Aggregation Of Fe3O4 Research Articles

Fabrication of core–shell Fe3O4@SiO2/graphite catalyst to improve the charge separation for enhanced photocatalytic toluene oxidation

Magnetite (Fe3O4) has been regarded as a potential photocatalyst for VOCs degradation. Nevertheless, the magnetism of Fe3O4 always leads to the aggregation of particles, which is adverse for gaseous VOCs degradation. Meanwhile, the fast charge recombination of Fe3O4 seriously limits the photocatalytic activity. Herein, a layer of SiO2 was coated on the surface of Fe3O4, and Fe3O4@SiO2 particles were combined with graphite to prepare the core–shell catalyst for photocatalytic toluene oxidation. Fe3O4@SiO2/G catalyst showed the toluene degradation efficiency of 85.09%, which was 3.2 and 1.3 times than those of Fe3O4 and Fe3O4/G. The coating of SiO2 prevented the aggregation of Fe3O4 and greatly enhanced the specific surface area. Experimental and theoretical calculation proved that the existence of SiO2 promoted the spatial charge separation and inhibited the charge recombination, resulting in the generation of abundant reactive oxygen species. These findings offered an insight into the catalyst design for photocatalytic VOCs oxidation.

Preparation of magnetic hydroxyapatite whisker and its adsorption capacity to cadmium ion

Hydroxyapatite (HA) is a safe and stable adsorbent that can be used for the removal of Cadmium ions (Cd2+), and non-generation of secondary pollution. In the study, plate-like HA whiskers with well-defined crystallinity, controllable dimensions, and high aspect ratios are synthesized by the hydrothermal method. Magnetic hydroxyapatite (HA@Fe3O4) is then formed by uniformly encapsulating the HA whiskers by nano Fe3O4. With a comparison of HA whiskers prepared with 10 mmol/L Ca2+ concentration, the hydrothermally synthesized HA whiskers with 33 mmol/L Ca2+ concentration exhibit uniform shape and high crystallinity with an aspect ratio of 40–50 and length of 60–100 µm. Not only modification capacity but also aggregation of Fe3O4 on HA whiskers increases with the increase of Fe3O4 content. The addition of 4% Fe3O4 has a higher modification efficiency to HA, low aggregation of Fe3O4 and excellent magnetic responsiveness. HA@Fe3O4 with 4% Fe3O4 demonstrates a strong capacity for cadmium ion immobilization. At an initial Cd2+ concentration of 30 ppm, the Cd2+ removal efficiency of HA@Fe3O4 with 4% Fe3O4 reaches 59% within 20 min, and the Cd2+ concentration remains relatively stable in 48 h. A substantial removal efficiency is 22% after 10 min in the solution of 3000 ppm Cd2+. Importantly, XPS and XRD results indicate that Ca2+ in HA crystals is displaced by Cd2+ and can effectively transform Cd2+ to a more stable state during the removal process. This study provides a simple and convenient method with stable adsorption and magnetic separating, which would be suitable for tackling Cd2+ contamination with different concentrations and have little impact on the environment.

Dual-responsive amplification strategy for ultrasensitive detection of norovirus in food samples: Combining magnetic relaxation switching and fluorescence assay

Ultra-sensitive, accurate, and specific diagnostic probes are urgently developed to overcome the limitations of conventional norovirus (NV) probes. Herein, we presented the fabrication of a dual-signal probe using multifunctionalized gold and magnetic nanoparticles hybrid composite (Fe3O4 @Au NPs) carriers for the specific detection of NV by magnetic relaxation-fluorescence bimodal sensing. The dual-specific probes were created by modifying Fe3O4 @Au NPs with antibody (Ab) and aptamer-FAM. The antigen-Ab immunoreaction caused aggregation of Fe3O4 @Au NPs, altering the magnetic relaxation signal; simultaneously, the aptamer-FAM that were originally adsorbed on the Au surface were desorbed and cleaved into the solution in the presence of NV, causing a change in the fluorescence signal. Ultrahigh detection sensitives of 0.38 and 3.45 pg/mL were obtained for the dual-modality detection platform, respectively. Furthermore, two quantitative methods obtained satisfactory spiked recoveries for NV-spiked oyster, scallop, strawberry, and tomato samples, consistent with the results of commercial ELISA kits. The results indicated that this dual-specificity assay not only was ultrasensitive but also markedly boosted analysis reliability and precision. Hence, the dual-mode biosensor exhibits high potential for NV detection in the field of food safety.

