Formation Of Ce Research Articles

A Comparative Study on Hexavalent Chromium Adsorption onto Chitosan and Chitosan-Based Composites.

Chitosan (Cs)-based composites were developed by incorporating silica (Cs–Si), and both silica and hydroxyapatite (Cs–Si–Hap), comparatively tested to sequester hexavalent (Cr(VI)) ions from water. XRD and FT-IR data affirmed the formation of Cs–Si and Cs–Si–Hap composite. Morphological images exhibits homogeneous Cs–Si surface, decorated with SiO2 nanoparticles, while the Cs–Si–Hap surface was non-homogeneous with microstructures, having SiO2 and Hap nanoparticles. Thermal analysis data revealed excellent thermal stability of the developed composites. Significant influence of pH, adsorbent dose, contact time, temperature, and coexisting anions on Cr(VI) adsorption onto composites was observed. Maximum Cr(VI) uptakes on Cs and developed composites were observed at pH 3. The equilibration time for Cr(VI) adsorption on Cs–Si–Hap was 10 min, comparatively better than Cs and Cs–Si. The adsorption data was fitted to pseudo-second-order kinetic and Langmuir isotherm models with respective maximum monolayer adsorption capacities (qm) of 55.5, 64.4, and 212.8 mg/g for Cs, Cs–Si, and Cs–Si–Hap. Regeneration studies showed that composites could be used for three consecutive cycles without losing their adsorption potential.

Crystallographic and Spectroscopic Investigations on Oxidative Coordination in the Heteroleptic Mononuclear Complex of Cerium and Benzoxazine Dimer.

Among lanthanide-based compounds, cerium compounds exhibit a significant role in a variety of research fields due to their distinct tetravalency, high economic feasibility, and high stability of Ce(IV) complexes. Herein, a systematic investigation of crystallographic information, chemical properties, and mechanistic formation of the novel Ce(IV) complex synthesized from cerium(III) nitrate hexahydrate and 2,2′-(methylazanediyl)bis(methylene)bis(4-methylphenol) (MMD) ligand has been explored. According to the analysis of the crystallographic information, the obtained complex crystal consists of the Ce(IV) center coordinated with two nitrate ligands and two bidentate coordinated (N-protonated and O,O-deprotonated) MMD ligands. The fingerprint plots and the Hirshfeld surface analyses suggest that the C–H⋯O and C–H⋯π interactions significantly contribute to the crystal packing. The C–H⋯O and C–H⋯π contacts link the molecules into infinite molecular chains propagating along the [100] and [010] directions. Synchrotron powder X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) techniques have been employed to gain an understanding of the oxidative complexation of Ce(IV)-MMD complex in detail. This finding would provide the possibility to systematically control the synthetic parameters and wisely design the precursor components in order to achieve the desired properties of novel materials for specific applications.

Role of Coulomb interaction in the phase formation of fcc Ce: Correlation matrix renormalization theory

The effect of electronic Coulomb interaction on the phase formation of fcc Ce lattice is investigated by full ab initio calculations without adjustable Coulomb $U$ and $J$ parameters using the Gutzwiller wavefunction-based correlation matrix renormalization theory (CMRT). Its total energy and pressure as a function of volume agree reasonably well with existing $\text{DFT}+\text{Gutzwiller}$ calculations and experiments, indicating correct capture of electronic correlation and screening effects within the CMRT formalism. A stable phase is found in line with the experimental $\ensuremath{\alpha}$-Ce phase, and a lurking phase is identified supposedly linked with the experimental $\ensuremath{\gamma}$-Ce phase. A criterion based on the local $4f$ electron charge fluctuation is introduced to confirm the distinct electronic correlation natures of both phases.

Study on Phases Formation and Modification Ability of Rare Earth Elements La, Ce, Sm and Er in Al–Zn–Mg–Cu–Zr Alloy

Study on Phases Formation and Modification Ability of Rare Earth Elements La, Ce, Sm and Er in Al–Zn–Mg–Cu–Zr Alloy

Design strategies for ceria nanomaterials: untangling key mechanistic concepts.

