Pulverization Control by Confining Fe3O4 Nanoparticles Individually into Macropores of Hollow Carbon Spheres for High-Performance Li-Ion Batteries

Lithiation of Anodic Magnetite-Hematite Nanotubes Formed on Iron

Electrochemically active iron oxide nanotubes formed by anodization are of high interest as battery components in various battery systems due to their 1D geometry, offering high volume expansion tolerance and applications without the use of binders and conductive additives. This work takes a step forward toward understanding lithium-ion storage in 1D nanotubes through the analysis of differential capacity plots d(Q - Q0)·dE-1 supported by in situ Raman spectroscopy observations. The iron oxide nanotubes were synthesized by anodizing polycrystalline iron and subsequently modified by thermal treatment in order to control the degree of crystallinity and the ratio of hematite (Fe2O3) to magnetite (Fe3O4). The electrochemical fingerprints revealed a quasi-reversible lithiation/delithiation process through Li2O formation. Significant improvement in electrochemical performance was found to be related to the high degree of crystallinity and the increase of the hematite (Fe2O3) to magnetite (Fe3O4) ratio. In situ mechanistic studies revealed a reversible reduction of iron oxide to metallic iron simultaneously with Li2O formation.

Optimization of heterogeneous Fenton-like process with Cu-Fe@CTS as catalyst for degradation of organic matter in leachate concentrate and degradation mechanism research

The heterogeneous Fenton-like process with bimetallic chelated magnetic chitosan aerogel (Cu-Fe@CTS) as catalyst was applied to treat pre-coagulated leachate nanofiltration concentrate. The process conditions were optimized by Box-Behnken Design (BBD) and the maximum UV₂₅₄ removal reached 96.06% under the conditions of temperature 87.62 °C, oxidant dosage 0.2395 mol/L and catalyst dosage 1 g/L. The TOC concentration was reduced from 847.5 to 99.7 mg/L and COD concentration was reduced from 1625 to 464 mg/L. The three-dimensional (3D) fluorescence analysis showed that most of Fulvic acid-like (FA-like) was removed. The adsorption experiment showed that the catalyst reached the adsorption balanced after 60 min and the corresponding FA adsorption removal reached 14.1%. The addition of Tert-butanol (TBA) reduced the FA removal by 59.4%, indicating that the hydroxyl radicals (OH) was the main active species. Experiments of the OH capture at different pH showed that the Fenton-like system produced more OH at pH of 4, at which the maximum FA removal was 96.61%, while the FA removal still reached 94.26% at pH of 7. The OH capture at different temperature showed that the Fenton-like system produced more OH at 90 °C. KI and TBA shielding experiments showed that OH was produced on the catalyst surface rather than being produced by catalysis of free metal ions in the solution.

Facile one-step synthesis of 3D honeycomb-like porous chitosan bead inlaid with MnFe bimetallic oxide nanoparticles for enhanced degradation of dye pollutant

Developing a sustainable, efficient and recyclable heterogeneous Fenton-like catalyst is important to wastewater treatment. Herein, well-dispersed MnO₂ and Fe₃O₄ nanoparticles inlaid in chitosan beads (MnO₂-Fe₃O₄/CH) was firstly fabricated and employed in the degradation of methylene blue (MB). The bead was prepared via a facile one-step method by dropwise addition of chitosan-metal salt solution into alkaline solution. Comparing with monometallic chitosan beads (MnO₂/CH, Fe₃O₄/CH) and naked MnO₂-Fe₃O₄, MnO₂-Fe₃O₄/CH displayed significantly higher activity for MB degradation with the assistance of hydrogen peroxide (H₂O₂), finally removing 96.8% MB under the optimal conditions (50 mg L^-1 MB, 4.0 g L^-1 catalyst, 30 g L^-1 H₂O₂, pH = 7, 60 min). Based on a series of characterizations, the large surface area (60.1 m² g^-1), well-developed porosity (0.3 cm³ g^-1), and intensified electron transport of MnO₂-Fe₃O₄/CH consequently enhanced the catalytic performance via a synergistic effect. Because the specific porous structure of MnO₂-Fe₃O₄/CH facilitated the adsorption/diffusion of reactants and exposure of active sites. Meanwhile, the electron transfer from Mn³⁺ to Fe³⁺ accelerated the Fe³⁺/Fe²⁺ cycle, which favored the production of dominant reactive species hydroxyl radical for MB degradation. Besides, the magnetic beads could be easily collected from the solution and reused for five times with a negligible leaching.

