Cerium Concentration Research Articles

Electrochemical biosensing of cerium with a tyrosine‐functionalized EF‐hand loop peptide

AbstractThe significance of easily detecting rare earth elements (REEs) has increased due to the growing demand for REEs. Addressing this need, we present an innovative electrochemical biosensor, focusing on cerium as a model REE. This biosensor utilizes a modified EF‐hand loop peptide sequence, incorporating cysteine for covalent attachment to a gold working electrode and tyrosine as an electrochemically active amino acid. The sensor was designed such that binding to cerium induces a conformational change in the peptide, affecting tyrosine's proximity to the electrode surface, modulating the current. A calibration curve was generated from cyclic voltammetry current peaks at ~0.55–0.65 V versus a silver pseudo‐reference electrode, with cerium concentrations ranging from 0 to 67 μM in artificial urine. The sensor exhibited a biologically relevant limit of detection of 35 μM and a sensitivity of −0.0024 ± 0.002 (μA μM)−1. These findings offer insights into designing peptide sequences for electrochemical biosensing.

Evaluating Effects of Cerium Concentration and Water Content on Diffusivity of Cerium Ions in PEFC Using Molecular Dynamics Simulations

We investigated effects of cerium concentrations and water content on diffusivity of cerium ions in Nafion membrane. The diffusion coefficients of cerium ions were taken, and the structural features that could change diffusivity were analyzed. Results show that difference in concentrations in this study is independent of diffusivity. Although there was a slight difference in structure depending on the concentration, it was suggested that this depended on the initial position of the cerium ion. The diffusion of cerium ions was found to be greatly affected by water content. When water content is 3, cerium ions coordinate with sulfonic acid group because of luck of water around cerium ion. As water content increase, cerium ions are fully hydrated, and they may have high diffusivity. The growth of water clusters, which are the transport pathway for the ions, is also thought to be the cause of the significantly larger diffusion coefficient.

Ce-doped ZnO nanonails synthesized by a simple thermal evaporation method for photocatalytic degradation

One-dimensional (1D) nanomaterials have garnered significant scientific and technological attention due to their potential applications in electronics devices, gas sensing, energy conversion, and photocatalysis. However, the development of a simple and low-cost technique for 1D nanostructure synthesis remains a challenge. The doping of ZnO nanostructures has proven to be an effective way to improve their internal properties. In this work, one-dimensional ZnO and Ce-doped ZnO nanorods and nanonails were synthesized by a simple thermal evaporation method using different weight ratios of ZnS and CeO2 precursor powders in a catalyst-free process. The effects of cerium doping concentration on the structural, morphological, and optical properties of the as-prepared samples were investigated. XRD analysis confirmed that the crystal structure was converted from the cubic ZnS phase to the hexagonal ZnO phase with increasing annealing temperatures. The UV–Vis spectra showed that the optical absorption edge of Ce-doped ZnO samples was slightly red-shifted. Additionally, the band gap energy decreases with increasing cerium concentration. SEM images showed that the morphology of the structures obtained changed from nanorods to nanonails as the Ce content increased. The incorporation of Ce ions into the ZnO matrix has been successfully confirmed by HRTEM, Raman, and EDX analysis. Photocatalytic activity studies showed that Ce-doped ZnO samples exhibited significantly enhanced photocatalytic performance compared to pure ZnO for the degradation of rhodamine B under UV radiation. These results may suggest the use of heterogeneous photocatalysis as an efficient, cheap, and environment-friendly alternative for the removal of pollutants from water and the use of Ce-doped ZnO as a promising candidate.

Structural, optical, and electronic properties of cerium doped BaTiO3: Experimental study and DFT calculation

The barium titanate Ba1-xCe2x/3TiO3 (BCTx, x = 0, 1, 2 and 3 %) have been produced using the sol-gel process. The impact of cerium concentration on structure and optical properties was examined using techniques such as X-ray diffraction, infrared spectroscopy, Raman spectroscopy and UV–visible spectroscopy. DFT calculation were carried out on BCTx to obtain an extensive comprehension of the relationship between the structure and electronic properties of BCTx. The findings demonstrate a tetragonal structure for BCT0 and a pseudo-cubic for the doped samples. The UV–visible study indicates a successive reduction in bandgap due to vacancies in the A site, lattice defect formation and local bond distortion. For every sample, the electronic band structure showed a direct band gap. The partial density of states (PDOS) revealed that the valence band was dominated by the 2p orbitals of the O atoms. However, the conduction band was formed by the 3d orbitals of the Ti atom.

