Ce Oxides Research Articles

The Analysis of the Effect of Mischmetal Addition on the Formation of Non-Metallic Inclusions in Liquid Steel

The study focuses on the effect of rare earth elements (REM) in mischmetal on the morphology and chemical composition of non-metallic inclusions in pre-oxidised steel. Calculations were carried out using the WYK_STAL computer program according to two calculation models, considering/ignoring the sulphur partition coefficient at the liquid steel-liquid slag interfacial boundary. It was found that the chemical composition of the resulting precipitates is a consequence of the order in which deoxidising additives were admixed. Simulations confirmed the presence of Ce oxides and sulphides. This was also confirmed by the analysis of samples taken from the steel ingot after laboratory melting. Non-metallic inclusions Ce2O3 and CeS, and the complex of precipitates: La2O3-Ce2O3 was also identified in the steel. Introduction of mischmetal in the final stage refining is the most effective method. Therefore, the oxygen content is reduced below 0.001%, and the sulphfur content can be reduced to 0.004%.

Catalytic Cracking of Waste Cooking Oil to Alkane-Based Hydrocarbon Over Activated Carbon Supported La and Ce Oxides

Catalytic Cracking of Waste Cooking Oil to Alkane-Based Hydrocarbon Over Activated Carbon Supported La and Ce Oxides

Unveiling the promoting mechanism of Mo on the performance of CuCeOx catalyst for simultaneously NH3-SCR denitration and CO oxidation under oxygen-rich conditions

NOx and CO coexisted in numerous actual industrial flue gases. The simultaneous removal of NOx and CO had great potential for application but remained still a challenge. Herein, a series of Mo-modified CuCeOx catalyst was developed to simultaneously achieve NH3-SCR denitration and CO oxidation. The results indicated that the CCM3 catalyst displayed the optimal performance with 91.2 % NOx conversion and 100 % CO conversion as well as excellent long-time stability and SO2 or/and H2O tolerance at 225 ℃. It was found that the strong interaction between Cu, Ce and Mo oxides resulted in the particles highly dispersed with smaller size on catalyst surface, which could provide abundant active sites to decreasing the competitive adsorption among reactive gases. Furthermore, the Mo modification promoted the production of more oxygen vacancies, Ce3+ and Oα species, which facilitated the redox recycle and the generation of intermediates. Moreover, the H2-TPR and NH3/CO/O2-TPD analysis illustrated that the reducibility and the capacity for reaction gas adsorption and activation were enhanced, which improved low-temperature activity. The in situ DRIFTS experiment revealed that the E-R and L-H mechanism were existed in NH3-SCR process on CC and CCM3 catalysts. What’s more, the stronger acidity and strengthened E-R mechanism on CCM3 catalyst hindered the adsorption of SO2 and weakened the inhibition effect of competitive adsorption among SO2 and NO. Additionally, both surface lattice oxygen and chemisorbed oxygen could react with Cu+–CO species to produce CO2, the pathway obeyed L-H and MvK mechanism. This work may provide a novel strategy for the treatment of CO and NOx pollutants in industrial flue gas.

Enthalpy of the Cerium (Ce) Chemi-Ionization Reaction and CeO+, CeC+, and CeCO+ Bond Energies Determined by Energy-Resolved Guided Ion Beam Mass Spectrometry Experiments.

