Electrochemically Induced Metal–Organic-Framework-Derived Amorphous V2O5 for Superior Rate Aqueous Zinc-Ion Batteries

The electrochemical performance of vanadium-oxide-based cathodes in aqueous zinc-ion batteries (ZIBs) depends on their degree of crystallinity and composite state with carbon materials. An in situ electrochemical induction strategy was developed to fabricate a metal–organic-framework-derived composite of amorphous V₂O₅ and carbon materials (a-V₂O₅@C) for the first time, where V₂O₅ is in an amorphous state and uniformly distributed in the carbon framework. The amorphous structure endows V₂O₅ with more isotropic Zn²⁺ diffusion routes and active sites, resulting in fast Zn²⁺ transport and high specific capacity. The porous carbon framework provides a continuous electron transport pathway and ion diffusion channels. As a result, the a-V₂O₅@C composites display extraordinary electrochemical performance. This work will pave the way toward design of ZIB cathodes with superior rate performance.     

Carbon-coated manganese dioxide nanoparticles and their enhanced electrochemical properties for zinc-ion battery applications

In this study, we report the cost-effective and simple synthesis of carbon-coated α-MnO_2nanoparticles(α-MnO_2@C) for use as cathodes of aqueous zinc-ion batteries(ZIBs) for the first time. α-MnO_2@C was prepared via a gel formation, using maleic acid(C_4H_4O_4) as the carbon source, followed by annealing at low temperature of 270 °C. A uniform carbon network among the α-MnO_2 nanoparticles was observed by transmission electron microscopy. When tested in a zinc cell, the α-MnO_2@C exhibited a high initial discharge capacity of 272 m Ah/g under 66 m A/g current density compared to 213 m Ah/g, at the same current density, displayed by the pristine sample. Further, α-MnO_2@C demonstrated superior cycleability compared to the pristine samples. This study may pave the way for the utilizing carbon-coated MnO_2 electrodes for aqueous ZIB applications and thereby contribute to realizing high performance eco-friendly batteries.     

Sandwich-like mesoporous graphene@magnetite@carbon nanosheets for high-rate lithium ion batteries

Sandwich-like mesoporous GS@Fe₃O₄@C nanosheets with a 2D nanoarchitecture have been successfully synthesized by one-step solvothermal treatment. Such type of 2D nanoarchitecture is made up of a number of Fe₃O₄ nanoparticles uniformly grown on a graphene sheet and an even amorphous carbon layer covering on their surface. The Li-cycling properties of GS@Fe₃O₄@C nanosheets have been evaluated by galvanostatic discharge-charge cycling and impedance spectroscopy. Results indicate that the GS@Fe₃O₄@C nanosheets with about 5 wt % of graphene content provides a very high discharge capacity of 913.2 mAh g⁻¹ at a current densities of 200 mA g⁻¹ after 100 cycles and reveals a stable discharge capacity of 483.2 mAh g⁻¹ at a rate of 1600 mA g⁻¹.     

Toward high-performance Li storage anodes: design and construction of spherical carbon-coated CoNiO2 materials

CoNiO₂ nanosheets were prepared by a simple hydrothermal process, and then the spherical CoNiO₂@C micro-nano structures composed of nanoparticles were designed by morphology reshaping for the first time. The results show that the carbon coating changes the morphology of CoNiO₂, and the CoNiO₂@C composite shows porous microsphere structure consisted of nanoparticles. The porous structure combined with highly conductive carbon shell indicates an improved electronic conductivity and charge transfer. The carbon shell decreases the charge-transfer resistance of CoNiO₂, and thus enhances the kinetic performances. The pristine CoNiO₂ and CoNiO₂@C (3, 5, and 10 wt%) composites deliver charge/discharge capacities of 511.7/526.9, 811.3/826.3, 997.1/1013.1, and 1216.1/1241.8 mAh g^?1 at 500 mA g^?1 after 200 cycles, respectively. The carbon coating improves the reversible capacity, rate capability, and cycle performance of CoNiO₂, especially at high rates. The improved rate performance, excellent cycle performance, and high kinetic performances are ascribed to the elaborate design of architecture and composition. Hence, such porous CoNiO₂@C microsphere consisted of nanoparticles can be regarded as promising candidates as anode materials for lithium-ion battery.     

