Variable Valence Metals Research Articles

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.

Influence of variable valence metal oxides on physico-chemical and antibacterial properties of semi-coated glazes

The paper presents the results of studies on the production of semi-coated glazes with antibacterial activity by introducing variable valence oxides CeO2, WO3, Bi2O3, Fe2O3, MnO2 and MoO3 into their composition. The raw polycomponent compositions were comprised of aluminosilicate multi-calcium glass frit, dolomite powder, feldspar, alumina, quartz sand, wet-enriched kaolin and refractory clay. The coatings were obtained by single firing on a ceramic-based porcelain stoneware at a temperature of 1 200 ± 5 °C in a high-speed mode for 60 ± 2 minutes. The study focused on the processes of glaze formation of coatings and the influence of the components of glaze charges on decorative and aesthetic characteristics of coatings (color, texture, gloss and whiteness). Parameters of physical and chemical properties were determined in accordance with the existing specification for the products, i. e. temperature coefficient of linear expansion, heat resistance, chemical resistance, microhardness, frost resistance, wear resistance, etc. Antibacterial activity of the coatings towards Escherichia coli ATCC 8739 and Staphylococcus aureus ATCC 6538 test strains was studied.

Biocompatible and capacitive PDA-Ov-Co3O4@CC anode augmented exoelectrogens enrichment and extracellular electron transfer in microbial fuel cells

Metal oxides rich in oxygen vacancies (Ov) possess excellent intrinsic conductivity, variable valence metal center and high capacitance, which were potential candidates as microbial fuel cells anode. However, their high bacterial toxicity greatly hindered the activity of biofilm. To solve this issue, in this work, polydopamine (PDA) covered capacitive Ov doped Co3O4 nanosheets were designed and successfully grown on carbon cloth (CC). The introduction of Ov significantly promoted the charge storage, the net charge and the accumulated charge were 217.1 and 2680.3 C/m2, respectively, surpassed Co3O4 anode without Ov. In addition, Ov also decreased the charge-transfer resistance (Rct), effectively accelerating EET. The Rct of PDA/Ov-Co3O4@CC was 29.51 Ω, lower than CC (382.10 Ω). The cover of PDA prevented the direct contact between metal ions and microorganisms, greatly enhanced the bacterial viability. The power density of MFCs with PDA/Ov-Co3O4@CC anode was 2.77 W/m2, 1.45 times higher than that of bare CC (1.90 W/m2). In addition, PDA/Ov-Co3O4@CC anode displayed excellent coulombic efficiency and daily COD removal amount (23.5 % and 147.6 mg/L/d), higher than the control groups. The community analysis showed the abundance of Geobacter on PDA/Ov-Co3O4@CC anode was 91 %, higher than other anodes. Present study developed a facile and effective PDA coating strategy to simultaneously enhance the biocompatibility and capacitance of Ov-rich metal oxides, which will be a promising method for the preparation of high performance MFCs anode.

Mechanisms of biological effectiveness of ionic forms of metals of variable valence in respiratory medicine

Background: The task to develop new drugs containing metals of variable valence requires systematization of our knowledge, experimental and clinical studies. The aim of the study: To investigate the mechanisms of the effectiveness of the mineral complex containing metals of variable valence in the treatment of respiratory diseases, to conduct preclinical trials and clinical testing of a new inhalation mineral solution. Materials and methods: The ability of cerium (III) ions to exhibit reducing properties was demonstrated by carrying out chemical reactions of cerium (III) chloride and sulfate with potassium permanganate in the presence of sodium hydroxide or sulfuric acid (respectively). Preclinical studies of acute toxicity were carried out on laboratory mice and rats in accordance with the rules of bioethics and with generally accepted ethical standards for the treatment of animals, based on the standard operating procedures of the university, which comply with the rules adopted by the European Convention for the Protection of Vertebrate Animals used for research and other scientific purposes (Strasbourg, 1986). Clinical testing of two forms of the mineral complex for inhalation (1. Inhalation solution for nebulizer – Renerium; 2. intranasal spray) was carried out on 6 groups of volunteers in compliance with human rights and the principles of conducting medical research involving a person as a subject, declared on the 18th General Assembly of the World Medical Association (Helsinki, Finland), voluntary informed consent, approved by the local ethical committee. Results: Mineral preparation for inhalation therapy of patients with acute respiratory diseases does not show acute toxicity in preclinical studies on laboratory animals. The mechanism of action of the drug is most likely associated with the regulation of redox reactions at the level of the cell membrane, mitochondria and cell nucleus, which is manifested by anti-inflammatory and regenerative activity in the mucous membrane of the respiratory tract and alveolar apparatus. Both forms of the drug are well tolerated. A pronounced clinical efficacy of the drug Renerium in the form of inhalation through a compressor inhaler was noted in the case of a 5-day course of treatment, 5 ml once a day. Conclusion: Experimental and clinical data have demonstrated pronounced anti-inflammatory and regenerative properties of a new mineral complex based on cerium (III), the mechanism of which is due to the regulation of redox reactions.

