Carbon-coated Fe3O4 Research Articles

Carbon-coated Fe3O4 derived from metal-organic frameworks on reduced graphene as electrochemical sensor platform for Hg(II) determination

Mercury, a well-known neurotoxicant, mainly occurs as Hg0, Hg2+ or Hg (CH3)2 in the environment. Therefore, there is an urgent need to develop new analytical methods to rapidly screen for mercury in natural water. In this work, rGO-MIL-101(Fe) was fabricated using reduced graphene oxide (rGO) and MIL-101 by one spot solvothermal method, and then was pyrolyzed at 500 °C to yield carbon-coated Fe3O4 dispersed on rGO (hereafter rGO-Fe@C). The rGO-Fe@C was characterized by SEM, TEM, TGA, XRD, XPS and Raman spectroscopic methods for its morphological features, particulate size & gradations, element redox states. An electrochemical sensing interface was constructed for Hg2+ determination using rGO-Fe@C modified glassy carbon electrode(rGO-Fe@C/GCE) by square wave anode stripping voltammetry (SWASV). The rGO-Fe@C/GCE exhibits high sensitivity for Hg2+ determination with a sensitivity of 34.47 μA/μM and a limit detection of 4.5 nM. The sensitive mechanism of Hg2+ in the electrochemical interface was investigated by XPS and DFT calculations. The presence of common cations as Cd2+, Cu2+ and Pb2+ in comparable molarities does not interfere with Hg2+ detection. Moreover, the electrode sensor possesses good stability and reproducibility for repetitive analysis of samples. The rGO-Fe@C/GCE sensor can be used in Hg2+ detection with minimal matrix interference by ions ubiquitous in natural water.

Polyaniline layered N-doped carbon-coated iron oxide nanocapsules for extremely active Li-ion battery anode and oxygen evolution reaction

We report the effective synthesis of polyaniline (PANi)-layered nitrogen-doped carbon-coated Fe3O4 (FNC@PANi) nanocapsules (NCs) for electrocatalysis of oxygen evolution reaction (OER) as well as anode material for lithium (Li)-ion batteries (LIBs) via a simple hydrothermal method and oxidative polymerization technique. The prepared FNC@PANi NCs revealed a dual core-shell structure, in which an intermediate carbon layer allowed excellent electrical conduction between the Fe3O4 NCs and PANi. The dual core-shell structure also allowed the Fe3O4 NCs to expand freely during the Li-ion insertion/extraction and OER processes without breaking the outer layer, thus providing a high surface area (147.85 m2 g−1) and enhanced electrical conductivity. These properties facilitate the application of the dual core-shell FNC@PANi NCs as an advanced electrode material for LIBs, delivering a high reversible specific capacity of 1556.48 mAh g−1 at 0.1 A g−1, excellent rate performance (896.96 mAh g−1 at 1 A g−1), and durable cycling life (680.12 mAh g−1 at 5 A g−1 for 3000 cycles). The dual core-shell FNC@PANi NCs exhibited high electrocatalytic activity in the OER, with a small Tafel slope of 108.7 mV dec−1 owing to synergistic effects between the copious active sites of the Fe3O4 NCs and the carbon core-shell structure and a modest overpotential of 219 mV at 10 mA cm−2. The electrodes showed excellent stability over 10 h, as determined by chronopotentiometry at 10 mA cm−1. The resultant dual-core-shell FNC@PANi NCs are efficient iron-oxide-based electrode materials for LIBs and OER electrocatalysts.