Ferrite nanoparticles (MFe2O4 NPs) as magnetically recoverable supports for catalysis in organic synthesis

Abstract

Heterogenization of organic and metallic catalysts with a solid support is an attractive and useful strategy to solve the separation and recovery problems of catalysts. During the last decade, magnetic nanoparticles (MNPs) in general ferrite nanoparticles (MFe₂O₄ NPs) have emerged as a highly efficient support for catalysis, due to their simple fabrication, modification, and large surface area ratio. In this paper, we provide an overview of the utilization of organic and metallic molecules immobilized on magnetic ferrite nanoparticles (MFe₂O₄ NPs) as attractive and efficient catalytic systems in wide variety of in organic reactions.     

Preparation of carbon coated Fe3O4 nanoparticles for magnetic separation of uranium

Uranium(VI) was removed from aqueous solutions using carbon coated Fe₃O₄ nanoparticles (Fe₃O₄@C). Batch experiments were conducted to study the effects of initial pH, shaking time and temperature on uranium sorption efficiency. It was found that the maximum adsorption capacity of the Fe₃O₄@C toward uranium(VI) was ∼120.20 mg g⁻¹ when the initial uranium(VI) concentration was 100 mg L⁻¹, displaying a high efficiency for the removal of uranium(VI) ions. Kinetics of the uranium(VI) removal is found to follow pseudo-second-order rate equation. In addition, the uranium(VI)-loaded Fe₃O₄@C nanoparticles can be recovered easily from aqueous solution by magnetic separation and regenerated by acid treatment. Present study suggested that magnetic Fe₃O₄@C composite particles can be used as an effective and recyclable adsorbent for the removal of uranium(VI) from aqueous solutions.     

CNT@Fe3O4@C Coaxial Nanocables: One‐Pot,Additive‐Free Synthesis and Remarkable Lithium Storage Behavior

By using carbon nanotubes (CNTs) as a shape template and glucose as a carbon precursor and structure‐directing agent, CNT@Fe₃O₄@C porous core/sheath coaxial nanocables have been synthesized by a simple one‐pot hydrothermal process. Neither a surfactant/ligand nor a CNT pretreatment is needed in the synthetic process. A possible growth mechanism governing the formation of this nanostructure is discussed. When used as an anode material of lithium‐ion batteries, the CNT@Fe₃O₄@C nanocables show significantly enhanced cycling performance, high rate capability, and high Coulombic efficiency compared with pure Fe₂O₃ particles and Fe₃O₄/CNT composites. The CNT@Fe₃O₄@C nanocables deliver a reversible capacity of 1290 mA h g^?1 after 80 cycles at a current density of 200 mA g^?1, and maintain a reversible capacity of 690 mA h g^?1 after 200 cycles at a current density of 2000 mA g^?1. The improved lithium storage behavior can be attributed to the synergistic effect of the high electronic conductivity support and the inner CNT/outer carbon buffering matrix.     

Green fabrication of sandwich-like and dodecahedral C@Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@C as high-performance anode for lithium-ion batteries

Sandwich-structured C@Fe₃O₄@C hybrids with Fe₃O₄ nanoparticles sandwiched between two conductive carbon layers have attracted more and more attention owing to enhanced synergistic effects for lithium-ion storage. In this work, an environment-friendly procedure is developed for the fabrication of sandwich-like C@Fe₃O₄@C dodecahedrons. Zeolitic imidazolate framework (ZIF-8)-derived carbon dodecahedrons (ZIF-C) are used as the carbon matrix, on which iron precursors are homogeneously grown with the assistance of a polyelectrolyte layer. The subsequent polydopamine (PDA) coating and calcination give rise to the formation of sandwiched ZIF-C@Fe₃O₄@C. When being evaluated as the anode material for lithium-ion batteries, the obtained hybrid manifests a high reversible capacity (1194 mAh g^?1 at 0.05 A g^?1), good high-rate behavior (796 mAh g^?1 at 10 A g^?1), and negligible capacity loss after 120 cycles.     

Confined Nanospace Pyrolysis for the Fabrication of Coaxial Fe3O4@C Hollow Particles with a Penetrated Mesochannel as a Superior Anode for Li‐Ion Batteries