Cerium (Ce) oxide, carbide, and carbonyl cation bond energies and the exothermicity of the Ce chemi-ionization (CI) reaction with atomic oxygen were investigated using guided-ion beam tandem mass spectrometry (GIBMS). The kinetic energy dependent product cross sections for reactions of Ce+ with O2, CO, and CO2 and CeO+ with O2, CO, Xe, and Ar were measured using GIBMS. For the reactions of Ce+ with O2 and CO2, CeO+ is formed through an exothermic reaction, whereas CeO+ formation is endothermic in the reaction with CO. This reaction also forms CeC+ and CeCO+ is formed in the reaction of Ce+ with CO2, both in endothermic processes. Reactions of CeO+ with all four gases led to endothermic collision-induced dissociation as well as exchange reactions to form CeO2+ for the O2 and CO reactants. Bond dissociation energies (BDEs) at 0 K were determined through analyses of the kinetic energy dependent cross sections for all endothermic reactions. We determined that the BDEs of CeO+, CeC+, and CeCO+ are 8.46 ± 0.15, 3.93 ± 0.16, and ≥0.25 ± 0.07 eV, respectively, where the CeO+ BDE is a weighted average of 6 independent 0 K threshold measurements. The CeO+ BDE is combined with the ionization energy (IE) of Ce to determine an exothermicity of 2.91 ± 0.15 eV for the Ce + O → CeO+ + e- chemi-ionization reaction. Combined with neutral BDEs from the literature, the thermochemistry determined here also provides IE(CeO) = 5.03 ± 0.12 eV and IE(CeC) = 6.50 ± 0.16 eV. Theoretical calculations for ground and some excited states were performed for CeO+, CeC+, and CeCO+ to provide insight into the bonding and a comparison with the experimentally determined BDEs for each molecule.

Influence of iron doping in mesoporous ceria on the physicochemical properties and catalytic activity in styrene oxidation

A series of nanosized Fe-Ce binary oxides (2, 5, 10, 20, and 30 wt% Fe) and pure oxides of Fe and Ce were prepared by the template-assisted coprecipitation method and evaluated for styrene oxidation. The synthesised binary oxides were investigated by Powder X-ray diffraction(PXRD), N2-physisorption, X-ray fluorescence (XRF), Field emission scanning electron microscopy (FE-SEM), Highresolutiontransmission electron microscopy (HR-TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), Ultraviolet–Visiblediffuse reflectance spectroscopy (UV–Vis DRS), X-ray photoelectron spectroscopies (XPS), and Hydrogen-temperature programmed reduction (H2-TPR). In particular, the influence of quantity of doped iron on the structure, phase composition, surface morphology, reducibility, and the catalytic performance of ceria is deeply investigated. All the synthesized Fe-doped ceria catalysts exhibited the formation of solid solutions, but a little α-Fe2O3 segregated on the surface of ceria at 20 and 30 wt% Fe doped ceria. Among all Fe-Ce binary oxides, the 10 wt% Fe-doped ceria catalyst demonstrated superior efficiency due to its optimal Fe content which achieved the high surface area, lattice oxygens, reducibility, and low crystallinity, as confirmed by BET (Brunauer-Emmett-Teller) measurements, XPS, H2-TPR and powder XRD analysis, respectively. To optimize the reaction conditions, effect of several experimental variables, such as reaction temperature, duration, catalyst quantity, styrene/tert-Butyl hydroperoxide (TBHP) mole ratio, and solvent polarity were investigated. Furthermore, the catalyst stability and consistent activity were confirmed by testing six reusability cycles.