Biodistribution of cerium dioxide and titanium dioxide nanomaterials in rats after single and repeated inhalation exposures

BackgroundPhysiologically based kinetic models facilitate the safety assessment of inhaled engineered nanomaterials (ENMs). To develop these models, high quality datasets on well-characterized ENMs are needed. However, there are at present, several data gaps in the systemic availability of poorly soluble particles after inhalation. The aim of the present study was therefore to acquire two comparable datasets to parametrize a physiologically-based kinetic model.MethodRats were exposed to cerium dioxide (CeO2, 28.4 ± 10.4 nm) and titanium dioxide (TiO2, 21.6 ± 1.5 nm) ENMs in a single nose-only exposure to 20 mg/m3 or a repeated exposure of 2 × 5 days to 5 mg/m3. Different dose levels were obtained by varying the exposure time for 30 min, 2 or 6 h per day. The content of cerium or titanium in three compartments of the lung (tissue, epithelial lining fluid and freely moving cells), mediastinal lymph nodes, liver, spleen, kidney, blood and excreta was measured by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) at various time points post-exposure. As biodistribution is best studied at sub-toxic dose levels, lactate dehydrogenase (LDH), total protein, total cell numbers and differential cell counts were determined in bronchoalveolar lavage fluid (BALF).ResultsAlthough similar lung deposited doses were obtained for both materials, exposure to CeO2 induced persistent inflammation indicated by neutrophil granulocytes influx and exhibited an increased lung elimination half-time, while exposure to TiO2 did not. The lavaged lung tissue contained the highest metal concentration compared to the lavage fluid and cells in the lavage fluid for both materials. Increased cerium concentrations above control levels in secondary organs such as lymph nodes, liver, spleen, kidney, urine and faeces were detected, while for titanium this was found in lymph nodes and liver after repeated exposure and in blood and faeces after a single exposure. Conclusion: We have provided insight in the distribution kinetics of these two ENMs based on experimental data and modelling. The study design allows extrapolation at different dose-levels and study durations. Despite equal dose levels of both ENMs, we observed different distribution patterns, that, in part may be explained by subtle differences in biological responses in the lung.

Enhanced Photocatalytic Degradation of Organic Dyes by Cerium‐Doped Zinc Oxide Nanocones

AbstractCerium‐doped zinc oxide (Ce‐ZnO) nanocones with cerium concentrations of 0, 0.5, 1, and 2 % were synthesized using a sol‐gel method. Their effectiveness as photocatalysts for degrading dyes such as Rhodamine B (RhB), Methylene Orange (MO), and Methylene Violet (MV) was evaluated. The optical and structural properties, particle size distribution, and morphology of these nanocones were examined using X‐ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet‐visible (UV‐Vis) spectrophotometry. XRD results confirmed that the nanocones were highly crystalline with a hexagonal wurtzite structure, and a noticeable blue shift was observed in the Ce‐doped ZnO nanocones compared to pure ZnO. The photocatalytic performance under UV exposure showed that cerium doping significantly improved the degradation of RhB, MO, and MV. Notably, ZnO nanocones doped with 1 % cerium exhibited the highest photocatalytic efficiency, achieving 100 % degradation of RhB within 60 minutes. Additionally, 1 % Ce‐ZnO nanocones demonstrated degradation efficiencies of 86.3 % for MO and 74.9 % for MV within the same time frame.

