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Fig. S1 XRD pattern of the product obtained by the calcination of the cerium oxalate precursor at 300 ℃ for 1 h.
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In this paper, a simple one-step hydrothermal method has been developed to prepare three-dimensional CeO2 microflower structures via a cerium oxalate precursor. X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FE-SEM) and thermal g...
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In this paper, a facile one-step hydrothermal method for the synthesis of crystalline/amorphous WO3-x core-shell nanopowders (nanoparticles, nanorods and nanowires) was reported. The core-shell structure, the size and the morphology of the core, and the shell ratio can be controlled by pH, the content of oxalic acid and the content of ammonium tung...
Vanadium pentoxide nanoflowers were synthesized through a simple hydrothermal method at low temperatures. The structure was fabricated by using NH4VO3 and oxalic acid as precursors with 0.1 M solution concentration. The morphology and structural properties of the nanoflowers were characterized using FESEM, XRD, Raman, and UV-Visible spectroscopy. T...
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... There was a clear link between the treatment temperature, pH of the solution, and the crystallite size and morphology of the final product. Recently, Baumann et al. 11 compared the hydrothermal and thermal conversion of Pu(IV) oxalate to nanocrystalline PuO 2 mentioning most of the positive aspects of the hydrothermal route: lower temperature, shorter reaction time, and lower content of residual carbon. All the above-mentioned works described a drastic change in the morphology of the starting powder during the process. ...
... Flower-like CeO 2 microcrystals were hydrothermally synthesized from an oxalate precursor in an alkaline environment and hydrogen peroxide. 11 A similar procedure yielding hierarchical mesoporous ceria was obtained in the presence of some amino acids previously. 12 Recently, mixed U 1Àx Ce x O 2+d Á nH 2 O (0.1 r x r 0.7) solid solutions were prepared using this method. ...
Hydrothemal conversion of lanthanide/actinide oxalate salts to nanocrystalline oxide has been gaining its technological significance. Here we present a study describing the mechanism behind cerium (and Ce-Gd) oxalate hydrothermal recrystallization and decomposition to oxide. Structure determination of all the intermediate nanocrystalline products was possible thanks to 3D electron diffraction. This work also points out the enormous structural abilities of simple oxalate ligand
... Muroyama et al. [23] further demonstrated that CeO 2 , as a rare earth oxide, could improve the catalytic activity of ADR because of its an excellent oxygen storage capacity and cerium ions transformation (Ce 4+ ↔ Ce 3+ ). Moreover, the effect of ceria morphology (rod [24], octahedron [25], cube [24], sphere [26], flower [27], etc.) on the catalytic performance have also been extensively reported. Generally, different morphologies of CeO 2 expose different specific facets: {100} for nanocubes, {100}/{110} for nanorods and {100}/{111} for nanospheres [25,28]. ...
... The XRD pattern of CeO 2 , 2% Cr, and 4% Cr doped CeO 2 nanoparticles is shown in Fig. 1 17 The cubic fluorite structure of CeO 2 in an fcc arrangement has eight oxygen atoms (each one at the tetrahedral position) surrounding each ceria atom. 18 The average crystallite size for CeO 2 , 2% Cr, and 4% Cr doped CeO 2 is found to be 16, 15.9, and 15.9 nm, respectively, using Debye-Scherrer's formula. ...
The consumption of electrical energy has greatly increased lately, and the requirement of portable charge storage devices has also increased. To fulfill this, a versatile rare earth element CeO 2 in nanoparticle form is selected and synthesized through a cost effective precipitation method for supercapacitor application. To improve its efficiency, 2% and 4% of transition metal chromium were doped into the ceria lattice, and their electrochemical properties were studied. The cubic fluorite structure with an average crystallite size of all the samples was 16 nm, which was confirmed through x-ray diffraction analysis. Peculiar rice shaped clusters are observed for 2% Cr doped samples through field emission scanning electron microscopy analysis. The N 2 adsorption desorption studies were performed to calculate the surface area of the prepared samples. A maximum specific capacitance of 42.6 F g ⁻¹ was obtained for the 2% Cr doped CeO 2 sample at 5 mV s ⁻¹ in 2M KOH in cyclic voltammetric studies. The galvanostatic charge–discharge and electrochemical impedance spectroscopy measurements were also taken to analyze the charge–discharge cycles and stability of the samples.
