Ferrite Spheres Research Articles

Black Phosphorus Nanosheets Decorated Multiscale Zinc Ferrite Spheres Toward Swift and Humidity-Tolerant Breath Acetone Sensing

Unreasonable acetone emission from various cosmetic and industrial products readily imposes severe ecological harm and human health through airborne transmission and groundwater circulation, thus necessitating the pressing requirement of sensitive and swift acetone detection. To this end, chemoresistive MEMS acetone sensors featuring the sensing layer of a few black phosphorus (BP) nanosheets-modified multiscale zinc ferrite (ZnFe2O4) spheres were leveraged in this work. After the optimization of constituent combination and operation temperature, the 0.5 wt% BP/ZnFe2O4 sensors could recognize 0.1–2 ppm acetone at 188 °C. With respect to pure ZnFe2O4 analog, the 0.5 wt% BP/ZnFe2O4 sensors delivered approximately twofold response enhancement (5.34 versus 2.73 toward 0.5-ppm acetone) and stronger sensitivity (5/ppm versus 3/ppm). Also, excellent selectivity, repeatability, and long-term stability were exhibited. The response/recovery times of 6/63 s toward 0.5-ppm acetone manifested a swift balance of gas–solid interaction. Inspiringly, the sensor showed an excellent humidity-resistant response toward 100-ppb acetone. Moreover, the simulated detection revealed a high application potential in diabetic monitoring featuring sub-ppm acetone and a high moisture environment. The ameliorated sensor performance after incorporating few but modest BP could be attributed to the consequent larger specific surface area, richer oxygen vacancies, and numerous p-n heterojunctions.

Multi-layered nano-hollow spheres for efficient electromagnetic wave absorption

Ferrite nano-hollow spheres (NHS) are of great significance to improve electromagnetic (EM) wave absorption performance. Herein, the deposition of dielectric SiO2 and ferrimagnetic CoFe2O4 (CFO) layers on MnFe2O4 (MnFO) NHS are found as an effective strategy to enhance EM wave attenuation. EM wave absorption properties of as-synthesized bare and bi-layered samples are investigated within a widely-used frequency range of 1–17 GHz. MnFO@CFO bi-layered NHSs exhibit an excellent reflection loss (RL) of −47.0 dB at only 20 wt% filler content with an effective broad bandwidth (BW) of ∼2.2 GHz (frequency region for RL < −10 dB). The attenuation constant is observed to increase from 191.6 Np m−1 to 457.8 Np m−1 for bare MnFO and MnFO@CFO NHSs respectively. Larger interfacial area, additional pairs of dipole, higher magnetic anisotropy, internal reflections and scattering from NHSs are responsible for superior absorption properties of MnFO@CFO NHSs. Moreover, the best impedance matching, ∣Z in /Z 0 ∣ ∼ 1, promotes the optimum RL in MnFO@CFO at 5.96 GHz. MnFO@SiO2 bi-layered NHSs result in a sufficiently high RL ∼ −30.0 dB with a composite absorber of a thickness of only 3 mm. Analysis from the λ/4 model for best matching thickness (t m ) displays a good agreement between experimental and simulated t m values. This study demonstrates optimized MnFO@CFO NHS as a highly promising low-cost and lightweight EM wave absorber suitable for practical high-frequency applications.

Simultaneous Voltammetric Determination of Uric Acid, Xanthine, and Hypoxanthine Using CoFe2O4/Reduced Graphene Oxide-Modified Electrode

In the present paper, the synthesis of cobalt ferrite/reduced graphene oxide (Co2Fe2O4/rGO) composite and its use for the simultaneous determination of uric acid (UA), xanthine (XA), and hypoxanthine (HX) is demonstrated. Cobalt ferrite hollow spheres were synthesized by using the carbonaceous polysaccharide microspheres prepared from aD-glucose solution as templates, followed by calcination. The CoFe2O4/rGO composite was prepared with the ultrasound-assisted method. The obtained material was characterized by using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, EDX elemental mapping, and nitrogen adsorption/desorption isotherms. The electrochemical behavior of UA, XA, and HX on the CoFe2O4/rGO-modified electrode was studied with cyclic voltammetry and differential pulse voltammetry (DPV). The modified electrode exhibits excellent electrocatalytic activity towards the oxidation of the three compounds. The calibration curves for UA, XA, and HX were obtained over the range of 2.0–10.0 μM from DPV. The limits of detection for UA, XA, and HX are 0.767, 0.650, and 0.506 μM, respectively. The modified electrode was applied to the simultaneous detection of UA, XA, and HX in human urine, and the results are consistent with those obtained from the high-performance liquid chromatography technique.

