Facile synthesis of nanocrystalline spinel NiFe2O4 via a novel soft chemistry route

A novel soft chemistry route (rheological phase reaction method) was developed to synthesize nanocrystalline NiFe₂O₄. The as-prepared samples were characterized by powder X-ray diffractometer (XRD), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM). The effects of the calcination temperature on the particle sizes and magnetic properties of the samples were investigated. The results indicated that the samples obtained by this method had the single-phase spinel. Particle sizes estimated from Scherrer's formula increased with the calcination temperature, which were consistent with the results of TEM. The magnetic properties of the samples were strongly affected by the calcination temperature. The coercivity initially increased and then decreased with increasing calcination temperature whereas the saturation magnetization continuously increased.     

Preparation and properties of NiFe2O4 nanowires

Polycrystalline NiFe₂O₄ nanowires have been synthesized by PEG assisted co-precipitation method. The formation mechanism of the nanowires proposed is by means of the orientational aggregation of individual nanoparticles. X-ray diffraction, high resolution scanning electron microscopy, transmission electron microscopy, microRaman and vibrating sample magnetometry studies were carried out. The results show that NiFe₂O₄ nanowires were in polycrystalline form with diameter of 58 nm. The synthesized nanowires show room temperature ferromagnetic property with high coercivity. This method is expected to be useful for large scale synthesis of NiFe₂O₄ nanowires for the application of magnetic recording.     

Synthesis of porous NiFe2O4 microparticles and its catalytic properties for methane combustion

In this paper, we report the obtention of agglomerate porous NiFe₂O₄ microparticles type-spinel with uniform size of 1-2 μm by the oxalic acid co-precipitation method. The structure, morphology and surface of microparticles as-synthesized were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), respectively. Fixed bed reactor test confirmed that the NiFe₂O₄ microparticles exhibit a good catalytic activity for methane combustion with the methane light-off temperature below 350 °C. XPS spectrum revealed that the excellent catalytic activity may be attributed to the surface oxygen vacancies arising from the peculiar inverse spinel structure with octahedral (Oh) site occupied by Fe²⁺ and Ni²⁺ cations.     

核壳结构SrFe12O19NiFe2O4复合纳米粉体的吸波性能

以Fe(NO₃)₃、 Ni(NO₃)₂和Sr(NO₃)₂为主要原料, 通过两步柠檬酸盐溶胶-凝胶法, 制备出核-壳结构SrFe₁₂O₁₉-NiFe₂O₄磁性纳米复合粉体。采用XRD、 TEM、 VSM及矢量网络分析仪对合成的粉体的结构、 形貌及吸波性能进行了分析研究。结果表明, 复合粉体的相结构与NiFe₂O₄含量有关, 当SrFe₁₂O₁₉与NiFe₂O₄的质量比为1∶2、 烧结温度为1050℃时, 复合纳米粉体的相与NiFe₂O₄接近, 核-壳结构SrFe₁₂O₁₉-NiFe₂O₄纳米复合粉体的饱和磁化强度(M_s)(51.4 emu/g)比单体SrFe₁₂O₁₉纳米粉体 (42.6 emu/g)的大; 但矫顽力(H_c) (336 Oe)比单体SrFe₁₂O₁₉纳米粉体的小, 在SrFe₁₂O₁₉ 与NiFe₂O₄的矫顽力5395～160 Oe之间。在频率为8～18 GHz范围内, 微波吸收逐渐增强, 当频率为12 GHz时, SrFe₁₂O₁₉-NiFe₂O₄纳米复合粉体的微波吸收达到最大值-9.7 dB, 是一种性能优良的吸波材料。      

NiFe2O4/T-ZnOW复合材料的制备及磁性能

采用化学镀法在四角氧化锌晶须(T-ZnO_W)表面包覆NiFe_2O_4镀层,制备了NiFe_2O_4/T-ZnO_W复合材料。利用X射线衍射仪、扫描电镜、能谱分析仪、振动样品磁强计对镀覆前后T-ZnOw的结构、形貌等进行了表征。结果表明,化学镀覆后,在T-ZnO_W表面包覆了致密的尖晶石型NiFe_2O_4镀层,T-ZnO_W针尖部位生成的镀层厚度比根部薄。NiFe_2O_4/T-ZnO_W复合材料具有软磁特性。随着退火温度的升高,复合材料的饱和磁化强度和矫顽力逐渐升高,在800℃达到最高。     

Microwave-assisted synthesis of hierarchical Bi2O3 spheres assembled from nanosheets with pore structure

Hierarchical Bi₂O₃ spheres assembled from nanosheets with nanopore structure have been successfully synthesized by thermal decomposition of the precursor at 400 °C for 3 h in air, which was prepared using Bi(NO₃)₃·5H₂O and poly(vinylpyrrolidone) (PVP) by a microwave-assisted heating method in ethylene glycol (EG) at 150 °C for 10 min. The morphology of Bi₂O₃ is similar to that of the precursor. The products were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectrometry (FT-IR), field-emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TG) and differential scanning calorimetric analysis (DSC). XRD pattern showed that the product had a high degree of crystallinity. FE-SEM micrograph indicated that hierarchical Bi₂O₃ spheres had sizes around 10 μm.     