Hydrothermal synthesis of Zr-doped chitosan carbon-shell protected magnetic composites (Zr–Fe3O4@C) for stable removal of Cr(VI) from water: Enhanced adsorption and pH adaptability

In this study, zirconium-doped carbon shell-protected magnetic Fe3O4 composite (Zr–Fe3O4@C) was synthesized by hydrothermal method with chitosan assistance. Chitosan as a stabilizer successfully prevented the aggregation of Fe3O4, resulting in approximately a 30.7% increase in the specific surface area of Zr–Fe3O4@C. TEM analysis revealed that Zr–Fe3O4@C exhibited a relatively uniform square shape with a size of about 120 nm. The synergistic effect between iron and zirconium oxides resulted in a nearly 20% increase in the adsorption capacity of Zr–Fe3O4@C (Fe/Zr molar ratio of 3:1) for Cr(VI) compared to Fe3O4. The introduction of zirconium also significantly improved the acid and base resistance (1–9) and environmental adaptability of Zr–Fe3O4@C composites. With good magnetic properties (53.5 emu/g) and separation recycling properties, Zr–Fe3O4@C showed rapid water separation within 20 s. At a pH of 3 and 30 °C, Zr–Fe3O4@C achieved a maximum adsorption capacity of 132.72 mg/g by the Langmuir isotherm. Furthermore, even after six consecutive treatments, the adsorption performance of Zr–Fe3O4@C for Cr(VI) only decreased by about 9.8%. The stable adsorption performance and regeneration ability suggested that Zr–Fe3O4@C would be considered a reliable candidate for Cr(VI) wastewater remediation.

A facile synthesis of raspberry-shaped Fe3O4 nanoaggregate and its magnetic and lithium-ion storage properties

Raspberry-shaped aggregates of Fe3O4 nanoparticles are synthesized via a facile hydrazine reduction method with high purity and good yield. The size of the Fe3O4 nanoparticles is in the range of 20–50 nm, which joins together to form raspberry-shaped secondary aggregates. In the absence of hydrazine, only Fe2O3 nanoparticles are formed. The Fe3O4 shows superparamagnetic behavior along with the coercivity and saturation magnetization value of 480 Oe and 41 emu/g at 5 K. The Fe3O4 aggregates show good lithium-ion storage capability with a combination of multi-walled carbon nanotubes. The electrode maintains a high reversible capacity of 662 mAhg−1 after 100 cycles at 50 mAg−1. Therefore, this can be a promising material for magnetic and lithium-ion battery applications.

Magnetic graphene oxide-containing chitosan‑sodium alginate hydrogel beads for highly efficient and sustainable removal of cationic dyes

Developing recyclable and efficient adsorbents for cationic dyes removal from wastewater is crucial for ensuring green ecology and drinking water safety. Herein, we demonstrated a novel magnetic gel bead adsorbent that was synthesized by employing graphene oxide (GO) modified Fe3O4 as magnetic nanoparticles doped sodium alginate (SA)/chitosan (CS) gel (SA/GO@Fe3O4/CS). The GO@Fe3O4 sample was prepared based on GO by the chemical co-precipitation method, which not only reduced the aggregation of Fe3O4 but also increases the specific surface area of the composite gel beads. The prepared gel beads were used to adsorb methylene blue (MB), neutral red (NR), and safranine T (ST). The experimental results showed that the adsorption capacity of SA/GO@Fe3O4/CS gel beads for MB, NR, and ST reached 21.325 mg/g, 44.654 mg/g and 44.313 mg/g. After five recycles, the removal rates could still reach more than 90% of the original, exhibiting a high recovery rate. Therefore, this paper provides a strategy for the preparation of high efficiency and recyclable cationic dye adsorbents with a large specific surface area.

