Ferrite Hollow Spheres Research Articles

Enhanced Visible-Light Photocatalytic Activity of Bismuth Ferrite Hollow Spheres Synthesized via Evaporation-Induced Self-Assembly.

Semiconductor hollow spheres have garnered significant attention in recent years due to their unique structural properties and enhanced surface area, which are advantageous for various applications in catalysis, energy storage, and sensing. The present study explores the surfactant-assisted synthesis of bismuth ferrite (BiFeO3) hollow spheres, emphasizing their enhanced visible-light photocatalytic activity. Utilizing a novel, facile, two-step evaporation-induced self-assembly (EISA) approach, monodisperse BiFeO3 hollow spheres were synthesized with a narrow particle size distribution. The synthesis involved Bi/Fe citrate complexes as precursors and the triblock copolymer Pluronic P123 as a soft template. The BiFeO3 hollow spheres demonstrated outstanding photocatalytic performance in degrading the emerging pollutants Rhodamine B and metronidazole under visible-light irradiation (100% degradation of Rhodamine B in <140 min and of metronidazole in 240 min). The active species in the photocatalytic process were identified through trapping experiments, providing crucial insights into the mechanisms and efficiency of semiconductor hollow spheres. The findings suggest that the unique structural features of BiFeO3 hollow spheres, combined with their excellent optical properties, make them promising candidates for photocatalytic applications.

Hydrothermal Synthesis of Bismuth Ferrite Hollow Spheres with Enhanced Visible-Light Photocatalytic Activity.

In recent years, semiconductor hollow spheres have gained much attention due to their unique combination of morphological, chemical, and physico-chemical properties. In this work, we report for the first time the synthesis of BiFeO3 hollow spheres by a facile hydrothermal treatment method. The mechanism of formation of pure phase BiFeO3 hollow spheres is investigated systematically by variation of synthetic parameters such as temperature and time, ratio and amount of precursors, pressure, and calcination procedures. The samples were characterized by X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and UV-vis diffuse reflectance spectroscopy. We observe that the purity and morphology of the synthesized materials are very sensitive to synthesis parameters. In general, the chemically and morphologically very robust hollow spheres have diameters in the range of 200 nm to 2 μm and a wall thickness of 50-200 nm. The synthesized BiFeO3 hollow spheres were applied as catalysts in the photodegradation of the model pollutant Rhodamine B under visible-light irradiation. Notably, the photocatalyst demonstrated exceptionally high removal efficiencies leading to complete degradation of the dye in less than 150 min at neutral pH. The superior efficiencies of the synthesized material are attributed to the unique features of hollow spheres. The active species in the photocatalytic process have been identified by trapping experiments.

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.

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.

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.

Polypyrrole‐Coated Zinc Ferrite Hollow Spheres with Improved Cycling Stability for Lithium‐Ion Batteries

Here, ZnFe2 O4 double-shell hollow microspheres are designed to accommodate the large volume expansion during lithiation. A facile and efficient vapor-phase polymerization method has been developed to coat the ZnFe2 O4 hollow spheres with polypyrrole (PPY). The thin PPY coating improves not only the electronic conductivity but also the structural integrity, and thus the cycling stability of the ZnFe2 O4 hollow spheres. Our work sheds light on how to enhance the electrochemical performance of transition metal oxide-based anode materials by designing delicate nanostructures.

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.

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.

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.

Hierarchical flower-like Co3−xFexO4 ferrite hollow spheres: facile synthesis and catalysis in the degradation of methylene blue

A facile method is proposed for the synthesis of three-dimensional (3D) flower-like Co3-xFexO4 ferrite (CF) hollow spheres, using SiO2@FeOOH as precursor. The CF hollow spheres are efficient for the catalytic degradation of methylene blue (MB) in the presence of H2O2 at 80 °C. The obtained CF hollow spheres were characterized using transmission electron microscopy, field emission scanning electron microscopy, X-ray diffraction, X-ray photo-electron spectroscopy, and N2 adsorption-desorption isotherm measurements. The formation of 3D hierarchical flower-like superstructure was influenced by the relative amount of urea used. As the mole ratio of CoCl2 and urea decreased, the structure of the products was tailored from yolk-like spheres to hollow spheres with different sized void interiors. Moreover, N2 adsorption-desorption isotherm analysis showed that the CF hollow spheres have a large specific surface area (163 m(2) g(-1)) which provided more activity sites. The CF hollow spheres can catalyze the oxidation of MB efficiently. These results indicate that the designed CF hollow spheres exhibit promising capability for the degradation of dyes.