Next-generation of a Fe-Ce double variable-valence metals modulated high-efficiency nanozyme

High catalytic efficiency is the continuous pursuit for the preparation of high-performance nanozymes. In this work, a Fe-Ce double variable-valence metals nanozyme (Fe-Ce-MOL) was constructed based on metal–organic layers (MOLs), a class of two-dimensional metal–organic frameworks with ultra-thin structure, for peroxidase (POD) mimicking. Fe-Ce-MOL exhibited significantly enhanced catalytic activity in comparison with that of natural horseradish peroxidase and single variable-valence metal nanozyme (Fe-Zr-MOL). Density functional theory calculations demonstrated that the Fe site of Fe-Ce-MOL had a stronger adsorption effect on H2O2 compared to Fe-Zr-MOL and more heat was released in the catalytic reaction of H2O2, making the reaction easier to occur. Moreover, there was more electron transfer between Fe and Ce double variable-valence metals, also accelerating the catalytic process. These results indicated that the ultra-thin structure of Fe-Ce-MOL provided more catalytic sites and Fe and Ce double variable-valence metals could regulate the process of oxidation–reduction and promote the efficiency of electron transfer synergistically. As a proof of concept, the proposed Fe-Ce-MOL was used in biosensing and antibacterial applications. These results suggested that Fe-Ce-MOL had great potential as a new-generation nanozyme. This work pioneers a new approach for the rational design of highly efficient nanozymes.

A sensitive electrochemical immunosensor based on high-efficiency catalytic cycle amplification strategy for detection of cardiac troponin I

An electrochemical immunosensor based on the novel high efficiency catalytic cycle amplification strategy for the sensitive detection of cardiac troponin I (cTnI). With its variable valence metal elements and spiny yolk structure, the Cu2O/CuO@CeO2 nanohybrid exhibits high speed charge mobility and exceptional electrochemical performance. Notably, fluorite-like cubic crystal CeO2 shell would undergo redox reaction with Cu2O core, which successfully ensures the continuous recycling occurrence of “fresh” Cu (II)/Cu (I) and Ce (Ⅳ)/Ce (Ⅲ) pairs at the electrode interface. The “fresh” active sites continue to emerge constantly, resulting in a significant increase in the current signal. In light of the electrochemical characterization, the electron transfer pathway and catalytic cycle mechanism among CeO2, Cu2O and CuO were further discussed. The developed electrochemical immunosensor detected cTnI from 100 fg/mL to 100 ng/mL with a LOD of 15.85 fg/mL under optimal conditions. The analysis results indicate that the immunosensor would hold promise for broad application prospects in the biological detection for other biomarkers.

Sp2-c linked Cu-based metal-covalent organic framework for chemical and photocatalysis synergistic reduction of uranium

The reduction of hexavalent uranium to tetravalent uranium is an effective strategy for controlling uranium contamination in wastewater. Herein, a CC bonded metal-covalent organic framework (Cu-TMT) was synthesized via the Aldol condensation reaction by using the metal cluster Cu3(PyCA)3 and 2,4,6-trimethyl-1,3,5-triazine (TMT) for the chemical and photocatalytic synergistic reduction of uranium. In the Cu-TMT, the low-valent Cu in the metal clusters provides the framework with numerous distributed redox sites being capable of chemically reducing UVI. Meanwhile, the encapsulating Cu clusters in long-range ordered frameworks can provide fast transport channels for intramolecular charge transfer and effectively inhibit electron/hole complexation, making Cu-TMT suitable for photocatalytic reduction of uranium. The chemical reduction of uranium by Cu-TMT was verified under light-avoidance conditions, reaching 659.5 mg g−1. After exposure of Cu-TMT to light, the amount of reduced uranium further increases to 1438.8 mg g−1 with 98.1 % removal rate of actual uranium containing wastewater. This study not only expands the range of applications of variable valence metal covalent organic frameworks, but also provides unique insights into the effective combination of chemical and photocatalytic reduction strategies for removing UVI in a single material.