Constructing and Investigating a Ceria-Based Electro-Chemo-Resistivity Switch

Coupling between an electrochemical reaction and a functional material property has been termed electro-chemo-X, or EC-X, where X can refer to mechanical, optical, magnetic, or thermal properties. Recently, our group has demonstrated a two-terminal electro-chemo-mechanical (ECM) membrane actuator operating under ambient conditions and containing a Ce0.8Gd0.2O1.9 (20GDC) solid electrolyte (SE) layer sandwiched between two Ti oxide/Ce0.8Gd0.2O1.9 (Ti-GDC) nanocomposite thin films. Reducing one nanocomposite film while oxidizing the other was observed to produce reversible volume change thereby driving actuator operation. Here, we use the same electrolyte and nanocomposite layers to further explore the EC-X effect: we present, as proof-of-concept, a functioning, three-terminal, thin film based EC-electrical switching device operating at room temperature.The stacked lamellar structure which comprises the device (Figure 1) was fabricated by first depositing, using magnetron sputtering, a ~200nm thick layer of Ti metal on a sapphire substrate. This was followed by patterning with photolithography and etching, using a commercial, buffered oxide etch solution, thereby creating a 1mm wide channel. The resulting bottom electrode pair ("source" and "drain"), which could be temporarily shorted together when necessary, were subsequently covered by the WB/SE/RV stack, where the same co-sputtered, ~200nm thick Ti-GDC nanocomposite (<40nm grain size; 39at% Ti) was used for both the working body (lower: WB) and the reservoir (upper: RV) layers; a ~400nm thick 20GDC layer served as the SE. Upon WB deposition, the 1mm channel between the source and drain electrodes was filled with the nanocomposite material. The upper electrical contact, a ~200nm Ti layer, covered the RV, and using the same photolithography and etching process already described, the top "gate" electrode was defined. To avoid oxidation of the ion reservoir (RV) surface by atmospheric oxygen during device operation, a ~500 nm thick Ta-oxide layer was deposited by reactive magnetron sputtering and patterned by lift-off techniques.We find that following two hours application of -/+ 6V bias between the "gate" and (temporarily shorted) "source" / "drain" electrodes under ambient conditions, the average change in ohmic resistance of the WB in the 1mm channel upon reversal of electrode bias was determined, by cyclic voltammetry between the source and drain electrodes, to be 6.5 ±1.8Gohm with statistical uncertainty based on at least 3 cycles, 5 samples. Negative "gate" bias produced the lower resistance values. The low resistance state decayed during approx. 24 hours, as monitored by cyclic voltammetry. Raising the temperature above ambient (333K) further reduced resistance. We interpret these observations as follows: Negative bias voltage application to the "gate" produces a gradient of the chemical potential of diffusing oxygen ions at the SE-WB interface. This gradient leads to the injection of ions into the WB, thereby promoting an electrochemical oxidation reaction. The nanocomposite in the 1mm channel decays from the more highly conductive state during approximately twenty-four hours. Reversing the bias polarity extracts ions from the WB, with the opposite results. To complement the findings of the E-field promoted oxidation, we performed annealing at 633K for 23 hours in air of a device which lacked the SE/RV/"gate" electrode/Ta-oxide layers, i.e. the WB was uncovered. We observed an increase of two orders of magnitude in the conductivity of the nanocomposite in the 1mm channel, which then relaxes with time. As a control, the same thermal treatment was conducted under vacuum. In this case no change was observed in channel conductivity.A possible explanation for how oxidation increases the Ti-GDC nanocomposite conductivity may be found in a suitable variant of the space charge model [1, 2]. We note that nanocrystallinity introduces such a high density of interfaces/grain boundaries that total conductivity may become interfacially controlled. Grain boundaries in doped ceria lack long range order and are relatively rich in oxygen vacancies (VO) and Ce3+, which, along with a space charge zone which forms for charge neutrality, produce a blocking effect for ion conduction. Oxidation of Ce3+ => Ce4+ leads to a lowering of total real charge, causing the spatial extent of the space charge zone to shrink as well. Finally, this succeeds in lowering the potential barrier for ion diffusion across the grain boundary, which increases the overall conductivity. Reduction of the Ti-GDC nanocomposite produces the opposite effect.[1] S. K. Kim, S. Khodorov, I. Lubomirsky, S. Kim, Phys Chem Chem Phys 2014, 16, 14961, https://doi.org/10.1039/c4cp01254b[2] S. Kim, J. Maier, J. Elecrochem. Soc. 2002, 149, J73, https://doi.org/10.1149/1.1507597 Figure 1

Cerium-based sorbent with 100% Ce(III) and high dispersion for enhanced phosphate removal from wastewater

