Valence Metal Ions Research Articles

Surface oxygen vacancy regulation strategy enhances the electrochemical catalytic activity of CoFe2O4 cathode for solid oxide fuel cells

Oxygen vacancies are crucial for enhancing oxygen ion transport in solid-state materials. Therefore, an approach was established to efficiently adjust the surface oxygen vacancy concentration in the solid oxide fuel cell (SOFC) cathodes. This method employs NaBH4 solution to capture lattice oxygen on the cathode surface, enabling precise control over both the surface oxygen vacancy concentration and the transition metal ion valence states in spinel CoFe2O4 (CFO) by modulating the NaBH4 treatment duration. The results indicate that CFO-10, treated with NaBH4 solution for 10 min, exhibits optimal electrochemical catalytic activity. This enhancement is primarily attributed to the improved oxygen adsorption-dissociation and charge transfer processes. At 750 °C, CFO-10 shows a polarization resistance (Rp) of 0.032Ω cm2, representing a reduction of 42.8 % compared to CFO. Additionally, CFO-10 achieves a peak power density (PPD) of 923 mW·cm−2, representing a 78.5 % increase compared to CFO. This study provides new insights for optimizing SOFC spinel oxide cathode performance and opens a promising avenue for the development of other high-performance catalytic materials.

Oxygen Vacancy Sites Enable Efficient Photocatalytic Oxidation of Nitric Oxide: The Role of W/Mo Valence Transition in Bi2W(Mo)O6‐x

AbstractOxygen vacancy (Ov) sites play a critical role in the activation and deep oxidation of nitric oxide (NO). However, controlling the concentration and type of Ov remains a significant challenge. In this study, Bi2W(Mo)O6‐x is investigated as a model system and demonstrates that increasing the concentration of Ov substantially enhances the efficiency of air NO removal. Increasing the Ov concentrations in Bi2WO6‐x and Bi2MoO6‐x improves NO removal efficiency ≈12‐ and 11‐fold, respectively, compared to their low‐Ov counterparts. This enhancement is attributed to improved adsorption and activation of NO/O2 molecules, better separation and transfer of photogenerated carriers, and increased visible light absorption. Notably, Bi2WO6‐x remains highly stable over ten recycling tests for continuous air NO deep photooxidation, while Bi2MoO6‐x shows a 43.5% decrease in efficiency after ten runs. This sustained performance is attributed to stable Ovs without changes in metal ion valence, unlike Bi2MoO6‐x, where instability arises from the reduction of Mo6+ to Mo4+. In situ DRIFTS reveals possible pathways for the deep photooxidation of NO to nitrate (NO3−). This study provides valuable insights into designing high‐performance, durable catalysts by effectively controlling Ov concentration and type, paving the way for efficient photocatalytic air purification technologies.

Superactivity of Bimetallic CuFeO2 Submicron Particles towards Selective Proteolysis, Depending on their Surface Hydroxyls.

Nano bimetallic oxides as nanoproteases have the great advantages in the heterogeneous hydrolysis of proteins. Here, we report that bimetallic delafossite CuFeO2 submicron particles (CuFeO2 SMPs) display a high protease activity towards selective cleavage of peptide bond involving hydrophobic residue at 25 °C. CuFeO2 SMPs have excellent regeneration performance with high structural stability. The strong Lewis acidity of Fe3+ and the strong nucleophilicity of Cu+ bound hydroxyl groups are both necessary for the high protease activity of CuFeO2 SMPs. Low-valent metal ion has a great advantage in that low-valent Cu+ bound hydroxyl has strong nucleophilicity, resulting in promotion of protein hydrolysis via high-efficient bimetallic catalysis. This study provides evidence that the protease activity of CuFeO2 SMPs depends on metal ion-bound hydroxyls on their surface. Our findings highlight that the valence of metal ions in artificial protease and their surface hydroxyls are two important factors that determine their catalytic efficiency.