Incorporation of Fe3O4 nanoparticles in three-dimensional carbon nanofiber/carbon nanotube aerogels for high-performance anodes of lithium-ion batteries

Recently, Fe3O4 based materials have been widely investigated to serve as anode materials of lithium-ion batteries (LIBs) because of the high theoretical capacity (924 mA h g−1). Unfortunately, the actual capacity of these materials are low and they suffer from poor cycling stability. Herein, carbon nanotube/carbon nanofiber composite aerogels (CA) were used as scaffold to fabricate Fe3O4-CA composites for anode materials. Fe3O4 nanoparticles were evenly presented on the external surface and internal channel of the 3-dimensional (3D) CA network. The 3D conductive network can buffer the volume expansion of anode materials. Additionally, such structure can prevent the aggregation of Fe3O4. Therefore, the structure of the Fe3O4-CA composite electrode can be maintained during lithiation/delithiation processes. The Fe3O4-CA composites delivered a high reversible capacity of 825.1 mA h g−1 after 100 cycles. Additionally, an ultra-high coulombic efficiency closed to 100% was obtained. The excellent performance of the Fe3O4-CA composites may be due to the synergistic effect of the Fe3O4 nanoparticles and 3D conductive network structure.

In-situ preparation of Fe3O4/graphene nanocomposites and their electrochemical performances for supercapacitor

Fe3O4 has a broad application prospect in electrode materials of supercapacitors due to its high theoretical specific capacitance, low cost, and environmental friendliness. However, its easy agglomeration property and low charge/discharge cycle stability limit its further application. In order to overcome these issues, the preparation conditions for Fe3O4 nanoparticles with high specific capacitance were optimized. Then the Fe3O4 was used as the feedstock to prepare the Fe3O4/graphene nanocomposites using solvothermal method for the in-situ reduction of graphene oxide and the combination of Fe3O4 nanoparticles with graphene. The Fe3O4 nanoparticles, graphene oxides and Fe3O4/graphene nanocomposites were characterized by X-ray diffraction (XRD), N2 adsorption, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The capacitance and stability of these samples were obtained from charge/discharge curves and cyclic voltammograms. The results show that during preparation process, Fe3+ ions could combine with the O-containing functional groups on the surface of graphene oxide to form Fe3O4 nanoparticles, and the graphene oxide could be in-situ reduced to form graphene simultaneously. This could effectively prevent aggregation of Fe3O4 and stacking of graphene as electrode materials. Moreover, the optimal conditions for preparing Fe3O4/graphene nanocomposites (BF24G60) are 60% of graphene theoretical percentage in Fe3O4/graphene nanocomposites, 205 °C of preparation temperature, and 24 h of reaction time. For the BF24G60 sample, it has excellent cycle stability (93% after 500 cycles) and specific capacitance (300 F/g at 0.4 A/g), which is higher than that of the single graphene (77 F/g) and Fe3O4 nanoparticles (222 F/g).

Fabrication of core-shell magnetic covalent organic frameworks composites and their application for highly sensitive detection of luteolin

In this work, a novel core-shell structured magnetic covalent organic frameworks (denoted as Fe3O4@TAPB-DMTP-COFs (TAPB, 1,3,5-tris(4-aminophenyl)benzene; DMTP, 2,5-dimethoxyterephaldehyde) was fabricated via a facile step-by-step assembly approach. The resulting material was characterized by transmission electron microscopy, powder X-ray diffraction, Fourier transform-infrared spectroscopy, X-ray photoelectron spectroscopy and voltammetric methods. Fe3O4@TAPB-DMTP-COFs was further coated on the surface of glassy carbon electrode to construct an electrochemical sensor for the determination of luteolin. TAPB-DMTP-COFs with highly ordered porous structure not only provide more active sites, but also avoid the aggregation of Fe3O4. Meanwhile, Fe3O4 magnetic nanoparticles can obviously accelerate the electron transport. Under the optimal conditions, the method displayed low detection limit (0.0072 μmol L−1), wide linear range (0.010–70 μmol L−1), and good recoveries (98.5–102.0%). Moreover, there are no significant effects from the interferents. The feasibility of this method was applied to trace luteolin in chrysanthemum tea and carrot. We consider this COFs-based porous material would become one of the most promising materials in electrochemical sensor.