In-situ precipitation zero-valent Co on Co2VO4 to activate oxygen vacancies and enhance bimetallic ions redox for efficient detection toward Hg(II)

Despite the widespread utilization of variable valence metals in electrochemistry, it is still a formidable challenge to enhance the valence conversion efficiency to achieve excellent catalytic activity without introducing heterophase elements. Herein, the in-situ precipitation of Co particles on Co2VO4 not only enhanced the concentration of oxygen vacancies (Ov) but also generated a greater number of low-valence metals, thereby enabling efficient reduction towards Hg(II). The electroanalysis results demonstrate that the sensitivity of Co/Co2VO4 towards Hg(II) was measured at an impressive value of 1987.74 μA μM−1 cm−2, significantly surpassing previously reported results. Further research reveals that Ov acted as the main adsorption site to capture Hg(II). The redox reactions of Co2+/Co3+ and V3+/V4+ played a synergistic role in the reduction of Hg(II), accompanied by the continuous supply of electrons from zero-valent Co to expedite the valence cycle. The Co/Co2VO4/GCE presented remarkable selectivity towards Hg(II), with excellent stability, reproducibility, and anti-interference capability. The electrode also exhibited minimal sensitivity fluctuations towards Hg(II) in real water samples, underscoring its practicality for environmental applications. This study elucidates the mechanism underlying the surface redox reaction of metal oxides facilitated by zero-valent metals, providing us with new strategies for further design of efficient and practical sensors.

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.

Property Enhancement of Waste Printed Circuit Boards Powders Reinforced Polypropylene by In Situ Magnesium Hydroxide Impregnation from Waste Lye.

Using alkali pretreatment can effectively remove residual variable-valence metals from non-metallic powder (WPCBP) in waste printed circuit boards. However, substantial amounts of waste lye are generated, which causes secondary pollution. On this basis, this study innovatively utilized waste alkali lye to prepare nano-magnesium hydroxide. When the dispersant polyethylene glycol 6000 was used at a dosage of 3 wt.% of the theoretical yield of magnesium hydroxide, the synthesized nano-magnesium hydroxide exhibited well-defined crystallinity, good thermal stability and uniform particle size distribution, with a median diameter of 197 nm. Furthermore, the in situ method was selected to prepare WPCBP/Mg(OH)2 hybrid filler (MW) and the combustion behavior, thermal and mechanical properties of PP blends filled with MW were evaluated. The combustion behavior of the PP/MW blends increased with the increasing hybrid ratio of Mg(OH)2, and the MW hybrid filler reinforced PP blends showed better thermal and mechanical properties compared to the PP/WPCBP blends. Furthermore, the dynamic mechanical properties of the PP/MW blends were also increased due to the improved interfacial adhesion between the MW fillers and PP matrix. This method demonstrated high economic and environmental value, providing a new direction for the high value-added utilization of WPCBP.

Construction of dual functional CuAl-LDHs nanocomposite loaded with IGF2BP3 siRNA for enhanced therapy of gastric cancer

