Facile synthesis and properties of ZnFe2O4 and ZnFe2O4/polypyrrole core-shell nanoparticles

We demonstrated that ZnFe₂O₄/polypyrrole core-shell nanoparticles could be facilely synthesized via in situ chemical oxidative polymerization of pyrrole monomers on the surface of ZnFe₂O₄ nanoparticles. The shell thickness of core-shell nanoparticles could be easily controlled by adjusting the amount of pyrrole monomers. The phase structures, morphologies and properties of the as-prepared products were investigated by XRD, TEM, SEM, VSM, and FTIR spectra. Magnetic studies revealed that the saturation magnetization (M_s) and coercivity (H_c) of ZnFe₂O₄/PPy core-shell nanoparticles is 17.8 emu/g and 130 Oe, respectively. The electromagnetic characteristics of products showed that ZnFe₂O₄/PPy core-shell nanoparticles exhibit excellent microwave absorption performance than ZnFe₂O₄ nanoparticles, such as more powerful absorbing property and wider electromagnetic wave absorbing frequency band due to the proper matching of the permittivity and the permeability of ZnFe₂O₄/PPy core-shell nanoparticles.     

Fabrication, characterization and magnetic behaviour of alumina-doped zinc ferrite nano-particles

Zinc ferrite nano-powders with a nominal composition of ZnFe₂O₄ were prepared by combustion synthesis using mixture of urea and ammonium nitrate as fuel. The influence of alumina-doping on the structural, morphological and magnetic properties of ZnFe₂O₄ nano-particles was investigated by means of X-ray powder diffraction (XRD), infrared (IR) spectroscopy, scanning and transmission electron microscopy (SEM and TEM) and vibrating sample magnetometer (VSM). XRD and IR analyses confirm the cubic spinel phase of ZnFe₂O₄ nano-particles. The Zn ferrite presented a uniform microstructure with grain size in nano-scale. Alumina-doping brought about a change in the morphology of the as prepared ferrite from sphere-like to regular hexagon. Al₂O₃-treatment led to a decrease in the coercivity (H_c), magnetization (M_s) and magnetic moment (n_B) of the investigated system. The maximum decrease in the values of H_c, M_s and n_B due to the treatment with 1.5 wt% Al₂O₃ attained 13.5, 17.4 and 13.5%, respectively. The observed results can be explained on the basis of particle size and the Fe³⁺ concentration in the octahedral and tetrahedral sites involved in the cubic spinel structure.     

One-pot hydrothermal synthesis of reduced graphene oxide/zinc ferrite nanohybrids and its catalytic activity on the thermal decomposition of ammonium perchlorate

Reduced graphene oxide/Zinc ferrite (rGO/ZnFe₂O₄) nanohybrids are successfully decorated on the surface of the rGO sheets through a simple, one-step hydrothermal method. ZnFe₂O₄ nanoparticles (NPs) are homogeneously anchored on the rGO sheets. The rGO/ZnFe₂O₄ hybrids are characterized by XRD, FT-IR, XPS, TEM, Raman, BET. The rGO/ZnFe₂O₄ hybrids demonstrate amazing catalytic activity on thermal decomposition of ammonium perchlorate (AP), which is better than that of bare ZnFe₂O₄ NPs. TG-DTA results indicate that the ZnFe₂O₄ NPs in the hybrids with increasing ratio (1%, 3%, 5%) could decrease the second decomposition temperature of AP by 42.7?°C, 55.0?°C, 68.1?°C, respectively, and reduce the apparent activation energy of AP from 160.2?kJ?mol^?1 to 103.8?kJ?mol^?1. This enhanced catalytic performance is mainly attributed to the synergistic effect of ZnFe₂O₄ NPs and rGO.     

Graphene anchored with ZnFe2O4 nanoparticles as a high-capacity anode material for lithium-ion batteries

Heterostructured ZnFe₂O₄–graphene nanocomposites are synthesized by a facile hydrothermal method. The as-prepared ZnFe₂O₄–graphene nanocomposites are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) analysis and galvanostatic charge and discharge measurements. Compared with the pure ZnFe₂O₄ nanoparticles, the ZnFe₂O₄–graphene nanocomposites exhibit much larger reversible capacity up to 980 mAh g⁻¹, greatly improved cycling stability, and excellent rate capability. The superior electrochemical performance of the ZnFe₂O₄–graphene nanocomposites could be attributed to the synergetic effect between the conducting graphene nanosheets and the ZnFe₂O₄ nanoparticles.     