In this study, a method is developed to fabricate Fe₃O₄@C particles with a coaxial and penetrated hollow mesochannel based on the concept of “confined nanospace pyrolysis”. The synthesis involves the production of a polydopamine coating followed by a silica coating on a rod‐shaped β‐FeOOH nanoparticle, and subsequent treatment by using confined nanospace pyrolysis and silica removal procedures. Typical coaxial hollow Fe₃O₄@C possesses a rice‐grain morphology and mesoporous structure with a large specific surface area, as well as a continuous and flexible carbon shell. Electrochemical tests reveal that the hollow Fe₃O₄@C with an open‐ended nanostructure delivers a high specific capacity (ca. 864 mA h g^?1 at 1 A g^?1), excellent rate capability with a capacity of about 582 mA h g^?1 at 2 A g^?1, and a high Coulombic efficiency (>97 %). The excellent electrochemical performance benefits from the hollow cavity with an inner diameter of 18 nm and a flexible carbon shell that can accommodate the volume change of the Fe₃O₄ during the lithium insertion/extraction processes as well as the large specific surface area and open inner cavity to facilitate the rapid diffusion of lithium ions from electrolyte to active material. This fabrication strategy can be used to generate a hollow or porous metal oxide structure for high‐performance Li‐ion batteries.     

Rational Construction of 2D Fe3O4@Carbon Core–Shell Nanosheets as Advanced Anode Materials for High-Performance Lithium-Ion Half/Full Cells

Transition metal oxides have vastly limited practical application as electrode materials for lithium-ion batteries (LIBs) due to their rapid capacity decay. Here, a versatile strategy to mitigate the volume expansion and low conductivity of Fe₃O₄ by coating a thin carbon layer on the surface of Fe₃O₄ nanosheets (NSs) was employed. Owing to the 2D core–shell structure, the Fe₃O₄@C NSs exhibit significantly improved rate performance and cycle capability compared with bare Fe₃O₄ NSs. After 200 cycles, the discharge capacity at 0.5 A g⁻¹ was 963 mA h g⁻¹ (93 % retained). Moreover, the reaction mechanism of lithium storage was studied in detail by ex situ XRD and HRTEM. When coupled with a commercial LiFePO₄ cathode, the resulting full cell retains a capacity of 133 mA h g⁻¹ after 100 cycles at 0.1 A g⁻¹, which demonstrates its superior energy storage performance. This work provides guidance for constructing 2D metal oxide/carbon composites with high performance and low cost for the field of energy storage.     

One-Step Route to Fe2O3 and FeSe2 Nanoparticles Loaded on Carbon-Sheet for Lithium Storage

Iron-based anode materials, such as Fe₂O₃ and FeSe₂ have attracted widespread attention for lithium-ion batteries due to their high capacities. However, the capacity decays seriously because of poor conductivity and severe volume expansion. Designing nanostructures combined with carbon are effective means to improve cycling stability. In this work, ultra-small Fe₂O₃ nanoparticles loaded on a carbon framework were synthesized through a one-step thermal decomposition of the commercial C₁₅H₂₁FeO₆ [Iron (III) acetylacetonate], which could be served as the source of Fe, O, and C. As an anode material, the Fe₂O₃@C anode delivers a specific capacity of 747.8 mAh g⁻¹ after 200 cycles at 200 mA g⁻¹ and 577.8 mAh g⁻¹ after 365 cycles at 500 mA g⁻¹. When selenium powder was introduced into the reaction system, the FeSe₂ nano-rods encapsulated in the carbon shell were obtained, which also displayed a relatively good performance in lithium storage capacity (852 mAh g⁻¹ after 150 cycles under the current density of 100 mA·g⁻¹). This study may provide an alternative way to prepare other carbon-composited metal compounds, such as FeN_x@C, FeP_x@C, and FeS_x@C, and found their applications in the field of electrochemistry.     

Synthesis of monodispersed Fe3O4@C core/shell nanoparticles

We report a facile method to synthesize dispersed Fe₃O₄@C nanoparticles（NPs）. Fe₃O₄ NPs were firstly prepared via the high temperature diol thermal decomposition method. Fe₃O₄@C NPs were fabricated using glucose as a carbon source by hydrothermal process. The obtained products were characterized by X-ray diffraction（XRD）, transmission electron microscopy（TEM）, vibrating sample magnetometer（VSM） and Raman spectra. The results indicate that the original shapes and magnetic property of Fe₃O₄ NPs can be well preserved. The magnetic particles are well dispersed in the carbon matrix. This strategy would provide an efficient approach for existing applications in Li-ion batteries and drug delivery. Meanwhile, it offers the raw materials to assemble future functional nanometer and micrometer superstructures.     

