Self-propagating Room Temperature Research Articles

Investigation of the Effects of Yb and Nd Doping and Operating Temperature on CeO2 Photocatalyst Properties

Abstract: This study investigated the effects of the co-doping of Yb and Nd elements and the operating temperature on photocatalytic degradation. Composites of Ce0.96Nd0.04O2 (CN), Ce0.96Yb0.04O2 (CY), and Ce0.92Nd0.04Yb0.04O2 (CNY) were obtained by self-propagating room temperature reaction method, involving several sequential steps. The composites were sintered at 500 and 600 °C. The structural and morphological properties of the compounds were examined via X-ray powder diffractometry (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and UV-vis spectroscopy. In the degradation study, methylene blue was chosen as the dyestuff. Although the operating temperature affected the degradation negatively, co-doping had a positive effect. The lowest bandgap (2.70 eV) was found for the CNY compound and the CNY without applied operating temperature had the highest percentage of degradation (80.76%). Keywords: CeO2, Self-propagating reaction, Co-doping, Photocatalytic, Rare earth element.

Synthesis, densification and characterization of Ag doped ceria nanopowders

Nanosized Ag-doped ceria (Ce1-xAlxO2-δ)powders (0.1 ≤ x ≤ 0.04) were obtained by self-propagating room temperature reaction. The solid solubility of Ag into ceria lattice was the highest reported so far. X-ray diffraction analysis and field emission scanning microscopy results showed that the doped samples are single phase solid solutions with fluorite-type structure and all prepared powders were nanometric in size. The average size of Ce1-xAgxO2-▯ particles lies at about 4 nm. Raman spectra revealed an increase in the amount of oxygen vacancies with the increase of Ag concentration, such as is foreseen. The thermal stability of solid solution was followed by XRD. Microstructure development was studied by scanning electron microscopy. By controlling the processing variables, it was possible to obtain high density samples with homogeneous microstructure at low sintering temperature.

Confined space self-propagating room temperature synthesis of carbon-encapsulated Fe3O4 nanocrystals and its lithium storage performance

A self-propagating reaction between ferrocene and iron nitrate nonahydrate that is initiated at room temperature is discovered. Amorphous carbon-encapsulated Fe3O4 nanocrystals (Fe3O4@C) can be one-step prepared in an autoclave through this reaction. The equiaxed Fe3O4 nanocrystals have typical dimensions in the range of 5–60 nm with a median size of 24.1 nm, and their weight percent is up to 82.3%. The course of the reaction is recorded, and the formation mechanism of Fe3O4@C with the core–shell structure is proposed. The scaling-up synthesis is also achieved, and 52.1 g of the Fe3O4@C can be obtained in a single batch. The shock wave appeared in the fast gas release self-propagating reaction in confined space plays a decisive role in the preparation of homogeneous Fe3O4@C with a core–shell structure. The Fe3O4@C anode shows excellent capacity retention with a high specific capacity of 494 mAh g−1 at 1 A g−1 in the 200th cycle.

Electronic structure of surface complexes between CeO2 and benzene derivatives: A comparative experimental and DFT study

Surface modification of CeO2 nano-powder, synthesized by a self-propagating room temperature method with salicylate-type ligands (salicylic acid and 5-aminosalicylic acid) as well as catecholate-type ligands (catechol, 3,4-dihydroxybenzoic acid, caffeic acid and 2,3-dihydroxy naphthalene), induces the appearance of absorption in the visible spectral region due to the interfacial charge transfer (ICT) complex formation. Thorough characterization involving transmission electron microscopy, XRD analysis, and nitrogen adsorption-desorption isotherms, revealed that loosely agglomerated CeO2 particles of the size ranging from 2 to 4 nm have cubic fluorite structure and specific surface area of 140 m2/g. The attachment of salicylate- and catecholate-type of ligands to the surface of CeO2 powders leads to the formation of colored powders with tunable absorption in the visible spectral region. The density functional theory calculations with properly design model systems were performed to estimate the alignment of energy levels of various inorganic/organic hybrids. A reasonably good agreement between calculated values and experimental data was found.