Transition Metal (Molybdenum)-Doped Drug-like Conformational Nanoarchitectonics with Altered Valence States (Mn2+/Mn4+ and Mo5+/Mo6+) for Augmented Cancer Theranostics.

Despite the advancements in cancer therapy, delivering active pharmaceutical ingredients (APIs) using nanoparticles remains challenging due to the failed conveyance of the required drug payload, poor targeting ability, and poor biodistribution, hampering their clinical translation. Recently, the appropriate design of materials with intrinsic therapeutic functionalities has garnered enormous interest in the development of various intelligent therapeutic nanoplatforms. In this study, we demonstrate the fabrication of transition metal (molybdenum, Mo)-doped manganese dioxide (MnO2) nanoarchitectures, exhibiting diagnostic (magnetic resonance imaging, MRI) and therapeutic (chemodynamic therapy, CDT) functionalities. The facile hydrothermal approach-assisted Mo-doped MnO2 flower-like nanostructures offered tailorable morphologies in altered dimensions, precise therapeutic effects, exceptional biocompatibility, and biodegradability in the tumor microenvironment. The resultant defects due to doped Mo species exhibited peroxidase and oxidase activities, improving glutathione (GSH) oxidation. The two sets of variable valence metal ion pairs (Mn2+/Mn4+ and Mo5+/Mo6+) and their interplay could substantially improve the Fenton-like reaction and generate toxic hydroxyl radicals (•OH), thus achieving CDT-assisted antitumor effects. As inherent T1-MRI agents, these MnO2 nanoparticles displayed excellent MRI efficacy in vitro. Together, we believe that these conformational Mo-doped MnO2 nanoarchitectures with two pairs of variable valence states could potentiate drugless therapy in pharmaceutics.

Controlled Sol-Gel Transitions of Metal-Organic Membrane-Enveloped Cellulose Nanofibrils via Metal Coordination in Aqueous Media.

We report a metal coordination-driven sol-gel transition system where cellulose nanofibrils are enveloped by a rationally designed metal-organic membrane (MOM) in an aqueous medium. Specifically, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized bacterial cellulose (TOBC) is encapsulated within an MOM comprising Zn2+ and the chelator phytic acid (PA), denoted TOBCMOM. Using the DLVO theory, we elucidate how tuning the metal ion valence in TOBCMOM modulates the sol-gel transition by controlling interfibrillar attractive forces. Notably, TOBCMOM fluids exhibit relaxation times consistent with the Kohlrausch-Williams-Watts (KWW) function. Significantly, we demonstrate reversible, sustainable sol-gel transitions in TOBCMOM under stepwise mechanical strain. This facile approach enables rheological tailoring of aqueous media, promising for the development of advanced stimuli-responsive smart fluids for applications in cosmetics, food science, and pharmaceutical formulations.

Building mesoporous channels in lignin-derived microporous carbons to remold the electrochemical behaviors of supercapacitors

The mesoporous structure of the porous carbon electrodes could promote the in-pore diffusion of electrolyte ions. However, the effect of large mesopores with pore sizes larger than 20 nm in the microporous carbons on the diffusion of different electrolyte ions remains unclear. Herein, porous carbon electrodes with mesopores sizes of 23 nm and 40 nm, respectively, are prepared using the ZnO as a hard template. The electrochemical behavior of porous carbon electrodes with large mesopores and microporous carbon electrodes in different sulfate electrolytes are studied and compared. Electrochemical impedance spectroscopy (EIS) tests demonstrate that the wide and short diffusion path provided by large mesopores can reduce the hindrance of multivalent metal cations and SO42−, thus significantly improving the diffusion efficiency of the multivalent metal sulfate cations. Due to the small size and low valence of monovalent metal ions, it is difficult for large mesopores to promote the diffusion of monovalent metal sulfate ions. Therefore, the large mesopores have little impact on the diffusion of monovalent metal ions, whereas they significantly enhance the diffusion of multivalent metal ions.