Modified Hard-Template Synthesis of Superparamagnetic Hollow Spinel Ferrite Spheres and Their Characterization

Herein, we present a simple modified hard-template approach for the fabrication of uniform superparamagnetic hollow maghemite ( $\gamma $ -Fe2O3) spheres. Hollow spheres were prepared by the attachment of ferric and ferrous ions onto the surface of the spherical silica (SiO2) particles synthesized by the Stober process. The synthesis consisted of four major steps. In the first step, monodispersed spherical silica particles with a narrow size distribution of around (497.5 ± 4.5) nm were prepared as hard templates. Second, Fe2+/Fe3+ ions were adsorbed onto the surface of the SiO2 particles in the aqueous solution. In the third step, Fe2+/Fe3+ ions at the SiO2 surface slowly nucleated and crystallized in the form of spinel $\gamma $ -Fe2O3 nanoparticles. SiO2 templates were dissolved simultaneously when [NaOH/NaHCO3] (pH 11) and [Na2CO3/NaHCO3] (pH 9) buffer solutions were added successively until the reaction medium reached pH of 3.0 ± 0.1. In the fourth step, the addition of an alkali solution accelerated the crystallization and formation of $\gamma $ -Fe2O3 nanocrystallites via the precipitation mechanism. The formation of the hollow spherical structures and their morphology were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The crystallinity and the phase analysis of the samples were characterized by means of X-ray powder diffractometry [X-ray diffraction (XRD)] and Fourier-transform infrared (FTIR) spectroscopy. The specific surface area and the specific magnetization of the prepared samples were also defined. It is important to note that the third step presents a novel approach [Patent GB 2526659] for the preparation of superparamagnetic hollow spheres, avoiding high temperatures of calcination or environmentally questionable etching, which usually employ strong solvents and acids. Consequently, our synthesis is faster, more economical and environmentally friendly when compared with other relevant procedures described in the literature.

Hierarchical structure of CoFe2O4 core-shell microsphere coating on carbon fiber cloth for high-performance asymmetric flexible supercapacitor applications

Designing hierarchical core-shell microsphere electrode materials with ideal composition and structure is a promising strategy to improve electrochemical properties of flexible electrodes. Here, we design and synthesize hierarchical CoFe2O4 core-shell microsphere coat on carbon fiber cloth (CFC) via a mild hydrothermal. The as-synthesized cobalt ferrite spheres have three stages of nanospheres, microspheres, and core-shell microspheres. The CFC/CoFe2O4 core-shell microsphere electrode shows an outstanding capacitance of 393 mF cm−2 at 1 A cm−2 and outstanding hydrophilicity. An aqueous flexible asymmetric supercapacitor (AFAS) at 1.6 V achieves a well specific capacitance of 226.2 mF cm−3 at a current density of 1 A cm−3, and the maximum energy density is 75.4 mWh cm−3 at a power density of 1151.2 mW cm−3. AFAS, with its advantages of low cost, high capacity, and simple manufacturing process, is one of the excellent candidate flexible asymmetric supercapacitors for the new generation of high-performance supercapacitors. These obvious effects have showed that the CFC/CoFe2O4 electrode may supply us a new chance for designing high-performance flexible supercapacitors.

Self-Assembly of Hollow Bismuth Ferrite Spheres from Nitrate Solutions

Using the ultrasonic spray pyrolysis method, a controllable process is realized for self-assembly of spherical BiFeO3 aggregates. Powders are obtained, which exhibit as the pronounced ferromagnetic properties (the coercive force Hc at 8.8 kOe and the residual magnetization Mp at 0.08 emu/g) characteristic of conventionally sol–gel produced BiFeO3 samples (Hc and Mp approaching zero). Various manifestations of ferromagnetism are discussed. It is found that the ultimate values of magnetic characteristics are related to destruction of the antiferromagnetic cycloid as the shells of hollow BiFeO3 spheres are formed. The aggregates thus formed may be considered as an advanced type of bismuth ferrite nanostructure with no coverage in the literature.

A simple gas sensor based on zinc ferrite hollow spheres: Highly sensitivity, excellent selectivity and long-term stability

Novel ZnFe2O4 hollow spheres constructed by numerous ZnFe2O4 nanoparticles are successfully prepared via a simple one-step hydrothermal treatment and subsequent calcination, in which carbon sheets act as the template. Compared with ZnFe2O4 nanoparticles, the obtained ZnFe2O4 hollow spheres exhibit enhanced gas sensing performance, especially in terms of excellent sensitivity to ethylene glycol and long-term stability. The improved sensing properties are mainly results from its unique hollow structure, higher specific surface area and larger pore size.