Optical and magnetic properties of small-size core–shell Fe3O4@C nanoparticles

Core–shell Fe₃O₄@C magnetic nanoparticles which are of great interest for research have a widely applied prospect. However, people know little about the optical and magnetic properties of the small-size Fe₃O₄@C nanoparticles due to the difficulty of uniformly coating small size Fe₃O₄ nanoparticles. In this paper, the influence of carbon shell coating on the optical and magnetic properties of small size Fe₃O₄ nanoparticles was presented. Carbon coating can strengthen the absorption intensity in the UV–visible light region through the introduction of oxygen defects on the surface of the nanoparticles by nitric acid treatment. Fe₃O₄ and Fe₃O₄@C nanoparticles both display typical superparamagnetic behavior in the high-temperature regime and a blocked state at low temperature from hysteresis loop, zero-field cooled and field cooled curves. Carbon coating reduce the surface uniaxial anisotropy, thus the average blocking temperature <T_B> decreases from 59 K of Fe₃O₄ nanoparticles to 50 K of Fe₃O₄@C nanoparticles.     

Indirect Transformation of Coordination‐Polymer Particles into Magnetic Carbon‐Coated Mn3O4 (Mn3O4@C) Nanowires for Supercapacitor Electrodes with Good Cycling Performance

Carbon‐coated Mn₃O₄ nanowires (Mn₃O₄@C NWs) have been synthesized by the reduction of well‐shaped carbon‐coated bixbyite networks and characterized by TEM, X‐ray diffraction, X‐ray photoelectron spectroscopy, and electrochemical experiments. To assess the properties of 1D carbon‐coated nanowires for their use in supercapacitors, cyclic voltammetry and galvanostatic charging–discharging measurements were performed. Mn₃O₄@C NWs could be charged and discharged faster and had higher capacitance than bare Mn₃O₄ nanostructures and other commercial materials. The capacitance of the Mn₃O₄@C NWs was 92 % retained after 3000 cycles at a charging rate of 5 A g^?1. This improvement can be attributed to the carbon shells, which promote fast Faradaic charging and discharging of the interior Mn₃O₄ core and also act as barriers to protect the inner core. These Mn₃O₄@C NWs could be a promising candidate material for high‐capacity, low‐cost, and environmentally friendly electrodes for supercapacitors. In addition, the magnetic properties of the as‐synthesized samples are also reported to investigate the influence of the carbon coating.     

Electrocatalytic Activity of Nanohybrids Based on Carbon Nanomaterials and MFe2O4 (M=Co,Mn) towards the Reduction of Hydrogen Peroxide

We report the advantages of hybrid nanomaterials prepared with electrogenerated ferrites (MFe₂O₄; M: Co, Mn) and multi‐walled carbon nanotubes (MWCNTs) or thermally reduced graphene oxide (TRGO) on the electro‐reduction of hydrogen peroxide. Glassy carbon electrodes (GCE) modified with these hybrid nanomaterials dispersed in Nafion/isopropanol demonstrated a clear synergism on the catalytic reduction of reduction of hydrogen peroxide at pH 13.00. The intimate interaction between MFe₂O₄ and carbon nanomaterials allowed a better electronic transfer and a facilitated regeneration of M²⁺ at the carbon nanomaterials, reducing the charge transfer resistances for hydrogen peroxide reduction and increasing the sensitivities of the amperometric response.     

Fe3O4@C Nanotubes Grown on Carbon Fabric as a Free-Standing Anode for High-Performance Li-Ion Batteries

Recently, Li-ion batteries (LIBs) have attracted extensive attention owing to their wide applications in portable and flexible electronic devices. Such a huge market for LIBs has caused an ever-increasing demand for excellent mechanical flexibility, outstanding cycling life, and electrodes with superior rate capability. Herein, an anode of self-supported Fe₃O₄@C nanotubes grown on carbon fabric cloth (CFC) is designed rationally and fabricated through an in situ etching and deposition route combined with an annealing process. These carbon-coated nanotube structured Fe₃O₄ arrays with large surface area and enough void space can not only moderate the volume variation during repeated Li⁺ insertion/extraction, but also facilitate Li⁺/electrons transportation and electrolyte penetration. This novel structure endows the Fe₃O₄@C nanotube arrays stable cycle performance (a large reversible capacity of 900 mA h g⁻¹ up to 100 cycles at 0.5 A g⁻¹) and outstanding rate capability (reversible capacities of 1030, 985, 908, and 755 mA h g⁻¹ at 0.15, 0.3, 0.75, and 1.5 A g⁻¹, respectively). Fe₃O₄@C nanotube arrays still achieve a capacity of 665 mA h g⁻¹ after 50 cycles at 0.1 A g⁻¹ in Fe₃O₄@C//LiCoO₂ full cells.     