The growth of ordered ZnAl2O4 nanostructures using AAO as a reactive template

The use of anodic aluminum oxide (AAO) as a reactive template in the fabrication of ordered arrays of spinel ZnAl₂O₄ nanostructures is demonstrated. This involves the growth of monocrystalline Zn nanowires into an AAO template using a pulse dc electrodeposition technique followed by a heat treatment in air at 800 °C. The formation of ZnAl₂O₄ nanotubes in the solid-state reaction is driven by the Kirkendall effect. In addition, the formation of such ZnAl₂O₄ nanostructure arrays requires that the molar ratio of ZnO to Al₂O₃ be less than unity. This corresponds to a ratio of pore radius to half inter-pore separation of 0.63 which serves as a guide to the initial template geometry required for the formation of an array of discrete nanotubes.     

Synthesis of sphere-like Co3O4 nanocrystals via a simple polyol route

A simple polyol method was developed to synthesize uniform sphere-like Co₃O₄ nanocrystals in ethylene glycol. Powder X-ray diffraction (XRD) and electron diffraction (ED) showed that the as-prepared sample was indexed as the cubic spinel structure. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated that the Co₃O₄ nanocrystals were spherical with the crystallite size in the range of 90-110 nm. Infrared spectra and Raman spectra confirmed the formation of the Co₃O₄ nanocrystals. The magnetic properties of the Co₃O₄ nanocrystals were measured by using a superconducting quantum interference device (SQUID) magnetometer, which showed that the as-prepared sample exhibited a tiny hysteresis loop with the magnetization value of 2.4 emu/g and the coercivity of 110 Oe.     

Synthesis of SrAl2O4 from a mixed-metal citrate precursor

A mixed-metal citrate precursor method was used to synthesize SrAl₂O₄. The effects of the pH of the starting solutions and the molar ratio of citric acid to total metal cations concentration (CA/M) on the formation of SrAl₂O₄ were studied. DTA, TG, FT-IR, XRD and field emission scanning electron microscopy (FESEM) were used to characterize the precursors and the derived oxide powders. XRD analysis showed that single-phase SrAl₂O₄ was synthesized from CA/M = 2 precursors at a temperature of 900 °C for 2 h, without the formation of any intermediate phase.     

Ferric oxide and ZnFe2O4 nanotubes derived from nano ZnO/FeOx core/shell structures

The ZnO/FeO_x core/shell nanorods were prepared with ZnO nanorods as templates, on which ferric oxide was deposited by thermal decomposition of Fe(acac)₃ in solution. The thickness of the ferric oxide shell could be precisely controlled by the concentration of Fe(acac)₃. The amorphous ferric oxide nanotubes were fabricated by wet-etching the ZnO core nanorods in HAc solution and polycrystalline ZnFe₂O₄ nanotubes were prepared by annealing the core/shell ZnO/FeO_x nanocomposites in air. The obtained ZnFe₂O₄ nanotubes showed paramagnetism at room temperature.     

Syntheses of Mn3O4 and LiMn2O4 nanoparticles by a simple sonochemical method

Mn₃O₄ and LiMn₂O₄ nanoparticles were prepared by a simple sonochemical method which is environmentally benign. First, Mn₃O₄ nanoparticles were prepared by reacting MnCl₂ and NaOH in water at room temperature through a sonochemical method, operated at 20 kHz and 220 W for 20 min. Second, LiOH was coated onto the resulting Mn₃O₄ under the same sonochemical conditions as above. The thickness of coated LiOH on Mn₃O₄ obtained from the reaction ratio of 3:1 between LiOH and Mn₃O₄ was about 4.5–5.5 nm range. Then, by heating those LiOH-coated Mn₃O₄ particles at the relatively low temperature of 300–500 °C for 1 h, they were transformed into phase-pure LiMn₂O₄ nanoparticles of about 50 to 70 nm size in diameter.     

Synthesis and electrochemical properties of nanostructured LiMn2O4 for lithium-ion batteries

Spinel LiMn₂O₄ crystal with the grain sizes of about 15 nm is firstly synthesized by hydrothermal route at 180 °C using MnO₂ as a precursor. The LiMn₂O₄ powders synthesized by hydrothermal technique and sol-gel reaction were investigated by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The LiMn₂O₄ samples were used as cathode materials for lithium-ion battery, whose electrochemical properties were investigated. The results show that the sample obtained by hydrothermal route has higher capacity than that prepared by sol-gel method.     