Cavity magnon polaritons with lithium ferrite and three-dimensional microwave resonators at millikelvin temperatures

Single crystal lithium ferrite (LiFe) spheres of sub-mm dimension are examined at mK temperatures, microwave frequencies, and variable dc magnetic field, for use in hybrid quantum systems and condensed matter and fundamental physics experiments. Strong coupling regimes of the photon-magnon interaction (cavity magnon polariton quasiparticles) were observed with coupling strength of up to 250 MHz at 9.5 GHz (2.6%) with magnon linewidths of order 4 MHz (with potential improvement to sub-MHz values). We show that the photon-magnon coupling can be significantly improved and exceed that of the widely used yttrium iron garnet crystal, due to the small unit cell of LiFe, allowing twice the spins per unit volume. Magnon mode softening was observed at low dc fields and, combined with the normal Zeeman effect, creates magnon spin-wave modes that are insensitive to first-order magnetic-field fluctuations. This effect is observed in the Kittel mode at 5.5 GHz (and another higher order mode at 6.5 GHz) with a dc magnetic field close to 0.19 tesla. We show that if the cavity is tuned close to this frequency, the magnon polariton particles exhibit an enhanced range of strong coupling and insensitivity to magnetic field fluctuations with both first-order and second-order insensitivity to magnetic field as a function of frequency (double magic point clock transition), which could potentially be exploited in cavity QED experiments.

Nonstoichiometric Zn Ferrite and ZnFe2O4/Fe2O3 Composite Spheres: Preparation, Magnetic Properties, and Chromium Removal

Monodisperse and porous nonstoichiometric Zn ferrite can be prepared by a solvothermal method. Such non-Zn ferrite was used to be the precursor for synthesis of ZnFe2O4/Fe2O3 composite via calcination at 600°C for 3 h in air. X-ray powder diffractometer (XRD) and Energy Dispersive Spectrometer (EDS) proved the nonstoichiometry of Zn ferrite synthesized by solvothermal method and the formation of ZnFe2O4/Fe2O3 composite via calcination. TEM image showed that non-Zn ferrite spheres with wormlike nanopore structure were made of primary nanocrystals. BET surface area of non-Zn ferrite was much higher than that of ZnFe2O4/Fe2O3 composite. Saturation magnetization of non-Zn ferrites was significantly higher than that of ZnFe2O4/Fe2O3 composites. Calcination of non-Zn ferrite resulted in the formation of large amount of non-magnetic Fe2O3,which caused a low magnetization of composite. Because of higher BET surface area and higher saturation magnetization, non-Zn ferrite presented better Cr6+ adsorption property than ZnFe2O4/Fe2O3 composites.

Solvothermal synthesis of cobalt ferrite hollow spheres with chitosan

Cobalt ferrite hollow spheres with chitosan (CoFe2O4/CS) were synthesized by two different approaches using the solvothermal method. The first approach involves in-situ incorporation of FeCl3:6H2O and CoNO3:6H2O in the solvothermal reaction (M1) and in second approach already prepared CoFe2O4 nanoparticles (NPs) using the thermal decomposition method was placed in the solvothermal reaction to form the hollow spheres (M2). Structural identification of the samples were characterized by Fourier transform infrared spectra (FTIR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analyses (DSC-TGA) and energy dispersive X-ray spectroscopy (EDX). The magnetic properties were evaluated using a vibrating sample magnetometer (VSM). The presence of chitosan on the hollow sphere was confirmed by FTIR. The XRD analyses proved that the synthesized samples were cobalt ferrite with spinel structure. The structure of the surface and the average particle size of the spheres were observed by SEM and TEM showing the nano scale of the CoFe2O4 component. Structural characterization demonstrating that chitosan does not affect the crystallinity, chemical composition, and magnetic properties of the CoFe2O4/CS. This work demonstrates that the CoFe2O4/CS prepared using the as synthesized CoFe2O4 NPs have better structural and magnetic properties.