兼具电磁性能的PANI/ZnFe2O4纳米复合材料的制备

运用改进的溶胶凝胶-原位聚合法制备出了兼具电、磁性能的PANI/ZnFe2O4纳米复合材料,借助TEM、XRD、FTIR、四探针电导率仪和VSM(振动样品磁强计)等技术研究了复合材料的结构及其电磁性能。结果表明,通过该法可以实现ZnFe2O4与PANI的有机复合,制得纳米尺寸的、ZnFe2O4与PANI相间以化学键结合的纳米复合材料;复合材料兼具电、磁性能,其导电率随ZnFe2O4含量增加而降低,饱和磁化强度随之而升高,复合物的矫顽力在所研究的含量范围内均较纯ZnFe2O4大,且随ZnFe2O4含量的增加呈先升高后降低的变化趋势。此外,对ZnFe2O4进行HNO3预处理可以有效改善复合材料的电磁性能。     

Preparation and characterization of magnetic TiO2/ZnFe2O4 photocatalysts by a sol–gel method

A magnetic TiO₂/ZnFe₂O₄ photocatalyst was prepared by a sol-gel method, and X-ray diffraction (XRD), magnetic and photocatalytic properties analysis were employed to characterize this photocatalyst. The XRD results show that ZnFe₂O₄ can prevent the transformation of titania from anatase to rutile. The magnetic properties analysis indicates that TiO₂/ZnFe₂O₄ is of large saturation magnetization value and low coercivity. The photocatalytic experimental results show that TiO₂/ZnFe₂O₄=3 and 4 are superior in photocatalytic reactivity to other proportions. TEM shows that TiO₂/ZnFe₂O₄ has a fine core-shell fabric. After being used for four times during the photocatalytic reaction, the TiO₂/ZnFe₂O₄ nanoparticles have good photocatalytic stability.     

Superparamagnetic and ferromagnetic behavior of ZnFe2O4 nanoparticles synthesized by microwave-assisted hydrothermal method

Zinc ferrite (ZnFe₂O₄) nanoparticles were successfully synthesized from Zn(NO₃)₂ · 6H₂O and Fe(NO₃)₃ · 9H₂O by microwave hydrothermal method at 150°C for 1 h. Cubic ZnFe₂O₄ with particle size below 7 nm was formed in the solution at pH ≥ 6. The crystallinity and particle size of ZnFe₂O₄ nanoparticles were increased after calcination. The effects of pH of the precursor solution and calcination on the particle size and crystallinity of the particles were studied. At room temperature the products show superparamagnetic and ferromagnetic properties, determined by their size. The formation mechanism of ZnFe₂O₄ was also discussed according to the experimental results.

     

Hole concentration in the three-CuO2-plane copper-oxide superconductor Cu-1223

Strongly overdoped samples of the three-CuO₂-plane copper-oxide superconductor, CuBa₂Ca₂Cu₃O_8+z or Cu-1223, were obtained through high-pressure synthesis and post-annealed to various hole-doping levels so as to have the value of T_c range from 65 to 118 K. A concomitant decrease in the average valence of copper from ∼2.20 to ∼2.05 was evidenced by means of wet-chemical and thermogravimetric analyses and Cu L-edge X-ray absorption near-edge structure (XANES) spectroscopy. The valence value as low as ∼2.05 that corresponds to the highest T_c (=118 K) may be understood by taking into account multiple ways for holes to be distributed among the different Cu-O layers. In terms of actual chemical composition of the Cu-1223 phase, both Cu L-edge and O K-edge XANES results suggest that some portion of charge-reservoir copper atoms may have been replaced by CO, i.e., (Cu_1−xC_x)Ba₂Ca₂Cu₃O_8+x+z. The variation range of excess oxygen was estimated at Δz≈0.3.     