The morphologies of ceria nanocrystals play an essential role in determining their redox and catalytic performances in many applications, yet the effects of synthesis variables on the formation of ceria nanoparticles of different morphologies and their related growth mechanisms have not been systematised. The design of these morphologies is underpinned by a range of fundamental parameters, including crystallography, optical mineralogy, the stabilities of exposed crystallographic planes, CeO2-x stoichiometry, phase equilibria, thermodynamics, defect equilibria, and the crystal growth mechanisms. These features are formalised and the key analytical methods used for analysing defects, particularly the critical oxygen vacancies, are surveyed, with the aim of providing a source of design parameters for the synthesis of nanocrystals, specifically CeO2-x. However, the most important aspect in the design of CeO2-x nanocrystals is an understanding of the roles of the main variables used for synthesis. While there is a substantial body of data on CeO2-x morphologies fabricated using low cerium concentrations ([Ce]) under different experimental conditions, the present work fully maps the effects of the relevant variables on the resultant CeO2-x morphologies in terms of the commonly used raw materials [Ce] (and [NO3-] in Ce(NO3)3·6H2O) as feedstock, [NaOH] as precipitating agent, temperature, and time (as well as the complementary vapour pressure). Through the combination of consideration of the published literature and the generation of key experimental data to fill in the gaps, a complete mechanistic description of the development of the main CeO2-x morphologies is illustrated. Further, the mechanisms of the conversion of nanochains into the two variants of nanorods, square and hexagonal, have been elucidated through crystallographic reasoning. Other key conclusions for the crystal growth process are the critical roles of (1) the formation of Ce(OH)4 crystallite nanochains as the precursors of nanorods and (2) the disassembly of the nanorods into Ce(OH)4 crystallites and NO3--assisted reassembly into nanocubes (and nanospheres) as an unrecognised intermediate stage of crystal growth.

Antioxidant and antidiabetic properties of biocompatible ceria oxide (CeO2) nanoparticles in mouse fibroblast NIH3T3 and insulin resistant HepG2 cells

This work synthesized the ceria oxide nanoparticles (CeO2 NPs) using the plant extract of Stachys japonica Miq and determined their antioxidant and antidiabetic activities. The characterization results demonstrated the successful formation of spherical shaped CeO2 NPs with average size of 21 nm with PDI of 0.121. The FTIR peak of CeO2 NPs revealed the capping of phyto-molecules and a peak at 470.92 cm−1 indicated the formation of Ce–O of CeO2 NPs. The CeO2 NPs scavenged the free radicals of ABTS+ and DPPH, with IC50 of 12.16 ± 0.12 μg. mL−1 and 109.5 ± 0.26 μg. mL−1 respectively. The 50 μg mL−1 of CeO2 NPs showed the maximum inhibitory effect on α-glucosidase (19.78 ± 0.95%) and α-amylase (43.24 ± 1.14%). The cellular assay revealed the non-toxicity of CeO2 NPs in NIH3T3 and HepG2 cells. Cell antioxidant assay demonstrated that CeO2 NPs attenuated the staurosporine (STS) induced-oxidative stress in NIH3T3 cells through preventing the MMP loss and nucleus damage. The treatment of CeO2 NPs was broken the insulin resistance in IR-HepG2 cells and increased the glucose uptake through strengthening the mitochondria from oxidative stress. These antioxidant and antidiabetic properties of CeO2 NPs have opened a new avenue for extending future study on CeO2 NPs regulated glucose metabolism and its underlying molecular mechanism for beneficial therapy of diabetes.