Under the double pressure of eutrophication and phosphorus deficiency, there is an urgent need to remove excess phosphate from wastewater efficiently. Preparing cerium-based materials with excellent application potential inevitably leads to Ce(III) oxidation to Ce(IV), which reduces the phosphate adsorption effect and restricts its development. To solve this problem, we introduced a protective agent and successfully synthesised cerium-modified activated carbon sorbent containing 100 % Ce(III) during the synthesis process. Compared with CeAC without a protecting agent, CeAC-A contained more Ce(III) (100 %) and exchange groups (–OH accounted for 82.76 %), achieving an adsorption capacity of up to 448.57 mg-P/g Ce, improving of 4.3 times. At the same time, the size of the cerium active component was reduced from the micron level to the nanometer level, and the mass transfer rate was significantly improved. In addition, with the enormous specific surface area and well-developed pore structure of activated carbon, it showed high dispersibility, with P/Ce molar ratio as high as 2.03, which is 1.1–4.8 times higher than other cerium-based adsorbents. Phosphate was removed primarily through electrostatic attraction and ligand exchange. In treating municipal wastewater with complex water quality, CeAC-A showed strong selectivity, a wide range of adaptability and easy repeat regeneration, making it a promising adsorbent for phosphate uptake from wastewater.

CeCoaOx catalysts derived from metal-organic frameworks for enhancing catalytic toluene oxidation by tuning surface oxygen property

Rod-shaped CeCoaOx catalysts with varying Co doping ratios (a = 0.012, 0.017, 0.022) were synthesized by calcinating the Ce-MOF, prepared using a water bath and trimesic acid as an organic ligand. This method ensured a high degree of elemental mixing, abundant pore channels and a large specific surface area are all beneficial for enhancing toluene catalytic oxidation activity. Raman, XPS, and catalytic activity tests confirmed strong interactions between the Ce and Co oxides, promoting the formation of more Ce3+ and oxygen vacancies. Among these catalysts, CeCo0.012Ox exhibited superior catalytic performance for toluene oxidation under weight hourly space velocity of 40,000 mL·g−1·h−1. The temperature at toluene conversion of 10 %, 50 % and 90 % was 140, 205 and 226 °C, respectively, which was 61, 12 and 14 °C higher than those over pure phase CeO2. CeCo0.012Ox also demonstrated excellent activity stability under high humidity (10 vol%H2O). H2-TPR, O2-TPD and in situ DRIFTS also revealed that surface-absorbed oxygen species played a crucial role in catalytic activity, with CeCo0.012Ox benefiting from abundant oxygen vacancies and effective oxygen species mobility.

Facile Synthesis of Sodium Alginate (SA)-Based Quaternary Bio-Nanocomposite (SA@Co-Zn-Ce) for Antioxidant Activity and Photocatalytic Degradation of Reactive Red 24

This study introduces a new strategy for the environmentally friendly catalytic degradation of Reactive Red 24 (RR24) dye using sunlight. We developed a cost-effective quaternary nanocomposite by immobilizing a sodium alginate biopolymer over bioengineered Co-Zn-Ce nanoparticles, forming an SA@Co–Zn–Ce nanocomposite (where SA means sodium alginate). This composite also demonstrated an exceptional antioxidant potential of approximately 89%, attributed to the synergistic effect of sodium alginate and green-synthesized Co–Zn–Ce nanoparticles (biosynthesized using Ocimum sanctum leaf extract as a reducing agent). Scanning electron microscopy revealed grain sizes of 28.6 nm for Co–Zn–Ce NPs and 25.59 nm for SA@Co–Zn–Ce nanocomposites (NCs). X-ray diffraction showed particle sizes of 16.87 nm and 15.43 nm, respectively. Co–Zn–Ce NPs exhibited a zeta potential of 1.99 mV, whereas the sodium alginate-anchored Co–Zn–Ce showed −7.99 mV. This indicated the entrapment of negatively charged ions from sodium alginate, altering the surface charge characteristics and enhancing the photocatalytic degradation of RR24. Dynamic light scattering revealed an average particle size of approximately 81 nm for SA@Co–Zn–Ce NCs, with the larger size due to the influence of water molecules in the colloidal solution affecting hydrodynamic diameter measurement. The SA@Co–Zn–Ce NCs exhibited a CO2 adsorption capacity of 3.29 mmol/g at 25 °C and 4.76 mmol/g at 40 °C, indicating temperature-dependent variations in adsorption capabilities. The specific surface area of Co–Zn–Ce oxide NPs, measured using Brunauer–Emmett–Teller (BET) analysis, was found to be 167.346 m2/g, whereas the SA@Co–Zn–Ce oxide nanocomposite showed a surface area of 24.14 m2/g. BJH analysis revealed average pore diameters of 34.60 Å for Co–Zn–Ce oxide NPs and 9.26 Å for SA@Co–Zn–Ce oxide NCs. Although the immobilization of sodium alginate on Co–Zn–Ce oxide NPs did not increase the adsorption sites and porosity of the composite, as evidenced by the N2 adsorption–desorption isotherms, the SA@Co–Zn–Ce oxide NCs still demonstrated a high photocatalytic degradation efficiency of RR24.

