Higher Ce Content Research Articles

Physiological responses and chromosomal aberration in root tip cells of Allium sativum L. to cerium treatments

Lower concentrations of REEs promote plant growth, whereas higher concentrations of REEs negatively affect plant growth, soil accumulation, and environmental pollution. To clarify the mechanism of cerium (Ce) toxicity on Allium sativum, the effects of Ce(IV) on mitosis in root tip cells and physiological responses were studied. Roots growth, mitosis, chlorophyll and malondialdehyde contents, and activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase were measured after treatments with Ce(IV). Lower Ce concentrations (0.4 and 4 μM) increased leaf chlorophyll content and enhanced SOD and catalase activities. Higher Ce concentrations (40 and 100 μM) decreased chlorophyll content and inhibited root growth, but enhanced malondialdehyde contents and catalase and APX activity in roots and leaves. SOD activity was inhibited after 12 days of treatment with 100 μM Ce. Treatment with >100 μM Ce caused chromosomal aberrations (e.g., sticky chromosomes, chromosomal fragments, and bridges) in root tip cells. Chromosomal aberrations in root cells induced by high Ce concentrations might be associated with inhibition of root growth. Changes in antioxidant enzyme activities suggested that Ce(IV) induced antioxidative stress responses and that Ce(IV) treatment first damaged root cells and subsequently affected physiological processes in leaves.

Leaching of rare earth elements from waste lamp phosphor mixtures by reduced alkali fusion followed by acid leaching

Because of the complex crystal structures of the blue powder and green powder in waste rare earth phosphor powder and the relative high content of Ce and Tb, efficient extraction of rare earth elements (REEs) is difficult. The highest leaching efficiency of REEs is only about 90% with present processes, and utilization of the REEs is low. To improve the leaching efficiency of waste rare earth phosphor, a novel process of reduced alkali fusion followed by acid leaching to recover REEs from waste phosphor powder is proposed. Under the conditions of mass ratio of reductive iron powder to waste rare earth phosphor of 1:200, alkali to phosphor mass ratio of 2:1, alkali fusion temperature of 700°C, alkali fusion time of 3h, hydrochloric acid concentration of 3molL−1, liquid to solid ratio (v/w) of 7.5:1, acid leaching temperature of 70°C, and acid leaching time of 1h, the total leaching efficiency of REEs is as high as 99.35%, and the leaching efficiencies of Ce, Eu, Tb, and Y are 98.12%, 99.93%, 99.37%, and 99.60%, respectively. The results indicate that the REEs in waste phosphor powder can be efficiently recovered by the proposed process.

Tetravalent Ce in the Nitrate-Decorated Hexanuclear Cluster [Ce6(μ3-O)4(μ3-OH)4]12+: A Structural End Point for Ceria Nanoparticles

We describe the synthesis and characterization of three glycine-stabilized hexanuclear CeIV cluster compounds, each containing the [Ce6(μ3-O)4(μ3-OH)4]12+ core structure. Crystallized from aqueous nitrate solutions with pH < 0, the core cluster structures exhibit variable decoration by nitrate, glycine, and water ligands depending on solution conditions, where increased nitrate and glycine decoration of the cluster core was observed for crystals synthesized at high Ce and nitrate concentrations. No other crystalline products were observed using this synthetic route. In addition to confirming the tetravalent oxidation state of cerium in one of the reported clusters, cyclic voltammetry also indicates that CeIV is reduced at ∼+0.60 V vs Ag/AgCl (3 M NaCl), which is significantly less than the standard electrode potential. This large decrease in the CeIV/CeIII reduction potential suggests that CeIV is significantly stabilized relative to CeIII within the examined cluster. These compounds are discussed in term...