Mn-Ce solid solution growth on Mn2O3 surface to form heterostructure catalysts with multiple active sites for toluene degradation

A solid solution-heterostructure catalyst with abundant active sites was successfully constructed in this study by in situ growth of Mn-Ce solid solution on the surface of Mn2O3. The solid solution structures with optimum physical and chemical properties were synthesized initially by controlling the Mn-Ce ratios. Subsequently, the reaction time was controlled to realize the orderly growth of the solid solution on the Mn2O3 surface. The catalyst (M−CeMn0.5) with solid solution-heterostructure formed by the reaction of Ce3Mn1 and Mn2O3 for 0.5 h could reach more than 90 % toluene degradation rate at 183 °C and was operated continuously for 15 h without deactivation. XRD showed that the appropriate reaction time resulted in the active components on the catalyst surface exhibiting lower crystallinity and reduced grain size. The reduction capacity (2.28 → 10.47 mmol/g) and the mobility of lattice oxygen were significantly enhanced in the M−CeMn0.5 catalyst compared to the Mn-Ce solid solution. Meanwhile, a high content of low valent metal ions (Ce3+/Ce4+ 0.33, Mn3+/Mn4+ 1.64) and reactive oxygen species (Oads/Olatt 0.53) were also present on the catalyst surface. The DFT demonstrated that the Mn atoms and Mn-O bridge sites on the solid solution surface exhibited high adsorption energy values for toluene (−0.8402/-0.8406 eV) and oxygen (−1.6546/-1.661 eV) molecules. The TEM indicated that lattice distortion and oxygen vacancies were formed at the interface between the solid solution and Mn2O3 at the interface. The synergy of multiple active sites favors the generation of reactive oxygen species and thus promotes p-methyl dehydrogenation. Meanwhile, the high mobility of lattice oxygen facilitates the breakage of benzene ring. This study provides a new strategy for the synthesis of efficient Mn-Ce-based catalysts.

Engineering VOx structure by integrating oxygen vacancies for improved zinc-ion storage based on cation-doping regulation with electric density.

Aqueous zinc-ion batteries (ZIBs) have attracted enormous attention for future energy-storage devices owing to their high theoretical capacity and environmental friendliness. However, obtaining cathodes with a high specific capacity and fast reaction kinetics remains a huge challenge. Herein, Cu-VOx material with a thin sheet microsphere structure composed of nanoparticles was prepared by a simple hydrothermal reaction, which improved reaction kinetics and specific capacity. Pre-embedding Cu2+ into V2O5 to introduce abundant oxygen vacancies extended the interlayer distance to 1.16 nm, weakened the effect of the V-O bonds, and improved the electrical conductivity and structural stability. At the same time, the influence of different valence metal ions (M = K+, Cu2+, Fe3+, Sn4+, Nb5+, and W6+) pre-embedded in V2O5 was studied. Benefiting from a large interlayer spacing, high electrical conductivity, and excellent structural stability, the Cu-VOx electrode demonstrated a high specific capacity of 455.9 mA h g-1 at 0.1 A g-1. Importantly, when the current density was increased to 6 A g-1, the Cu-VOx electrode still achieved a high specific capacity of 178.8 mA h g-1 and maintained a high capacity retention of 76.5% over 2000 cycles.