Synthetic opal decorated by Co and Ce oxides as a nanoreactor for the catalytic CO oxidation

Macroporous synthetic opal grown from non-porous silica nanoparticles and decorated by Co and Ce oxides was applied for the catalytic CO oxidation in the inert (TOX) and H2-rich (PROX) gas mixtures. Prepared materials were studied by methods of SEM, TEM, EDX, XRD, XPS and FTIR spectroscopy. The relationship between synthesis conditions, structure, and catalytic behavior of composites is discussed. The best Co-O-Ce interaction and the highest activity in the CO-TOX and PROX are achieved when cerium oxide was added prior to the addition of cobalt oxide. In this case highly dispersed particles of Co3O4 and CeO2 are located in close proximity on the silica surface and anchored between the opal spheres. The use of Co/Ce decorated synthetic opal as a nanoreactor for the catalytic oxidation of CO in the H2 excess makes it possible to achieve 99.5 % conversion of CO at 150°C, the high efficiency and selectivity of the process are maintained in multiple cyclic tests in heating and cooling modes. The synergistic activity of Co and Ce oxides was observed when they both were located together on the outer surface of non-porous SiO2 nanospheres. These results are superior to known data for other catalysts based on Co and Ce oxides.

Block catalysts, based on Ce and Mn oxides and cordierite ceramics, for ozone decomposition

Block catalysts, based on Ce and Mn oxides and cordierite ceramics, for ozone decomposition

Elucidation of synergism in Ce-Zr/SBA-15 mesoporous catalysts and the effects on the activity in selective glycerol to lactic acid reaction

The continued conversion of glycerol to value-added chemicals is essential in ensuring the sustainable development of the biodiesel industry. Selective catalytic oxidation of glycerol to lactic acid provides an alternative approach to valorizing glycerol. A mesoporous SBA-15 supported mixed-metallic oxide catalyst is deemed essential to selectively produce lactic acid in this mixed parallel and multi-step reaction. SBA-15-supported bimetallic Ce and Zr oxides were proved to be highly efficient catalysts for the selective glycerol oxidation into lactic acid in base-free media. The synergism between Ce and Zr in the bimetallic oxide compounds could enhance the creation of oxygen vacancies in the catalyst via the reduction of Ce4+ to Ce3+. The 2:1CeZr/SBA-15 catalyst exhibited prominent catalytic activity in selectively oxidizing glycerol to lactic acid, with a glycerol conversion of 91.8% and a lactic acid yield of 35.1%. This work achieved superior catalytic performance compared to previously conducted studies, primarily due to the significantly higher initial glycerol concentration employed in this study. To ascertain the intrinsic active sites of the catalyst, the physicochemical properties of the catalyst were thoroughly examined using BET, FTIR, XRD, FESEM, TEM, CO2-TPD, O2-TPD, and H2-TPR analysis. This work concluded that the synergistic interaction of the active sites, which led to the formation of active oxygen species, facilitated primary dehydrogenation of the terminal -OH bond in glycerol. Hence, in this work, a plausible glycerol conversion mechanism over the 2:1CeZr/SBA-15 catalyst was also proposed.