The studies of granitoids from the Sobótka region in light of theories of the origin of colour in minerals

AbstractThe article presents the results of the studies of 19 feldspar-quartz raw materials samples, coming from deposits located in the Sobótka region, in light of four distinct physical theories explaining mechanisms for creating the colour of minerals. This is a successive stage of research carried out by the author on reasons for colour variation of samples after firing at 1200°C. This step encompassed a detailed chemical analysis for main and trace elements contents of all the investigated samples as well as Mössbauer studies of two of them. The chemical analysis reveals that the darkest samples are characterised by the highest contents of the following colouring compounds and elements: Fe2O3, MnO, Th, U, Ce, Nd, and V, accompanied by a relatively low amount of TiO2. The Mössbauer studies demonstrated the quantitative predominance of Fe2+over Fe3+in the sample of a relatively darker hue with a high Fe2O3content, while its spectra parameters suggest that Fe2+is located in octahedral coordination that can result in a cold blue tint. Cations Fe3+(located probably in the tetrahedral position) prevail in the other analysed sample that contain less Fe2O3and a relatively high content of TiO2, Ce, and Nd. This probably causes a warm, reddish shade of the sample. The above-mentioned observations and examinations lead to the finding that, at this stage of the investigations, the crystal field theory could be the best suited for the interpretation of colour of the studied samples. This formalism associates the colour origin with ions of the transition elements, some REE and actinides located in the structure of minerals, and their ability to selectively absorb visible light.

Cerium stable isotope ratios in ferromanganese deposits and their potential as a paleo-redox proxy

The cerium (Ce) anomaly observed in rare earth element (REE) patterns has been used to estimate the redox state of paleo-marine environments. Cerium is unique because it forms tetravalent cations under oxic conditions, in contrast to the other REEs that occur in a trivalent state. This characteristic leads to anomalously high or low Ce concentrations relative to neighboring REEs. However, the use of Ce anomaly as a paleo-redox proxy is not well calibrated. This study shows that coupling of the Ce anomaly and Ce stable isotope ratio (δ142Ce) is more quantitative redox proxy to distinguish suboxic and oxic redox conditions. Our results revealed a progressive enrichment in heavy Ce isotopes in consecutive formations of iron (Fe) and manganese (Mn) precipitate from hot spring water without any associated change in REE patterns. The δ142Ce values of Mn precipitates were approximately 0.35‰ heavier than those of the Fe precipitates, which was consistent with experiment-based predictions. The δ142Ce values of marine ferromanganese deposits with three different formation processes were hydrogenetic (+0.25‰)>diagenetic (+0.10‰)⩾hydrothermal (+0.05‰), which also reflects redox conditions of their formation environment. These observations suggest that the Ce stable isotope ratios yield more quantitative information regarding redox state than REE patterns alone. We thus suggest that this novel proxy can be successfully utilized to reconstruct marine redox states, particularly from slightly oxic to highly oxic conditions such as the Great Oxidation Event (GOE).

Designing CuOx Nanoparticle-Decorated CeO2 Nanocubes for Catalytic Soot Oxidation: Role of the Nanointerface in the Catalytic Performance of Heterostructured Nanomaterials

This work investigates the structure-activity properties of CuOx-decorated CeO2 nanocubes with a meticulous scrutiny on the role of the CuOx/CeO2 nanointerface in the catalytic oxidation of diesel soot, a critical environmental problem all over the world. For this, a systematic characterization of the materials has been undertaken using transmission electron microscopy (TEM), transmission electron microscopy-energy-dispersive X-ray spectroscopy (TEM-EDS), high-angle annular dark-field-scanning transmission electron microscopy (HAADF-STEM), scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS), X-ray diffraction (XRD), Raman, N2 adsorption-desorption, and X-ray photoelectron spectroscopy (XPS) techniques. The TEM images show the formation of nanosized CeO2 cubes (∼25 nm) and CuOx nanoparticles (∼8.5 nm). The TEM-EDS elemental mapping images reveal the uniform decoration of CuOx nanoparticles on CeO2 nanocubes. The XPS and Raman studies show that the decoration of CuOx on CeO2 nanocubes leads to improved structural defects, such as higher concentrations of Ce(3+) ions and abundant oxygen vacancies. It was found that CuOx-decorated CeO2 nanocubes efficiently catalyze soot oxidation at a much lower temperature (T50 = 646 K, temperature at which 50% soot conversion is achieved) compared to that of pristine CeO2 nanocubes (T50 = 725 K) under tight contact conditions. Similarly, a huge 91 K difference in the T50 values of CuOx/CeO2 (T50 = 744 K) and pristine CeO2 (T50 = 835 K) was found in the loose-contact soot oxidation studies. The superior catalytic performance of CuOx-decorated CeO2 nanocubes is mainly attributed to the improved redox efficiency of CeO2 at the nanointerface sites of CuOx-CeO2, as evidenced by Ce M5,4 EELS analysis, supported by XRD, Raman, and XPS studies, a clear proof for the role of nanointerfaces in the performance of heterostructured nanocatalysts.

