Fe3O4 Hollow Spheres Research Articles

Sea urchin-like Fe3O4 hollow microspheres/fatty amines composites phase change materials for highly efficient light-to-thermal conversion and heat storage

Pure phase change materials (PCMs) have limited photothermal conversion capabilities. To improve the photothermal conversion capability of PCMs, we developed composite phase change materials (FHS@PCMs) of sea urchin-like Fe3O4 hollow spheres (FHS) loaded with fatty amines (hexadecylamine (HDA) and octadecylamine (ODA)). The material composition and the surface nano-raised structure of FHS enable FHS@PCMs to exhibit excellent light absorption (up to 90 %, without any additional modification) and thermal conductivity. Moreover, the internal hollow spherical structure would prevent the leakage of PCM during the phase change process. Interestingly, FHS and FHS@PCMs exhibit inherent superhydrophobic properties with a water contact angle greater than 150°, thus endowing them with self-cleaning properties. FHS possesses strong magnetic properties that aid in material collection. Furthermore, the prepared FHS@PCMs exhibited exceptional thermal properties. The latent heat of FHS@HDA and FHS@ODA was 139.21 J∙g−1 and 140.13 J∙g−1, respectively. Additionally, FHS@PCMs maintained their excellent thermal properties even after 50 and 100 thermal cycles. Under one solar radiation, FHS@PCMs show a photothermal conversion efficiency of 89.63 % and 88.02 %, respectively. Taking of these advantages, the as-prepared composite phase change material may have significant potential in the fields of solar energy conversion and storage.

A multifunctional platform based on ZIF-67 templated NiCo-LDH and Fe3O4 hollow spheres for photocatalytic CO2 conversion and supercapacitors

This work presented a series of hybrid materials F@P-LDHs exhibiting the core-shell structure with PPy as the interface modifier, explored as dual-functional materials for studying photocatalytic reduction of CO2 and electrochemical behaviors. F@P-LDHs served as photocatalysts, effectively convert CO2 into CO without using any sacrificial agents and photosensitizers via the gas-solid mode under the visible light irradiation. The generation rate of CO was as high as 10.32 μmol g−1h−1, which was 5.4 and 6.4 times higher than the original Fe3O4@PPy and NiCo-LDH. The well performance might be ascribed to the generation of type Z heterojunction with the interface modifier PPy, jointly accelerating the separation and migration of photo-generated charge carriers between Fe3O4@PPy and NiCo-LDH. Besides, F@P-LDHs were also developed as supercapacitors, and their electrochemical behaviors were investigated. Their good electrochemical performances were attributed to the synergistic effect among hollow Fe3O4 microspheres, polypyrrole and NiCo-LDH. Therefore, as dual-functional materials, the hybrid materials have great potential in the field of CO2 conversion and supercapacitors.

Rheological properties and suspension stability of magnetorheological fluid based on Fe3O4 hollow spheres

Magnetorheological fluid (MRF) is a material whose viscosity can be changed by a magnetic field. However, one of the challenges with MRF is that the magnetic particles (MPs) used often settle out of suspension, reducing its effectiveness. To improve the suspension stability and rheological properties of MRF to some extent, this paper prepares Fe3O4 hollow spheres using a simple, one-step synthetic solvothermal method. The surface morphology, particle size distribution, and crystal structure of Fe3O4 hollow spheres are characterized. The results show that the shell thickness of Fe3O4 hollow spheres forms about 100 nm and a saturation magnetization intensity of 86.33 emu/g at a ratio of FeCl3·6H2O to CO(NH2)2 substance of 1:10 when the porosity agent urea is 0.06 mol. Furthermore, MRF is prepared using dimethyl silicone oil as the base carrier fluid. Suspension stability and rheological properties of MRF are investigated by varying the content ratio of Fe3O4 hollow spheres. While increasing the mass fraction of Fe3O4 hollow spheres, the viscosity and shear yield stress of MRF increase. MRF based on Fe3O4 hollow spheres significantly improves the suspension stability and rheological properties of the fluid, making it more suitable for practical applications.