Fabrication of a carbon-coated Fe3O4 for ozone catalysis to facilitate HO2− formation during ozonation

In the O3 self-decomposition process, the poor HO2− formation efficiency limits O3 decomposition and •OH production. Although the addition of Fenton’s reagent facilitates this process, H2O2 consumption and Fe(III) sedimentation must be addressed. In this study, carbon-coated Fe3O4 (Fe3O4@C) samples were prepared using the metal–organic frameworks (MOFs) modification method for the catalytic ozonation of aromatics, which effectively solved the above challenges. The fabricated 4-Fe3O4@C catalyst not only exhibited a yolk-shell structure, but also increased •OH production by 9-fold, resulting in optimal target removal, mineralization, and O3 decomposition efficiency. Further investigation confirmed that the activity of 4-Fe3O4@C was owing to the combined action of Fe(II) on the catalyst surface and the H2O2 produced from aromatic degradation. Furthermore, the outer carbon layer with reducing properties regenerated Fe(II) in a timely manner, ensuring catalyst durability. Finally, a clear pathway for enhancing O3 decomposition and •OH generation is proposed.

Fabrication of porous X-shaped Fe3O4@C core-shell structures for tunable microwave absorption

Designing porous materials with low density and high specific surface area is one of the strategies to obtain excellent wave absorbing properties. In this study, the carbon-coated porous X-shaped Fe3O4 composites used as microwave absorption materials were prepared by heat treatment of FeOOH@Polydopamine (PDA) core-shell precursors. It revealed that the X-shaped Fe3O4 core showed improved magnetic loss in GHz band due to its special shape anisotropy and large specific surface area. In addition, the modification of carbon enabled the Fe3O4 absorbers to have stronger polarization and higher electrical conductivity. The composites exhibited great freedom in performance tunability, allowing for strong absorption (RL<−40 dB) at different frequencies. For composites with thick carbon shell, the reflection loss reached the optimal value of − 64.92 dB at 15.04 GHz at the thickness of 1.75 mm, and the effective bandwidth was up to 4.64 GHz (13.04–17.68 GHz). The impressive performance of the as-prepared Fe3O4 @C core-shell composites was mainly attributed to the complementary behaviors of strong dielectric loss and magnetic loss.

AgNWs/Fe3O4@NC Conductive Network Hierarchical Assembly to Prepare Flexible EMI Shielding Textile.

With the rapid development of high-power electronic instruments and communication technology, efficient electromagnetic shielding materials with strong absorption of electromagnetic waves and low reflection characteristics have become the focus of the world's attention. This study designs and synthesizes N-doped carbon-coated hollow Fe3O4 nanospheres (Fe3O4@NC) by spraying Ag nanowires (AgNWs) on textiles as conductive networks. Because of the high permeability and hollow structure Fe3O4@NC, electromagnetic wave goes through a unique process of "absorption, reflection, and reabsorption" when it passes through the surface of the composite textile. In X-band (≈8.2-12.4GHz), the average electromagnetic interference shielding effectiveness (EMI SE) reaches 50.1dB, while the reflectance shielding efficiency (SER) is only 2.6dB, and the average reflectance power coefficient (R) is as low as 0.45. The composite fabric has excellent properties and provides an effective strategy for electromagnetic interference shielding based on absorption.

Design and Construction of Carbon-Coated Fe3 O4 /Cr2 O3 Heterostructures Nanoparticles as High-Performance Anodes for Lithium Storage.

Transition metal oxides, highly motivated anodes for lithium-ion batteries due to high theoretical capacity, typically afflict by inferior conductivity and significant volume variation. Architecting heterogeneous structures with distinctive interfacial features can effectively regulate the electronic structure to favor electrochemical properties. Herein, an engineered carbon-coated nanosized Fe3 O4 /Cr2 O3 heterostructure with multiple interfaces is synthesized by a facile sol-gel method and subsequent heat treatment. Such ingenious components and structural design deliver rapid Li+ migration and facilitate charge transfer at the heterogeneous interface. Simultaneously, the strong coupling synergistic interactions between Fe3 O4 , Cr2 O3 , and carbon layers establish multiple interface structures and built-in electric fields, which accelerate ion/electron transport and effectively eliminate volume expansion. As a result, the multi-interface heterostructure, as a lithium-ion battery anode, exhibits superior cycling stability maintaining a reversible capacity of 651.2 mAh g-1 for 600 cycles at 2 C. The density functionaltheorycalculations not only unravel the electronic structure of the modulation but also illustrate favorable lithium-ion adsorption kinetics. This multi-interface heterostructure strategy offers a pathway for the development of advanced alkali metal-ion batteries.