Retracting interphasial stored Li+ ions by transition metal/metal carbide nanoparticles for enhanced Li+ ion storage capacity

Herein, we report the synthesis of metal/metal carbide (Co, Ni, and Fe₃C) nanoparticles (NPs) encapsulated nitrogen-doped carbon nanotubes (NCNT) and its application as the anode materials for lithium-ion battery (LIB). The electron microscopy images confirm the encapsulation of metal NPs inside the carbon nanotubes, which can inhibit the NPs aggregations and offer long cycle life for LIB. The metal/metal carbide encapsulated NCNT as anode material exhibits higher specific capacity than pure NCNT. The cyclic voltammetry studies reveal that Co, Ni, and Fe₃C NPs can oxidize and reduce the solid electrolyte interphase (SEI) layer components of the anode. This offers the extra specific capacity to Fe₃C/NCNT, Co/NCNT, and Ni/NCNT anodes by retracting the interphasial stored Li⁺ ions. Moreover, in this study, the catalytic activity of Co, Ni, and Fe₃C NPs for tailoring the SEI components are compared for the first time, and it shows Fe₃C/NCNT anode has the highest catalytic activity than Co/NCNT and Ni/NCNT. Co/NCNT and Fe₃C/NCNT also exhibit good cycle life up to 1300 cycles at a current density of 1 A g^-1. Overall, this work demonstrates an effective strategy to improve the performance of LIB anode by retracting the interphasial stored Li⁺ ions.

MoS2-based composite nanozymes with superior peroxidase-like activity for ultrasensitive SERS detection of glucose

An ultrasensitive biosensor with high peroxidase-like catalytic activity and excellent SERS properties is developed based on PANI@MoS2@Fe3O4@Au nanozymes.

Inner-Stress-Optimized High-Density Fe3O4 Dots Embedded in Graphitic Carbon Layers with Enhanced Lithium Storage

The volume variation of electrode materials will lead to poor cyclability of lithium-ion batteries during the lithiation/delithiation process. Instead, inner-stress fragmentation is creatively used to change carbon-layer-capped Fe₃O₄ particles ∼30 nm in diameter into high-density Fe₃O₄ dots ∼4 nm in size embedded in ultrathin carbon layers. The optimized structure shows a remarkable 45.2% enhancement of lithium storage from 804.7 (the 10th cycle) to 1168.7 mA h g^-1 (the 250th cycle) at 500 mA g^-1, even retaining 1239.5 mA h g^-1 after another 550 cycles. The electrochemical measurements reveal the enhanced capacitive behavior of the high-density Fe₃O₄ dots@C layers, which have more extra active sites for the insertion/extraction of Li⁺ ions, confirmed by the differential capacity plots, leading to remarkably increased specific capacity during cycling. The restructured electrode also shows a superior rate capacity and excellent cycling stability (938.7 and 815.4 mA h g^-1 over 2000 cycles at 1000 and 2000 mA g^-1, respectively). X-ray photoelectron spectroscopy and transmission electron microscopy characterizations show that the optimized structure has stable structural and componential stability even at large rates. This work presents an MOF-guided synthesis of high-density Fe₃O₄-dots' anode material optimized by inner-stress fragmentation, showing a feasible route to design high-efficiency electrode materials.

Electrostatically Fabricated Three-Dimensional Magnetite and MXene Hierarchical Architecture for Advanced Lithium-Ion Capacitors

Conversion-type magnetite shrewdly shows abundance, nontoxicity, and high lithium storage capacity. However, either pristine magnetite or nanocomposites with two-dimensional materials cannot prevent restacking, pulverization, and poor structural homogeneity simultaneously because of a lack of universal interfacial interactions. Here, an electrostatic self-assembly strategy is uncovered between hollow Fe₃O₄/C microspheres (with H⁺-induced quasi-intrinsic positive charge) and few-layer MXenes (with intrinsic negative charge from terminating functionalities). This strategy realizes the uniform and interconnected architecture of Fe₃O₄/C@MXene that favors fast Li⁺ diffusion, easy electron/charge transfer, and suppressed pulverization. Specifically, after the long-term cycling, an undegraded specific capacity of 907 mA h g^-1 remains at 0.5 A g^-1. Further adoption of such superior anode in 4.0 V lithium-ion capacitors results in a high energy density of 130 W h kg^-1, a maximum power density of 25,000 W kg^-1, and excellent cycling stability. This work thus sheds light on a generic self-assembly process where intrinsic electrostatic interaction plays an essential role.