Assessing tungsten-based electrodes coated with W and Ce oxides for pH sensing applications

This study assessed tungsten-based materials with and without dispersed CeO2 for potential use as pH sensors. Specifically, three types of tungsten electrodes were characterized: tungsten electrodes without CeO2 but with native oxide, tungsten electrodes without CeO2 that were oxidized, and a tungsten electrode containing dispersed CeO2 that was oxidized, resulting in a mixture of WO3, CeO2, and Ce2O3. The characterization was performed using SEM/EDAX, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques. The oxide coatings showed higher oxygen contents compared to native tungsten. XPS confirmed the presence of a thick layer of WO3 and cerium oxides. The electrodes exhibited good reproducibility and stability in pH measurements. A linear relationship was found between the open circuit potential and pH, with slopes of 44.9, 40.8, and 46.9 mV pH−1 for native oxide, WO3, and WO3 with CeO2 and Ce2O3, respectively. The latter showed the highest sensitivity and lowest hysteresis. The response times ranged from 14.5–23.5 s and were faster in acidic solutions. Overall, the inexpensive tungsten-based electrodes demonstrated promising capabilities for pH sensing, but in particular ceriated tungsten electrodes.

Oxygen vacancy-engineered P-doped MoO3/Ce2Mo4O15 bimetallic heterojunction nanosheet array for enhanced oxygen evolution reaction

Surface oxygen vacancies in defective metals have the capacity to enhance oxygen evolution reaction (OER) activity but easily suffer from instability and deactivation in continuous electrocatalysts. Heterojunction engineering is important for achieving effective catalysis, but its simultaneous engineering remains a challenge. Therefore, it is necessary to develop an effective heterojunction catalyst to improve the electrocatalytic stability of defective metallic oxygen vacancies. In this work, we report a Ce, Mo bimetallic defective heterojunction P-MoO3/Ce2Mo4O15@NF-1 via a facile one-step hydrothermal method and annealing in a tube furnace. Bimetallic oxide heterojunctions offer several advantages over conventional single-metal heterojunctions, including stable structure, more active sites, faster rates of electron transfer, and less pollution of the environment. Meanwhile, P-doped catalyst could enhance the metallicity significantly. In addition, the prepared catalyst P-MoO3/Ce2Mo4O15@NF-1 showed extraordinary catalytic activity for OER in alkaline media. The overpotential and Tafel slope of the catalyst at a current density of 50 mA cm-2 were 270 mV and 87.27 mV dec‑1, respectively. It maintains an impressive balance between electrocatalytic activity and stability. This research explores the co-effects of Ce and Mo bimetallic oxide in defective electrocatalysts and also provides ideas for designing OER catalysts with defective metal heterojunctions.

Degassing-Driven Oxidation Promotes HREE Enrichment in South China Granites

Abstract Heavy rare earth elements (HREEs) are critical metals in advanced technologies. Here, we report unusual REE patterns and O–Hf–Nd isotopic compositions of composite granites from the Zhaibei HREE deposit. The complex consists of two Mesozoic granites with ages of 188 and 170 Ma. The older granites are characterized by higher HREE contents and negative Ce anomaly and contain cerianite veinlets. Their REE-rich minerals also show strong Ce depletion, indicating a high oxidation state. Magmatic zircons have variables δ18O (6.1–9.4‰) and εHf(t) (−6 to 0), towards a depleted mantle contribution. Lower δ18O (~5.4 vs 6.6‰) and higher εNd(t) (approximately −3 vs −11) values in the altered apatite rim compared to the core and primary phase result from subduction-derived fluids. In contrast, the younger granites have lower REE contents and lack a Ce anomaly. They show mantle-derived Nd (apatite εNd(t) = 1–2), Hf (zircon εHf(t) = 3–8), and O (zircon and apatite δ18O = 4.6–5.7‰) isotopic compositions. Therefore, we infer that a REE-rich fluid migrated from the flat subducting slab and flushed the subsolidus granitic mush in the Early Jurassic. This caused volatile saturation and degassing, leading to the generation of highly oxidized fluids. These processes may cause temporary oxidizing conditions in post-magmatic hydrothermal stages, resulting in the oxidation of Ce3+ to Ce4+. The resulting Ce fractionation from other REE3+ promoted HREE enrichment in the granites.