Preparation of hollow microspheres of Ce3+ doped NiCo ferrite with high microwave absorbing performance

Hollow microspheres of Ce3+ doped NiCo-ferrites were synthesized by template-based-deposition and surface reaction method with carbon sphere as the template. The phase structure, morphology, magnetic properties and wave absorbing properties of the sample were characterized by X-ray powder diffraction(XRD), Scanning electronic microscopy(SEM), Vibration sample magnetometer (VSM) and a network vector analyzer (NVA), respectively. The results indicated that the particle size of the carbon sphere sample prepared by hydrothermal method was about 0.5µm and the particle size of the Ni0.5Co0.5Fe2O4 sample prepared by template-based method was about 300nm. The influence of the amount of rare earth element on the magnetic and absorbing properties of sample was studied. The saturation magnetization and coercivity decreased gradually with the increase of the content of Ce. When the content of Ce was 0.02, the maximal saturation magnetization value and coercivity was 75.72emu•g−1 and 789.88Oe, respectively. The associated ferrite hollow spheres have good absorbing performance, and the return loss value was −18.8dB at 5500MHz.

A NH4Ac-assisted solvothermal fabrication and properties of size-controlled cobalt ferrite nanospheres

Monodisperse cobalt ferrite nanospheres with the mean size 100 nm have been synthesized via a simple solvothermal method by using NH4Ac as protective agent. The sizes of the particles can be controlled from 20 to 200 nm by changing reaction time or protective agents. Magnetic and microwave absorption properties of Co ferrite nano spheres with the different sizes were investigated in details. Magnetic studies revealed that the saturation magnetization (Ms) and the coercivity (Hc) increased with the increase in particle size, that is, the Ms and Hc are 53.5 A·m2/kg and 14.6×103 A·m-1 (100 nm), 68.9 A·m2/kg and 49.9×103 A·m-1 (125 nm) and 72.5 A·m2/kg and 54.5×103 A·m-1 (200 nm), respectively. Electromagnetic and resulting microwave adsorption properties showed that the maximum magnitudes of the dips are -11.96 dB (at 9.00 GHz for 100 nm), -23.02 dB (at 5.55 GHz for 125nm), and -32.79 dB (at 10.47 GHz for 200 nm), respectively.

Preparation and electrochemical evaluation of manganese ferrite spheres as anode materials for half and full lithium-ion batteries

A simple hydrothermal method combined with a post annealing treatment is developed to produce high crystallinity manganese ferrite (MnFe2O4) spheres. The lithium storage properties of the material as an anode in both half and full lithium-ion batteries are investigated. And the electrochemical behaviors of the electrode during lithiation and delithiation process are clarified. Benefited from its sphere-like morphology, the MnFe2O4 electrode exhibits better lithium storage exhibitions than commercial MnFe2O4 particles in half cell system. When assembled with LiCoO2 to construct a full lithium-ion battery (LiCoO2//MnFe2O4), the spheres could deliver a reversible capacity of higher than 600mAhg−1 at a current density of 0.1Ag−1 in the potential range of 1.2–3.8V. This work clearly demonstrates the possibility of using LiCoO2//MnFe2O4 configuration for practical high-performance lithium-ion batteries in the near future.

Nonstoichiometric M-ferrite porous spheres: preparation, shape evolution and magnetic properties

We developed a simple one-pot solvothermal process to prepare porous M-ferrite (M=Ni, Zn, Co, Mn, Mg) magnetic spheres using different M2+ and Fe3+ with the introduction of dodecylamine. As-prepared ferrites were characterized in detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and selective area electron diffraction (SAED). XRD and EDS results showed that M-ferrites were nonstoichiometric in nature. Monodispersed magnetic ferrite spheres had a size distribution of 100–500nm with different composition of M2+. Morphology evolution of ferrites upon reaction time and different metal doping has been studied. Furthermore, magnetic properties of M-ferrite spheres could be tuned by changing substituted metal cations. The influence of calcination on the phase and magnetic property was also investigated.

Mesoporous Nickel Ferrites with Spinel Structure Prepared by an Aerosol Spray Pyrolysis Method for Photocatalytic Hydrogen Evolution

Submicron-sized mesoporous nickel ferrite (NiFe2O4) spheres were prepared by an aerosol spray pyrolysis method using Pluronic F127 as a structure-directing agent, and their photocatalytic performance for hydrogen (H2) evolution was examined in an aqueous MeOH solution by visible light irradiation (λ > 420 nm). The structure of the spherical mesoporous nickel ferrites was studied by transmission electron microscopy, powder X-ray diffraction, and N2 adsorption–desorption isotherm measurements. Mesoporous NiFe2O4 spheres of high specific surface area (278 m2 g–1) with a highly crystalline framework were prepared by adjusting the amount of structure-directing agent and the calcining condition. High photocatalytic activity of mesoporous NiFe2O4 for H2 evolution from water with methanol was achieved due to the combination of high surface area and high crystallinity of the nickel ferrites.