The role of surface properties of silicotungstic acid doped CeO2 for selective catalytic reduction of NOx by NH3: Effect of precipitant

The present work elucidated the precipitants effect of pure CeO2 on the activity of silicotungstic acid supported on CeO2 catalysts toward NOx reduction. The results implied that the silicotungstic acid doped CeO2 prepared by the NH3·H2O precipitant showed the best SCR performance and nearly 100% NOx conversion was obtained at 225–450°C. Silicotungstic acid doped CeO2 prepared by NH3·H2O (Cat-A) was enclosed by (111) and (220) planes; the catalyst with (NH4)2CO3 (Cat-B) predominantly exposed (220) and (200) surfaces, and the catalyst with the mixture of NH3·H2O and (NH4) 2CO3 (Cat-C) merely exhibited the (200) planes. Moreover, the aggregated WO3 was observed over the Cat-B and Cat-C, the BET surface areas and total pore volume of the two samples significantly decreased compared with Cat-A. Besides, the Brönsted (B) acid sites only appeared on the Cat-A catalyst and the intensity of Lewis acid was visibly stronger than that of Cat-B and Cat-C. Importantly, the Cat-A possessed its higher concentration of Ce3+ and surface chemisorbed oxygen Oα. As a result, the structure geometry and surface acidity were different on the (111) and (2 00) surfaces of CeO2, which were dependence on the different precipitants.

Promising nanostructured gold/metal oxide catalysts for oxidative coupling of benzylamines under eco-friendly conditions

Designing Au nanocatalysts supported on nanosized metal oxides has drawn much attention due to remarkable nanoscale influenced metal-support interactions and their favorable role in heterogeneous catalysis. This work reports development of Au nanocatalysts dispersed on nanosized CeO2 and CeO2-ZrO2 supports for solvent- and base-free oxidative coupling of benzylamines into N-benzylbenzaldimines using O2 as a green oxidant. The physicochemical characterization of nanocatalysts has been undertaken using HRTEM, UV–vis DRS, XRD, Raman, BET, TG-DTA, AAS, and XPS techniques. HRTEM images reveal the formation of nanosized CeO2 and CeO2-ZrO2 supports with an average diameter of ∼10 and 7nm, respectively. HRTEM images also indicated that Au/CeO2-ZrO2 catalyst has smaller Au nanoparticles (∼2.1nm) compared with that of Au/CeO2 catalyst (∼3.7nm). Raman and XPS studies showed that the addition of ZrO2 to CeO2 leads to abundant oxygen vacancies and higher concentration of Ce3+, respectively. The Au/CeO2-ZrO2 catalyst exhibited a higher efficiency in benzylamine conversion (∼95%) followed by Au/CeO2 (∼78%), CeO2-ZrO2 (∼51%), and CeO2 (∼39%). The Au/CeO2-ZrO2 catalyst was also found to effective for oxidative coupling of various benzylamines, and moderate to good product yields were obtained. The presence of smaller Au particles (2.1nm) and improved surface-defect properties of nanoscale CeO2-ZrO2 support are found to be key factors for high performance of Au/CeO2-ZrO2 catalyst. Additionally, the reaction temperature is one of the important factors for the performance of catalysts. Remarkably, ∼99.6–99.9% selectivity for N-benzylbenzaldimines was found in the amine oxidation, which highlights the significance of present work in the selective oxidation catalysis.

Biochemical Characterization of a Lanthanide-Dependent DNAzyme with Normal and Phosphorothioate-Modified Substrates.

A trivalent lanthanide (Ln(3+))-dependent RNA-cleaving DNAzyme, Ce13d, was recently isolated via in vitro selection. Ce13d is active in the presence of all Ln(3+) ions. Via introduction of a single phosphorothioate (PS) modification at the cleavage site, its activity with Ln(3+) decreases while all thiophilic metals can activate this DNAzyme. This property is unique to Ce13d and is not found in many other tested DNAzymes. This suggests the presence of a well-defined but general metal binding site. Herein, a systematic study of Ce13d with the PO substrate (using Ce(3+)) and the PS substrate (using Cd(2+)) is performed. In both the PO and PS systems, the highest activity was with ∼10 μM metal ions. Higher concentrations of Ce(3+) completely inhibit the activity, while Cd(2+) only slows the activity. A comparison of different metal ions suggests that the role of metal is to neutralize the phosphate negative charge. Both systems follow a similar pH-rate profile with a single deprotonation step, indicating similar reaction mechanisms. The activity difference between the Rp and Sp form of the PS substrate is <10-fold, which is much smaller than most known RNA-cleaving enzymes. Mutation studies identified eight highly conserved purines, among which the two adenines play mainly structural roles, while the guanines are likely to be involved in metal binding. Ce13d can serve as a model system for further understanding of DNAzyme biochemistry and bioinorganic chemistry.

