A general method has been developed for the synthesis of homogeneous hollow core−shell microspheres of spinel ferrites (MFe2O4, M = Zn, Co, Ni, Cd) by using carbonaceous saccharide microspheres as template. The products were characterized by X-ray powder diffraction, inductively coupled plasma-atomic emission spectroscopy, scanning electronic microscopy, transmission electron microscopy, and nitrogen sorption measurement. The effects of the concentration of metal salts have been studied using ZnFe2O4 as an example. Increasing the concentration of metal salts could avoid the generation of impurity phase. The core size and shell thickness of hollow spheres obtained can be manipulated by changing the concentration of metal salts. Gas-sensor investigations revealed the ZnFe2O4 hollow spheres used as gas-sensor materials possess high sensitivity and quick responses to organic gases such as ethanol.
Monodisperse magnetic C 18 microspheres were prepared based on the three-step reactions of solvothermal reduction, silanization and alkylation. The microspheres are of uniform sizes in the range of 200–260 nm. The structure of synthesized magnetic C 18 microspheres was studied by transmission electron microscopy, scanning electron microscopy, X-ray diffraction patterns, element analysis and vibrating sample magnetometry. This material has a high magnetic saturation value of 59 emu g −1 and is easy to manipulate under a magnet. The prepared material was used for the preconcentration of the polycyclic aromatic hydrocarbon in water. The effects of desorption solvent and the amount of adsorbent on the preconcentration were also investigated. The results showed that the developed method was beneficial for the preconcentration of PAHs of middle molecular weight.
The spinel-type magnetic manganese ferrite (MnFe2O4) microspheres synthesized by simple solvothermal method were used as a novel adsorbent for selective enrichment and effective isolation of phosphopeptides. The uniform MnFe2O4 magnetic affinity microspheres (MAMSs) had a narrow particle size distribution between 250 and 260nm, and displayed superparamagnetism with a saturation magnetization value of 67.0emu/g. Comprehensively, the possible formation mechanism of MnFe2O4 microspheres with ferric and manganous sources as dual precursors was elucidated by comparison with those of Fe3O4 nanoparticles and MnOOH nanosheets respectively with either ferric or manganous source as single precursor. It was suggested that the spherical or sheet nanostructures could be achieved via secondary recrystallization or Ostwald ripening. The MnFe2O4 MAMSs probe exhibited excellent dispersibility in aqueous solution, and rapid magnetic separation within 15s, as well as good reusability. More importantly, MnFe2O4 was highly selective for phosphopeptides because of the strong coordination interaction between metal ions (Fe3+ and Mn2+) and phosphate groups of phosphopeptdies. This high specificity was demonstrated by effectively enriching phosphopeptides from digest mixture of β-casein and bovine serum albumin (BSA) with high content of non-phosphopeptides, and embodied further in phosphopeptides enrichment from non-fat milk digests and human serum. Consequently, the prepared MnFe2O4 affinity materials are expected to possess great potential in phosphoproteome research. [Display omitted] •The synthesis of MnFe2O4 particles is described.•The characterization of synthetized MnFe2O4 was carried out.•The mechanism for the formation of MnFe2O4 was purposed.•MnFe2O4 was used as novel adsorbent for phosphopeptide enrichment.
Display omitted] ► Mesoporous MnFe2O4 microspheres were synthesized using solvothermal method. ► Obtained mesoporous MnFe2O4 microspheres had high surface areas (60.2–86.8m2g−1). ► After calcined at 600°C, MnFe2O4 microspheres were decomposed to Mn2O3 and Fe2O3. ► The mesoporous MnFe2O4 calcined at 400°C showed the best electrochemical property. We report the synthesis and characterization of the mesoporous manganese ferrite (MnFe2O4) microspheres as anode materials for Li-ion batteries. MnFe2O4 microspheres were synthesized by a facile solvothermal method using Mn(CH3COO)2 and FeCl3 as metal precursors in the presence of CH3COOK, CH3COOC2H5, and HOCH2CH2OH. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermal gravimetric, X-ray photoelectron spectroscopy, temperature programmed reduction, and temperature programmed oxidation. The synthesized mesoporous MnFe2O4 microspheres composed of nanoparticles (10–30nm) were 100–500nm in diameter and had surface areas between 60.2 and 86.8m2g−1, depending on the CH3COOK amounts added in the preparation. After calcined at 600°C, MnFe2O4 was decomposed to Mn2O3 and Fe2O3 mixture. The mesoporous MnFe2O4 microspheres calcined at 400°C showed a capacity of 712.2mAhg−1 at 0.2C and 552.2mAhg−1 at 0.8C after 50cycles, and an average capacity fading rate of around 0.28%/cycle and 0.48%/cycle, much better than those of the samples without calcination and calcined at 600°C. The work would be helpful in the fabrication of binary metal oxide anode materials for Li-ion batteries.