Superior corrosion protection and adhesion strength of epoxy coating applied on AZ31 magnesium alloy pre-treated by PEO/Silane with inorganic and organic corrosion inhibitors

PEO/Silane/Epoxy coating system with inorganic inhibitor (Ce(NO3)3) in the plasma electrolytic oxidation (PEO) layer as well as organic inhibitors in the silane layer was investigated in terms of active corrosion protection properties and adhesion strength. The results of electrochemical impedance spectroscopy (EIS), electrochemical noise (EN) and pull-off tests indicated that the presence of the 8-Hydroxyquinoline (8-HQ) organic inhibitor provides the optimal performance for coating systems. The formation of Ce(OH)3 in the PEO coating structure and the complex chelate of Mg(HQ)2 in the silane layer lead to the creation of active corrosion protection properties for the coating systems.

Electrochemical and photocatalytic applications of Ce-MOF

We report on the applicability of an easy and general synthesis procedure for the formation of Ce(IV)-MOFs. Cerium-based metal–organic frame (Ce-MOF) was successfully synthesized by a simple, cost-effective and green route. Highly homogeneous topology, nano-sized crystals, stable oxidation states Ce(III) and Ce(IV) at room temperature, significant surface area and thermal stability up to 320°C are the notable properties achieved by Ce-MOF. Electron transferability of the cerium electrode was used for the detection of methylene blue (MB) analyte in acidic buffer solution. Also the effect of different pH buffer solutions on electrode response has been studied. Photocatalytic performance of nano-Ce-MOF was studied on the degradation of MB analyte under visible light.

IR Spectroscopy of the Cesium Iodide-Water Complex.

There has been much interest in I-(H2O) as a simple model for a hydrated iodide ion. Here we explore how this fundamental ion-solvent interaction is modified by the presence of a counterion, specifically Cs+. This has been achieved by forming the CsI(H2O) complex in superfluid helium nanodroplets and then probing this system using infrared spectroscopy. The complex retains the ionic hydrogen bond between the I- and a water OH group seen in I-(H2O), but the Cs+ ion substantially alters the anion-water interaction through formation of a cyclic Cs+-O-H-I- bonding motif. As with I-(H2O), the OH stretching band derived from the hydrogen-bonded OH group shows substructure, splitting into a clear doublet. However, in contrast to I-(H2O), where a tunneling splitting arising from hydrogen atom exchange plays a role, the doublet we observe is attributed solely to an anharmonic vibrational coupling effect.

Thiophenethieno[2,3-b]pyridine-chitosan nanorods; synthesis, characterization, BSA-Binding and kinetic interactions with BSA, antibacterial and in-vitro release studies

The current work aimed to developed and investigate the potential of thiophenethieno[2,3−b]pyridine-chitosan nanorods (CS−TTP) for the drug delivery system, BSA-binding and antibacterial activity for biomedical applications. Thiophenethieno[2,3−b]pyridine (TTP), a new member of thieno[2,3−b]pyridine containing thiophene moiety, has been synthesized and loaded on chitosan nanoparticle to give CS−TTP nanorods. Interestingly, CS−TTP showed a rod-like structure with a thickness of 5 nm and a length of 40 nm with uniform size over their entire length. The in vitro TTP release from CS−TTP was investigated in different pH media and the basic medium was found to be the optimal release condition. In-vitro BSA−binding to TPT, TTP, and CS−TTP were investigated because the potential of these compounds to act as pharmaceutical agents depends on their binding ability. The stopped-flow technique was used to obtain the kinetic parameters and also to suggest a mechanism. The results showed that the formation of CS−TTP nanorods enhances the binding rate and kinetic stability through coordination affinity compared to TPT and TTP and also change the pathway mechanism. Additionally, the antibacterial assessments on four bacteria strain correlated very well with the kinetic stability as BSA−CS−TTP is the kinetically most stable and also showed better antibacterial activity compared to BSA−TPT and BSA−TTP.