Influence of temperature and dopant concentration on structural, morphological and optical properties of nanometric Ce1−xErxO2−δ (x = 0.05–0.20) as a pigment

Ceramic pigments based on cerium oxide were synthesized by self-propagating room temperature method and their color properties were assessed from the viewpoint of potential environmentally non-toxic pink pigments. Thermal stabilities of the pigments were examined at 600, 900 and 1200 °C. According to X-ray powder diffraction and Raman spectroscopy results, all obtained pigments were single-phase solid solutions of cerium oxide, independent of the concentration of dopants. The X-ray analysis showed that the crystallites were of nanometric dimensions, as recorded and by transmission electron microscopy analysis. Color characteristics of solid solutions, which depended on concentration erbium ions and calcination temperature, and their position in the chromaticity diagram were studied by ultraviolet–visible spectrophotometry, which confirmed potential application of environmentally friendly pigments of desired color. The color efficiency of pigments was also evaluated by colorimetric analysis.

Anti-cancer effects of cerium oxide nanoparticles and its intracellular redox activity

Data on medical applications of cerium oxide nanoparticles CeO2 (CONP) are promising, yet information regarding their action in cells is incomplete and there are conflicting reports about in vitro toxicity. Herein, we have studied cytotoxic effect of CONP in several cancer and normal cell lines and their potential to change intracellular redox status. The IC50 was achieved only in two of eight tested cell lines, melanoma 518A2 and colorectal adenocarcinoma HT-29. Self-propagating room temperature method was applied to produce CONP with an average crystalline size of 4nm. The results confirmed presence of Ce3+ and O2− vacancies. The induction of cell death by CONP and the production of reactive oxygen species (ROS) were analyzed by flow-cytometry. Free radicals related antioxidant capacity of the cells was studied by the reduction of stable free radical TEMPONE using electron spin resonance spectroscopy. CONP showed low or moderate cytotoxicity in cancer cell lines: adenocarcinoma DLD1 and multi-drug resistant DLD1-TxR, non-small cell lung carcinoma NCI-H460 and multi-drug resistant NCI-H460/R, while normal cell lines (keratinocytes HaCaT, lung fetal fibroblasts MRC-5) were insensitive. The most sensitive were 518A2 melanoma and HT-29 colorectal adenocarcinoma cell lines, with the IC50 values being between 100 and 200μM. Decreased rate of TEMPONE reduction and increased production of certain ROS species (peroxynitrite and hydrogen peroxide anion) indicates that free radical metabolism, thus redox status was changed, and antioxidant capacity damaged in the CONP treated 518A2 and HT-29 cells. In conclusion, changes in intracellular redox status induced by CONP are partly attributed to the prooxidant activity of the nanoparticles. Further, ROS induced cell damages might eventually lead to the cell death. However, low inhibitory potential of CONP in the other human cell lines tested indicates that CONP may be safe for human usage in industry and medicine.

Studies on structural, morphological and electrical properties of Ce1−xErxO2−δ (x = 0.05–0.20) as solid electrolyte for IT – SOFC

A series of four different powders ceria doped Ce1−xErxO2−δ (0.05 ≤ x ≤ 0.20) were synthesized by applying self-propagating reaction at room temperature (SPRT method). SPRT procedure is based on the self-propagating room temperature reaction between metal nitrates and sodium hydroxide, wherein the reaction is spontaneous and terminates extremely fast. The method is known to assure very precise stoichiometry of the final product in comparison with a tailored composition. XRPD, Raman spectroscopy, TEM and BET measurements were used to characterize the nanopowders at room temperature. It was shown that all obtained powders were single phase solid solutions with a fluorite-type crystal structure and all powder particles have nanometric size (about 3–4 nm). Densification was performed at 1550 °C, in an air atmosphere for 2 h. XRPD, SEM and complex impedance method measurements were carried out on sintered samples. Single – phase form was evidenced for each sintered materials. The best value of conductivity at 700 °C amounted to 1.10 × 10−2 Ω−1 cm−1 for Ce0.85Er0.15O2−δ sample. Corresponding activation energies of conductivity amounted to 0.28 eV in the temperature range 500–700 °C.