Electrospun Au/CeO2 nanofibers: A highly accessible low-pressure drop catalyst for preferential CO oxidation

Au/CeO2 catalysts shaped as nanofibers were obtained by supporting Au nanoparticles (ca. 3nm) on CeO2 nanofibers of around 200nm diameter. The CeO2 support was prepared by calcining electrospun polymer nanocomposite fibers with a high Ce content; then gold nanoparticles were either synthesized in situ or deposited from a suspension. The prepared catalysts were used in the preferential oxidation of CO in a hydrogen-rich stream. The catalysts prepared by deposition of preformed gold nanoparticles were less stable and underwent sintering due to a weaker nanoparticle–support interaction. In contrast, the catalysts with Au nanoparticles synthesized in situ were active (90% conversion and 46% selectivity) and stable. The fiber-shaped catalyst was able to give maximum reactant access at a much lower pressure drop than catalyst in powder form.

Sizes effect of CeSn3 on the whiskers growth of SnAgCuCe solder joints in electronic packaging

The relationship between Ce content/CeSn3 sizes and the whiskers growth is newly reported systematically. The whiskers growth can be observed in the surface of bulk CeSn3 particles, the rate of whisker growth was significantly slowed with Ce content lower than 0.1 wt%. At higher concentration of Ce, whisker growth rate becomes higher and noticeable. It is thought that the higher Ce chemical potential for oxidation provides a path for the mechanism of whisker growth. With all the other benefits of Ce addition, the potential to promote whisker growth indicate that only dilute concentration of Ce can be tolerated in SnAgCu alloys without whiskering effect. The results demonstrated that the trace amount of Ce can be utilized as additive into SnAgCu solder in microelectronic industry.

REE patterns of microbial carbonate and cements from Sinemurian (Lower Jurassic) siliceous sponge mounds (Djebel Bou Dahar, High Atlas, Morocco)

Marine microbialites serve as robust seawater rare earth element and yttrium (REE+Y) proxies through many intervals of Earth history, but questions remain about the partitioning of REEs into different coeval carbonate phases, potential syn-depositional contaminants and elemental redistribution during diagenesis. Microbial carbonates, cements and background sediments were analysed for stable isotopes (O, C) and trace element geochemistry in Sinemurian (Lower Jurassic) mid- to outer ramp siliceous sponge microbial mounds from the High Atlas, Morocco. Trace elements were analysed using laser ablation-inductively coupled plasma-mass spectrometry. Microbialites, non-luminescent radial/radiaxial fibrous (RF) cement and well-preserved brachiopods have stable isotope values similar to published Early Jurassic marine values. Luminescent blocky sparite (BS) cements have lighter stable isotope values consistent with burial diagenesis. Early marine RF cement has shale-normalised (subscript sn) REE+Y patterns with characteristics of oxygenated seawater, whereas cavity-occluding BS cement has high concentration bell-shaped (REE+Y)sn patterns, very unlike seawater. Allomicrite has relatively high REE concentrations with flatter (REE+Y)sn patterns. Microbialites include three subclasses distinguished on the basis of petrography and (REE+Y)sn patterns. Clotted peloidal microbialites (MC1) have (REE+Y)sn patterns broadly consistent with seawater, but with variable Ce anomalies and higher concentrations and slightly less LREE depletion relative to RF cements. Other clotted peloidal to leiolitic microbialites (MC2) have flatter (REE+Y)sn patterns and variable Ce anomalies, whereas leiolitic microbialites (MC3) have patterns similar to allomicrite. Hence, MC1 microbialites and early marine RF cements preserved seawater-like REE+Y patterns despite subsequent diagenesis, confirming that Early Jurassic marine REE distributions were similar to late Palaeozoic, Late Jurassic and Holocene distributions. Importantly, LREE enrichment in allomicrite and some microbialites (MC2, MC3) highlights the occurrence of LREE-enriched components that may represent marine particulate matter that preferentially scavenged LREEs from the water column prior to sedimentation. The Sinemurian siliceous sponge microbial mounds accumulated in well-oxygenated settings rather than on the edge of an oxygen minimum zone. Some of the high Ce contents in the microbialites may reflect redistribution of Ce during earliest diagenesis in suboxic pore fluids, or incorporation of LREE enriched particles or LREE uptake in the growing microbialite consistent with scavenging on organic ligands in the biofilm itself. This study demonstrates how various sedimentary sources and diagenetic processes can significantly affect otherwise robust marine REE patterns in microbial mounds within a relatively siliciclastic-free carbonate environment.