A High-matched Melamine Sensor Using Core/shell Nano Particles of Fe3O4@Polyrutin-COOH and Ionic Liquid as Imprinted Polymeric Monomers.

We describe here a magnetic molecular imprinted polymeric ionic liquid (MMIPIL) film by using a functionalized ionic liquid (3-vinyl-4-amino-5-imidazole carboxamide chloride, IL) and Fe3O4@Polyrutin-COOH as a functional monomer and supporting materials. The change in the direction of the charge density in the structure of MMIPIL polymer resulted in a red shift of about 100 nm for the characteristic group of -C=O. Polyrutin containing an electron-rich benzene ring and multiple hydroxyl groups not only prevented the aggregation of Fe3O4, but also benefitted to immobilize template molecules. More symmetric amino groups in the template molecules generated more hydrogen bonds and other synergistic effects between MEL and the functional monomers, which resulted in a highly-matched and highly stable MMIPIL sensor. The proposed magnetic sensor lowered the matching potential, and enhanced the signal for the detection of melamine (MEL) in milk powder. Under the optimum conditions, the MEL template molecule showed a significant linear relationship between 5.0 × 10-3 and 0.8 μg/L with a detection limit (S/N = 3) of 1.5 × 10-3 μg/L. The MMIPIL sensor showed wonderful selectivity and exhibited facile, fast and efficient results in the monitoring MEL with recoveries of between 96.5 and 108.3%.

Understanding the Formation Mechanism of Magnetic Mesocrystals with (Cryo-)Electron Microscopy

Magnetite (Fe3O4) nanoaggregates with a flower-like morphology are considered promising materials in the field of magnetically induced hyperthermia in cancer therapy due to their good heating efficiency at low applied alternating magnetic fields. Although the structure and the magnetic state of such flower-like aggregates have been investigated previously, the mechanism that leads to the hierarchical morphology is still poorly understood. Here, we study the formation mechanism of Fe3O4 aggregates synthesized through the partial oxidation of ferrous hydroxide in the presence of poly(acrylic acid) by using cryogenic electron microscopy. The aggregates are formed through a multistep process involving first the conversion of ferrous hydroxide precursors in ∼5 nm primary particles that aggregate into ∼10 nm primary Fe3O4 crystals that finally arrange into the secondary mesocrystal structure. High-resolution electron tomography is used to show that the Fe3O4 mesocrystals are composed of ∼10 nm subunits, often showing a uniform crystallographic orientation resulting in single-crystal-like diffraction patterns. Furthermore, electron holography reveals that mesocrystals have a single magnetic domain despite polymeric interfaces between subunits being present throughout the mesocrystal. Our findings could be used to design materials with specific properties by modulating the morphology and/or magnetic state that is suitable for biomedical application.

HS-β-cyclodextrin-functionalized Ag@Fe3O4@Ag nanoparticles as a surface-enhanced Raman spectroscopy substrate for the sensitive detection of butyl benzyl phthalate.

In recent years, there have been incidents involving the illegal addition of phthalic acid esters (PAEs) to liquors. It is well known that PAEs such as butyl benzyl phthalate (BBP) have estrogen-like effects, so high PAE levels in the body can lead to a decreased sperm count in males and altered sexual organ development in children, for example. The rapid detection of PAEs in liquor is therefore an important task. Compared with traditional methods of testing for PAEs, surface-enhanced Raman spectroscopy (SERS) offers higher sensitivity and the ability to search for chemical fingerprints, allowing the rapid detection of particular PAEs. In the present work, we synthesized Ag@Fe3O4@Ag/β-cyclodextrin (CD) nanoparticles for use as a SERS-active substrate. Fe3O4 aggregates quickly under the influence of an external magnetic field, making it possible to magnetically separate out the NPs, which simplifies sample processing. The detection limit of the system for PAEs is also improved because the β-CD acts as a functional group with a cavity structure that is capable of adsorbing BBP to form a host (β-CD)-guest (BBP) complex. This substrate was shown to possess good repeatability and sensitivity when using malachite green (MG) as a probe molecule. Furthermore, the nanoparticle-based SERS substrate permitted the detection of BBP down to a level of 1.3mg/kg in liquor, which is low enough to be able to detect BBP in real-world liquor samples. We expect that this method will prove useful for the rapid detection of PAEs in food. Graphical abstract.