Electrochemical Amalgamation Optimization as Part of the Development of the OREATE Process

Oxide reduction by electrochemical amalgamation and thermal extraction (OREATE) is an electrochemical process in which metal oxides are converted to highly pure metals. This process that is currently being developed at LANL involves the dissolution and chlorination of the metal oxide into an acidic medium. This metal cation is then electrochemically amalgamated via reduction using a mercury pool cathode. Finally, mercury's high vapor pressure allows an easy thermal extraction process to obtain the metal. In addition to its ability to electrochemically form amalgams, mercury is used because it has a high hydrogen evolution overpotential, allowing for a higher current efficiency for reduction of the metals in acidic solution. As a critical step of the OREATE process, the electrochemical amalgamation reaction must be optimized in order to advance the overall performance.In this work, we studied the electrochemical amalgamation of cerium through anodic stripping voltammetry (ASV) experiments using a silver-based mercury film electrode (SBMFE). The SBMFE allows for the electrochemical amalgamation to be optimized at a smaller scale than the mercury pool, which not only minimizes the amount of mercury needed, but also drastically reduces the experiment time. This study included several different experimental parameters such as the pH of the buffered solution, concentration of cerium, reduction potential, and temperature. For each parameter, the reaction rate and current efficiency were evaluated to determine the optimal conditions for the electrochemical amalgamation reaction.The results showed that the pH of the buffered solution must be 3.5 or lower to avoid the formation of cerium hydroxides, which can passivate the surface of the mercury electrode. However, an increasingly acidic solution promotes the hydrogen evolution reaction, which directly competes with the electrochemical reduction of cerium, decreasing the overall current efficiency. Likewise, it has been demonstrated that an increase of the cerium concentration in solution drops the current efficiency of the electrochemical amalgamation reaction. This effect can be explained by the fact that cerium is a small cation with a +3 charge that leads to a high degree of solvation. Therefore, as the cerium concentration in solution increases, more water molecules are brought to the electrode surface during electrochemical amalgamation. This favors the water reduction reaction that increases hydrogen evolution and lowers current efficiency. However, increasing the concentration of cerium enhances the reaction rate of the electrochemical amalgamation, resulting in more cerium entering the mercury film. Furthermore, as the reduction potential is moved towards more negative potentials, the reaction rate increases. However, a more negative reduction potential promotes a faster hydrogen evolution reaction, which diminishes the current efficiency. Finally, it has been demonstrated that temperature increases the reaction rate, though it does not have a significant effect on the current efficiency.In conclusion, a variety of system parameters were explored for their effect on current efficiency and reaction rate of the electrochemical amalgamation reaction. This allowed for the determination of the optimal parameters to be used during the electrochemical amalgamation in the large-scale OREATE process.

OREATE as a High Yield and Purity Electrochemical Process for Transition and Rare Earth Metal Recovery

Developing a process that can consistently convert transition and rare earth metal oxides to chemically pure metals in near quantitative yield will have significant impact in many levels, from fundamental science to national security-related applications. Traditional separation methods of lanthanides and actinides from aqueous media have been based on liquid-liquid extractions that have proven to be quite efficient, though they are expensive and require complex engineering. Likewise, separation by pyro-chemistry provides a good recovery performance but requires the use of high temperatures that adds technological difficulties to the process. An alternative method that has grown interest in the last few years is the utilization of the difference in the metals’ reduction potentials from ionic state to metallic state. However, this electrochemical approach requires more negative reduction potentials than hydrogen evolution, which requires a very challenging control of their electrolytic deposition onto solid cathodes.In recent years, our team at LANL has been working on the development of OREATE (Oxide Reduction by Electrochemical Amalgamation and Thermal Extraction). OREATE is a holistic electrochemical approach that involves an initial step wherein the metal oxide is dissolved and chlorinated into an acidic medium. The dissolved metal cation is then electrochemically amalgamated via reduction using a mercury pool cathode. Finally, mercury's high vapor pressure allows an easy thermal extraction process to obtain the metal. From the conceptual perspective and preliminary results, the OREATE process appears easier and simpler than traditional separation methods and is suitable for small- and large-scale preparation of high purity metals.The results obtained using Cerium (Ce) as a surrogate metal demonstrated near quantitative yield of the electrochemical amalgamation (yield > 99%), almost complete mercury recovery during the thermal extraction (Hg recovery > 99.5%), and high purity of the Ce metal product (purity > 99%). Moreover, a variety of system parameters such as the pH of the buffered solution, concentration of cerium, reduction potential, and temperature were explored to evaluate the effect that the scaling up of the OREATE process may have on reaction rate, current efficiency, process yield, and temperature management.