Improvement of catalytic activity in selective oxidation of styrene with H2O2 over spinel Mg–Cu ferrite hollow spheres in water

Uniform spinel Mg–Cu ferrite hollow spheres were prepared using carbon spheres as templates. For comparison, solid Mg–Cu ferrite nanocrystals were also prepared by sol–gel auto-combustion, hydrothermal and coprecipitation methods. All the samples were characterized by Fourier transform infrared spectrophotometry (FT-IR), X-ray diffractometry (XRD), transmission electron microscopy (TEM) and N2 physisorption. The samples were found to be efficient catalysts for oxidation of styrene using hydrogen peroxide as oxidant. Especially, in the case of Mg0.5Cu0.5Fe2O4 hollow spheres, obvious improvement on catalytic activity was observed, and 21.2% of styrene conversion and 75.2% of selectivity for benzaldehyde were obtained at 80°C for 6h reaction in water. The catalyst can be magnetically separated easily for reuse and no obvious loss of activity was observed when reused in six consecutive runs.

Large-Scale Synthesis of Monodisperse Magnesium Ferrite via an Environmentally Friendly Molten Salt Route

Sub-micrometer-sized magnesium ferrite spheres consisting of uniform small particles have been prepared using a facile, large-scale solid-state reaction employing a molten salt technique. Extensive structural characterization of the as-prepared samples has been performed using scanning electron microscope, transmission electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction, and X-ray diffraction. The yield of the magnesium ferrite sub-micrometer spheres is up to 90%, and these sub-micrometer spheres are made up of square and rectangular nanosheets. The magnetic properties of magnesium ferrite sub-micrometer spheres are investigated, and the magnetization saturation value is about 24.96 emu/g. Moreover, the possible growth mechanism is proposed based on the experimental results.

Magnetic separation of uranium by CoFe2O4 hollow spheres

Cobalt ferrite hollow spheres were prepared by a simple solvothermal method. The obtained CoFe2O4 was applied as magnetic adsorbent for the extraction of uranium(VI) ions from aqueous solutions. The maximum adsorption capacity was observed at pH 6.00. Maximum removal of 96.8% was observed for an initial concentration of 50mg/L at pH 6.00 and an adsorbent dose of 0.05g, displaying a high efficiency for the removal of uranium(VI) from aqueous solution. Equilibrium was achieved in approximately 180min. The results indicate that CoFe2O4 has potential as an adsorbent for sorption uranium(VI), using a simple, fast separation method for removal of uranium(VI) ions from aqueous solution.

A facile bubble-assisted synthesis of porous Zn ferrite hollow microsphere and their excellent performance as an anode in lithium ion battery

Pure porous hollow Zn ferrite (ZnFe2O4) microspheres have been successfully synthesized by a facile bubble assisted method in the presence of ammonium acetate (NH4Ac) as an anode material in lithium ion battery. The shape, size, and morphology of Zn ferrite are investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Furthermore, the probable bubble-assisted formation mechanism of porous hollow Zn ferrite spheres based on the experimental results is proposed. With the porous hollow structure, the obtained pure Zn ferrite particle as an anode in lithium ion battery demonstrates high capacity and excellent cycle ability. The high initial discharge specific capacity is approximately 1,400 mAh g−1 and a reversible specific capacity approaches 584 mAh g−1 after 100 cycles at a constant current density of 100 mA g−1. The excellent electrochemical performance of the as-prepared Zn ferrite could be attributed to the special structure with which the volume expansion and pulverization of the particles became increasingly reduced.

One-pot hydrothermal preparation and catalytic performance of porous strontium ferrite hollow spheres for the combustion of toluene

Strontium ferrite (SFO) hollow spheres with or without porous shells were fabricated via a novel one-pot hydrothermal route with the assistance of glucose and/or ethylenediamine. Physicochemical properties of the materials were characterized by means of a number of analytical techniques, and their catalytic performance was evaluated for the combustion of toluene. It is shown that the SFO samples possessed an orthorhombic structure and displayed a porous hollow spherical morphology with a surface area of 18–27m2/g. The SFO sample (SFO-3) derived hydrothermally at 170°C with a glucose/ethylenediamine volumetric ratio of 0.3/1.0 exhibited the highest surface area and oxygen adspecies concentration and the best low-temperature reducibility. Among the SFO samples, the SFO-3 sample showed the best catalytic activity for toluene combustion, and the T10%, T50%, and T90% were ca. 145, 255, and 298°C at a space velocity of 20,000mL/(gh), respectively. It is concluded that the good catalytic performance of SFO-3 was associated with its surface oxygen species concentration and better low-temperature reducibility.