Dioxomolybdenum(VI) and oxovanadium(IV) organo-complexes of tartrato-dihydrazone ligand as reactive antitumor and antimicrobial agents. ctDNA interactive nature

Form the condensed > C = O of salicyldehyde with -NH2 of tartric dihydrazide, a new chelating bis-tridentate tartrato-dihydrazone ligand (HTL) was constructed. Due to the high applicability of metal aryl/aroyl-hydrazone complexes, its ligational behavior versus two high valent dioxo/oxo-metal ions of MoO22+ and VO2+ ions was explored to build up two new organo-dimetallic complexes (MoO2TL and VOTL, respectively). Chemical structure elucidation of HTL, MoO2TL, and VOTL was formulated through the analyses of different spectroscopic tools, along with the thermogravimetric and micro-elemental analyses, the conductance and magnetic measurements.The inhibition strength of the current compounds against the growth of various entitled microorganisms and tumor cell lines of humans was evaluated regarding the role action of the high valent metal ions (MoO22+ and VO2+ ions in their metallodrug candidates). Both MoO2TL and VOTL displayed a significant inhibition action more than that of HTL based on the inhibition zone areas in mm for the microbial series and the half inhibitory concentration in µM (IC50) for the tumor cell lines of their cells’ growth.Also, the interactive and binding nature of HTL, MoO2TL, and VOTL with calf thymus DNA (ctDNA) was evaluated viscometric and spectrophotometric titrations. The interactive modes of HTL, MoO2TL, and VOTL was estimated within the chromism type, the Gibb’s free energy, and binding constant values (ΔGb≠ and Kb, respectively), with reported magnitudes ΔGb≠ (Gibb’s free energy) = -42.06, −48.11 and −47.67 kJ mol−1, and Kb (binding constant) = 14.09, 17.11 and 16.89 × 107 mol−1 dm3, respectively. The bio-reactivity of both MoO2TL and VOTL complexes was modified compared to that of HTL towards ctDNA with covalent/non-covalent and replacement binding interaction.

Improving strength and toughness of graphene film through metal ion bridging

The fangs, jaws, and mandibles of marine invertebrates such as Chiton and Glycera show excellent mechanical properties, which are mostly contributed to the interactions between metal (Fe, Cu, Zn, etc.) and oxygen-containing functional groups in proteins. Inspired by these load-bearing skeletal biomaterials, we improved tensile strength and toughness of graphene films through bridging graphene oxide (GO) nanosheets by metal ions. By optimizing the metal coordination form and density of cross-linking network. We revealed the relationship between mechanical properties and the unique spatial geometry of the GO nanosheets bridged by different valence metal ions. The results demonstrated that the divalent metal ions form tetrahedral geometry with carboxylate groups on the edges of the GO nanosheets, and the bond energy is relatively low, which is helpful for improving the toughness of resultant graphene films. While the trivalent metal ions are easily to form octahedral geometry with the GO nanosheets with higher bond energy, which is better for enhancing the tensile strength of graphene films. After reduction, the reduced GO (rGO) film bridged by divalent metal ions shows 43% improvement in toughness, while the rGO film bridged by trivalent metal ions shows 64% improvement in tensile strength. Our work reveals the mechanism of metal coordination bond energy and spatial geometry to improve the mechanical properties of graphene films, which lays a theoretical foundation for improving the tensile strength and toughness of resultant graphene films, and provides an avenue for fabricating high-performance graphene films and other two-dimensional nanocomposites.

Alginate-based adsorbents with adjustable slit-shaped pore structure for selective removal of copper ions

Adopting effective and efficient techniques for the treatment of heavy metal pollution in water bodies plays an important role in guaranteeing the quality of water and the sustainable development of water resources. In this study, GO, MMT and SA were used as raw materials to compare the adsorption behaviors of three alginate-based adsorbents crosslinked with different valence metal ions (Ca2+, Fe3+ and Zr4+) on Cu(II). The aerogels were based on sodium alginate as the matrix material with unique slit-shaped pore structures formed by stacking effect of sheets and chemical bonding. It was found that the pore structures of the aerogels were denser and more orderly with the increase of the valence states of the crosslinked ions, and the affinity for Cu(II) in planar configuration was stronger. The Zr4+-GMSA aerogel had the maximum adsorption capacity of 126.68 mg/g and the Kd of Cu(II) was up to 50.80 L/g, which exhibited good preferential adsorption performance. The adsorption mechanism of Mn+-GMSA aerogels on Cu(II) was mainly ionic exchange, surface complexation and physical adsorption, which was explored by combining XPS and EDS characterizations of Mn+-GMSA before and after adsorption. This scheme can provide valuable and meaningful contribution to realize the selective recovery of Cu(II).