Preparation of ZnFe2O4 Nanofibers by Sol‐Gel Related Electrospinning Method

Zinc ferrite gel fibers were prepared from the sol precursor by the electrospinning method, and the ZnFe₂O₄ polycrystalline nanofibers were obtained upon calcination of the gel fibers. The obtained ZnFe₂O₄ nanofibers composed of 20–30 nm nanocrystals were about one hundred to several hundred nanometers in diameter. The materials have been characterized by means of SEM, TEM, XRD, TGA, and IR techniques.     

Photothermal performance of MFe2O4 nanoparticles

Photothermal therapy (PTT) has emerged as one of the promising cancer therapy approaches. As a representative photothermal agent (PTA), magnetite possesses many advantages such as biodegradability and biocompatibility. However, photothermal instability hampers its further application. Herein, we systematically synthesized three kinds of ferrite nanoparticles and detailedly investigated their photothermal effect. Compared with Fe₃O₄ and MnFe₂O₄ nanoparticles, ZnFe₂O₄ nanoparticles exhibited a superior photothermal effect. After preservation for 70 days, the photothermal effect of Fe₃O₄ and MnFe₂O₄ nanoparticles observably declined while ZnFe₂O₄ nanoparticles showed slight decrease. Furthermore, in vitro experiment, ZnFe₂O₄ nanoparticles showed little toxicity to cells and achieved outstanding effect in killing cancer cells under NIR laser irradiation. Overall, through synthesizing and studying three kinds of ferrite MFe₂O₄ nanoparticles, we obtained ferrites as PTAs and learned about their changing trend in photothermal effect, expecting it can inspire further exploration of photothermal agents.     

Ceramic Tl-oxide based superconductors reinvestigated by magnetic separation technique and SQUID measurements

Ceramic samples of Tl₂Ba₂Ca₂Cu₃O₁₀ (Tl-2223) and TlBa₂Ca₂Cu₃O₉ (Tl-1223) superconductor were resynthesized by using several preparation procedures and investigated by means of magnetic separation technique, allowing evaluation of the superconducting critical temperature of individual grains as small as 25 μm. Although an onset of diamagnetism detected by SQUID measurements was observed around 130 K in Tl-2223 and 134 K in Tl-1223, no grains with T_c > 125 K were found for Tl-2223 and with T_c > 130 K for Tl-1223. Furthermore, the volume fraction of superconductivity of such ceramics was less than 5% and 3% in best samples of Tl-2223 and Tl-1223, respectively. Here we provide a detailed comparison of results obtained by magnetic separation technique with those by SQUID applied to individual grains and bulk samples.     

Low temperature synthesis of zinc ferrite nanoparticles

Zinc ferrite (ZnFe₂O₄) nanocrystalline powder materials with various particle sizes were prepared by a unique solid-state combustion method. Phase purity of ZnFe₂O₄ was confirmed by X-ray diffraction studies. High resolution transmission electron microscopic analysis and selected area diffraction pattern also confirmed the correct crystalline phase formation. Particle size was determined from both the transmission electron microscopic images and also from the XRD peak broadening analysis. Oxidation states of different elements present in ZnFe₂O₄ were determined by X-ray photoelectron spectroscopy. Frequency dependent dielectric constant and a.c. conductivity were measured as a function of particle size and both of them were found to decrease with decreasing particle size. These studies indicated that good quality zinc ferrite nanocrystalline powdered materials can be synthesized at low temperature.     

Enhanced Photocatalytic Degradation of 17α‐Ethinylestradiol Exhibited by Multifunctional ZnFe2O4–Ag/rGO Nanocomposite Under Visible Light

In this paper, ZnFe₂O₄, a visible light active photocatalyst, was comodified by graphene oxide (GO) and Ag nanoparticles (NPs) to form ZnFe₂O₄–Ag/rGO nanocomposite (NC) by facile one‐pot hydrothermal method. Reduction of GO and formation of ZnFe₂O₄ and Ag nanoparticles occurred simultaneously during hydrothermal reaction. The photocatalytic activity of the NC was investigated under visible light, for the degradation of 17α‐ethinylestradiol (EE2), a nondye compound, which also is an emerging pollutant with endocrine‐disrupting activity. The pseudo rate constant (k′) of as‐synthesized ZnFe₂O₄–Ag/rGO NC was higher by the factor of 14.6 and 5.6 times than the corresponding ZnFe₂O₄ and ZnFe₂O₄/rGO respectively. The synergistic interactions between ZnFe₂O₄, Ag and rGO leading to decreased aggregation of the NPs, increased surface area, better absorption in visible region, effective electron–hole generation transfer. However, in the presence of humic acid (HA), the photosensitization effect was predominated by competitive interaction resulting in only 80% removal of EE2 within the same time. Moreover, the composite can easily be magnetically separated for reuse.     