Polyaniline-based networks combined with Fe3O4 hollow spheres and carbon balls for excellent electromagnetic wave absorption

Polyaniline (PANI)-based networks combined with Fe 3 O 4 hollow spheres and carbon balls (FCP) for improved electromagnetic wave (EMW) absorption were investigated using an easy-to-industrialize solvothermal and physical method. Hollow structure Fe 3 O 4 spheres with a lower density than that of the common solid sphere were prepared. As a thin and light magnetic material, Fe 3 O 4 hollow spheres generate magnetic loss, carbon balls and PANI networks generate dielectric loss. The magnetic and conductive parts play appropriate roles in achieving complementarity in the EMW absorption. The relatively high specific surface area introduced by PANI networks promotes interfacial polarization and further supports dielectric loss. In conclusion, the above reasons provide multiple attenuation mechanisms. Samples FCP1 (−65.109 dB, at 12.800 GHz, 1.966 mm, from 5.6 to 18.0 GHz) and FCP2 (−61.033 dB, at 8.480 GHz, 3.328 mm, from 4.3 to 18.0 GHz) demonstrated a wide bandwidth, a small thickness, a minimum reflection loss (R L ), and a low loading ratio (25%) in paraffin-based composites. Specifically, their loading ration of 25% is much lower than the loading ratio of conventional materials (usually 50% and above). In addition, the bandwidth is excessively wide, above 12 GHz, possessing good absorption performance in continuous intervals with different thicknesses. Such excellent characteristics have rarely been reported in literature.

Hollow iron submicron spheres with strong ferromagnetism

Hollow iron submicron spheres with high saturation magnetization at room temperature were successfully developed for the first time. By means of spray pyrolysis, α -Fe2O3 hollow spheres with the diameter ranging from 0.5 µm to 2.5 µm and an average shell thickness of approximately 20 nm could be obtained in large scale. In subsequent reductive annealing under dilute hydrogen atmosphere, as-synthesized α -Fe2O3 can be transformed into Fe3O4, unstable FeO, and Fe in sequence with an increase in annealing temperature from 350 °C to 600 °C. An optimal reductive temperature of 425 °C was proposed to obtain perfect iron hollow spheres showing a maximum saturation magnetization up to 184 emu/g, which is greater than literature reported values and can be ascribed to curvature effect and symmetrical structural feature.

Size-morphology control, surface reaction mechanism and excellent electromagnetic wave absorption characteristics of Fe3O4 hollow spheres

This paper designs and regulates unique monodisperse Fe3O4 hollow spheres through solvothermal method. Hollow structure provide light-weight property which is required for electromagnetic wave (EMW) absorbing materials. First and foremost, the size (700–350 nm) and surface of Fe3O4 hollow spheres can be adjusted by different urea contents, which realizes the morphology control of “big to small” and “smooth to rough”. Secondly, we select different reaction time to study how morphology of Fe3O4 hollow sphere changes, such as the flower-like (F6, 24 h). Thirdly, our work explores the relationship between morphology and property. In addition, the data shows the “double peaks” characteristic of EMW absorption. Overall, the sample F2 has the balance of bandwidth (4.56–9.24 GHz, 4.68 GHz), thickness (3.62 mm) and RL value (−56.90 dB, at 8.32 GHz), leading excellent performance. Finally, Fe3O4 hollow spheres may be widely applied not only in EMW absorption but also in energy storage, biomedical field, etc.