Elucidating Electrochemical Energy Storage Performance of Unary, Binary, and Ternary Transition Metal Phosphates and their Composites with Carbonaceous Materials for Supercapacitor Applications

Transition metal compounds (TMCs) are being researched as promising electrode materials for electrochemical energy storage devices (supercapacitors). Among TMCs, transition metal phosphates (TMPs) have good, layered structures owing to open framework and protonic exchange capability among different layers, good surface area due to engrossed porosity, rich active redox reaction sites owing to octahedral structure and variable valance metallic ions. Hence TMPs become more ideal for supercapacitor electrode materials compared to other TMCs. However, TMPs have got some issues like low conductivity, rate performance, stability, energy, and power densities. But these problems can be addressed by making their composites with carbonaceous materials, e.g., carbon nanotubes (CNTs), graphene oxide (GO), graphitic carbon (GC), etc. A few factors like high surface area, excellent electrical conductivity of carbon materials and variable valence metal ions in TMPs caused great enhancement in their electrochemical performance. This article tries to discuss and compare the published data, majorly in last decade, regarding the electrochemical energy storage potential of pristine unary, binary, and ternary TMPs and their hybrid composites with carbonaceous materials (CNTs, GOs/rGOs, GC, etc.). The electrochemical performance of the hybrids has been reported to be higher than the pristine counterparts. It is hoped that the current review will open a new gateway to study and explore the high performance TMPs based supercapacitor materials.

Divalent metal ions under low concentration environment improved the thermal gel properties of egg yolk

To improve the thermal gel properties of egg yolk, the effect of several valence metal ions (K+, Ca2+, Mg2+ and Fe3+) with different concentrations (0-0.72%) on the rheological, gel, and structural properties of egg yolk were investigated. Results showed that monovalent and divalent ions were beneficial to the formation of uniform and dense gel network, especially with the addition of 0.72% magnesium ion, which further improved gel hardness, water holding capacity (WHC) and viscoelastic properties, the properties of egg yolk gel increased with the increase of the concentration of mono-bivalent metal ions. Adding ferric ion remarkably increased the average particle size (d4,3) and apparent viscosity of egg yolk, destroying the disulfide bonds and the hydrophobic interactions in gel. Fourier transform infrared spectroscopy (FT-IR) and fluorescence spectra analysis revealed that metal ions promoted the hydrophobic aggregation among egg yolk proteins and induced the transition of protein secondary structure from ordered to disordered. This work will provide a theoretical reference for the development of low salt and nutrient fortified egg yolk products.

Density Functional Theory Investigation of Cu, Ni, and Ag Inclusion in ZSM-5 to Study Dihydrogen Binding for Cryogenic Molecular Sieve Bed Adsorber in Nuclear Fusion Systems

A computational investigation of Cu-, Ni-, and Ag-introduced ZSM-5 as potential hydrogen storage materials for nuclear fusion energy systems is performed. Among the 24 distinct tetrahedral sites of the monoclinic phase of ZSM-5, systematic periodic density functional theory (DFT) computations have been carried out on 15 experimentally identified T sites that show clear Al site preference and stability in high Si ZSM-5. Adsorption energies estimated from DFT studies have revealed that the T sites in the sinusoidal channels T4 and T10 are the most stable for including all three metal ions. Hence, these should also be considered as potential active sites for dihydrogen binding investigations in addition to the common T12 site in the intersection. The average hydrogen binding energies at these representative T sites were −79 to −45 kJ/mol, which correlates well with both the metal-H2 distance and H-H bond elongation distance. The computed hydrogen bond stretching frequency values were in the 3300 to 3755 cm−1 range upon adsorption of H2 onto the Ni, Cu, and Ag, indicating Kubas-type dihydrogen complex formation. The evidence for dihydrogen binding was also obtained from investigating the σ donation and back donation between the metal ion valence orbitals and the H2σ, H2σ* orbitals through projected density of states and natural bond order analysis. Our analysis indicates that Ni is better stabilized in the framework sites and is considered a potential candidate for dihydrogen binding.