Gastric cancer (GC) is a prevalent malignancy in China, necessitating innovative treatments. Recent advancements in nucleic acid drugs, particularly small interfering RNAs (siRNAs), have shown promise in therapeutic applications. Biodegradable layered double hydroxides (LDHs), as a class of typical two-dimensional (2D) materials, hold great prospects in biomedical and drug delivery systems. Building on our previous research, which identified the upregulated insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3) promoted GC progression, we devised a strategy that leverages the unique properties of LDHs carriers with siRNA therapeutics. Herein, we synthesized CuAl-LDHs containing variable valence metal cations (Cu2+), capable of inducing a Fenton-like reaction in the tumor micro-acid environment (TME) of GC. Subsequently, we constructed si-IGF2BP3/CuAl-LDHs nanocomposites to protect and deliver si-IGF2BP3 via the CuAl-LDHs carrier. The obtained nanocomposites demonstrated significant efficacy in inhibiting GC cell proliferation by silencing the IGF2BP3 gene at both the mRNA and protein levels, accelerating oxidative stress in GC cells through a Fenton-like reaction, and achieving greater suppression of tumor volume than CuAl-LDHs alone. The remarkable anti-tumor effect was attributed to the CuAl-LDHs carrier’s superior siRNA immobilization and delivery capabilities, as well as the catalytic ability of Cu in CuAl-LDHs, facilitating the Fenton-like reaction within TME. Overall, this integrated GC therapy strategy employing LDHs nano-carriers may represent a significant advancement in developing next-generation therapeutic systems. It underscores the potential of LDHs as an effective platform for targeted GC therapy.

A novel highly thermostable and stress resistant ROS scavenging metalloprotein from Paenibacillus

Reactive oxygen species (ROS) are unstable metabolites produced during cellular respiration that can cause extensive damage to the body. Here we report a unique structural metalloprotein called RSAPp for the first time, which exhibits robust ROS-scavenging activity, high thermostability, and stress resistance. RSAPp is a previously uncharacterized DUF2935 (domain of unknown function, accession number: cl12705) family protein from Paenibacillus, containing a highly conserved four-helix bundle with binding sites for variable-valence metal ions (Mn2+/Fe2+/Zn2+). Enzymatic characterization results indicated that RSAPp displays the functionality of three different antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). In particular, RSAPp exhibits a significant SOD-like activity that is remarkably effective in eliminating superoxide radicals (up to kcat/KM = 2.27 × 1011 mol−1 s−1), and maintains the catalytical active in a wide range of temperatures (25–100 °C) and pH (pH 2.0–9.0), as well as resistant to high temperature, alkali and acidic pH, and 55 different concentrations of detergent agents, chemical solvents, and inhibitors. These properties make RSAPp an attractive candidate for various industrial applications, including cosmetics, food, and pharmaceuticals.

Construction of an S-scheme Ce/Ti-MOFs heterojunction with abundant Oxygen vacancies (Ovs) for efficient charges separation: Performance and mechanism insight

The S-scheme heterojunction in the semiconductors can effectively enhance the photocatalytic activity by retaining strong light-generated electrons (e−) and holes (h+) while recombining meaningless charge carriers. In this work, a Ce/Ti-MOFs (CT-MOFs) heterojunction material with plentiful oxygen vacancies (Ovs) was synthesized via the hydrothermal method. The catalysts were employed for the degradation of Tetracycline (TC) in the aquatic environment under simulated sunlight. The Ce/Ti-MOFs (CT 1–4) sample exhibited the best photocatalytic activity, with a rate constant of 0.01243 min−1, which is 7.49 times greater than that of Ce-MOF, and 2.40 times higher than that of MIL-125 (Ti), respectively. The experimental results show that the constructed CT-MOFs can increase the density of Ovs, accelerate charge transfer, and improve photocatalytic performance. Furthermore, the Ti4+/Ti3+ variable valence metal cycle in CT 1–4 compensates for charge balance and promotes rapid carrier separation. The difference between the Fermi energy level and work function drives the electron transfer from the MIL-125(Ti) side to the Ce-MOF side. The above results indicate that the successful establishment of the S-scheme heterojunction preserves the strong redox effects of e− and h+, prolongs the electron lifetime, and facilitates the carrier's separation.

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.

Kinetics, Mechanism, and Reactivity of the Cerium(IV)-Oxalatereaction in a Sulphate Medium