Microwave absorption performance of magnetic-dielectric Fe3O4@C@PPy composites with a core-double-shell structure prepared by a low-temperature self-propagation method

Microwave absorbers have been developed to counter electromagnetic pollution, and enhancing their performance remains an ongoing concern. In this paper, carbon-coated Fe3O4 and polypyrrole (PPy) were combined to construct composites with a core-double-shell structure, and the influences of multiple synergistic effects from ternary components, carbon defects, and microstructure on the electromagnetic properties of Fe3O4@C@PPy composites were investigated. The Fe3O4@C@PPy composites were successfully prepared by the low-temperature self-propagation method and in-situ oxidation polymerization process, achieving a −53.67 dB reflection loss at 12.24 GHz when the sample thickness was 2.13 mm, and the effective absorbing (RL < 10 dB) band covered 4.16 GHz (13.84–18 GHz) with a corresponding thickness of only 1.63 mm. The core-double-shell structure perfectly integrated various advantages of each component as well as provided multiple reflections and scatterings. Meanwhile, the polarization loss was notably enhanced by heterogeneous interfaces, and the dielectric-magnetic loss mechanism cooperatively accelerated the dissipation of electromagnetic wave energy.

Carbon-coated mesoporous Fe3O4 nanospindles with interconnected porosities as polysulfide mediator for lithium–sulfur batteries

Lithium-sulfur batteries are plagued by the shuttle effect and sluggish kinetics in the redox reaction of lithium polysulfides (LiPSs) to Li2S, resulting in a limited capacity and shortened lifetime. To address these issues, it is crucial to develop an efficient catalytic sulfur host by creating active sites that can both confine LiPSs and accelerate their conversion. Herein, we developed carbon-coated mesoporous Fe3O4 (C@M−Fe3O4) nanospindles and applied them as sulfur host material to improve the electrochemical performance of Li–S batteries. Besides, the conductive C@M−Fe3O4 particles with rich sites of electrolyte/Fe3O4/carbon ‘‘triple-phase’’ can also accelerate the conversion of LiPSs and promote the nucleation and growth of Li2S. With these merits, our C@M-Fe3O4/S electrode shows good cycling stability with a remaining capacity of 1064.3 mAh/g at 0.2 C after 100 cycles and delivers an initial capacity of 712.0 mAh/g at 2 C. The proposed synthetic method could pave the way for designing similar porous transition metal-based compounds with different precursors (e.g. carbonates, hydroxides, oxalates) for other electrochemical applications.

Octahedral/Tetrahedral Vacancies in Fe3 O4 as K-Storage Sites: A Case of Anti-Spinel Structure Material Serving as High-Performance Anodes for PIBs.

Potassium-ion batteries (PIBs) have attracted more and more attention as viable alternatives to lithium-ion batteries (LIBs) due to the deficiency and uneven distribution of lithium resources. However, it is shown that potassium storage in some compounds through reaction or intercalation mechanisms cannot effectively improve the capacity and stability of anodes for PIBs. The unique anti-spinel structure of magnetite (Fe3 O4 ) is densely packed with thirty-two O atoms to form a face-centered cubic (fcc) unit cell withtetrahedral/octahedralvacanciesin the O-closed packingstructure, which can serve as K+ storage sites according to the density functional theory (DFT) calculation results. In this work, carbon-coated Fe3 O4 @C nanoparticles are prepared as high-performance anodes for PIBs, which exhibit high reversible capacity (638 mAh g-1 at 0.05 A g-1 ) and hyper stable cycling performance at ultrahigh current density (150 mAh g-1 after 9000 cycles at 10 A g-1 ). In situ XRD, ex-situ Fe K-edge XAFS, and DFT calculations confirm the storage of K+ in tetrahedral/octahedral vacancies.