The photocatalyst with a strong internal electric field grown in situ on the surface of copper foam collaborates with peroxymonosulfate to enhance directional charge transfer and achieve ultra-fast Mn+/M(n+1)+ cycling

To address three pressing problems that limit the application of photocatalytic synergic peroxymonosulfate (PMS) technology, namely difficult reuse, low photogenerated carrier separation efficiency, and sluggish metallic ions redox cycle, we utilized an in-situ growth method to construct a vertical nanosheet heterojunction on the surface of copper foam (CF). This heterojunction is characterized by a strong internal electric field (IEF) that serves as both a “pump” for the rapid and efficient migration of electrons and a driving force for the activation of PMS by these electrons. In the CF@CCS@CO-3/7/Vis/PMS system, the photoelectrons generated by photocatalysis quickly replenish the high valence metals activated by PMS, allowing for highly efficient cycling of differently valenced metal ions and reducing the dissolution of high valence metal ions produced by PMS. As a result, close to 100 % of ciprofloxacin (CIP) was degraded within 60 min in the CF@CCS@CO-3/7/Vis/PMS system with a reaction rate constant k of 0.0621 min−1, which is about 3.22 times higher than that of the CF@CCS@CO-3/7/Vis system and 2.65 times higher than that of the CF@CCS@CO-3/7/PMS system. Moreover, the in-situ growth of active ingredients with vertical nanosheet structure on the CF surface can well maintain structure and reactivity in complex environments, allowing more than 10 cycles to be realized. The results of the free radical burst assay and EPR analysis indicated that SO4∙−, ∙O2− and h+ were the main reactive species involved in the catalytic process. Building upon CF@CCS@CO-3/7, we assembled a fixed-bed continuous treatment device that enables high mineralization flow treatment of pharmaceutical wastewater (after Secondary biological treatment).

In Situ Fast Construction of Ni3S4/FeS Catalysts on 3D Foam Structure Achieving Stable Large-Current-Density Water Oxidation.

By increasing the content of Ni3+, the catalytic activity of nickel-based catalysts for the oxygen evolution reaction (OER), which is still problematic with current synthesis routes, can be increased. Herein, a Ni3+-rich of Ni3S4/FeS on FeNi Foam (Ni3S4/FeS@FNF) via anodic electrodeposition to direct obtain high valence metal ions for OER catalyst is presented. XPS showed that the introduction of Fe not only further increased the Ni3+ concentration in Ni3S4/FeS to 95.02%, but also inhibited the dissolution of NiOOH by up to seven times. Furthermore, the OER kinetics is enhanced by the combination of the inner Ni3S4/FeS heterostructures and the electrochemically induced surface layers of oxides/hydroxides. Ni3S4/FeS@FNF shows the most excellent OER activity with a low Tafel slope of 11.2mVdec-1 and overpotentials of 196 and 445mV at current densities of 10 and 1400mAcm-2, respectively. Furthermore, the Ni3S4/FeS@FNF catalyst can be operated stably at 1500mAcm-2 for 200h without significant performance degradation. In conclusion, this work has significantly increased the high activity Ni3+ content in nickel-based OER electrocatalysts through an anodic electrodeposition strategy. The preparation process is time-saving and mature, which is expected to be applied in large-scale industrialization.