This work presents an approach for studying the kinetics, mechanism, and reactivity of intermediates in a wide class of the redox reactions for which the rate-limiting step is the redox-decomposition of an intermediate complex. This approach is applied to investigate the oxalic acid (H2Ox) oxidation by cerium(IV) in sulfuric acid medium, which is an integral part of the cerium-catalyzed oscillatory Belousov–Zhabotinsky (BZ) reaction. Using experimental, mathematical and computational techniques commonly used to study metal complexes in a stable oxidation state (OS), kinetically generalized by the authors for studying variable-valence metal complexes, the characteristics of intermediate complexes of the cerium(IV)-oxalate reaction were studied, the general rate law was derived on the basis of a set of equations describing the rapid establishment of preequilibria in the system and the subsequent nonequilibrium process. A quantitative reaction model is proposed that includes two parallel reaction pathways, for which two different intermediate cerium(IV)-oxalate complexes with close reactivity have been identified and characterized that may be due to the similarity in the structure of their inner coordination spheres and an inner sphere mechanism of electron transfer in the complexes. Based on the developed model, the distribution diagram was also constructed for the computed fractions of all the detectable cerium(IV) species under conditions of the BZ reaction, which testify to the necessity to take into account under these conditions the formation of intermediate complexes CeOHOx (n = 1, 2) during oxidation of oxalic acid. The main difference of the proposed model of the cerium(IV)-oxalate reaction as part of the BZ-reaction from the previous models is the explicit accounting of the formation of intermediate cerium(IV) complexes with anions of oxalic acid and sulfate background.

Manganese doping of hematite enhancing oxidation and bidentate-binuclear complexation during As(III) remediation: Experiments and DFT calculation

Iron and manganese oxides are commonly found in nature, such as hematite and pyrolusite, which strongly affect the migration and transformation of As(III). In this study, a series of hematite materials modified by MnO2 (Hm-Mn) were synthesized to achieve the adsorption-oxidation bifunctionality of hematite toward As(III). The maximal As(III) adsorption capacity of Hm-Mn (80.0 mg g−1) was nearly 3 times higher than that of pure hematite (28.5 mg g−1). The ratio of As(V) immobilized on Hm-Mn reached 71.5%, which was significantly higher than that of Hm (17.9%). The kinetic results indicated that chemisorption is the dominant adsorption behavior. Density functional theory (DFT) calculations revealed that manganese modification reduced the adsorption and oxidation energy of Hm-Mn, confirming that manganese modification was beneficial to both of the adsorption and oxidation of As(III). Bidentate-binuclear complex was the primary coordination type of arsenic binding on the Hm-Mn facets. Crystal orbital Hamilton population (COHP) analysis implied that the bonding of Hm-Mn with arsenic was stable. Specially, the bonding of Fe-O-As was stronger than that of Mn-O-As. Altogether, Hm-Mn provides a feasible solution for arsenic-contaminated water, and the fundamental theoretical data offer new perspective for understanding the remediation mechanisms of variable valence metal pollutants.

Experimental Study of the Process of Interaction of Hydrogen with Igneous Melts in the Conditions of the Earth’s Crust

Abstract —We report new experimental data on the interaction of igneous melts with hydrogen at temperatures of 1100–1250 °C and hydrogen pressures of 1–100 MPa in strongly reducing conditions: fO2=10−12−10−14. The experiments were conducted using an original high-gas-pressure unit equipped with a unique device that provides long-term experiments at high temperatures and pressures of hydrogen. The experiments used natural samples of igneous rocks: the magnesian basalt of the Northern Breakthrough of the Tolbachik Volcano (Kamchatka) and the andesite of the Avacha Volcano (Kamchatka). On the basis of the experiments, the following features of the process of interaction of hydrogen with igneous melts have been established: (1) Despite the high reduction potential of the H2–igneous melt system, the reactions of hydrogen oxidation and complete reduction of oxides of metals of variable valence in the melt do not go to the end. The cessation of redox reactions in basaltic and andesitic melts is due to the formation of H2O in the melt, which buffers the reduction potential of hydrogen; (2) The initially homogeneous igneous melt becomes heterogeneous: The formed H2O dissolves in the melt and in the fluid phase (at first pure hydrogen), and melts of variable, more acidic composition and small metallic isolations of the liquation structure are formed; (3) The complex process of metal–silicate liquation in magmatic melts when they interact with hydrogen can be carried out at real magma temperatures in nature (≤1200 °C), significantly lower than the corresponding melting points of iron and its alloys with nickel and cobalt; (4) The structure and dimensions of the experimentally established metal isolations are consistent with natural data on the finds of small quantities of native metals, primarily iron and its alloys with nickel and cobalt, in igneous rocks of different compositions and genesis.