Promising methane-sensing characteristics of hydrothermal synthesized magnesium zinc ferrite hollow spheres

We have synthesized hollow magnesium zinc ferrite (Mg0.5Zn0.5Fe2O4) spheres via a spherical carbon template-mediated hydrothermal synthesis route. The phase formation behavior, microstructure evaluation and methane-sensing characteristics of the synthesized hollow spheres have been investigated. The promising methane-sensing characteristics (i.e. per cent response, response and recovery time) identified for Mg0.5Zn0.5Fe2O4 hollow sphere-based sensing elements are attractive for developing chemoresistive-type non-conventional complex oxide-based combustible gas sensors.

In situ carbon template-based strategy to fabricate ferrite hollow spheres and their magnetic property

In this paper, a series of MFe 2O 4 (M=Mg, Co, Ni, Zn) hollow spheres are successfully prepared by hydrothermal treatment of the mixed solution of glucose, Fe 3+ and M 2+ and a subsequent calcination process. After the calcination process, the carbon core of the hydrothermally prepared composite carbon spheres was removed and the metal components were transformed to pure phase ferrites. The final products (ferrite hollow spheres) were characterized using X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy and the magnetic properties were evaluated using a SQUID magnetometer.

Synthesis, Properties, and Formation Mechanism of Zinc Ferrite Hollow Spheres

Hollow spheres of zinc ferrite were prepared via a surfactant‐assisted hydrothermal approach. The morphology and composition of the final products were characterized by X‐ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy. It was observed from the microscope images that the final products were composed of spherical nanostructures about 70–100 nm in diameter. Anti‐ferromagnetic transition at the temperature of about 18.06 K was observed from the temperature–magnetic susceptibility curve of the ZnFe2O4 hollow spheres. Possible formation mechanism of the hollow sphere has been discussed. This work may provide us a new synthesis route for the preparation and fabrication of other ferrite nanostructures.

Ferrite hollow spheres with tunable magnetic properties

We developed a simple process to prepare monodispersed ferrite hollow spheres with tunable magnetic properties, which were fabricated by coating ferrite nanoparticles on the surface of monodispersed polystyrene spheres and removing of the core polymer subsequently. Transmission electron microscopy images show that magnetic shells of these spheres are composed of ferrite nanoparticles with an average diameter of 15 nm. Scan electron microscopy images show that most of the hollow spheres are complete and structurally intact. Furthermore, the magnetic properties of MFe2O4 ferrite spheres could be tuned by changing the substituted metal cation (M=Mn, Mg, Zn, Ni, Co). The influence of surface modification and calcination on the magnetic properties of ferrite shell was also investigated. It is anticipated that these ferrite hollow spheres can be widely used in various fields of biotechnology and material science.

Synthesis of Amphiphilic Superparamagnetic Ferrite/Block Copolymer Hollow Submicrospheres

Self-assembly can be a powerful, but simple, synthetic method for the fabrication and surface modification of nanometer- to micrometer-sized hollow spheres. Here we report a facile route for preparation of submicrometer ferrite hollow spheres which are amphiphilic and superparamagnetic. This unique approach involves the formation of ferrite nanocrystals and the simultaneous self-assembly of nanocrystals and block copolymer PEO-PPO-PEO into hollow spheres. Furthermore, this approach is general for the preparation of a series of ferrite hollow spheres, including Fe3O4, Co1-xFe2+xO4, and Mn1-xFe2+xO4. Unlike conventional hollow spheres, which are either hydrophobic or hydrophilic, the products we obtained exhibit excellent dispersibility in both polar and nonpolar solvents.

Synthesis and magnetic behavior of silica-coated cobalt ferrite hollow spheres

We have used functional polymer poly(methyl methacrylate-co-methacrylic acid) latex (500nm) as a core template to prepare magnetic hollow SiO2∕CoFe2O4 spheres. The mean crystallite sizes of coated CoFe2O4 nanoparticles, depending on the calcined temperature, are in the range from 2.2to10.1nm. The thickness of the CoFe2O4∕SiO2 composite shell is between 40 and 50nm and the content of CoFe2O4 in the composites is 73wt%. The magnetic properties of the hollow spherical particles can go from superparamagnetic to ferromagnetic behavior depending on the sizes of CoFe2O4 nanoparticles.