... Firstly, the CeO 2 -precursor (CeO(CO 3 ) 2 ·H 2 O, JCPDS card No. 44-0617) was obtained from the hydrothermal treatment of Ce 3+ with CO(NH 2 ) 2 , as shown in Fig. 2. 42 Then, the same crystalline CeO 2 (JCPDS card No. 34-0394) as in the previous α-MnO 2 /CeO 2 composite, was prepared via calcination under air. 43 Figure 3 shows the impact of the different CeO 2 dopant content on the morphology of MnO 2 /CeO 2 . As shown in Fig. 3a, the dispersed α-MnO 2 microfibres (MO-140-12) were more than 2 μm long and had non-uniform diameters ranging from 40-150 nm. ...
We synthesized MnO2/CeO2 electrocatalysts by in situ decoration of α–MnO2 with CeO2 particles during a one-step hydrothermal process. The morphology, composition, and electrochemical properties were studied in the context of application to the oxygen reduction reaction (ORR) and Mg-air battery. According to the results, α–MnO2/CeO2 microfibers exhibited better ORR performance than α–MnO2 microfibers due to the synergistic result between the introduction of Ce3+ in CeO2 lattice and the enhancement of Mn3+ content in MnO2 lattice. α–MnO2/CeO2 microfibers provided a higher surface area and more catalytic active sites than α–MnO2 microfibers by controlling the molar ratio of Ce3+/Mn7+ for the precursor. When the mole ratio of Ce3+ and Mn7+ in the precursors was 10%, the four-electron transfer process of the MnO2/CeO2 microfibers (MC-140-12-10) was found to be similar to that of the 20 wt% Pt/C commercial catalysts. MC-140-12-10 microfibers also showed the excellent long-term stability after 25,000 s and superior Mg–air battery performances than α–MnO2. Hence, the work paves the way for developing Mg-air batteries through a simple synthesis and cost-effective ORR catalyst.
... After this stage, no thermal changes occur for all samples when heated to 800 °C, which means that all samples attain the thermal stability after 350 °C. Many authors indicated that there is an exothermic effect at elevated temperatures between 600 and 700 °C and is attributed to the cerium phosphate phase transition from hexagonal to monoclinic phase [48,[54][55][56]. In the present study, this exothermic peak at the higher temperatures is not observed, which may indicate the formation of the monoclinic structure at the as-prepared conditions. ...
... As shown in the figure, in the case of the lower molar ratio of phosphates compared to cerium (CeP0.5) the sample exhibits diffraction peaks corresponding to the cubic fluorite structure of the CeO 2 phase (JCPDS card no. 34-0394) [56]. In addition, when the molar ratio of cerium and phosphate are equal (CeP1), the sample exhibits a monazite type monoclinic phase of the cerium phosphate (JCPDS card no. ...
In this work, a series of cerium phosphate catalysts with different cerium phosphate molar ratios have been synthesized. The prepared catalysts were characterized by means of FTIR, DTA, TGA, XRD, N2 adsorption–desorption and SEM. Also, the acidic centers of the prepared catalysts were abundantly studied and characterized in terms of type and strength using different techniques. The characterization tools used explained the variety of acidic centers in terms of type and strength due to the variation of cerium to phosphate molar ratio. Its worthy to mentioned that the highly acidic performance of the prepared catalysts was successfully applied in the synthesis of tetrahydrocarbazoles derivatives via Borsche–Drechsel cyclization reaction. The catalysts showed great catalytic activity in the selected reaction as high product yields were obtained using a very small amount of the catalysts under mild reaction conditions. The % yield and the reaction mechanism proves the role played by Brønsted acid sites of the catalyst in indorsing the reaction. The results also demonstrated a high ability of the catalysts to be reused ten times without a significant decrease in the catalytic activity. The synthesized tetrahydrocarbazole derivatives via heterogenous acid-catalyzed Borsche–Drechsel cyclization reaction can be considered as highly efficient and eco-friendly strategy towards many other carbazoles and open a new era in green chemistry as well.
... One of the simple, effective and low-cost CeO2 synthesis routes is oxalic precipitation followed by a calcination step [7][8][9][10]. The process takes advantage of the high insolubility of oxalate salts to recover REEs. ...
... Zhang et al. have tested different amino-acids crystallization modifiers to control the hierarchical nanoarchitectures [10]. Liu et al achieved the formation of 3D "flower-like" particles with high specific surface area, adding polyvinylpyrrolidone (PVP) in the Ce salt solution before its reaction with oxalic acid, in stoichiometric proportion [8]. Similar compact and organized cerium oxalate particles were synthesized by Jehannin et al. in over-stoichiometric conditions, and considering a ternary mixture of water, propanediol and octanol, with low water content [22]. ...