Tailored Alkali Resistance of DeNOx Catalysts by Improving Redox Properties and Activating Adsorbed Reactive Species

SummaryIt is still challenging to develop strongly alkali-resistant catalysts for selective catalytic reduction of NOx with NH3. It is generally believed that the maintenance of acidity is the most important factor because of neutral effects of alkali. This work discovers that the redox properties rather than acidity play decisive roles in improving alkali resistance of some specific catalyst systems. K-poisoned Fe-decorated SO42−-modified CeZr oxide (Fe/SO42−/CeZr) catalysts show decreased acidity but reserve the high redox properties. The higher reactivity of NHx species induced by K poisoning compensates for the decreased amount of adsorbed NHx, leading to a desired reaction efficiency between adsorbed NHx and nitrate species. This study provides a unique perspective in designing an alkali-resistant deNOx catalyst via improving redox properties and activating the reactivities of NHx species rather than routinely increasing acidic sites for NHx adsorption, which is of significance for academic interests and practical applications.

Behaviour of cerium(III) in the presence of components of soils and its humate complex

ABSTRACT The behaviour of cerium, as a prototype of the lanthanide group, against the inorganic components of two types of soils (one from an Abisreligiosa forest (IM-F) and the other from a semiarid zone (IM-S)) was investigated. The pseudo-second order model applied to the kinetics adsorption data for both soils indicated chemical adsorption; the equilibrium was reached in less than 4 h, the adsorption of Ce(III) in these conditions were 15.6 and 3.5 mg g−1 for IM-F and IM-S respectively. The adsorbents showed a buffer effect in alkali conditions, the adsorption was highest at 5 > pHeq < 6 for both adsorbents. The adsorption isotherms showed that the IM-F surface is homogeneous with a maximum adsorption capacity of 15.7 mg g−1 and that of IM-S is heterogeneous. IM-F is more efficient at low adsorbent dosage, whereas this parameter virtually does not affect the IM-S efficiency but the adsorption percentage increases as the dosage increases. The thermodynamic parameters showed an exothermic and chemical adsorption process using IM-F (ΔH0 = −96.6 KJ mol−1) and an endothermic and physicochemical process using IM-S (ΔH0 = 29 KJ mol−1). Finally, the competition of the adsorption by IM-F and the formation of the complex with humic acids showed the complex formation of Ce:(HA)n, (1:1) with a log .

CeO2 for Water Remediation: Comparison of Various Advanced Oxidation Processes

Three different Advanced Oxidation Processes (AOPs) have been investigated for the degradation of the imidacloprid pesticide in water: photocatalysis, Fenton and photo-Fenton reactions. For these tests, we have compared the performance of two types of CeO2, employed as a non-conventional photocatalyst/Fenton-like material. The first one has been prepared by chemical precipitation with KOH, while the second one has been obtained by exposing the as-synthetized CeO2 to solar irradiation in H2 stream. This latter treatment led to obtain a more defective CeO2 (coded as “grey CeO2”) with the formation of Ce3+ sites on the surface of CeO2, as determined by Raman and X-ray Photoelectron Spectroscopy (XPS) characterizations. This peculiar feature has been demonstrated as beneficial for the solar photo–Fenton reaction, with the best performance exhibited by the grey CeO2. On the contrary, the bare CeO2 showed a photocatalytic activity higher with respect to the grey CeO2, due to the higher exposed surface area and the lower band-gap. The easy synthetic procedures of CeO2 reported here, allows to tune and modify the physico-chemical properties of CeO2, allowing a choice of different CeO2 samples on the basis of the specific AOPs for water remediation. Furthermore, neither of the samples have shown any critical toxicity.

Novel smart and self-healing cerium phosphate-based corrosion inhibitor for AZ31 magnesium alloy

Tri(bis(2-ethylhexyl)phosphate) (Ce(DEHP)3) was used as novel corrosion inhibitor for protection of AZ31 coated with an epoxy-silane hybrid coating. Electrochemical Impedance Spectroscopy (EIS) in 0.05 M NaCl showed that Ce(DEHP)3-modified coating offered superior corrosion protection compared to a reference coating. Localized electrochemical techniques (Localized Electrochemical Impedance Spectroscopy – LEIS, Scanning Vibrating Electrode Technique – SVET, and Scanning Ion-Selective Electrode Technique – SIET) were employed to assess the corrosion healing effect of Ce(DEHP)3 in defect-containing coatings. Results showed that Ce(DEHP)3 introduces cyclic pH-dependent corrosion inhibition, involving the combined action of cerium and organophosphate ions through formation of protective Ce- and P-containing species.