Thrombolysis Enhancing by Magnetic Manipulation of Fe₃O₄ Nanoparticles.

In this paper, an effective method of accelerating urokinase-administrated thrombolysis through a rotating magnetic field (RMF) of guided magnetic nanoparticles (NPs) in the presence of low-dose urokinase is proposed. The dispersed Fe3O4 NPs mixed with urokinase were injected into microfluidic channels occluded by thrombus prepared in vitro. These magnetic NPs aggregated into elongated clusters under a static magnetic field, and were then driven by the RMF. The rotation of Fe3O4 aggregates produced a vortex to enhance the diffusion of urokinase to the surface of the thrombus and accelerate its dissolution. A theoretical model based on convective diffusion was constructed to describe the thrombolysis mechanism. The thrombus lysis speed was determined according to the change of the thrombus dissolution length with time in the microfluidic channel. The experimental results showed that the thrombolysis speed with rotating magnetic NPs is significantly increased by nearly two times compared with using the same dose of pure urokinase. This means that the magnetically-controlled NPs approach provides a feasible way to achieve a high thrombolytic rate with low-dose urokinase in use.

A novel recyclable surface-enhanced Raman spectroscopy platform with duplex-specific nuclease signal amplification for ultrasensitive analysis of microRNA 155

In this work, a recyclable surface-enhanced Raman spectroscopy (SERS) biosensor was fabricated for ultrasensitive detection of miRNA 155 by using magnetic substrate (Fe3O4@PDA/Pt) and duplex-specific nuclease signal amplification (DSNSA) strategy. Here, the Fe3O4@PDA/Pt was used as SERS platform to immobilize toluidine blue Raman reporter and capturing DNA (S1), in which polydopamine (PDA) could avoid the aggregation of Fe3O4 and enhance the biocompatible of platform. When Au nanoflowers (AuNFs) modified probe DNA (S2) was partly hybridized with S1, an initial strong Raman signal (“on” status) was obtained by the approaching between AuNFs and TB. In the presence of target microRNA 155, they could completely hybridize with S2, which led to the isolation of S2 from substrate. Under the assistance of DSN enzyme, the S2 in the DNA/RNA duplex was hydrolyzed to release target miRNA 155, which could trigger another cycle. Thus the AuNFs were departed from TB with an obviously decreased signal. More important, with the application of AuNFs-modified S2, the Raman reporter was continuously assembled on the substrate throughout the detection. After the adding of S2, the S1 could re-hybridize with S2, which led the SERS biosensor return to “on” status, therefore the regeneration of biosensor was easily realized. From this principle, the recyclable biosensor could achieve a wide linear range from 1 fM to 10 μM and the detection limit was 0.28 fM. Herein, we proposed a novel method to construct the ultrasensitive and recyclable SERS platform, which was expected to be used in the clinical applications.

Elastic MCF Rubber with Photovoltaics and Sensing on Hybrid Skin (H-Skin) for Artificial Skin by Utilizing Natural Rubber: 2nd Report on the Effect of Tension and Compression on the Hybrid Photo- and Piezo-Electricity Properties in Wet-Type Solar Cell Rubber.