... a sharp transition from compact micro-flowers, synthetized at lower oxalic excess, to less compact aggregates (needles in the more extreme cases) at higher oxalic excess was observed [30]. Smaller particles, but with similar morphologies were also evidenced in PVP-aqueous solutions, where micro-flowers (2-3µm) form at stoichiometric conditions, whereas irregular branchlike microrods (7-8 µm) form when oxalic acid is in excess, and twomicron size rods crossed together precipitate for under-stoichiometric conditions [8]. Star-like assemblies of needles have also been observed after synthesis of cerium oxalate in pure water, at low temperature, with acidic conditions and for a specific pathway for reactant addition (cerium salt added in oxalic acid) which correspond to an excess of oxalic acid during the synthesis [14]. ...
The ability to control the morphology of precipitated cerium oxalate material results in determinate evidence to its final properties. In this study, we demonstrate that surfactant-free nanostructured low-water solvents have a huge potential for controlling the morphology of a cerium oxalate powder. To this aim, an in-depth investigation of the reaction between cerium nitrate and oxalic acid is carried out, by varying both the relative concentration of the two reagents (around the stoichiometric value) and the composition of the water/propanediol/octanol ternary solvent (especially in the low-water content nanostructured domain). Thanks to the complementary of observation methods: microscopy (confocal microscopy with fluorophores and environmental SEM) and X-ray scattering (SAXS and WAXS), we evidenced the role of the solvent in the growth kinetics and directional aggregation of the precipitates—the two major factors determining the final morphology of the particles. Besides the possible confinement effect in nanodroplets, compact “dense-branching” particles, achieved in low-water content solvents, unveil the strong role of the surface forces in the aggregation mechanisms. This is consistent with the prevailing capillary forces at water/oil/solid triple points in ternary solvents. These new results confirm the high potential of nanostructured solvents for controlling the size and shape of hydrated precipitated particles.
... We firstly compared CO oxidation behavior of our undoped ceria electrospun fiber to other undoped ceria catalysts reported the literature. In all cases, hydrogen was not in the feed gas. Figure 4 shows CO conversion comparison [33][34][35][36][37][38]. The conversion curves indicate that the current electrospinning-firing (600 °C, 3 h) process, as expected form the high calcination temperature, was not as efficient as nanosphere fabrication [33] or flowerlike structure formation [34] in terms of nanostructuring. ...
... In all cases, hydrogen was not in the feed gas. Figure 4 shows CO conversion comparison [33][34][35][36][37][38]. The conversion curves indicate that the current electrospinning-firing (600 °C, 3 h) process, as expected form the high calcination temperature, was not as efficient as nanosphere fabrication [33] or flowerlike structure formation [34] in terms of nanostructuring. However, it is clearly more effective than precipitating from nitrate source (500 °C, 5 h calcination) [37]. ...
... However, it is clearly more effective than precipitating from nitrate source (500 °C, 5 h calcination) [37]. The low temperature CO conversion behavior of the undoped electrospun ceria catalyst is very similar to the one from oxalate precipitation (300 °C, 1 h calcination) [34]. The necessity of high temperature to burn off polymer imposes limitation in nanostructuring for electrospun fibers. ...
We investigated CO oxidation behavior of doped cerium oxide fibers. Electrospinning technique was used to fabricate the inorganic fibers after burning off polymer component at 600 °C in air. Cu, Ni, Co, Mn, Fe, and La were doped at 10 and 30 mol% by dissolving metal salts into the polymeric electrospinning solution. 10 mol% Cu-doped ceria fiber showed excellent catalytic activity for low temperature CO oxidation with 50% CO conversion at just 52 °C. This 10 mol% Cu-doped sample showed unexpected regeneration behavior under simple ambient air annealing at 400 °C. From the CO oxidation behavior of the 12 samples, we conclude that absolute oxygen vacancy concentration estimated by Raman spectroscopy is not a good indicator for low temperature CO oxidation catalysts unless extra care is taken such that the Raman signal reflects oxide surface status. The experimental trend over the six dopants showed limited agreement with theoretically calculated oxygen vacancy formation energy in the literature.