Thermodynamic properties and cation distribution of the ZnFe2O4Fe3O4 spinel solid solutions at 900°C

The thermodynamic properties of the Fe₃O₄ZnFe₂O₄ spinel solid solution were determined at 900°C by the use of the solid electrolyte galvanic cell Fe₂O₃ + Fe₃O₄|O^2?|Fe₂O₃ + Zn_xFe_3?xO₄The activity values obtained exhibit slight negative deviation from the ideal solution model. An analysis of the free energy of mixing of the spinel solid solution provided information on the distribution of cations between the tetrahedral and octahedral sites of the spinel lattice. This is the basis for the estimation of the free energy of formation of pure zinc ferrite from oxides. ΔG⁰_ZnFe2O4 = ?2740 ? 1.6 T cal mole^?1     

Investigation of structural and thermal characteristics of PVDF/ZnO nanocomposites

The structural and thermal behavior of PVDF/ZnO nanocomposites have been investigated by employing scanning electron microscopy (SEM),TEM, DSC, powder X-ray diffraction (XRD), thermally stimulated discharge current (TSDC), and transient current techniques. SEM/TEM observation indicated the homogeneous dispersion of functionalized ZnO nanoparticles throughout PVDF matrix. DSC shows that the crystallinity is influenced by the presence of ZnO nanoparticles in the PVDF matrix because the filler acts as efficient nucleating agent to facilitate PVDF crystallization. DSC results indicated the enhancement of the glass transition temperature (T _g), melting temperature (T _m) and crystallization temperature (T _c) of nanocomposites compared to pristine PVDF. XRD shows that the full-width at half maximum decreases with increasing ZnO content, which is attributed to the improvement in crystallinity. The incorporation of ZnO nanoparticles influences the modification of polarization process in PVDF as observed by means of TSDC and transient current study.     

Surfactant Assisted Hydrothermal Synthesis of Superparamagnetic ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanoparticles as an Efficient Visible-Light Photocatalyst for the Degradation of Organic Pollutant

Super paramagnetic ZnFe₂O₄ nanoparticles were prepared by a surfactant assisted (ethylamine) hydrothermal method along with heat treatment. The nanoparticles were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, high resolution scanning electron microscopy, Transmission electron microscopy, vibrating sample magnetometer and diffuse reflectance spectra technique. From the analyses, influence of calcination temperature on the structural, vibrational, morphological, magnetic and optical properties of ZnFe₂O₄ nanoparticles were investigated. The ZnFe₂O₄ nanoparticles with an average particle size of 17 nm showed high photocatalytic activity in the degradation of methylene blue (90 %). This work demonstrates that ZnFe₂O4 can be used as a potential monocomponent in visible-light photocatalysis for the degradation of organic pollutants. Furthermore, the products were super paramagnetic and could be conveniently separated within 15 min and recycled by using simple magnet, which is very beneficial for the degradation of organic pollutants.     

In-situ high-pressure x-ray diffraction study of zinc ferrite nanoparticles

We have studied the high-pressure structural behavior of zinc ferrite (ZnFe₂O₄) nanoparticles by powder X-ray diffraction measurements up to 47 GPa. We found that the cubic spinel structure of ZnFe₂O₄ remains up to 33 GPa and a phase transition is induced beyond this pressure. The high-pressure phase is indexed to an orthorhombic CaMn₂O₄-type structure. Upon decompression the low- and high-pressure phases coexist. The compressibility of both structures was also investigated. We have observed that the lattice parameters of the high-pressure phase behave anisotropically upon compression. Further, we predict possible phase transition around 55 GPa. For comparison, we also studied the compression behavior of magnetite (Fe₃O₄) nanoparticles by X-ray diffraction up to 23 GPa. Spinel-type ZnFe₂O₄ and Fe₃O₄ nanoparticles have a bulk modulus of 172 (20) GPa and 152 (9) GPa, respectively. This indicates that in both cases the nanoparticles do not undergo a Hall-Petch strengthening.     