► Microwave absorptive composition comprising Ag-coated Ni–Zn ferrite microspheres. ► A conductive Ag layer was coated on the ferrite spheres by electroless plating. ► The ferrite-rubber composites exhibit high dielectric constant and dielectric loss. ► A reduced matching thickness is predicted with the conductive ferrite microspheres. This investigation presents an electromagnetic radiation absorptive composition comprising Ag-coated ferrite microspheres dispersed in a silicone rubber matrix for use as a thin microwave absorber in GHz frequencies. Ni–Zn ferrite microspheres with an average diameter of 50 μm were prepared by spray-drying and sintering at 1130 °C. A conductive Ag layer was coated on the ferrite spheres by electroless plating. Uniform Ag coating can be obtained using the plating solution with a high AgNO 3 concentration. For particle compacts of the conductive Ni–Zn ferrite spheres, electrical resistance is reduced to as low as 10 −2 Ω. Rubber composites containing the Ag-plated ferrite spheres exhibit a high value of both real and imaginary parts of complex permittivity, while the complex permeability spectrum is not significantly changed with Ag plating. Due to the conductive and magnetic property of the microspheres, matching thickness can be reduced to as low as 2 mm at the frequency of 7.6 GHz, which is much thinner than non-coated ferrite absorbers.
Monodisperse Ni–Zn ferrites (Ni x Zn 1− x Fe 2O 4) microspheres have been synthesized via solvothermal method. X-ray diffraction pattern (XRD), transmission electron microscope (TEM), field emission-scanning electron microscopy (FE-SEM) and vibrating sample magnetometry are used to characterize the shape, structure, size and magnetic properties of the as-synthesized magnetic microspheres. The powder XRD patterns revealed the formation of the single phase spinel structure for the synthesized materials. TEM and FE-SEM show the size and morphology of the as-synthesized sample in detail. The maximum magnetic saturation value of the Ni 0.2Zn 0.8Fe 2O 4 microspheres can reach 60.6 emu g −1. These magnetic Ni x Zn 1− x Fe 2O 4 microspheres are expected to have wide applications in bionanoscience and electronic devices technology.
Hard magnetic composites—hollow microsphere (core)/titania (intermediate layer)/barium ferrite (magnetic shell) (M/T/B) were prepared by wet-chemical method. Barium ferrite nanoparticles were directly coated on the rutile titania-coated hollow microsphere forming light hard magnetic composites using sol–gel technique. The prepared composites were characterized with FESEM, EDS, XRD and vibrating sample magnetometry. The composites are composed of barium ferrite, hematite, titania and mullite. For the samples with 40 wt.% barium ferrite, its specific saturation magnetization with titania is increased to 17.88 emu/g in comparison with 9.6 emu/g without titania. The function of titania in the composites is also discussed.
CoFe2O4 flower-like microspheres are prepared via a surfactant- and template-free method, involving the controlled hytrothermal synthesis firstly and a subsequent thermal decomposition treatment. The microspheres with diameters of 3–4 μm are characterized by the assembly of numerous porous and inter-connected lamella structures. Lithium-ion batteries electrodes based on the as-prepared CoFe2O4 microspheres show a high specific capacity of 733.5 mAh g−1 after 50 cycles at a current density of 200 mA g−1 and a good cyclic stability, as well as excellent rate capability. The enhanced electrochemical performance can be attributed to the hierarchical microsphere structure with high sufficient interfacial contact area between the microspheres and electrolyte, the short diffusion distance of Li+, better accommodation of structural stress and volume change with the lithiation/delithiation process. It is suggested that the CoFe2O4 microsphere is one of the most promising candidates for high-performance lithium-ion batteries. CoFe2O4 flower-like microspheres were synthesized by a controlled AA-assisted hydrothermal process and subsequent annealing. The discharge capacity and cycle stability were greatly enhanced. [Display omitted] •We prepared CoFe2O4 flower-like microspheres via a AA-assisted method.•The microspheres are assembled by numerous porous and inter-connected lamella structures.•The electrode shows high capacity, good cycle stability and enhanced rate performance.