... Chemically synthesized Ce-or La-oxalate invariably take the form of plate-like single crystals and their sizes can vary from 10 to 300 μm in length depending on the precipitation method and concentrations of reagents (Claparede et al., 2011;Maslennikov et al., 2017;Yu et al., 2017). A rare case of flower-like aggregates of tabular crystals was reported for cerium oxalate decahydrate [Ce 2 (C 2 O 4 ) 3 Á10H 2 O] which were abiotically precipitated using pure oxalic acid (Liu et al., 2013). Few previous studies have paid attention to the mycogenic transformation of lanthanide elements. ...
Monazite is a naturally‐occurring lanthanide (Ln) phosphate mineral [Lnx(PO4)y] and is the main industrial source of the rare earth elements (REE), cerium and lanthanum. Endeavours to ensure the security of supply of elements critical to modern technologies view bioprocessing as a promising alternative or adjunct to new methods of element recovery. However, relatively little is known about microbial interactions with REE. Fungi are important geoactive agents in the terrestrial environment and well known for properties of mineral transformations, particularly phosphate solubilization. Accordingly, this research examined the capability of a ubiquitous geoactive soil fungus, Aspergillus niger, to affect the mobility of REE in monazite and identify possible mechanisms for biorecovery. It was found that A. niger could grow in the presence of monazite and mediated the formation of secondary Ce and La‐containing biominerals with distinct morphologies including thin sheets, orthorhombic tablets, acicular needles, and rosette aggregates which were identified as cerium oxalate decahydrate (Ce2(C2O4)3·10H2O) and lanthanum oxalate decahydrate (La2(C2O4)3·10H2O). In order to identify a means for biorecovery of REE via oxalate precipitation the bioleaching and bioprecipitation potential of biomass‐free spent culture supernatants was investigated. Although such indirect bioleaching of REE was low from the monazite with maximal lanthanide release reaching >40 mg L‐1, leached REE were efficiently precipitated as Ce and La oxalates of high purity, and did not contain Nd, Pr and Ba, present in the original monazite. Geochemical modelling of the speciation of oxalates and phosphates in the reaction system confirmed that pure Ln oxalates can be formed under a wide range of chemical conditions. These findings provide fundamental knowledge about the interactions with and biotransformation of REE present in a natural mineral resource, and indicate the potential of oxalate bioprecipitation as a means for efficient biorecovery of REE from solution. This article is protected by copyright. All rights reserved.
... As an alternative to the materials described before, other nanostructured materials like ceria nanoparticles (CeNPs) are currently receiving special attention. The nanocrystalline cerium oxide is a rare earth oxide, that attracted researchers with its unusual physical and chemical properties at the nano-dimensional level emerged as a very interesting material for variety applications due its high oxygen storage capacity, high thermal and mechanical stability, high electrical conductivity, diffusivity and biocompatibility [19][20][21] . Nanoceria has been used in the development of oxygen sensors, ultraviolet absorber 22,23 , polishing agent 24 , catalyst 25,26 , supercapacitors 27 , fuel cells 28 , as well as in the environmental chemistry 29 , biotechnology and in medicine 24,30 . ...
... [22] However, pure ceria exhibits low catalytic activity due to limited number of anion defects and oxygen vacancy. [23,24] Doping of additional metals is an effective way to enhance catalytic performance and longtime stability and homogeneous doping is essential for achieving superior catalytic properties. [16,25] For instance, in our previous work, we reported copper (Cu) doped CeO 2 nanosheets applied in CO oxidation. ...
We report a facile preparation method of Ti‐doped CeO2 nanosheets and their use as supports for palladium (Pd) deposition. The nanosheets were fabricated by the coordination‐precipitation method, and Pd nanoparticles were placed on the surfaces in situ. The obtained Pd‐loaded nanosheets TixCe1–xO2‐Pd were applied as catalysts in the hydrogenation of 4‐nitrophenol (4‐NP). While the catalyst supported by pure CeO2 nanosheets exhibited a 4‐NP conversion of 40 % in 10 min, doping a small amount of Ti into the support led to a faster 4‐NP reduction of 80 % in 10 min and quantitative conversion in 30 min. The hydrogenation of 4‐NP catalyzed by Ti0.1Ce0.9O2‐Pd exhibited a relatively high apparent reaction rate constant (k = 0.134 min‐1). This high catalytic activity could be attributed to the synergetic effect of the Pd nanoparticles with high dispersion and the TixCe1–xO2 supports with high oxygen vacancies. Furthermore, these catalysts displayed high reproducibility and chemical stability: they can be recycled and reused for at least 5 times with negligible loss of catalytic activity.