Thermal stability of Ce0.5Gd0.5O1.75 nanoparticles in contact with an amorphous SiO2

Morphology, microstructure and phase evolution of nanocrystalline Ce0.5Gd0.5O1.75 mixed oxide supported on amorphous SiO2 were studied in oxidizing and reducing atmosphere by XRD, TEM and SEM-EDS. The Ce0.5Gd0.5O1.75/SiO2 samples were prepared by two methods: impregnation of the support with an aqueous solution of nitrates and deposition of homogeneous Ce0.5Gd0.5O1.75 nanoparticles synthesized using the microemulsion method. The latter system is structurally and chemically stable in the oxidizing atmosphere up to 1000°C, exhibiting only a small increase of the mean crystallite size of the mixed oxide from 2 to 3nm. Prolonged heating at 1100°C for 24h caused partial decomposition of the mixed oxide and formation of small amount of B-Gd2Si2O7. In the reducing atmosphere the Ce0.5Gd0.5O1.75 underwent amorphization and spreading over SiO2 already at 900°C to form an amorphous silicate. Most of the silicate remained amorphous even after reduction at 1100°C, but certain amount crystallized into particles with strongly defected structure. The system prepared by impregnation exhibited significantly worse thermal stability due to chemical inhomogeneity. The complex systems synthesized in this work, containing nanocrystalline particles of mixed silicate with high concentration of Ce3+ ions, may be interesting as scintillating materials.

Chemostratigraphic Characterization of Siliciclastic Rocks in Parts of the Eastern Dahomey Basin, Southwestern Nigeria

Chemostratigraphy, involving the application of inorganic geochemistry for the characterization of sedimentary sequences has been applied in the study of siliciclastic rocks in parts of the eastern Dahomey basin, Southwest Nigeria, with the aim of characterizing the rocks based on variations in inorganic geochemistry. The present study is based on 15 surface samples carefully selected from exposed sedimentary sequence near Igbile and 5 subsurface samples retrieved from cores of a drilled hole in Ijagun and these were subjected to geochemical analyses using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) to determine the major and trace elements concentration. Results of the geochemical analyses revealed eleven (11) Major elements of which SiO2 having a percentage (%) range value of 45.35%-96.98% and Al2O3 with a percentage (%) range value of 0.8%-37.49% being the highest major element concentrations. Twenty-four (24) Trace elements were represented with Zr ranging value of between 150.7 ppm-1651.6 ppm being the most significant trace element. Sixteen (16) Rare Earth elements of which Ce ranging in value between 10.8ppm-251.3ppm show the highest concentration. The high percentage concentration of Al2O3 is an indication of abundant clay minerals whereas the high concentration of Zr in parts per million suggests sedimentary reworking of the sediments. High Ce concentration is indicative of oxic conditions. Based on variations in elements and element ratios such as Th/U, Cr, Zr, P2O5, V and Mo, the rocks analyzed have been subdivided into two (2) geochemical packages and three (3) geochemical units. Ratios of SiO2 and Al2O3 indicate three (3) sedimentary facies namely sandstone, siltstone and claystone while the variation in the ratios of Ga/Rb and Al2O3/(Na2O+CaO+K2O+MgO) depicts fluctuating paleoclimate during the deposition of the sedimentary sequence. Sediment provenance became increasingly felsic from an initial mafic source as inferred from the variation in ratios of Cr/Al2O3, TiO2/Nb, Nb/Al2O3 as well as the discriminant function analysis.