Influence of Ce and Ti oxides doping on the PMMA polymer: structural, optical, THz, dielectric, and antimicrobial characteristics

Influence of Ce and Ti oxides doping on the PMMA polymer: structural, optical, THz, dielectric, and antimicrobial characteristics

The adsorption of cerium on synthetic δ-MnO2: Implications for Ce uptake behavior of hydrogenetic and early diagenetic ferromanganese nodules from the Western Pacific

Cerium (Ce) anomalies can be used to distinguish diagenetic and hydrogenetic nodules, making them an important discriminator for the genesis of marine ferromanganese nodules. To understand the enrichment and adsorption mechanisms of Ce in different types of ferromanganese nodules, we conducted mineralogical and geochemical studies on ferromanganese nodule layers formed through both hydrogenetic and early diagenetic processes as well as adsorption experiments on synthetic δ-MnO2 to monitor the Ce uptake during the different processes. The major and trace element contents of natural ferromanganese nodule layers were investigated by SEM, EPMA and LA-ICP-MS analysis. The marine nodule studied in this study consisted of a core of fish tooth and a rim that could be divided into the hydrogenetic (type I) and early diagenetic (type II) layers based on their mineralogy and Mn/Fe ratios. The Mn oxide mineral assemblage is composed of todorokite, buserite, birnessite, and vernadite (δ-MnO2) and occurred in both type I and II layers. The type I layer has laminated structures with a low Mn/Fe ratio (1.1–3.2; averaging at 1.7), and low Cu, Ni and Mg contents consistent with a hydrogenetic genesis. The type II layer has a columnar and stromatolitic structure with a high Mn/Fe ratio (5.1–54.0; averaging at 23.3) and high Cu, Ni and Mg contents that are similar to early diagenetic nodules. The ΣREE contents in type I and type II layers are 1405–3506 ppm (averaging at 2091 ppm) and 199–1232 ppm (averaging at 674 ppm), respectively, indicating that the REE is enriched in the hydrogenetic type I layers. Strong positive Ce anomalies are present type I layers ranging from 1.2 to 2.5 (averaging 1.9), but only slightly positive are seen in type II ranging from 0.4 to 2.4 (averaging at 1.0). Synthetic experiments to monitor the Ce uptake process show that Ce can be adsorbed onto δ-MnO2 with the XRD and FTIR patterns suggesting that the structure of δ-MnO2 did not change significantly, consistent with Ce behavior in hydrogenetic nodules. The results suggest that Ce is predominantly concentrated in hydrogenetic nodules in an oxic environment, whereas in the early diagenetic layer, there is less oxidation and fixation of Ce due to the suboxic conditions. Our findings are consistent with Ce anomalies in marine Fe-Mn nodules being the result of Mn oxide oxidation adsorption and then fixation (oxidation) after adsorption.

A Gd-doped ceria/TiOx nanocomposite as the active layer in a three terminal electrochemical resistivity switch.

Coupling between an electrochemical reaction and a functional material property has been termed electro-chemo-X, or EC-X, where X can refer to mechanical, optical, magnetic or thermal properties. Recently, our group has demonstrated a two-terminal electro-chemo-mechanical (ECM) membrane actuator operating under ambient conditions and containing a Ce0.8Gd0.2O1.9 solid electrolyte layer sandwiched between two Gd-doped ceria/TiOx nanocomposite thin films. Reducing one nanocomposite film while oxidizing the other was observed to produce reversible volume change thereby driving membrane actuator operation. Here, we use the same electrolyte and nanocomposite layer pair (the upper one as the ion reservoir and the lower, as the active layer) to further explore the EC-X effect. We demonstrate the suitability of the nanocomposite for a three-terminal, thin film-based resistivity switch. We find that application of ±6 V (<60 kV/cm) bias to the gate terminal for two hours under ambient conditions changes the nanocomposite conductivity in the channel between the source and drain by at least 40%. When the bias is negative, the active layer remains in a more highly conductive state for approximately twenty-four hours. Impedance spectroscopy and cyclic voltammetry reveal oxygen ion migration taking place between the active layer and the reservoir. X-ray photoelectron spectroscopy indicates that, in the absence of negative gate bias, thermal oxidation of Ce+3 - > Ce+4 is similarly effective in leading to increased nanocomposite conductivity, while reduction produces the opposite effect. With the expectation that the response time can be significantly shortened, the proposed resistivity switch may be suitable for future applications such as sensors, neuromorphic computing or spintronics.