Insights into the lithium diffusion process in a defect-containing porous crystalline POM@MOF anode material

A crystalline POM@MOF material with high Li-ion storage capacity with surface uncoordinated N atoms (defect sites) is reported. The Li-ion diffusion sites are confirmed via ex situ XPS and off-line XRD measurements.

Cobalt-promoted fabrication of 3D carbon with a nanotube-sheet mutual support structure: scalable preparation of a high-performance anode material for Li-ion batteries

Currently, the design of carbon-based composite as a high-performance anode material for lithium-ion batteries (LIBs) presents challenges for commercial application. Herein, we developed a three-dimensional carbon-based material with a nanotube-sheet mutual support structure (MS-CNTS) engineered by the catalytic effect of Co species. The present work highlights a concise 'solvent-free' synthetic method allowing for large-scale output, which is potentially available for low cost commercial use. With the readily available acetylacetonate and cobalt (II) acetylacetonate as starting chemicals, this nanostructured carbonaceous material is fabricated with aldol condensation to construct a Co-contained carbon-link network polymer precursor followed by annealing under argon. It is composed of brim-curled graphene-like carbon nanosheets and carbon nanotubes, which support each other's structures to effectively avoid agglomeration. Therefore, it enables high performance in LIBs. In spite of the trace amount of cobalt, the carbon-based MS-CNTS anode delivers a high charge capacity of 1028 mAh g-1 at 0.1 A g-1, high rate capacity of 495 mAh g-1 at 2 A g-1, and ultra-long cycling life with a very low capacity decay of 0.008% per cycle over 1000 cycles at 0.5 A g-1, accompanied by 100% Coulombic efficiency. From full cell measurements, we further confirm the considerable promise of MS-CNTS as anodes with a long cycling life.

A composite of Fe3O4@C and multilevel porous carbon as high-rate and long-life anode materials for lithium ion batteries

The iron oxide-based anode materials are widely studied and reported due to their abundance, low cost, high energy density and environmental friendliness for lithium ion batteries (LIBs). However, the application of LIBs is always limited by the poor rate capability and stability. In order to tackle these issues, a novel material with carbon-encapsulated Fe₃O₄ nanorods stuck together by multilevel porous carbon (Fe₃O₄@C/PC) is prepared through directly carbonizing the Fe-based metal-organic framework under a nitrogen atmosphere. This novel material shows a high specific capacity and rate performance. The initial specific capacity can reach 1789 mAh g^-1 at a current density of 0.1 A g^-1, and the specific capacity still remains 1105.3 mAh g^-1 and 783.5 mAh g^-1 after 150 cycles at the current densities of 0.1 A g^-1 and 1 A g^-1, respectively. Even under a current density as high as 12 A g^-1, the specific capacity can achieve 309 mAh g^-1 after 2000 cycles with an average attenuation rate of 0.019% per cycle. Overall, the simple strategy, low cost and high capacity can make the practical application possible.

Carbothermal Synthesis of Nitrogen-Doped Graphene Composites for Energy Conversion and Storage Devices

Metal oxides and carbonaceous composites are both promising materials for electrochemical energy conversion and storage devices, such as secondary rechargeable batteries, fuel cells and electrochemical capacitors. In this study, Fe₃O₄ nanoparticles wrapped in nitrogen-doped (N-doped) graphene nanosheets (Fe₃O₄@G) were fabricated by a facile one-step carbothermal reduction method derived from Fe₂O₃ and liquid-polyacrylonitrile (LPAN). The unique two-dimensional structure of N-doped graphene nanosheets, can not only accommodate the volume changes during lithium intercalation/extraction processes and suppress the particles aggregation but also act as an electronically conductive matrix to improve the electrochemical performance of Fe₃O₄ anode, especially the rate capability. What's more, by etching Fe₃O₄@G to remove the iron-based oxide template, porous N-doped graphene composites (NGCs) were prepared and presented abundant pore structure with high specific surface area, delivering a specific capacitance of 172 F·g^-1 at 0.5 A·g^-1. In this way, Fe₂O₃ was both template and activator to adjust the pore size of graphene. And the effect of specific surface area and pore size tuned by the Fe₂O₃ activator were also revealed.