Investigation of surface defect states in CeO2-y nanocrystals by Scanning−tunneling microscopy/spectroscopy and ellipsometry

Synthesis process strongly influences the nanocrystalline CeO2-y defective structure. The presence of surface defects, in the form of oxygen vacancies in different charge states (F centers), can change the electronic properties of ceria nanocrystals. Nanocrystalline CeO2-y samples were synthesized using three different methods (precipitation, self-propagating room temperature, and hydrothermal synthesis). Raman spectroscopy was used to identify the presence of oxygen vacancies which presumably were formed at the nanoparticle surface. The defect concentration depended on the crystallite size of differently prepared CeO2-y samples. Scanning tunneling microscopy/spectroscopy and ellipsometry were employed to investigate the electronic band structure of defective CeO2-y nanocrystals. Scanning tunneling spectroscopy measurements demonstrated that inside the band gap of CeO2-y nanocrystals, besides the filled 4 f states, appeared additional states which were related to occupied and empty F center defect states. From the ellipsometric measurements, using the critical points model, the energy positions of different F centers states and the values of the reduced band gap energies were determined. The analysis of obtained data pointed out that depending on the synthesis method, different types of F centers (F+ and F0) can be formed in the CeO2-y nanocrystals. The formation of different F center defect states inside the ceria gap have a strong impact on the electrical, optical, and magnetic properties of ceria nanocrystals.

Nanocrystalline CeO2-δ as effective adsorbent of azo dyes.

Ultrafine CeO2-δ nanopowder, prepared by a simple and cost-effective self-propagating room temperature synthesis method (SPRT), showed high adsorption capability for removal of different azo dyes. Batch type of adsorption experiments with fixed initial pH value were conducted for the removal of Reactive Orange 16 (RO16), Methyl Orange (MO), and Mordant Blue 9 (MB9). The equilibrium adsorption data were evaluated using Freundlich and Langmuir isotherm models. The Langmuir model slightly better describes isotherm data for RO16 and MO, whereas the Freundlich model was found to best fit the isotherm data for MB9 over the whole concentration range. The maximum adsorption capacities, determined from isotherm data for MO, MB9, and RO16 were 113, 101, and 91 mg g(-1) respectively. The adsorption process follows the pseudo-second-order kinetic model indicating the coexistence of chemisorption and physisorption. The mechanism of azo dye adsorption is also discussed.

Novel simple methods for the synthesis of single-phase valentinite Sb2O3

Several methods with solid and dissolved reactants were investigated as possible routes for synthesis of single-phase valentinite Sb2O3. The methods are based on simple chemical reaction between SbCl3 and NaOH. The method with solid state reactants was established on self-propagating room temperature reaction (SPRT), while wet syntheses were based on the same chemical reaction, and performed in either distilled water or absolute ethanol. The prepared powders were characterized by X-ray powder diffraction, scanning electron microscopy and field emission scanning electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction (SAED) and UV/vis diffuse reflectance spectroscopy. SPRT and aqueous solution syntheses resulted in single-phase valentinite Sb2O3, but with significantly different morphologies. In the case of SPRT method the obtained powder contains well crystallized prismatic shaped submicronic particles, with hexagonal or lozenge basis typical for valentinite crystal structure, while aqueous solution synthesis resulted in powder containing micronic agglomerates. The ethanolic solution synthesis product was Sb2O3 with cubic senarmontite as predominant phase and traces of orthorhombic valentinite. It was confirmed that not only the aggregate state, but also the choice of solvent has a great influence on the structural and optical characteristics of synthesized Sb2O3 powders.

Yb3+, Er3+ doped Y2O3 nanoparticles of different shapes prepared by self-propagating room temperature reaction method

In this report, a cost- and time-effective method for synthesis of Y2O3:Yb3+, Er3+ nanoparticles that exhibit up-conversion emission under infrared excitation is presented. The synthesis method is based on the self-propagating, room-temperature reaction between metal nitrates and sodium hydroxide, and a subsequent calcination process. Series of samples were prepared with calcinations at various temperatures (600°C, 800°C and 1100°C) for 1h, and also with different Yb3+–Er3+ ratios (10:1, 5:1 and 2:1). All calcined samples crystallized in a cubic bixbyite crystal phase with crystallite size from 12 to 44nm in diameter, for samples calcined at 600°C and 1100°C, respectively. Different nanoparticle morphologies were obtained after calcinations on different temperatures; at temperatures under 1100°C rod-like particles were obtained, while at 1100°C spherical particles were formed. In all samples up-conversion emissions and corresponding lifetimes were measured after excitation in room temperature at 978nm. The most intense emission originates from the characteristic intra-shell f–f electronic transitions of Er3+ ions: [2H9/2→4I15/2] in blue (407–420nm); [(2H11/2, 4S3/2)→4I15/2] green: 510–590nm; and [4F9/2→4I15/2] in red (640–720nm) spectral regions.