In-situ grown hollow Fe3O4 onto graphene foam nanocomposites with high EMI shielding effectiveness and thermal conductivity

With the increasing packaging density and multi-functionality, thermal management and electromagnetic pollution in electronic devices are crucial. In this work, we propose a novel method to in-situ grow hollow Fe3O4 sphere (h-Fe3O4, inner and outer diameter of 870 nm and 975 nm, respectively) onto three-dimensional graphene foam (GF) surface and then filled it with polydimethylsiloxane (PDMS) to fabricate nanocomposites with high electromagnetic interference shielding effectiveness (70.37 dB from 8.2 to 12.4 GHz) and thermal conductivity (28.12 ± 1.212 W m−1 K−1) at room temperature. Moreover, conductive networks inside composites show super-flexible performance with high electrical conductivity (84.02 ± 8.385 S cm−1). The effect of in-situ growth hollow Fe3O4 spheres in the enhancement of EMI SE has been demonstrated via comparing with different contents, morphologies and preparation processing. Besides, the mechanism of thermal conductivity has been investigated by FEM simulation and theoretical modeling. Finally, the usage of GF/h-Fe3O4/PDMS composites as thermal interface materials (TIMs) for chip cooling is proved to be successful, and the corresponding temperature under usage power density is accurately predicted. These comprehensive properties of GF/h-Fe3O4/PDMS composite open a potential application for next-generation TIMs in chip packaging.

Effect of Reaction Time on Microwave Absorption Properties of Fe3O4 Hollow Spheres Synthesized via Ostwald Ripening.

Hollow magnetic structures have great potential to be used in the microwave absorbing field. Herein, Fe3O4 hollow spheres with different levels of hollowness were synthesized by the hydrothermal method under Ostwald ripening effect. In addition to their microstructures, the microwave absorption properties of such spheres were investigated. The results show that the grain size and hollowness of Fe3O4 hollow spheres both increase as the reaction time increases. With increasing hollowness, the attenuation ability of electromagnetic wave of Fe3O4 spheres increases first and then decreases, finally increases sharply after the spheres break down. Samples with strong attenuation ability can achieve good impedance matching, which it does preferentially as the absorber thickness increases. Fe3O4 hollow spheres show the best microwave absorption performance when the reaction time is 24 h. The minimum reflection loss (RL (min)) can reach −40 dB, while the thickness is only 3.2 mm.

Excellent Microwave Absorption Properties Derived from the Synthesis of Hollow Fe₃o₄@Reduced Graphite Oxide (RGO) Nanocomposites.

Magnetic nanoparticles, such as Fe3O4 and Co3O4, play a vital role in the research on advanced microwave absorbing materials, even if problems such as high density and narrow band impedance matching are still unsolved. Herein, the study of lightweight hollow Fe3O4@reduced graphite oxide (RGO) nanocomposites synthesized via the solvothermal method is presented. The microstructure and crystal morphology of the materials were characterized by X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. Single crystalline hollow Fe3O4 spheres were grown onto RGO flakes, leading to the formation of heterojunction, which further influenced the microwave absorption properties. The latter were evaluated by standard microwave characterization in the frequency range of 2–18 GHz. It was found that, for a specific Fe3O4@0.125 g RGO composite, the minimum reflection loss can reach −41.89 dB at 6.7 GHz, while the reflection loss was less than −10 dB from 3.4 GHz to 13.6 GHz for a nanocomposite sample thickness in the range of 1–4 mm. The combination of these two materials thus proved to give remarkable microwave absorption properties, owing to enhanced magnetic losses and favorable impedance matching conditions.

Partial self-sacrificing templates synthesis of sandwich-like mesoporous C[sbnd]N@Fe3O4@C[sbnd]N hollow spheres for high-performance Li-ion batteries