Operando X-Ray Fluorescence Analysis of Dynamic Cerium Radical Quencher Motion Perpendicular to MEA

Polymer electrolyte fuel cells (PEFCs) are required to have a durability of over 50,000 hours. One of the degradation factors is chemical degradation of perfluorosulfonic acid (PFSA) electrolyte membrane. The reaction of hydrogen peroxide with iron impurities produces hydroxyl radicals that break the chemical bonds in the PFSA membrane. Cerium ions are added to electrolyte membranes to absorb these radicals and act as a radical quencher, contributing to improved membrane durability.1 However, cerium ions have been shown to move in both the planar and through-plane directions under fuel cell operating conditions.2,3 The spatial scale of migration in the membrane planar direction is large, and therefore the time scale is also large, where analysis of end-of-life samples has been reported. On the other hand, the observation of the movement in the membrane direction is not easy because the thickness of the electrolyte membrane is 10 micrometers, and it is estimated to be significantly different between the post-disassembly condition and the operating condition. Therefore, it is necessary to establish operando measurement technique for cerium ion concentration with high spatial and temporal resolution in the direction perpendicular to the membrane. We developed an operando X-ray fluorescence spectroscopy technique using a combination of high-energy X-rays and a focused microbeam, and analyzed the behavior of cerium concentration change under current-applied conditions.4 The distribution behavior of cerium ions in the membrane is significantly different depending on the current and humidity. In a high-humidity environment, the ions move in the membrane in the vertical direction in about 1 second. Therefore, in this study, we developed a method to continuously measure the cerium ion concentration in the membrane on a sub-second scale and were able to estimate the effective cerium diffusion coefficient. It was also found that cerium ions migrate to the cathode layer under current-applied conditions. This behavior is accelerated in low humidity environments. This is because the diffusion coefficient of cerium ions is smaller at lower humidity and the back-diffusion flux is smaller.This work is based on results obtained from the project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan.[1] E. Endoh, ECS Trans., 16, 1229–1240 (2008).[2] Y. Lai, K. M. Rahmoeller, J. H. Hurst, R. S. Kukreja, M. Atwan, A. J. Maslyn,C. S. Gittleman, J. Electrochem. Soc., 165, F3217-F3229(2018).[3] S.M. Stewart, D. Spernjak, R. Borup, A. Datye, F. Garzon, ECS Electrochem. Lett., 3, F19-F22 (2014).[4] Y. Orikasa, A. Takezawa, K. Amemiya, Y. Tsuji, T. Asaoka, M. Ohki, O. Sekizawa, K. Nitta, ECS Trans., 109 109 (2022).

Study of Concentration Quenching and Energy Transfer Mechanism in Ce Doped Y2O3 Nanomaterials.

We study concentration quenching and energy transfer mechanisms of yttrium oxide (Y2O3) nanomaterials doped with different concentrations (0-5mol%) of cerium (Ce). Photoluminescence (PL) spectra recorded under an excitation wavelength of 350nm show a broad emission band at ∼ 406nm and a feeble emission band at ∼ 463nm in the undoped Y2O3 sample. The doping of Ce in Y2O3 induced multiple PL peaks within the blue-green region of the spectrum in all the doped samples with the peak at ∼ 466nm being notably the prominent one. This prominent emission band exhibits a decrease in intensity with increasing Ce concentration due to concentration quenching. Analysis of Time-resolved photoluminescence (TRPL) spectra reveal that the average emission lifetime of Ce-doped Y2O3 is shorter than that of the undoped Y2O3 sample. The concentration quenching effect and the decrease of average emission lifetime of the dominant emission band are explained on the basis of energy transfer from the host Y2O3 to the Ce3+ ion centres. The critical quenching concentration of Ce3+ ion in Y2O3:Ce phosphor was identified to be 1mol% and the critical transfer distance was estimated to be 23.74 Å. Analysis reveal that the concentration quenching mechanism involves nearest-neighbour interaction.