Influence of cerium addition on microstructure and properties of Sn–Cu–(Ag) solder alloys

Abstract In the present work, the effect of Ce concentration on microstructure refinement, melting behavior and mechanical properties of a series of near-eutectic Sn–Ag–Cu alloys have been investigated. Twelve different alloys with Ce concentration between 0.005 and 0.171 wt% were prepared by melting of the pure elements in high purity argon, followed by quenching to room temperature. The samples microstructure and phase constitution were investigated by a combination of light microscopy, scanning electron microscopy, X-ray diffraction, and energy dispersive X-ray spectroscopy. In the alloys a total of five different phases have been identified: β-Sn, Cu 6 Sn 5 , Ag 3 Sn, CeO 2 , and CeSn 3 . The Ce addition is found to contribute to the refinement of mostly eutectic microstructures. The CeO 2 and/or CeSn 3 phases are observed in alloys with high Ce concentration. The absence of these particles in alloys with low Ce concentration (0.005–0.011 wt%) shows a complete dissolution of Ce in the β-Sn solid solution. The elongation and ultimate tensile strength of the alloys were determined under a constant strain rate of 2 mm min −1 . Moreover, the toughness (i.e. specific fracture energy) was calculated from the area underneath the force–extension curve. Melting temperatures are found to change slightly with bulk Ce concentration. Solution strengthening by Ce atoms, grain refinement, and the stress concentration along both types of Ce-rich particles of undesirable shapes are considered to be the main factors influencing the mechanical properties of the investigated alloy systems.

Catalytic activity of CeIVO2/Ce2IIIO3-silica mesoporous composite materials for oxidation and esterification reactions

Bifunctional catalytic performance of various ceria-containing mesoporous silica samples have been investigated for oxidation as well as acid-catalyzed esterification reactions under mild conditions. Hexagonal (p6mm) and cubic (Ia3d) ordered mesoporous silica materials with incorporated CeIVO2 were synthesized with high Ce content and successfully reduced to Ce2IIIO3-silica species under H2 gas flow. Small angle X-ray scattering (SAXS) analysis of the samples shows ordered patterns of the materials studied. The surface area and porosity of the samples were determined from N2 adsorption isotherms. Both the oxidation states of ceria have been proved as highly efficient catalysts for liquid phase oxidation of numerous hydrocarbons like cyclohexene, styrene, benzyl alcohol, and xylene and so on at room temperature under solvent-free conditions, whereas Lewis basicity of cerium oxide has been explored for esterification reaction of various alcohols like benzyl alcohol, octanol, and decanol and so on using acetic acid under mild conditions. The surface acidic sites present on both CeIVO2-silica and Ce2IIIO3-silica composites have been measured and compared by ammonia-TPD analysis performed at 393K. The reusability and heterogeneity of the catalysts with minimum loss have also been examined under identical conditions.

X-ray crystallography and mineral chemistry of bastnaesite from Kanigiri granite, Prakasam district, Andhra Pradesh, India

Abstract The authors report the results of X-ray diffraction (XRD) and geochemical studies on bastnaesites (lanthanum cerium fluoro-carbonate) hosted in alkali Kanigiri Granite of the Prakasam district in Andhra Pradesh, India. The XRD pattern of the investigated bastnaesite displays sharply-defined reflections. The observed d-spacings of the bastnaesite are in very close agreement with those published for bastnaesite standard in International Centre for Diffraction Data (ICDD) Card No. 11–340. The calculated unit cell parameters (a o; c o) and unit cell volume (V) of the studied bastnaesite (a o 7.1301–7.1413 Å, c o 9.7643–9.7902Å and V 429.8940–432.3875 Å3) are almost equal to values published for bastnaesite standard (c o 7.1290 Å, c o 9.7744 Å and V 430.19 Å3) in the relevant data card. Geochemical data of bastnaesite reveals high content of Ce (mean 27.22%) followed by La (mean 16.82%), Nd (mean 6.12%) and Pr (mean 1.91%). Compared to light REE (LREE) content (mean 437165 ppm), heavy REE (HREE) content (mean 5867 ppm) is drastically low, with unusually high LREE/HREE ratio (mean 80). The chondrite-normalised plot also exhibits drastic enrichment of LREE relative to HREE with pronounced negative Euanomaly (mean Eu/Eu* = 0.15). High (LREE)N / (HREE)N, (La/Lu)N, (La/Yb)N and (Ce/Yb)N ratios reveal higher fractionation of LREE relative to HREE. The rare earth element (REE) contents of the studied bastnaesite are very close to REE contents of bastnaesite hosted in alkali syenite from Madagascar. The presence of bastnaesite in Kanigiri Granite and soils derived from it enhances the scope of further exploration for bastnaesite in several bodies of alkaline rocks and alkali granitoids present along the eastern margins of the Cuddapah basin, Andhra Pradesh.