Electrical and microstructural properties of Yb-doped CeO2

Nanopowdered Ce1−xYbxO2−δ solid solutions (0 ≤ x ≤ 0.2) were synthesized by a self-propagating room temperature synthesis. XRD and SEM were used to study the properties of these materials as well as the Yb solubility in CeO2 lattice. Results showed that all the obtained powders were solid solutions with a fluorite-type crystal structure and with nanometric particle size. The average size of Ce1−xYbxO2−δ particles was approximately 3 nm. Electrochemical impedance spectroscopy for the sintered pellets depicted that it was possible to separate Rbulk and Rgb in the temperature interval of 550–800 °C. The activation energy for the bulk conduction was 1.03 eV and for grain boundary conduction was 1.14 eV. Grain boundary resistivity dominates over the other resistivities. These measurements confirmed that Yb3+-doped CeO2 material had a potential as electrolyte for intermediate-temperature solid oxide fuel cell applications.

F-centre luminescence in nanocrystalline CeO2

Nanocrystalline CeO2 powders were synthesized by two cost-effective methods: the self-propagating room temperature (SPRT) method and the precipitation method. Differently prepared samples exhibited different temperature-dependent photoluminescence (PL) in the ultraviolet and visible regions. The PL signals originated from different kinds of oxygen-deficient defect centres with or without trapped electrons (F0, F+ or F++ centres). The temperature-dependent PL spectra were measured using different excitation lines, below (457, 488 and 514 nm) or comparable (325 nm) to the ceria optical band gap energy, in order to investigate the positions of intragap localized defect states. Evidence for the presence of F+ centres was supported by the signals observed in electron paramagnetic resonance (EPR) measurements. Based on PL and EPR measurements it was shown that F+ centres dominate in the CeO2 sample synthesized by the SPRT method, whereas F0 centres are the major defects in the CeO2 sample synthesized by the precipitation method. The luminescence from F++ states, as shallow trap states, was registered in both samples. Energy level positions of these defect states in the ceria band gap were proposed.

Annealing and doping concentration effects on Y2O3: Sm3+ nanopowder obtained by self-propagation room temperature reaction

In this report, structure, morphology and luminescence of Y2O3:Sm3+ nanoparticles prepared by self-propagating room temperature reaction are presented. This new, simple and cost effective synthesis allows obtaining desired phase composition by mixing appropriate amounts of yttrium and samarium nitrates together with sodium hydroxide. A set of samples is prepared with different Sm3+ concentrations (0.1, 0.2, 0.5, 1 and 2 at %) in order to observe changes of luminescence properties. Also, effects of post synthesis annealing at several temperatures (600?C, 800?C and 1100?C) are analyzed. For all samples X-ray diffraction showed that powders have cubic bixbyite structure (Ia-3), and TEM analysis showed particles of less than 100 nm. Luminescence emission spectra clearly show peaks characteristic for electronic spin-forbidden transition of Sm3+ ions 4G5/2?6H5/2, 6H7/2 and 6H9/2 centered at 578, 607 and 654 nm, respectively. Emission lifetime values decrease with Sm3+ ion concentration increment, from 1.94 ms for 0.1 at% to 0.97 ms for 2 at%. In addition, enlargement of lifetime value is observed when thermal treatment is done at the highest temperature due to the elimination of luminescence quenching species from the surface of particles.