Ultrasensitive fluorometric determination of daclatasvir in exhaled breath condensate samples after magnetic solid-phase extraction by carbon-coated Fe3O4 magnetic nanoparticles: method optimization via central composite design combined with desirability function

Ultrasensitive fluorometric determination of daclatasvir in exhaled breath condensate samples after magnetic solid-phase extraction by carbon-coated Fe3O4 magnetic nanoparticles: method optimization via central composite design combined with desirability function

Carbon-coated Fe3O4 nanocomposites anchored on Ti3C2 nanosheets for enhanced Li-storage

Fe3O4 is a promising anode material for high-power rechargeable lithium-ion batteries (LIBs) benefiting from its high reversible capacity, rich natural resources, and easy preparation. However, the rate capability and the cyclability of the Fe3O4 electrode are still unsatisfactory limited by its poor electronic conductivity and tremendous volume variation during Li+ insertion/desertion progress. To tackle these difficulties, carbon-coated Fe3O4 nanocomposites anchored on few-layered Ti3C2 nanosheets (Fe3O4 @C/Ti3C2) were prepared by a facile and scalable citric acid-assisted sol-gel process. As an anode material for LIBs, the Fe3O4 @C/Ti3C2 electrode delivers a high reversible capacity of 1285 mAh g−1 at 100 mA g−1 and a high rate capacity of 405 mAh g−1 at 5 A g−1. Moreover, the Fe3O4 @C/Ti3C2 electrode presents a steady cyclability for more than 1000 cycles at 5 A g−1. The enhanced Li-ion storage performance of the Fe3O4 @C/Ti3C2 electrode could be attributed to the high electrical conductivity and the mechanical robustness of the Ti3C2 nanosheets.

Synthesis of amorphous carbon functionalized Fe3O4 nanoparticles as a smart nanosorbent for organic dyes removal

Illustration of process for synthesis of carbon coated Fe3O4 (CCF) nanocomposites and their application as nanosorbents with recoverability and regenerability for the sorption of organic dyes.

Immobilization of hexamolybdate onto carbon-coated Fe3O4 nanoparticle: A novel catalyst with high activity for oxidation of alcohols

A novel core-shell structural magnetic nanocatalyst involving carbon coatings on magnetic Fe3O4 nanoparticle (Fe3O4@C) for immobilizing polyoxometalate hexamolybdate (HM), were prepared by a facile chemical approach. The catalyst was identified by various techniques such as FE-SEM, EDX, VSM, XRD, TG, TEM, and FT-IR spectroscopy. This nanocatalyst were applied in the oxidation of alcohols using tert-butyl hydroperoxide, an oxidant in acetonitrile. The oxidation product was obtained at a high yield. The new nanocatalyst showed good recoverability without any significant loss of activity within successive runs.

Constructing carbon-coated Fe3O4 hierarchical microstructures with a porous structure and their excellent Cr(VI) ion removal properties

A facile solvothermal method coupled with an annealing strategy is developed to synthesize Fe3O4/carbon (Fe3O4@C) magnetic composite microstructures with different morphologies, including flower-like, hollow spheres and egg-like. The unique multiporous and hollow structure of the as-prepared hierarchical Fe3O4@C hollow microsphere results in an appealing performance as an absorber of Cr(VI) ions in aqueous solution, delivering a high capacity of ~ 197.2 mg/g. Meanwhile, the magnetic Fe3O4 ‘‘core’’ in the hierarchical microstructures can be easily separated from aqueous systems by magnetic separation. Furthermore, the carbon layers effectively prevent the aggregation of magnetic Fe3O4 nanoparticles. The excellent absorbing ability of Cr(VI) ions and easy separation process strongly suggest that the Fe3O4@C magnetic microstructures would have a great potential as adsorbing materials in the large-scale application in environmental purification.