Investigating the influence of cerium doping on the structural, optical and electrical properties of ZnNiMgFe2-xCexO4 soft ferrites

The present work reports the optical, structural, and electrical properties of cerium-doped Zn0.6Ni0.2Mg0.2Fe2-xCexO4 soft ferrites by green synthesis method that unwrap transformative insights and find technological applications through X-ray diffraction (XRD), UV visible spectroscopy and IV-point probe techniques. Ferrites with different cerium concentrations (x = 0.0, 0.0250, 0.0375) show an enormous difference in the optical, structural, and electrical behavior of the ferrites. The crystallite size increases to 46.9 nm, with a concomitant increase in lattice constants up to 8.550 Å for x = 0.0375. A similar structural shift was noticed in X-ray and bulk densities from 5.031 to 4.982 g/cm³ and 3.83 to 3.97 g/cm³, respectively. The optical explorations revealed a remarkable bandgap reduction from 2.768 eV to 2.758 eV improving the utility of the material substantially in magneto-optic devices. Conversely, the refractive index increases from 2.420 to 2.423, and the imaginary dielectric constant goes up from 10.654 to 10.667, giving a herald of advancement in photonic technologies. Electrically, the study marks a drastic reduction in DC resistivity from 1.95 × 105 to 6.13 × 103 ohm-cm with the Ce doping, which indicates higher conductivity suitable for telecommunication. This extensive work on Ce-doped soft ferrites now opens up newer avenues of applications in electronics and magneto-optics, blending scientific inquiry with practical utility.

Kinetic Studies on Ruthenium(III) Chloride‐Catalyzed Oxidation of Benzyl and Homobenzyl Alcohols Using Cerium(IV) Sulfate under Acidic Medium

AbstractThis study investigates the kinetics of oxidative conversion of benzyl and homobenzyl alcohols to carbonyls using cerium(IV) sulfate in the presence of ruthenium(III) complex under mild acidic conditions. The results revealed that the low concentration of both alcohols and cerium(IV) ions drives the reaction to a first‐order kinetics, whereas a higher concentration induces zero‐order kinetics. In addition, the kinetics of the reaction were altered by the additives of hydrogen ions, cerium(III) ions, and chloride ions. We hope this study will be helpful in understanding the reaction kinetics of the oxidation of primary alcohols.

Probing the structural, mechanical, biomineralization, resorbability and biocompatibility characteristics of ZrO2–CaSiO3 composite dependent on cerium substitutions

Composites comprising mechanically stronger ceramic and bioactive alongside resorbable ceramic are a most welcomed choice in load-bearing bone replacement. In this pursuit, the present study aims to investigate the varied levels of cerium additions in the ZrO2–CaSiO3 composite. The influence of cerium concentration on the structural, mechanical, apatite formation, resorbability and in-vitro biological behaviour of the ZrO2–CaSiO3 composite has been undertaken in the current study. Sol-gel synthesis technique has been adopted to yield composite powders and the structural behaviour of the resultant has been performed using various analytical techniques. The results envisaged the crucial role of Ce3+ concentration in accomplishing a phase stable t/c-ZrO2-α-CaSiO3 composite after heat treatment at 1300 °C. XPS analysis revealed the presence of dual oxidation state (+3 and + 4) of cerium in the composite powders and a homogeneous mixture of the composite has been determined from morphological analysis. Mechanical properties determined from nanoindentation indicated better strength displayed by the composite than the natural bone. The immersion tests conducted in simulated body fluids indicated the development of apatite crystals on the composite. Resorbability and biocompatibility tests demonstrated the virtuous appropriateness of the 30 wt% Ce3+/Ce4+ doped t/c-ZrO2-α-CaSiO3 composite for load-bearing bone replacement.