Effects of cerium dopant concentration on structural properties and photocatalytic activity of electrospun Ce-doped TiO2 nanofibers

Electrospun \(\hbox {TiO}_2\) and Ce-doped \(\hbox {TiO}_2\) nanofibers were prepared with 0.5, 2.0 and 8.0 % weight Ce. The structural properties and phase composition were characterized using high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction and X-ray absorption near edge spectroscopy (XANES) at the Ti K-edge. The undoped nanofibers are composed of an assembly of \(\hbox {TiO}_2\) nanoparticles and their crystal structure is a mixture of anatase and rutile phases with an anatase:rutile volume ratio close to 3:1. As Ce is introduced, the nanoparticles decrease in size and the rutile phase volume decreases. Ce \(\hbox {L}_3\)-edge XANES probed the local structure of Ce dopants. At 0.5 % Ce, most Ce ions are incorporated in the \(\hbox {Ce}^{3+}\) charge state but, at 2 % Ce, the majority are \(\hbox {Ce}^{4+}\). Visible light absorption indicated that \(\hbox {Ce}^{3+}\) act as shallow acceptors that only participate in absorption of wavelengths below 420 nm but \(\hbox {Ce}^{4+}\) impurity states are associated with absorption of wavelengths up to 550 nm. Photocatalytic performance of the nanofibers was assessed by measuring the degradation of adsorbed Rhodamine B in aqueous solution under visible and ultraviolet light. The 0.5 % Ce-doped \(\hbox {TiO}_2\) nanofiber showed the best visible-light photocatalytic activity, which is probably due to the majority presence of \(\hbox {Ce}^{3+}\). At higher Ce concentration, the photocatalytic reaction rate was lower than undoped nanofibers, indicating that recombination at the \(\hbox {Ce}^{4+}\) sites is rate limiting.

Reduced erbium-doped ceria nanoparticles: one nano-host applicable for simultaneous optical down- and up-conversions.

This paper introduces a new synthesis procedure to form erbium-doped ceria nanoparticles (EDC NPs) that can act as an optical medium for both up-conversion and down-conversion in the same time. This synthesis process results qualitatively in a high concentration of Ce3+ ions required to obtain high fluorescence efficiency in the down-conversion process. Simultaneously, the synthesized nanoparticles contain the molecular energy levels of erbium that are required for up-conversion. Therefore, the synthesized EDC NPs can emit visible light when excited with either UV or IR photons. This opens new opportunities for applications where emission of light via both up- and down-conversions from a single nanomaterial is desired such as solar cells and bio-imaging.

Structure–Activity Relationships of NiO on CeO2 Nanorods for the Selective Catalytic Reduction of NO with NH3: Experimental and DFT Studies

CeO2 nanorods impregnated with 2.5 atom % of NiO (NiO/CeO2 nanorods) were successfully synthesized and examined as catalysts for the NH3-selective catalytic reduction (NH3-SCR) of nitric oxide (NO). The catalytic activity of NiO/CeO2 nanorods resulted in up to ∼90% NO conversion at 250 °C, which is superior to that of pure CeO2 nanorods or NiO nanoparticles. Subsequently, extensive studies of the NiO/CeO2-catalyzed reduction of NO were conducted using X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction, temperature-programmed desorption, and density functional theory periodic calculations. Compared to that of the pure CeO2 nanorods, the results demonstrated that the NiO/CeO2 nanorods resulted in (i) a higher concentration of Ce3+ chemical species, (ii) a larger amount of active Oα, (iii) lower temperature reducibility, (iv) a lower amount of energy required for oxygen vacancy distortion, and (v) a significant adsorption of and strong interaction between NO and NH3 molecules. Our findings therefore elucidated considerable details of the structural properties of the NiO/CeO2 nanorods that were decisive for achieving a highly efficient conversion of NO by the NH3-SCR process at low temperatures.