Monazite transformation into Ce- and La-containing oxalates by Aspergillus niger.

Monazite is a naturally occurring lanthanide (Ln) phosphate mineral [Ln x (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 (C2 O4 )3 ·10H2 O) and lanthanum oxalate decahydrate (La2 (C2 O4 )3 ·10H2 O). 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.

High temperature oxidation resistance and TGO growth mechanism of laser remelted thermal barrier coatings

In the present work, ZrO2–Y2O3 thermal barrier coatings (YSZ TBCs) and La2Zr2O7/ZrO2–Y2O3 thermal barrier coatings (LZ/YSZ TBCs) were prepared by atmospheric plasma spraying (APS) respectively, and then were surface remelted by laser remelting process. Thereupon, high temperature oxidation experiment was carried out at 1100 °C. The results showed that the compactness of these two kinds of as-sprayed TBCs was enhanced by remelting treatment. Hence, compared with the as-sprayed TBCs, the weight gains of the remelted TBCs were smaller, the thermally grown oxide (TGO) was thinner, and no obvious holes formed in the TGO. Al2O3, oxides of Cr, Co, Ni elements formed successively, eventually CS (spinel type oxides) formed in TGO of the remelted YSZ TBCs. However, due to the presence of La3+ in the remelted LZ/YSZ TBCs, the oxidation rate of Al, Cr, Co, Ni elements was slowed down, thus the formation of CS was delayed accordingly. Therefore, the high temperature oxidation resistance of the YSZ TBCs and the LZ/YSZ TBCs was improved by laser remelting treatment, and the remelted LZ/YSZ TBCs was superior to the remelted YSZ TBCs.

Chitosan/metal oxide nanocomposites: synthesis, characterization, and antibacterial activity

With the growing concern of biofilm-associated infections and drug-resistant bacteria, an increasing interest in developing novel antibacterial agents is an urgent priority. Metal oxide-based polymeric materials are able to distinguish mammalian cells from bacterial cells and thus provide long-term antibacterial growth inhibition. Herein, we report the preparation of MgO, NiO and chitosan-coated metal oxide (CS–MO) nanocomposites via a simple in situ chemistry approach. Fourier transform infrared spectroscopy, X-ray diffraction patterns and X-ray photoelectron spectra results proved the formation of CS–MgO and CS–NiO nanocomposites. Also, the particle sizes were observed to be 18.3 and 25.5 nm for CS–NiO and CS–MgO, respectively. All the samples exhibited antibacterial activities against the Escherichia coli and Staphylococcus aureus strains; however, more effective against S. aureus compared to E. coli. Noticeably, 5 μg/mL CS–NiO comparatively exhibited highest bactericidal capability where E. coli and S. aureus viabilities were reduced to 25–47% after 12 h incubation. After treatment with 15 μg/mL of CS–NiO, ∼98% of S. aureus and 92.3% of E. coli cells were inhibited.

Photocatalytic degradation of malachite green dye using chitosan supported ZnO and Ce–ZnO nano-flowers under visible light

Two types of chitosan-based composites (chitosan/ZnO and chitosan/Ce–ZnO composites) were synthesized under microwave irradiation and characterized as advanced catalysts of enhanced photocatalytic activity under the visible light. The morphological investigation reflected the formation of ZnO and Ce doped ZnO at stunning micro flowers of nano limps. Additionally, the optical studies reflected a reduction in the bandgap of ZnO from 3.3 eV to 2.85 eV and 2.5 eV after supporting it onto chitosan chains and after doping it with cerium, respectively. The synthetic composites were applied in photocatalytic removal of malachite green dye under a visible light source. The synthetic CH/ZnO and CH/Ce–ZnO showed enhancement in the photocatalytic removal of M.G by 54% and 87%, respectively, as compared to the pure ZnO. The synthetic composites are of high stability and can be reused for five photocatalytic degradation cycles at stunning removal percentages. The main oxidizing radicals during the removal of M.G by CH/ZnO are the generated electron-hole pairs as well as the hydroxyl radicals. The effective species in CH/Ce–ZnO photocatalytic system are the photogenerated hydroxyl radicals followed by the electron-hole pairs.

