystals

Single crystals of mixed cerium lanthanum oxalate (CLO) are grown by gel method. Over the hydro-silica gel prepared by mixing oxalic acid and sodium meta silicate, a mixture of aqueous solutions of cerium nitrate and lanthanum nitrate are poured gently. Cerium and lanthanum ions diffuse into the gel and react with oxalic acid to give colorless, transparent cerium lanthanum oxalate crystals with in a few days. Different growth parameters give crystals of various dimensions. Infrared (IR) spectrum confirms the presence of water molecules and carboxylic acid. X-ray diffraction (XRD) pattern of these samples reveals the crystalline nature. Diffraction peaks are indexed. Unit cell parameters are determined. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) data support the presence of 9 H20 molecules attached to the CLO crystal lattice which are lost around 2000C as revealed by the endotherm record. Exothermic peak around 350°C-425°C shows the release of CO and CO2. Elemental analysis done by energy dispersive X-ray fluorescence analysis (EDXRF) for the mixed rare earth compound is almost in good agreement with experimental and theoretical values.

Effect of the preparation method on the properties of zirconia-ceria materials

Zirconium-cerium mixed oxides were prepared by two methods: (i) sol-gel hydrolysis of alcoholic solutions of zirconium alkoxides (n-propoxide and n-butoxide) in the presence of aqueous solutions of cerium nitrate (method SG) or (ii) coprecipitation of aqueous solutions of zirconyl and cerium nitrates by ammonia (method NP). Dried or calcined solids were characterized by XRD, DTA, BET and oxygen storage capacity (OSC) measurements, O 2 adsorption was monitored by infrared spectroscopy. Regardless of the zirconium precursor, SG samples calcined at 900 °C have a fluorite-type structure with BET surface areas varying between 35 and 45 m 2 g –1 . Cerium-rich samples (0.85≤x≤0.90), with excellent OSC properties and high thermal stability can be prepared by the sol-gel method. FTIR studies of O 2 adsorption reveal the presence of stable superoxide species whose concentration strongly depends on the cerium content and the method of preparation. A good correlation between the relative amount of O 2 – species and OSC values was observed. Superoxide ions may be formed at the same anionic vacancies as those involved in oxygen storage.

ChemInform Abstract: Preparation of Cerium Dioxide Powders for Catalyst Supports.

AbstractCeO2 powder with a high, thermally stable BET surface area (50 m2/g) is prepared by spray drying an aqueous solution of cerium nitrate, citric acid, and HNO3.

Preparation of Cerium Dioxide Powders for Catalyst Supports

Studies of the mechanisms by which cerium dioxide enhances automotive catalyst performance would be facilitated by the use of pure, high‐surface‐area forms of cerium dioxide. A cerium dioxide powder with a BET area of 50 m2·g−1 has been prepared by spray drying an aqueous solution of cerium nitrate, citric acid, and nitric acid. The thermal stability of the BET area at temperatures from 500° to 1100°C has been determined and compares favorably to other CeO2 powders. Microstructure evolution during thermal treatments is discussed and pelleting procedures are reported.