Phase transition mechanism of the solid-state reaction of two variable-valence metal oxides: Cobalt and manganese oxides

Due to the state transition of variable-valence ions during the solid-state reaction, the reaction mechavnism is complex. As one of the function materials in supercapacitors and catalysts, there is much research on the property and function mechanism of MnCo2O4. But it’s necessary to study the chemical reaction and a productive method for realizing wide application. In this paper, solid-state reaction method with high efficiency was applied to produce MnCo2O4 and investigated the reaction process of oxides, the formation mechanism of MnCo2O4, respectively. Thermodynamic and roasting experiments of single metal oxides demonstrated the actual stability of MnO2 and Co3O4 in the air. Furthermore, Roasting experiments on different metal oxide systems revealed Mn2O3 and Mn3O4 were the effective reactants of MnCo2O4, which reacted with Co3O4 respectively to produce MnCo2O4. Moreover, the optimum condition of the preparation of MnCo2O4 was determined to be 1150 ℃ with a 90-minute in a 3:2 molar ratio of MnO2 and Co3O4. MnCo2O4 were composed of Mn2+, Mn3+, Co2+, and Co3+, the property of Mn-O and Co-O bonds at 1.50 Å and 1.54 Å all including tetrahedral and octahedral sites with a bond length of 1.9–1.92 Å and 1.93–1.94 Å, respectively. Mn and Co atoms are located at octahedral sites with two coordinated distances: MeOh-MeOh, MeOh-MeTd. The migration behavior of elements in MnO2-Co3O4 diffusion couple was found to manganese move to Co-based and generate a porous MnCo2O4 at the interface. The formation mechanism of spinel-type MnCo2O4 was explained: While Co3O4 was activated, Mn4+ was decomposed to Mn2+ and Mn3+ in the oxidation roasting process. Further, Mn2+ and Mn3+ replaced part of tetrahedral Co2+ and octahedral Co3+ in [Co(2+)][Co(3+)]2O4 to form a spinel-type [Mn(2+)Co(2+)][Mn(3+)Co(3+)]2O4.

Sandwich-type electrochemical immunosensor based on CuFe2O4-Pd for cardiac troponin I detection.

A sandwich-type electrochemical immunosensor was designed by highly efficient catalytic cycle amplification strategy of CuFe2O4-Pd for sensitive detection of cardiac troponin I. CuFe2O4 with coupled variable valence metal elements exhibited favorable catalytic performance through bidirectional cycling of Fe2+/Fe3+ and Cu+/Cu2+ redox pairs. More importantly, Cu+ acted as the intermediate product of the catalytic reaction, promoted the regeneration of Fe2+ and ensured the continuous recycling occurrence of the double redox pairs, and significantly amplified the current signal response. Pd nanoparticles (Pd NPs) loaded on the surface of amino-functionalized CuFe2O4 (CuFe2O4-NH2) served as electrochemical mediators to capture labeled antibodies (Ab2), and also as co-catalysts of CuFe2O4 to further enhance the catalytic efficiency, thusimproving the sensitivity of the electrochemical immunosensor. Under the optimal experimental conditions, the linear range was 0.001 ~ 100ng/mL, and the detection limit was 1.91fg/mL. The electrochemical immunosensor has excellent analytical performance, giving a new impetus for the sensitive detection of cTnI.

Fe-N-C catalysts decorated with oxygen vacancies-rich CeOx to increase oxygen reduction performance for Zn-air batteries

Platinum group metal (PGM)-free catalysts represented by nitrogen and iron co-doped carbon (Fe-N-C) catalysts are desirable and critical for metal-air batteries, but challenges still exist in performance and stability. Here, cerium oxides (CeOx) are incorporated into a two-dimensional Fe-N-C catalyst (FeNC-Ce-950) via a host-guest strategy. The Ce4+/Ce3+ redox system creates a large number of oxygen vacancies for rapid O2 adsorption to accelerate the kinetics of oxygen reduction reaction (ORR). Consequently, the as-synthesized FeNC-Ce-950 catalyst exhibits a half-wave potential (E1/2) of 0.921 V and negligible decay (<2 mV for ΔE1/2) after 5,000 accelerated durability cycles, significantly outperforming most of ORR catalysts reported in recent years and precious metal counterparts. When applied in a zinc-air battery, it demonstrates a peak power density of 175 mW cm−2 and a specific capacity of 757 mAh gZn−1. This study also provides a reference for the exploration of Fe-N-C catalysts decorated with variable valence metal oxides.