In contrast to ordinary solid-state solar cells, a flexible, elastic, extensible and light-weight solar cell has the potential to be extremely useful in many new engineering applications, such as in the field of robotics. Therefore, we propose a new type of artificial skin for humanoid robots with hybrid functions, which we have termed hybrid skin (H-Skin). To realize the fabrication of such a solar cell, we have continued to utilize the principles of ordinary solid-state wet-type or dye-sensitized solar rubber as a follow-up study to the first report. In the first report, we dealt with both photovoltaic- and piezo-effects for dry-type magnetic compound fluid (MCF) rubber solar cells, which were generated because the polyisoprene, oleic acid of the magnetic fluid (MF), and water served as p- and n- semiconductors. In the present report, we deal with wet-type MCF rubber solar cells by using sensitized dyes and electrolytes. Photoreactions generated through the synthesis of these components were investigated by an experiment using irradiation with visible and ultraviolet light. In addition, magnetic clusters were formed by the aggregation of Fe3O4 in the MF and the metal particles created the hetero-junction structure of the semiconductors. In the MCF rubber solar cell, both photo- and piezo-electricity were generated using a physical model. The effects of tension and compression on their electrical properties were evaluated. Finally, we experimentally demonstrated the effect of the distance between the electrodes of the solar cell on photoelectricity and built-in electricity.

High-energy flexible quasi-solid-state lithium-ion capacitors enabled by a freestanding rGO-encapsulated Fe3O4 nanocube anode and a holey rGO film cathode.

Flexible energy storage devices have become critical components for next-generation portable electronics. In the present work, a flexible quasi-solid-state lithium-ion capacitor (LIC) is developed based on graphene-based bendable freestanding films in a gel polymer electrolyte. A graphene encapsulated Fe3O4 nanocube hybrid film (rGO@Fe3O4) has been fabricated as the anode of LICs through a filtration assisted self-assembly and the subsequent thermal annealing process. In this hybrid architecture, flexible and ultrathin graphene shells uniformly enwrap the Fe3O4 within the whole film, which can effectively suppress the aggregation of Fe3O4 and also accommodate the volume change of Fe3O4 during the cycling process. As a consequence, the electrochemical performance of the rGO@Fe3O4 half-cell versus Li/Li+ shows high specific capacity (731 mA h g-1 at 0.1 A g-1), excellent rate capability (210 mA h g-1 at 10 A g-1) and superior cycling stability (98% retention after 600 cycles). After chemically etching rGO@Fe3O4 with hydrochloric acid, a holey rGO film is successfully obtained as a high-rate cathode of LICs. On the basis of such a flexible anode and cathode, the as-fabricated quasi-solid-state LIC device delivers a high energy density of 148 W h kg-1, a high power density of 25 kW kg-1 (achieved at 70 W h kg-1) and an excellent capacity retention of 82% after 2000 cycles. More importantly, the rGO@Fe3O4//holey rGO LIC shows good mechanical flexibility with stable Li-storage capacities under harsh bending.

Functionalization of paramagnetic nanoparticles for protein immobilization and purification

A paramagnetic nanocomposite coated with chitosan and N-(5-Amino-1-carboxy-pentyl) iminodiacetic acid (NTA) that is suitable for protein immobilization applications has been prepared and characterized. The nanoparticle core was synthesized by controlled aggregation of Fe3O4 under alkaline conditions, and Transmission Electron Microscopy revealed a size distribution of 10–50 nm. The nanoparticle core was coated with chitosan and derivatized with glutaraldehyde and NTA, as confirmed by Fourier Transform Infrared Spectroscopy. The final nanoparticles were used as a metal affinity matrix to separate a recombinant polyhistidine-tagged β-galactosidase from Bacillus subtilis directly from E. coli cell lysates with high purity (>95%). After loading with Ni2+, nanoparticles demonstrated a binding capacity of 250 μg of a polyhistidine-tagged β-galactosidase per milligram of support. The immobilized enzyme retained 80% activity after 9 cycles of washing, and the immobilized recombinant protein could be eluted with high purity with imidazole. The applications for these nanomagnetic composites extend beyond protein purification, and can also be used for immobilizing enzymes, where the β-galactosidase immobilized on the nanomagnetic support was used in multiple cycles of catalytic reactions with no significant loss of catalytic activity.