Structural and electronic properties of β-NaYF4 and β-NaYF4:Ce3+

In this work, the density functional theory approach with linear combination of atomic orbitals (LCAO) as implemented in the CRYSTAL17 computer code is applied to hexagonal β-NaYF4, located in three possible space groups of this compound: P6‾, P63/m and P6‾2 m. First, the disordered crystalline structure of NaYF4 was modelled in a large supercell containing 108 atoms. In order to obtain better agreement with the experimental data, we used several different exchange-correlation functionals. Basic properties, such as lattice constant, band gap and total energies were calculated and compared for all three space groups and three exchange-correlation functionals - HSE06, PWGGA and PWGGA+13%HF. It was found that for all three functionals, the minimum of total energy corresponds to P6‾ space group. Secondly, in order to study the effects associated with the Ce3+ impurity and the F center (radiation defect), the P6‾ β-NaYF4 structure with the F center and Ce3+ or with both was carefully modelled. Taking into account that fluorine atoms have different nearest neighbours, several types of fluorine vacancies were simulated and an appropriate formation energies were determined. Finally, the effects of Ce3+ ion substitution of Y ions in different positions as well as formation of Ce3+, the F center defect pairs were also studied and an appropriate incorporation energies were calculated.

Cr-Doped CeO2 Nanorods for CO Oxidation: Insights into Promotional Effect of Cr on Structure and Catalytic Performance

Development of non-noble metal catalysts for oxidation of CO is an important subject for reducing the automotive emissions. Recently, shape-controlled synthesis of CeO2 has increasingly attracted the attention of researchers due to its size- and morphology-dependent unique properties. Following this line of thinking, herein, we successfully report the synthesis of Cr-doped CeO2 (Ce1−xCrxO2−δ; X = 0.05, 0.1, and 0.15) nanorods with various Cr contents by a facile hydrothermal method. Structural, surface, optical, and redox properties of the Cr-doped CeO2 nanorods were investigated by various techniques, namely, ICP-OES, TEM-HRTEM, FE-SEM/EDX/EDS, XRD, BET, Raman, UV–vis DRS, PL, XPS, H2-TPR, and O2-TPD. The catalytic performance was evaluated for CO oxidation. For comparison, the efficiency of Cr2O3 was also studied for CO oxidation under identical conditions. As revealed by various characterization results, the chromium ions were doped into the ceria lattice (formation of Ce–O–Cr solid solution), which enhanced the intrinsic properties such as oxygen vacancy concentration and surface area. It was found that the Cr-doped CeO2 nanorods show superior CO oxidation activity than the pristine counterparts (CeO2 nanorods and Cr2O3). The highest CO oxidation efficiency was achieved with the light-off temperature of T50 = 261 °C, when the Cr doping amount was 10% (Ce0.9Cr0.1O2−δ). A high specific surface area, more number of surface oxygen vacancies, a high concentration of Ce3+, and enhanced oxygen reducibility of Ce0.9Cr0.1O2−δ nanorods were found to be responsible for its superior catalytic performance. Further, the Ce0.9Cr0.1O2−δ nanorods exhibited a steady CO conversion over a period of 55 h investigated. The obtained results are expected to have a significant impact on the use of non-noble metal based Cr-doped CeO2 nanorods in environmental applications. The Cr-doped CeO2 nanorods with Ce0.9Cr0.1O2−δ composition showed enhanced CO oxidation performance at a lower temperature (~ 261 °C) than that of pristine CeO2 nanorods (338 °C) and Cr2O3 (361 °C) catalyst. This behaviour is a result of enhancement of oxygen vacancies, surface Ce3+ species, low-temperature reducibility, and high surface area.