All-Graphitic Multilaminate Mesoporous Membranes by Interlayer-Confined Molecular Assembly.

Layered mesostructured graphene, which combines the intrinsic advantages of planar graphene and mesoporous materials, has become interestingly important for energy storage and conversion applications. Here, an interlayer-confined molecular assembly method is presented for constructing all-graphitic multilaminate membranes (MMG⊂rGO), which are composed of monolayer mesoporous graphene (MMG) sandwiched between reduced graphene oxide (rGO) sheets. Hybrid assembly of iron-oleate complexes and organically modified GO sheets enables the preferential assembly of iron-oleate precursors at the interlayer space of densely stacked GO, driven by the like-pair molecular van der Waals interactions. Confined pyrolysis of iron-oleate complexes at GO interlayers leads to close-packed, carbon-coated Fe3 O4 nanocrystal arrays, which serve as intermediates to template the subsequent formation of MMG⊂rGO membranes. To demonstrate their application potentials, MMG⊂rGO membranes are exploited as dual-functional interlayers to boost the performance of Li-S batteries by concurrently suppressing the shuttle of polysulfides and the growth of Li dendrites. This work showcases the capability of molecular-based hybrid assembly for synthesizing multilayer mesostructured graphene with high packing density and its use in electrochemical energy applications.

Controllable synthesis of carbon-coated Fe3O4 nanorings with high Li/Na storage performance

Fe3O4 with high capacity and low cost has been a promising anode for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). However, the intrinsic issues from the severe volume change of Fe3O4 during cycling and its inferior electronic conductivity result in poor capacity retention. Herein, carbon-coated Fe3O4 nanorings (R-Fe3O4@C) were fabricated by a facile method. The hollow nanorings with a small size below 80 nm are designed to mitigate the severe volume expansion of Fe3O4 upon cycles, whereas the amorphous carbon layer with a thickness of 12 nm is created to induce the fast electronic transfer. Benefiting from the unique carbon-coated nanostructure, R-Fe3O4@C exhibits superior electrochemical behaviors in both LIBs and SIBs. As an anode of LIBs, it delivers a high capacity of 1003.4 mAh g−1 at 0.5 A g−1 over 100 cycles, and of 421.2 mAh g−1 at 5 A g−1 over 800 cycles. Being an anode for SIBs, it shows a considerable capacity of 365.1 mAh g−1 at 0.1 A g−1 after 200 cycles, and of 160.3 mAh g−1 at 2 A g−1 after 300 cycles. Our work achieves the remarkable electrochemical properties of R-Fe3O4@C via the facile fabrication in which relatively low-cost ingredients are used.

In-situ plantation of Fe3O4@C nanoparticles on reduced graphene oxide nanosheet as high-performance anode for lithium/sodium-ion batteries

Fe3O4 is considered to be an ideal substitute for graphite anode due to its high lithium (Li) and sodium (Na) storage capacity, however, its sharp volume change after lithiation/sodiumization and poor electrical conductivity have brought huge challenges to the practical application. In this study, a lamellar Fe3O4-based electrode was constructed via an in-situ plantation of carbon-coated Fe3O4 nanoparticles on the surface of the reduced graphene oxide nanosheet. Owing to the ultra-small carbon-coated Fe3O4 nanoparticles (~12.5 nm) and unique two-dimensional lamellar structure, the obtained sample displays excellent cycle and rate performance in lithium/sodium-ion batteries. A high reversible capacity of 849 mA h g−1 is obtained at 500 mA g−1 after 120 cycles for lithium-ion batteries and a discharge capacity up to 429 mA h g−1 is remained at 100 mA g−1 after 300 cycles for sodium-ion batteries.

Encapsulation of a Core-Shell Porous Fe3O4@Carbon Material with Reduced Graphene Oxide for Li+ Battery Anodes with Long Cyclability.