Chemical modification of magnetite nanoparticles and preparation of acrylic-base magnetic nanocomposite particles via miniemulsion polymerization

Nowadays, magnetic nanocomposite particles have attracted many interests because of their versatile applications. A new method for chemical modification of Fe3O4 nanoparticles with polymerizable groups is presented here. After synthesis of Fe3O4 nanoparticles by co-precipitation method, they were modified sequentially with 3-aminopropyl triethoxysilane (APTES), acryloyl chloride (AC) and benzoyl chloride (BC) and all were characterized by FTIR, XRD, SEM and TGA analyses. Then the modified magnetite nanoparticles with unsaturated acrylic groups were copolymerized with methyl methacrylate (MMA), butyl acrylate (BA) and acrylic acid (AA) through miniemulsion polymerization. Although several reports exist on preparation of magnetite-base polymer particles, but the efficiency of magnetite encapsulationwith reasonable content and obtaining final stable latexes with limited aggregation ofFe3O4 are still important issues. These were considered here by controlling reaction parameters. Hence, a seriesofmagneticnanocomposites latex particlescontaining different amounts of Fe3O4 nanoparticles (0–10wt%) were prepared with core-shell morphology and diameter below 200nm and were characterized by FT-IR, DSC and TGA analyses. Their morphology and size distribution were studied by SEM, TEM and DLS analyses too. Magnetic properties of all products were also measuredby VSM analysis and the results revealed almost superparamagnetic properties for the obtained nanocomposite particles.

3D-0D Graphene-Fe3O4 Quantum Dot Hybrids as High-Performance Anode Materials for Sodium-Ion Batteries.

Transition metal oxides can be considered as appealing candidates for sodium ion battery anode materials because these low-cost materials possess high capacity and enhanced safety. However, the practical application of these materials is usually limited by their low electronic conductivity and serious volume change during the charging-discharging process. Herein, we report the fabrication of 3D-0D graphene-Fe3O4 quantum dot hybrids by a facile one-pot hydrothermal approach as anode materials for sodium-ion batteries. Fe3O4 quantum dots with an average size of 4.9 nm are anchored on the surface of 3D structured graphene nanosheets homogeneously. Such unique hierarchical structure are advantageous for enlarging the electrode/electrolyte interface area and enhancing the electrochemical activity of the hybrid materials, inhibiting particle aggregation of Fe3O4 and accommodating their volume change during the charging-discharging process as well as enabling fast diffusion of electrons and rapid transfer of electrolyte ions. Consequently, the 3D-0D graphene-Fe3O4 quantum dot hybrids exhibit ultrahigh sodium storage capacity (525 mAh g-1 at 30 mA g-1), outstanding cycling stability (312 mAh g-1 after 200 cycles at 50 mA g-1) and superior rate performance (56 mAh g-1 at 10 A g-1).

Facile synthesis of carbon-coated Fe3O4 core–shell nanoparticles as anode materials for lithium-ion batteries

Core–shell composites, carbon-coated Fe3O4 (Fe3O4@C) with ~30 nm Fe3O4 nanoparticles as cores and 3–7 nm carbon as shells, was successfully prepared through simple hydrothermal reaction followed by heat treatment. High-resolution transmission electron microscopy and energy dispersive spectroscopy mapping showed the formation of a highly developed core–shell structure with uniform carbon coating on the surface of Fe3O4 nanoparticle. In the Fe3O4@C composite, carbon coating layer provides an effective electron conductive paths. It acts as spacers to avoid the aggregation of Fe3O4 and buffers the volume changes of Fe3O4. Accordingly, nano-sized Fe3O4 core in the core–shell structure not only better accommodates large strains but also provides short diffusion paths for Li+ insertion/deinsertion. The Fe3O4@C composite exhibits good cyclability and delivers a high initial discharge capacity of 982 mAh g−1 and a reversible discharge capacity of 718 mAh g−1 after 100 cycles at 0.1 C. Even up to 2 C, a reversible capacity of 302 mAh g−1 is obtained.