Associations between urinary rare Earth elements with renal function: Findings from a cross-sectional study in Guangxi, China

BackgroundWith increased applications of rare earth elements (REEs) across various industries, evaluating the relationship between REEs exposure and potential health effects has become a public concern. In vivo experiments have established that REEs impact renal function. However, relevant epidemiological evidence on this relationship remains scarce. The objective of this study is to examine the impact of exposure to REEs on renal function. MethodsIn this cross-sectional study, 1052 participants were recruited from Guangxi, China. We measured urinary concentrations of 12 REEs using an inductively coupled plasma-mass spectrometer (ICP-MS). Multiple linear regression models were developed to explore the relationship between a single REEs exposure and the estimated glomerular filtration rate (eGFR), a marker of renal function. Weighted quantile sum (WQS) regression and Bayesian kernel machine regression (BKMR) were used to examine the combined effects of REE co-exposure on eGFR. ResultsIn the multiple linear regression analysis, increasing the concentrations of lanthanum (La, β: 8.22, 95% CI: 5.67–10.77), cerium (Ce, β:6.61, 95% CI: 3.80–9.43), praseodymium (Pr, β: 8.46, 95% CI: 5.85–11.07), neodymium (Nd, β:8.75, 95% CI: 6.10–11.41), and dysprosium (Dy, β:7.38, 95% CI: 4.85–9.91) significantly increased the eGFR. In the WQS regression model, the WQS index was significantly associated with eGFR (β: 4.03, 95% CI: 2.46–5.60), with Pr having the strongest correlation with eGFR. Similar results were obtained in the BKMR model. Additionally, interactions between Pr and La, and Pr and Nd were observed. ConclusionsCo-exposure to REEs is positively associated with elevated eGFR. Pr is likely to have the most significant influence on increased eGFRs and this might be exacerbated when interacting with La and Nd. Mixed exposure to low doses of REEs had a protective effect on renal function, which can provide some evidence for the exposure threshold of REEs in the environment. Trial registrationThe study has been approved by the Guangxi Medical University Medical Ethics Committee (#20170206–1), and all participants provided written informed consent.

Response of sunflower seeds (Helianthus annuus L.) to different concentrations of metals and doses of gamma radiation (241Am)

The sunflower crop (Helianthus annuus L.) presents great tolerance to heavy metals and in pre-determined doses of gamma (γ) radiation it presents gains in plant increments. This study aimed to evaluate the response to doses of γ radiation and different concentrations of toxic metals in the vegetative development of sunflower. Mirasol sunflower seeds were subjected to different doses of 241Am γ rays and concentrations of Aluminum, Cerium and Copper (mg L-1). Sunflower plants were evaluated only in the vegetative period for germination, aerial length, root length, aerial and root fresh mass, aerial and root dry mass. The doses of γ radiation promoted increases in the variables in the vegetative phase, especially for 5 and 10 minutes of exposure to γ rays. The concentrations of the toxic elements Al and Ce showed significant differences in all increments, however, doses higher than 85 mg L-1 demonstrated losses in length and mass of sunflower plants. For the Cu element, the doses did not have a significant effect, these being non-significant and the cultivar Mirasol resistant. Future studies should be carried out evaluating the reproductive phase and its gains in increasing biomass and production.

A study of the effect of cerium ion doping concentration on the structural, electrical, and thermoelectric properties of CaMnO3 nanoparticles

Abstract Universally, energy loss in the form of heat is predominant and this heat is irrecoverable waste heat that leads to global warming. Clean, green, eco-friendly, cost-effective, and renewable energy sources are the possible solutions for this energy crisis and global warming issues. Thermoelectric power generation is a promising technology by converting this irrecoverable waste heat directly into electricity without any greenhouse gas emission. Nanostructured CaMnO3 at various cerium concentrations have been successfully prepared by sol–gel hydrothermal method followed by annealing and sintering. Pure and doped samples were systematically characterized by DSC, powder XRD, RAMAN, SEM with EDAX and FTIR spectroscopy. Electrical and thermoelectrical measurements were carried out on the sintered pellets. The XRD analyses confirmed the formation of orthorhombic perovskite structure for all the samples and the average particle size lies in the range of 50–60 nm. FTIR analysis shows the presence of CaMnO3 nanoparticles without any impurities. The temperature dependence of physical properties was performed and analyzed between room temperature and 600 °C. Electrical resistivity strongly depends on the nature of substituent ions and negative values indicate that the electrons are major charge carriers. Large Seebeck coefficient value and high-power factor make Ca1−x Ce x MnO3 an efficient thermoelectric material for energy storage applications.