Anode materials are critical for energy devices based on Li-ion batteries (LIBs). This work reports on a facile method to produce anodes based on carbon-coated Fe3O4 (CP-Fe3O4) that is encapsulated in reduced graphene oxide (rGO) layers forming a porous core-shell structure Fe3O4@carbon (rGO-CP-Fe3O4). First, Fe3O4 particles were coated with carbon by hydrothermal and carbothermal reduction methods leading to an intermediate product termed CP-Fe3O4. Next, CP-Fe3O4 was encapsulated by two-dimensional layered rGO to obtain CP-Fe3O4 composites with a three-dimensional structure. The Fe3O4 volume expansion during LIB cycling was inhibited by carbon and rGO and a three-dimensional electron transport network was generated by the introduction of rGO. The rGO-CP-Fe3O4 composite showed excellent electrochemical properties (839 mA h g-1 at 0.3 A g-1 after 200 cycles) and rate capacities (165 mA h g-1 at 6.0 A g-1). In addition, the rGO-CP-Fe3O4 pseudocapacitance was equal to 65% of the overall capacity at 5 mV s-1.

A High-Efficient Carbon-Coated Iron-Based Fenton-Like Catalyst with Enhanced Cycle Stability and Regenerative Performance

Carbon coated iron-based Fenton-like catalysts are now widely studied in wastewater treatment. However, their poor stability is still a big challenge and the related regenerative performance is seldom investigated. Herein, a carbon-coated Fe3O4 on carbon cloth (cc/Fe3O4@C) was prepared with glucose as carbon source via electrodeposition and ethanol solvothermal methods. An amorphous carbon layer with polar C-groups covers the surface of Fe3O4, which presents a flaky cross-linked network structure on the carbon cloth (cc). The cc/Fe3O4@C exhibits an improved catalytic activity with nearly 84% phenol was removed within 35 min with polar C-groups. What’s more, around 80% phenol can still be degraded in 120 min after 14 degradation cycles. After the regeneration treatment, the degradation performance was restored to the level of the fresh in the first two regenerations. The enhanced cycle stability and regeneration performance of the catalyst are as follows: Firstly, the catalyst’s composition and structure were recovered; Secondly, the reduction effect of the amorphous carbon layer ensuring timely supplement of Fe2+ from Fe3+. Also, the carbon layer reduces Fe leaching during the Fenton-like process.

Efficient Mercury Removal at Ultralow Metal Concentrations by Cysteine Functionalized Carbon-Coated Magnetite

This work reports the preparation and utility of cysteine-functionalized carbon-coated Fe3O4 materials (Cys-C@Fe3O4) as efficient sorbents for remediation of Hg(II)-contaminated water. Efficient removal (90%) of Hg(II) from 1000 ppb aqueous solutions is possible, at very low Cys-C@Fe3O4 sorbent loadings (0.01 g sorbent per liter of Hg(II) solution). At low metal concentrations (5–100 ppb Hg(II)), where adsorption is typically slow, Hg(II) removal efficiencies of 94–99.4% were achievable, resulting in final Hg(II) levels of &lt;1.0 ppb. From adsorption isotherms, the Hg(II) adsorption capacity for Cys-C@Fe3O4 is 94.33 mg g−1, around three times that of carbon-coated Fe3O4 material. The highest partition coefficient (PC) of 2312.5 mgg−1µM−1 was achieved at the initial Hg (II) concentration of 100 ppb, while significantly high PC values of 300 mgg−1µM−1 and above were also obtained in the ultralow concentration range (≤20 ppb). Cys-C@Fe3O4 exhibits excellent selectivity for Hg(II) when tested in the presence of Pb(II), Ni(II), and Cu(II) ions, is easily separable from aqueous media by application of an external magnet, and can be regenerated for three subsequent uses without compromising Hg(II) uptake. Derived from commercially available raw materials, it is highly possible to achieve large-scale production of the functional sorbent for practical applications.