(Invited) Modulation of Photocatalytic Activity with Oxygen Vacancies in Metal Oxides

Oxygen vacancies commonly exist in metal oxides. The presence of oxygen vacancies alters electronic band structure, changes the chemical valences of metal ions, createS surface disorder and etc. This talk will discuss how oxygen vacancies will modulate light absorption, charge separation, migration, recombination and injection to electrolytes, which in turn affects photocatalytic activities of metal oxides.

Biosynthesis of JC-La2CoO4 magnetic nanoparticles explored in catalytic and SMMs properties

We have reported the synthesis of JC-La2CoO4 magnetic nanoparticles from Jatropha Curcas L. leaf extract in aqueous medium and potential application study in catalytic & Single Molecule Magnets (SMMs). Several techniques were used to investigate the structural, morphological, and elemental composition, particle size, optical properties, catalytic and magnetic properties by XRD, FTIR, SEM, EDAX, XPS, UV–visible and squid magnetic measurement. It was found that the crystallite sizes and grain sizes of JC-La2CoO4 NPs were 11.3 ± 1 and 24.1 ± 1 nm respectively and surface morphology of the nanoparticles looks spherical shape with good surface area. The band gap of JC-La2CoO4 was found to be 4.95 eV indicates good semiconductor in nature. XPS studies shows that La and Co present in + 3 and + 2 oxidation state respectively and suggest the composition formula is La2CoO4 with satisfied all the valency of metal ions. The photocatalytic efficiency of La2CoO4 shows good result against methylene blue (MB) compared to other dyes like MO, NO, RhB in presence of sunlight with rate constant 56.73 × 10–3 min-1 and completely degraded within 115 mints. The importance of JC-La2CoO4 has magnetic properties with antiferromagnetic coupling and SMMs properties with nature.

Investigation of variety of valence metal ions combinated novel Co‐rich high entropy oxides and its magnetic properties and microstructure

In this work, a series of five spinel-structured oxides were synthesized using a straightforward and effective solid-state methodology. Departing from the conventional design concept, we opted for the substitution of Fe3 + with five metal cations, all possessing trivalent average valence states and equivalent proportions. X-ray diffraction, scanning electron microscope, energy spectrum analyzer, vibrating sample magnetometer were used to detect the phase, micro-structure, element distribution, magnetism of the samples, respectively. The test results show that samples have the spinel structure (Fd3(_)m), and the element composition and distribution are the same as expected. The test results of magnetic properties reveal that these five samples exhibit the properties of soft magnetic materials. The maximum adjustment range of saturation magnetization (Ms) is increased from 23.5 emu/g to 34.8 emu/g by adjusting the elemental composition. Besides, the maximum adjustment range of coercivity (Hc) is increased from 11 Oe to 60 Oe. Furthermore, these materials exhibit a low remanent magnetization ratio, indicating that high-entropy oxides with spinel structures are highly sensitive to changes in an applied magnetic field. The high-entropy oxide is a new material with great prospect. It creates new possibilities for the design of magnetic materials.

Simultaneous detection of As(III/V), Cr(III/VI), and Fe(II/III) by a sensor array based on the morphology regulation of CeO2 oxidase.

To develop a convenient method for simultaneous detection of As(III/V), Cr(III/VI), and Fe(II/III), three morphologies of CeO2 oxidase have been prepared. Based on the difference in oxidase activity and binding ability with substrate TMB of CeO2of different morphologies, a 3 (Signal unit) × 6 (Target number) × 5 (Repetition) sensor array was constructed to realize simultaneous detection of six variable valence metal ions As(III/V), Cr(III/VI), and Fe(II/III). The lowestdetection limit of the array for metal ions was 1.68µg/L. The analysis of environmental samples with multiple metal ions (binary and ternary mixtures) co-existing has confirmed that the sensor array can achieve simultaneous qualitative and quantitative results for composite samples. This study not only revealed the influencing factors of crystal morphology regulation on oxidase activity, but also provided a scheme for the morphology detection of easily convertible metal ions in the field through the construction of the sensor array.