Integrating carbonaceous materials onto nano-scaled porous metal oxides to form shell-core-shell hollow structure has good prospects in the development of high-performance electrode materials for Li-ion battery, but it still remains challenging. Herein, with Fe3O4 hollow nanospheres as partial self-templates, we construct sandwich-like double nitrogen-doped C-shelled porous Fe3O4 hollow spheres by pyrolyzing polypyrrole (PPY) which is in situ polymerized on the interior and the exterior shells of Fe3O4 hollow spheres. And the polymerization time of PPY have important influence on thickness of carbon layer in the composites and further change their electrochemical performance. The shell-core-shell hollow structure offers highly contact between carbon and porous Fe3O4 and provides amount of volume stress buffer nanospaces during electrochemical processes, which promotes electron transport effectively and keeps good structural stability. The obtained sandwich-like double N-doped C-shelled porous Fe3O4 hollow spheres (CN@Fe3O4@CN HSs) are prepared as Li-ion battery anode and show an ultrahigh reversible specific capacity, high rate capability, remarkable cycle stability, excellent capacity retention (high capacity of 1048 mA h g−1 after 300 cycles at 0.1 A g−1, which is about 99.1% of the capacity in the 2nd cycle) and high coulombic efficiency (about 99% over 300 cycles). This research shows great potential of the sandwich-like shell-core-shell hollow structure in Li-ion batteries.

Pd(0) nanoparticle immobilized on cyclodextrin-nanosponge-decorated Fe 2 O 3 @SiO 2 core-shell hollow sphere: An efficient catalyst for C C coupling reactions

Abstract Amine-functionalized core-shell Fe2O3 hollow spheres (h-Fe2O3@SiO2 N) were decorated with Cl-functionalized cyclodextrin nanosponge, CDNS-Cl, covalently. The resulting hybrid system, h-Fe2O3@SiO2 CDNS, was then used as a magnetically separable support for immobilization of Pd(0) nanoparticles, derived from a bio-based approach. The obtained catalyst, Pd@h-Fe2O3@SiO2 CDNS, was characterized by using SEM/EDS, TEM, XRD, BET, ICP-AES, FTIR, TGA and VSM. Moreover, the catalytic activity of Pd@h-Fe2O3@SiO2 CDNS was confirmed for ligand and copper-free Heck and Sonogashira coupling reactions in aqueous media. Comparison of the catalytic activity of the Pd@h-Fe2O3@SiO2 CDNS and Pd@h-Fe2O3@SiO2, established superior catalytic activity of former indicating the role of CDNS in catalysis. Furthermore, the catalytic activity and recyclability of Pd@h-Fe2O3@SiO2 CDNS was higher than that of Pd@CDNS. The catalyst could be successfully recycled for several consecutive reaction times with slight loss of the catalytic activity. The ICP-AES analysis confirmed that the leaching of Pd nanoparticles was negligible upon each reaction cycle.

Preparation of hollow Fe3O4 spheres through a facile method and their applications

Fe3O4 hollow microspheres with good dispersibility and high saturation magnetization were synthesized through a facile one-step solvothermal method. The formation mechanism of the hollow structure was studied by taking time-dependent experiments. Porous [Formula: see text]-FeOOH and [Formula: see text]-Fe2O3 nanosheets were firstly fabricated. Fe3O4 solid spheres aggregated by small particles were obtained from the transition of [Formula: see text]-FeOOH and [Formula: see text]-Fe2O3. Finally, the solid sphere is transferred to hollow sphere through Ostwald ripening. The maximum saturation magnetization of the hollow spheres is [Formula: see text][Formula: see text]emu/g, which is higher than some results reported in references. The Fe3O4 hollow spheres show potential applications in microwave absorption and photocatalysis.

Template free solvothermal synthesis of single crystal magnetic Fe3O4 hollow spheres, their interaction with bovine serum albumin and antibacterial activities

Uniform sized single crystal magnetic Fe3O4 hollow spheres (MFHS) have been synthesized through simple solvothermal method using ferric chloride hexahydrate and 1,3-propanediamine. The reaction time and the amount of 1,3-propanediamine play major roles in the formation of magnetic Fe3O4 hollow spheres. The synthesized products are characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometry techniques. The crystalline Fe3O4 materials are composed of well-aligned hollow sphere magnetite nanoparticles and exhibit high saturation magnetization of 57.9 emu/g and a remnant magnetization of 17.6 emu/g at room temperature. MFHS interact strongly with bovine serum albumin (BSA) and brings out considerable conformational changes in BSA as evident from the UV–vis absorption, fluorescence and circular dichroism (CD) spectroscopic studies pertaining to the interaction of synthesized MFHS and BSA. The prepared MFHS effectively inhibit the growth of Pseudomonas aeruginosa and Staphylococcus aureus.