Isomorphic Insertion of Ce(III)/Ce(IV) Centers into Layered Double Hydroxide as a Heterogeneous Multifunctional Catalyst for Efficient Meerwein-Ponndorf-Verley Reduction.

The development of highly active acid-base catalysts for transfer hydrogenations of biomass derived carbonyl compounds is a pressing challenge. Solid frustrated Lewis pairs (FLP) catalysis is possibly a solution, but the development of this concept is still at a very early stage. Herein, stable, phase-pure, crystalline hydrotalcite-like compounds were synthesized by incorporating cerium cations into layered double hydroxide (MgAlCe-LDH). Besides the insertion of well-isolated cerium centers surrounded by hydroxyl groups, the formation of hydroxyl vacancies near the aluminum centers, which were formed by the insertion of cerium centers into the layered double hydroxides (LDH) lattice, was also identified. Depending on the initial cerium concentration, LDHs with different Ce(III)/Ce(IV) ratios were produced, which had Lewis acidic and basic characters, respectively. However, the acid-base character of these LDHs was related to the actual Ce(III)/Ce(IV) molar ratios, resulting in significant differences in their catalytic performance. The as-prepared structures enabled varying degrees of transfer hydrogenation (Meerwein-Ponndorf-Verley MPV reduction) of biomass-derived carbonyl compounds to the corresponding alcohols without the collapse of the original lamellar structure of the LDH. The catalytic markers through the test reactions were changed as a function of the amount of Ce(III) centers, indicating the active role of Ce(III)-OH units. However, the cooperative interplay between the active sites of Ce(III)-containing specimens and the hydroxyl vacancies was necessary to maximize catalytic efficiency, pointing out that Ce-containing LDH is a potentially commercial solid FLP catalysts. Furthermore, the crucial role of the surface hydroxyl groups in the MPV reactions and the negative impact of the interlamellar water molecules on the catalytic activity of MgAlCe-LDH were demonstrated. These solid FLP-like catalysts exhibited excellent catalytic performance (cyclohexanol yield of 45%; furfuryl alcohol yield of 51%), which is competitive to the benchmark Sn- and Zr-containing zeolite catalysts, under mild reaction conditions, especially at low temperature (T = 65 °C).

Energy transfer from Ce3+ to Eu3+ in the spinel structure of ZnAl2O4 phosphor for optoelectronic applications

Zinc aluminate (ZnAl2O4), with a spinel structure is known for its versatile applications as catalyst, ceramic material, and optoelectronic device. ZnAl2O4 is an excellent host for trivalent rare-earth ions such as Dy3+ , Tb3+, Eu3+ and Sm3+ has been extensively investigated for application in display devices. The focus of this work is on Ce3+ and Eu3+ co-dopants aiming to address issues such as multistage combustion synthesis routes, the formation of secondary phases, that often impact luminescence intensity. Through a systematic approach, we synthesized the ZnAl2O4 host with consistent cerium concentration and varying europium ions using one-step combustion synthesis route. The findings reveal that the synthesized material exhibits efficient energy transfer, mitigates concentration quenching and demonstrates favorable color chromaticity. The crystal structure analysis confirms phase purity and addresses concerns related to secondary phase formation. The simplified and cost-effective approach of one-step combustion synthesis method for synthesizing Ce3+ and Eu3+ co-doped ZnAl2O4 suggests that this phosphor has potential applications in ultraviolet photo-electronic technology and other opto-electronic devices.