Preparation of magnetically recyclable ZnFe2O4 nanoparticles by easy single‐step co‐precipitation method and their catalytic performance in the synthesis of 2‐aminothiophenes

In this work, a new synthetic route for the preparation of ZnFe₂O₄ nanoparticles through the chemical co‐precipitation using Fe²⁺ and Fe³⁺ ions in an alkaline solution was developed. The synthesized nanoparticles were characterized by XRD, FTIR, SEM, ICP‐MS, DRS, TGA, VSM and elemental analysis. Characterization results confirmed the formation of single ZnFe₂O₄ phase, with an average particle size of 40 nm and a high saturation magnetization of 34 emu g^?1. The prepared material was employed as a catalyst for the synthesis of 2‐aminotiophene derivatives through the Gewald reaction. This thermally and chemically stable nanocatalyst is environmentally benign, economical and reusable which can be easily recovered using an external magnet. Therefore, it appears that this methodology can be simply extended for industrial purposes.     

Preparation of ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles by mechanical alloying and annealing for sensitizing C-modified TiO<Subscript>2</Subscript> and acquirement of efficient photocatalyst

ZnFe₂O₄ nanoparticles sensitized by C-modified TiO₂ hybrids (ZnFe₂O₄–TiO₂/C) were successfully prepared by a feasible method. The ZnFe₂O₄ nanoparticles were prepared by mechanical alloying and annealing. The residual organic compounds in the synthetic process of TiO₂ were selected as the carbon source. The as-prepared composites were characterized by X-ray diffraction, Raman spectroscopy, X-ray fluorescence, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible light diffuse reflectance spectroscopy (UV–Vis) and N₂ adsorption–desorption analysis. The photocatalytic activity of the photocatalysts was measured by degradation of methyl orange under ultraviolet (UV) light and simulated solar irradiation, respectively. The results show that the carbon did not enter the TiO₂ lattice but adhered to the surface of TiO₂. The photocatalytic activity of the as-prepared C-modified TiO₂ (TiO₂/C) improved both under UV and simulated solar light irradiation, but the improvement was not dramatic. Introduction of ZnFe₂O₄ into the TiO₂/C could enhance the absorption spectrum range. The ZnFe₂O₄–TiO₂/C hybrids exhibited a higher photocatalytic activity both than that of the pure TiO₂ and TiO₂/C under either UV or simulated solar light irradiation. The complex synergistic effect plays an important role in improving the photocatalytic performance of ZnFe₂O₄–TiO₂/C composites. The optimum photocatalytic performance was obtained from the ZnFe₂O₄(0.8 wt%)–TiO₂/C sample.     

XRD and Mössbauer studies of crystallographic and magnetic transformations in synthesized Zn-substituted Cu-Ga-Fe compound

System of samples in the form of Cu_1−xZn_xFe_2−yGa_yO₄ with (0.0?x?1.0, y=0.0 and 1.0) is synthesized. X-ray diffraction study confirms the presence of a single-phase structure, where tetragonal unit cell is obtained for samples CuFe₂O₄ and CuGaFeO₄ with c/a>1. At compositional parameter x?0.25, tetragonal-to-cubic transformation occurs. The determined lattice parameter a for the cubic samples is found to decrease with increasing Zn content x. ⁵⁷Fe Mössbauer measurements at 293, 77 and 12 K show characteristic spectra of paramagnetic, magnetic, and electronic types for the different compositions. Cation distribution obtained from the spectral analysis at 12 K revealed transformation from the ferrimagnetic inverse spinel of CuFe₂O₄ to the antiferromagnetic normal spinel of ZnFe₂O₄. Hyperfine parameters are found to be strongly dependent on temperature and concentration parameter x. Low-temperature measurements are carried out using installed and well-calibrated closed-cycle variable temperature cryostat Model REF-399-D22. Low vibration is obtained through bellows, spacer, and exchange gas isolation and a difference of 0.018 mm s⁻¹ between the FWHM of a pure iron foil at room temperature and 12 K is achieved.