Magnetic field-assisted adsorption of phosphate on biochar loading amorphous Zr–Ce (carbonate) oxide composite

For metal-based phosphate adsorbents, the dispersity and utilization of surface metal active sites are crucial factors in their adsorption performance and synthesis cost. In this study, a biochar material modified with amorphous Zr–Ce (carbonate) oxides (BZCCO-13) was synthesized for the phosphate uptake, and the adsorption process was enhanced by magnetic field. The beside-magnetic field was shown to have a better influence than under-magnetic field on adsorption, with maximum adsorption capacities (123.67 mg P/g) 1.14-fold greater than that without magnetic field. The beside-magnetic field could also accelerate the adsorption rate, and the time to reach 90% maximum adsorption capacity decreased by 83%. BZCCO-13 has a wide range of application pHs from 5.0 to 10.0, with great selectivity and reusability. The results of XPS and ELNES showed that the "magnetophoresis" of Ce3+ under the magnetic field was the main reason for the enhanced adsorption performance. In addition, increased surface roughness, pore size and oxygen vacancies, enhanced mass transfer by Lorentz force under a magnetic field, all beneficially influenced the adsorption process. The mechanism of phosphate adsorption by BZCCO-13 could be attributed to electrostatic attraction and CO32–dominated ligand exchange. This study not only provided an effective strategy for designing highly effective phosphate adsorbents, but also provides a new light on the application of rare earth metal-based adsorbent in magnetic field.

Thermal decomposition behavior of Mountain Pass rare earth concentrate in air/CO2 atmosphere

The Mountain Pass mine is recognized as one of the world’s primary sources of rare earth minerals. These rare earth minerals mainly consist of bastnaesite and a small amount of monazite phosphate, which cannot be decomposed and recovered through conventional oxidative roasting and hydrochloric acid leaching process. An efficient, clean, and economical process called the "combined method" was proposed for the utilization of the Mountain Pass mine to extract rare earths from Mountain Pass rare earth concentrate (MPREC). The main steps of this process include weak oxidation atmosphere roasting, step leaching of hydrochloric acid, solid-liquid separation, the monazite slag with sulfuric acid roasting water leaching, etc. In this paper, the roasting process of MPREC under a weak oxidation atmosphere was investigated. The study examines the thermal decomposition kinetics, phase transition process, and leaching behavior of MPREC in air/CO2 atmosphere. Results show that, the activation energy (Ea) for MPREC thermal decomposition in air and CO2 atmosphere are 146 and 320 kJ/mol, respectively. At temperature above 500 °C in air or above 700 °C in CO2 atmosphere, REOF are generated from bastnaesite through an in-situ reaction with CaO, which is decomposed from CaCO3, to form CaF2 and rare earth oxide (REO). Thus, F is regulated into solid phase. In an oxidizing atmosphere, the thermal decomposition of bastnaesite is accompanied by the rapid oxidation of Ce(Ⅲ). In contrast, the oxidation of Ce(Ⅲ) in a CO2 atmosphere is significantly inhibited. At 700 °C, the oxidation rate of Ce in air is 74.09%, while in a CO2 atmosphere, it is only 33.83%. The hydrochloric acid leaching experiment shows that, the leaching rate of rare earth after roasting at 600 °C under an air atmosphere reaches to 82.9%, and it reaches 87% after roasting at 800 °C under a CO2 atmosphere. The reduction of Ce oxidation in a weak oxidizing atmosphere significantly improves the leaching rate of Ce.