Facile synthesis of Fe3O4@C hollow nanospheres and their application in polluted water treatment

Nanostructured carbon-based materials, such as carbon nanotube arrays have shown respectable removal ability for heavy metal ions and organic dyes in aqueous solution. Although the carbon-based materials exhibited excellent removal ability, the separation of them from the aqueous solution is difficult and time-consuming. Here we demonstrated a novel and facile route for the large-scale fabrication of Fe₃O₄@C hollow nanospheres, with using ferrocene as a single reagent and SiO₂ as a template. The as-prepared Fe₃O₄@C hollow nanospheres exhibited adsorption ability for heavy metal ions and organic dyes from aqueous solution, and can be easily separated by an external magnet. When the as-prepared Fe₃O₄@C hollow nanospheres were mixed with the aqueous solution of Hg²⁺ within 15 min, the removal efficiency was 90.3%. The as-prepared Fe₃O₄@C hollow nanospheres were also exhibited a high adsorption capacity (100%) as the adsorbent for methylene blue (MB). In addition, the as-prepared Fe₃O₄@C hollow nanospheres can be used as the recyclable sorbent for water treatment via a simple magnetic separation.     

Mesoporous MnSiO3@Fe3O4@C Nanoparticle as pH-responsive T1-T2* Dual-modal Magnetic Resonance Imaging Contrast Agent for Tumor Diagnosis

Mesoporous structured MnSiO₃@Fe₃O₄@C nanoparticles (NPs) were prepared via a facile and efficient strategy, with negligible cytotoxicity and minor side efforts. The asprepared MnSiO₃@Fe₃O₄@C NPs hold great potential in serving as pH-responsive T₁-T₂^* dual-modal magnetic resonance (MR) imaging contrast agents. The released Mn²⁺ shortened T₁ relaxation time, meanwhile the superparamagnetic Fe₃O₄ enhanced T₂ contrast imaging. The release rate of Mn ions reaches 31.66% under the condition of pH=5.0, which is similar to tumor microenvironment and organelles. Cytotoxicity assays show that MnSiO₃@Fe₃O₄@C NPs have minor toxicity, even at high concentrations. After intravenous injection of MnSiO₃@Fe₃O₄@C NPs, a rapid contrast enhancement in tumors was achieved with a significant enhancement of 132% after 24 h of the administration. Moreover, a significant decreasement of 53.8% was witnessed in T₂ MR imaging signal. It demonstrated that MnSiO₃@Fe₃O₄@C NPs can act as both positive and negative MR imaging contrast agents. Besides, owing to the pH-responsive degradation of mesoporous MnSiO₃, MnSiO₃@Fe₃O₄@C NPs can also be used as potential drug systems for cancer theranostics.     

Constructing oxygen-deficient V2O3@C nanospheres for high performance potassium ion batteries

Potassium ion batteries (PIBs) have been regarded as promising alternatives to lithium ion batteries (LIBs) on account of their abundant resource and low cost in large scale energy storage applications. However, it still remains great challenges to explore suitable electrode materials that can reversibly accommodate large size of potassium ions. Here, we construct oxygen-deficient V₂O₃ nanoparticles encapsulated in amorphous carbon shell (O_d-V₂O₃@C) as anode materials for PIBs by subtly combining the strategies of morphology and deficiency engineering. The MOF derived nanostructure along with uniform carbon coating layer can not only enables fast K⁺ migration and charge transfer kinetics, but also accommodate volume change and maintain structural stability. Besides, the introduction of oxygen deficiency intrinsically tunes the electronic structure of materials according to DFT calculation, and thus lead to improved electrochemical performance. When utilized as anode for PIBs, O_d-V₂O₃@C electrode exhibits superior rate capability (reversible capacities of 262.8, 227.8, 201.5, 179.8, 156.9 mAh/g at 100, 200, 500, 1000 and 2000 mA/g, respectively), and ultralong cycle life (127.4 mAh/g after 1000 cycles at 2 A/g). This study demonstrates a feasible way to realize high performance PIBs through morphology and deficiency engineering.     

Based on MFe2O4 (M=Co,Cu, and Ni): Magnetically recoverable nanocatalysts in synthesis of heterocyclic structural scaffolds

Abstract

Catalysis research under magnetically recoverable nanocatalysts is a well-known topic in organic synthesis. In recent times, catalysis research has clearly experienced a renaissance in the area of utility of ferrite nanoparticles based on their ability to recovery and reusability. In this review, the focus is on the fabrication, characterization and of application the MFe₂O₄ (M=Co, Cu, and Ni) nanocatalysts in synthesis of heterocyclic structural scaffolds.