Through-Plane Cerium Ion Migration and Diffusion Analysis on Plymer Electrolyte Membrane by Operando X-Ray Fluorescence Spectroscopy

High durability is a critical requirement for expanding the use of polymer electrolyte fuel cells (PEFCs). One degradation factor of PEFCs under typical operating conditions is electrolyte membrane degradation. Radical species formed from the reaction between hydrogen peroxide and impurities during fuel cell operation cause significant degradation of the PEM. To scavenge the radicals, cerium species are added to the PEM, which react with the radicals by redoxing the cerium ion [1]. To maintain the effectiveness of the cerium radical quencher in the PEM, the concentration of cerium in the PEM must be maintained during the long-term operation of the PEFC. However, cerium species easily diffuse and migrate out of the PEM [2]. If the cerium ion is depleted, the PEM will be severely attacked by radicals. To prevent such cerium depletion, it is important to understand the cerium migration phenomena. Experimental detection of cerium distribution phenomena through PEM by operando X-ray fluorescence spectroscopy with resolution of several micrometers has been reported [3]. We have also developed operando XRF using focused micron X-ray with submicrometer resolution [4]. In this study, we further develop the analysis method for cerium diffusion through planar PEM with sub-second time resolution. This method is used to estimate the apparent diffusion coefficient of cerium in PEM.MEAs were prepared by a conventional method using a Pt/C catalyst and a cerium-containing polymer electrolyte with a thickness of 12 μm(GORE-SELECT® MEMBRANEM788.12). The active electrode area was 1.0 cm2. Single cells were assembled using custom end plates with an X-ray permeation window. Operando X-ray fluorescence spectroscopy measurements were performed on BL37XU at SPring-8 (Japan). The monochromated X-ray at an energy of 45 keV was focused to less than 500 nm by a Kirkpatrick-Baez mirror. To detect the cerium distribution in MEA, the fluorescence intensity of Ce-Kα was counted with a Ge semiconductor detector by scanning the position of the cell.In the open circuit condition, most of the cerium is present in the PEM, but during cell loading, the cerium moves to the cathode layer. Immediately after the start of 2.0 A cm-2 loading, the intensity of cerium in the cathode layer increases in a few seconds. Simultaneously, a cerium concentration gradient is observed through the MEA. The cerium concentration gradient shows the current density dependence. When the current load is stopped, the concentrated cerium in the catalyst layer diffuses into the PEM. The diffusion coefficient of cerium ion is estimated from the time dependence of cerium concentration in PEM.Acknowledgments: This work is based on results obtained from the project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) of Japan. E. Endoh et al, ECS Electrochem. Lett., 2, F73 (2013).S. M. Stewart et al, ECS Electrochem. Lett., 3, F19 (2014).A. M. Baker et al, ECS Trans., 92, 107 (2019).Y. Orikasa et al, ECS Trans., 109 109 (2022).

Cerium Ion Adsorption to Fluorine-Doped Tin Oxide Electrodes

The f-elements are critical in many technologies including electronics, catalysis, magnetics, and clean energy. Additionally, these elements occur in very low abundance worldwide. Research has therefore been motivated in the detection, quantification, and reclamation of these elements from waste streams. In this presentation we explore the use of fluorine-doped tin oxide (FTO) electrodes as sensitive and cost-effective electrochemical sensors for cerium ions. We demonstrate that cerium adsorbs reversibly to bare FTO surfaces with a dependence on pH. Through voltammetry and XPS characterization, we demonstrate that the adsorbed cerium, which can undergo the quasi-reversible CeIV/CeIII redox transition, exists in more than one chemical environment. Based on these data, we posit that these different environments are due to the buildup of multiple layers of cerium ions on the FTO surfaces. At lower concentrations (< ca. 100 uM), we can use voltammetry to quantify the cerium adsorbed to the FTO and relate it to the concentration of cerium in solution, with a lower detection limit of about 10-6 M. The data fits to a pseudo second order rate law with a rate constant on the order of 107 (cm2 mol-1)2 s-1. The adsorption fits well to the Freundlich model, but we are working towards finding a non-empirical adsorption model than provide the equilibrium constant for the adsorption reaction.