Synthesis, calcination and characterization of Nanosized ceria powders by self-propagating room temperature method

Abstract Nanometric ceria powders with fluorite-type structure were obtained by applying self-propagating room temperature method. The obtained powders were subsequently thermally treated (calcined) at different temperatures for different times. Powder properties such as specific surface area, crystallite size, particle size and lattice parameter have been studied. Roentgen diffraction analysis (XRD), BET and Raman scattering measurements were used to characterize the as-obtained (uncalcined) powder as well as powders calcined at different temperatures. It was found that the average diameter of the as-obtained crystallites is in the range of 3–5 nm whereas the specific surface area is about 70 m 2 /g. The subsequent, 15 min long, calcination of as-obtained powder at different temperatures gradually increased crystallite size up to ∼60 nm and reduced specific surface down to 6 m 2 /g. Raman spectra of synthesized CeO 2− y depicts a strong red shift of active triply degenerate F 2 g mode as well as additional peak at 600 cm −1 . The frequency of F 2 g mode increased while its line width decreased with an increase in calcination temperature. Such a behavior is considered to be the result of particle size increase and agglomeration during the calcination. After the heat treatment at 800 °C crystallite size reached value larger than 50 nm. Second order Raman mode, which originates from intrinsic oxygen vacancies, disappeared after calcination.

Synthesis and characterization of Pr6O11 nanopowders

Amorphous Pr6O11 powder was obtained by applying self-propagating room temperature method (SPRT). After calcination, the amorphous powder converted to nanometric Pr6O11 powder with cubic fluorite-type structure. Powder properties such as crystallite size, lattice strain and lattice parameter were studied by X-ray diffraction (XRD) at room temperature. The crystallite size was estimated by means of the full width at half maxima (FWHM) of XRD peaks. Williamson–Hall plots were used to determine the lattice strain whereas the Ritveld analysis was employed for crystal structure refinement. It was found that the powder properties are affected by both calcination temperature and duration of thermal treatment. The crystallite size varied from 5 to ∼250nm, whereas the lattice parameter varied from 5.461 to 5.494Å. The powder obtained after four-hour long calcination was almost free of internal strain.

Nanocrystaline solid solution CeO2–Bi2O3

Abstract Nanocrystalline powders of solid solution CeO 2 –Bi 2 O 3 were synthesized by self-propagating room temperature reaction (SPRT) procedure with composition (Ce 1− x Bi x O 2− δ where the x = 0.1–0.5). X-ray diffraction analyses show that for x

Synthesis and characterization of Cu-doped ceria nanopowders

Nanopowdered solid solution Ce 1− x Cu x O 2− γ samples (0 ≤ x ≤ 0.15) were synthesized by self-propagating room temperature synthesis (SPRT). Raman spectroscopy and XRD at room temperature were used to study the vibration properties of these materials as well as the Cu solubility in ceria lattice. The solubility limit of Cu 2+ in CeO 2 lattice was found to be lower than published in the literature. Results show that obtained powders with low dopant concentration are solid solutions with a fluorite-type crystal structure. However, with Cu content higher than 7.5 mass%, the phase separation was observed and two oxide phases, CeO 2 and CuO, coexist. All powders were nanometric in size with high specific surface area.

Synthesis and characterization of (Ba, Yb) doped ceria nanopowders

Nanometric size (Ba, Yb) doped ceria powders with fluorite-type structure were obtained by applying selfpropagating room temperature methods. Tailored composition was: Ce0.95-xBa0.05YbxO2-? with fixed amount of Ba - 0.05 and varying Yb content 'x' from 0.05 to 0.2. Powder properties such as crystallite and particle size and lattice parameters have been studied. R?ntgen diffraction analyses (XRD) were used to characterize the samples at room temperature. Also, high temperature treatment (up to 1550?C) was used to follow stability of solid solutions. The mean diameters of the nanocrystals are determined from the full width at half maxima (FWHM) of the XRD peaks. It was found that average diameter of crystallites is less than 3 nm. Williamson- Hall plots were used to separate the effect of the size and strain in the nanocrystals.

Room-temperature synthesis of nanometric α-Bi 2O 3

Nanometric Bi 2O 3 powder was successfully synthesized by applying the method based on self-propagating room temperature reaction (SPRT) between bismuth nitrates and sodium hydroxide. X-ray powder diffraction (XRPD) and Rietveld's structure refinement method were applied to characterize prepared powder. It revealed that synthesized material is a single phase monoclinic α-Bi 2O 3 (space group P2 1/ c with cell parameters a = 5.84605(4)Å, b = 8.16339(6) Å, c = 7.50788(6) Å and β = 112.9883(8)). Powder particles were of nanometric size (about 50 nm). Raman spectral studies conformed that the obtained powder is single phase α-Bi 2O 3. Specific surface area of obtained powder was measured by Brunauer–Emmet–Teller (BET) method.