Green bio‐based synthesis of Fe2O3@SiO2‐IL/Ag hollow spheres and their catalytic utility for ultrasonic‐assisted synthesis of propargylamines and benzo[b]furans

A novel magnetic hybrid system containing nano‐magnetic Fe2O3 hollow spheres, silica shell, [pmim]Cl ionic liquid and silver nanoparticles was synthesized and characterized. The silver nanoparticles were prepared via biosynthesis using Achillea millefolium flower as reducing and stabilizing agent. The hybrid system was successfully used as an efficient and reusable catalyst for promoting green ultrasonic‐assisted A3 and KA2 coupling reactions as well as benzo[b]furan synthesis. It was found that decoration of the magnetic core with non‐magnetic moieties decreased the maximum saturation magnetization. However, the catalyst was still superparamagnetic and could be simply separated from the reaction mixture using an external magnet. The heterogeneous nature of the catalyst was also confirmed by studying its reusability and stability and the leaching of silver. Use of aqueous media, high yields, short reaction times, broad substrate tolerance and low required amount of catalyst are the merits of this protocol.

Templating synthesis of Fe2O3 hollow spheres modified with Ag nanoparticles as superior anode for lithium ion batteries

Ag-Fe2O3 hollow spheres are synthesized by using Ag@C core-shell matrix as sacrificial templates. The morphologies and structures of the as-prepared samples are characterized by scanning electron microscopy, X-ray powder diffraction energy dispersive, transmission electron microscopy and high resolution transmission electron microscopy. In contrast to Fe2O3 hollow spheres, Ag-Fe2O3 hollow spheres exhibit much higher electrochemical performances. The Ag-Fe2O3 composites exhibit an initial discharge capacity of 1030.9 mA h g−1 and retain a high capacity of 953.2 mA h g−1 at a current density of 100 mA g−1 after 200 cycles. Furthermore, Ag-Fe2O3 electrode can maintain a stable capacity of 678 mA h g−1 at 1 A g−1 after 250 cycles. Rate performance of Ag-Fe2O3 electrode exhibits a high capacity of 650.8 mA h g−1 even at 5 A g−1. These excellent performances can be attributed to the decoration of Ag particles which will enhance conductivity and accelerate electrochemical reaction kinetics. Moreover, the hollow structure and the constructing particles with nanosize will benefit to accommodate huge volume change and stabilize the structure.

Fe3O4/C composite with hollow spheres in porous 3D-nanostructure as anode material for the lithium-ion batteries

3d transition-metal oxides, especially Fe3O4, as anode materials for the lithium-ion batteries have been attracting intensive attentions in recent years due to their high energy capacity and low toxicity. A new Fe3O4/C composite with hollow spheres in porous three-dimensional (3D) nanostructure, which was synthesized by a facile solvothermal method using FeCl3·6H2O and porous spongy carbon as raw materials. The specific surface area and microstructures of composite were characterized by nitrogen adsorption-desorption isotherm method, FE-SEM and HR-TEM. A homogeneous distribution of hollow Fe3O4 spheres (diameter ranges from 120 nm to 150 nm) in the spongy carbon (pore size > 200 nm) conductive 3D-network significantly reduced the lithium-ion diffusion length and increased the electrochemical reaction area, and further more enhanced the lithium ion battery performance, such as discharge capacity and cycle life. As an anode material for the lithium-ion battery, the title composite exhibit excellent electrochemical properties. The Fe3O4/C composite electrode achieved a relatively high reversible specific capacity of 1450.1 mA h g−1 in the first cycle at 100 mA g−1, and excellent rate capability (69% retention at 1000 mA g−1) with good cycle stability (only 10% loss after 100 cycles).

Controllable Synthesis of Polyhedral Fe₃O₄ Hollow Spheres Using Hexamethylenetetramine as Structure-Directing Agent.

Polyhedral Fe₃O₄ hollow spheres were synthesized using hexamethylenetetramine as structure-directing agent and the effect of hexamethylenetetramine on the morphology was investigated in detailed. The comparison for samples prepared with and without hexamethylenetetramine indicated that hexamethylenetetramine played a vital role in the formation process of the hollow polyhedral structure. The formation process and growth mechanism of Fe₃O₄ spheres with hollow polyhedral morphology were preliminarily explored according to a detailed time-dependent morphology and structure evolution. It was deduced that the hollow polyhedral structure can be ascribed to the cooperation of oriented aggregation and Ostwald ripening mechanisms. The as-prepared Fe₃O₄ hollow spheres with polyhedral structures which possess high magnetization saturation value (73 emu/g) at room temperature, large cavity and huge specific surface area (57.12 m2·g–1) are expected to have wide potential applications, for example in the drug delivery process, magnetic separation and waste treatment in the future.

Preparation and properties of magnetic Fe3O4 hollow spheres based magnetic-fluorescent nanoparticles

In this paper, magnetic Fe3O4 hollow spheres based magnetic-fluorescent nanoparticles, hollow structured Fe3O4@Gd2O3:Eu3+, were synthesized through a homogeneous precipitation method. The microstructure, luminescence, and magnetic properties of the samples were investigated and discussed with the help of various analytic techniques including X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, cathodelumincence mapping, photoluminescence spectra and vibrating sample magnetometer. The hollow spheres nanoparticles, emitting at 612 nm dominantly under the 254 nm excitation, exhibited the photoluminescence intensity 2.45 times higher than the solid sphere samples, due to the. hollow spheres structure. The hollow Fe3O4@Gd2O3:Eu3+ nanoparticles were spherical, and had a particle size of about 1400 nm in diameter. They also showed a saturation magnetization of 1.33 emu/g, a coercivity Hc of 160 Oe and a remanence of 0.05 emu/g at room temperature, the saturation magnetization of hollow spheres nanoparticles is higher than the solid sphere samples. The enhanced photoluminescence and magnetic properties of the hollow structured nanoparticles allow them to be used in biomedical applications.

Super-paramagnetic nano-architecture and its tunable removal efficiency for organic pollutants

In this work, super-paramagnetic nano-architecture was designed to remove the organic pollutants effectively from the waste water. The nano-architectures are composed of super-paramagnetic Fe3O4 hollow spheres, conductive polymer and graphene sheets (RGO) to form binary and ternary nano-architectures. They could be magnetically separated and well-distributed into wastewater again for recycle use. Due to the special function of PPy shell, the binary Fe3O4@PPy core-shell structure exhibits pH-responsive removal efficiency for organic pollutants. Assembling the Fe3O4@PPy core-shell material with RGO sheets could largely improve their surface area, pore volume, and enhance their chemical stability in acid and alkaline solution. Therefore, the Fe3O4@PPy@RGO ternary nano-adsorbents could show favorable and robust removal performance for organic pollutants no matter in neutral, acidic and alkaline environment.

Extraction of Iron from Vanadium Slag Using Pressure Acid Leaching

The extraction of iron from vanadium slag was attempted using pressure acid leaching. The effects of the several parameters which included reaction time, H+/slag ratio, leaching temperature, and concentration of additive (Na2S) upon leaching efficiency of iron were investigated. The results showed that the leaching efficiency of iron could reach above 76% in the best leaching condition. By using Leaching solution as iron source, Fe2O3 hollow spheres have been successfully synthesized via facile hydrothermal method by using carbon spheres as template followed by a subsequent heat treatment. The experimental results show that hollow spheres structures of Fe2O3 with the mean particle size of 0.9-1.2μm is single hexagonal crystal system.