Photocatalytic degradation of RhB over MgFe2O4/TiO2 composite materials

MgFe₂O₄/TiO₂ (MFO/TiO₂) composite photocatalysts were successfully synthesized using a mixing-annealing method. The synthesized composites exhibited significantly higher photocatalytic activity than a naked semiconductor in the photodegradation of Rhodamine B. Under UV and visible light irradiation, the optimal percentages of doped MgFe₂O₄ (MFO) were 2 wt.% and 3 wt.%, respectively. The effects of calcination temperature on photocatalytic activity were also investigated. The origin of the high level of activity was discussed based on the results of X-ray diffraction, UV-vis diffuse reflection spectroscopy, scanning electron microscopy, transmission electron microscopy, and nitrogen physical adsorption. The enhanced activity of the catalysts was mainly attributed to the synergetic effect between the two semiconductors, the band potential of which matched suitably.     

Synthesis of Nb2O5 nanosheets and its electrochemical measurements

In this study, Nb₂O₅ nanosheets were first synthesized using NbO₂ particles as the precursor via a simple hydrothermal route. The synthesized Nb₂O₅ nanosheets are highly crystalline and their thicknesses are found to be ca. 3–5 nm. Based on the experimental results of XRD, SEM and TEM measurements, a possible mechanism for the formation of nanosheets was discussed. An electrode materials made of the product containing Nb₂O₅ nanosheets shows a larger capacity of 355 mAh g⁻¹ at a current density of 0.1 A g⁻¹. Cyclic measurements indicate that such an electrode exhibits a high reversible charge/discharge capacity and cycling stability. This might be attributed to the intrinsic characteristics of Nb₂O₅ nanosheets.     

Synthesis of nanocrystalline MgAl2O4 spinel powders by a novel chemical method

A novel chemical method for the preparation of nanocrystalline MgAl₂O₄ spinel powders has been developed in this paper. The mixed magnesium-aluminum hydroxide precipitates were initially formed in a three-dimensional space network microarea. After being calcined at above 700 °C, the nanocrystalline MgAl₂O₄ spinel powders were obtained. The precursor and as-calcined powders were characterized using TGA-DTA, XRD and TEM. The MgAl₂O₄ spinel powders calcined at 850 °C for 2 h are of narrow distribution, little agglomeration and small particle size of ∼ 24 nm. The reason for the synthesis of high-quality powders was explained.     

Varistor properties of ZnO-Pr6O11-CoO-Cr2O3-Y2O3-In2O3 ceramics

The varistor properties of the ZnO-Pr₆O₁₁-CoO-Cr₂O₃-Y₂O₃-In₂O₃ ceramics were investigated for different concentrations of In₂O₃. The increase of In₂O₃ concentration slightly increased the sintered density (5.60-5.63 g/cm³) and slightly decreased the average grain size (3.4-2.9 μm). The breakdown field increased from 6023 to 14822 V/cm with increasing concentration of In₂O₃. The nonlinear coefficient increased from 17.6 to 44.6 for up to 0.005 mol%, whereas the further doping caused it to decrease to 36.8. In₂O₃ acted as an acceptor due to the donor concentration, which decreases in the range of 1.02 × 10¹⁷ to 0.24 × 10¹⁷/cm³ with increasing concentration of In₂O₃.     

Synthesis of Co3O4 nanoparticles via the CTAB-assisted method

Cobalt oxide (Co₃O₄) nanoparticles were successfully synthesized by the cetyltrimethylammonium bromide (CTAB)-assisted method at normal pressure for the first time. The structure and morphology of the as-prepared Co₃O₄ nanoparticles were characterized by powder X-ray diffracton (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N₂-sorption analysis. XRD studies indicated that the as-prepared product was well-crystallized cubic phase of Co₃O₄ with a cell constant of α = 8.0722 Å. The EM images showed that the obtained Co₃O₄ sample consisted of dispersive quasi-spherical particles with the size ranged from 15 to 25 nm.     

A citrate complex process to prepare nanocrystalline PbBi2Nb2O9 at a low temperature

PbBi₂Nb₂O₉ nanocrystals with a perovskite-type structure were successfully synthesized at a relative low temperature via a citrate complex method. Metal ions were dispersed by citric acid in ethanol and ethylene glycol solvent, and then reacted with NH₄H₂[NbO(C₂O₄)₃·3H₂O] to form the gel. XRD results showed that pure PbBi₂Nb₂O₉ nanocrystals could be obtained after calcined treatment of xerogel at 800 °C. The average particles size was 57 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the sintering process led to the agglomeration of the nanoparticles. The photocatalytic test showed that the sample prepared by the citrate complex method exhibited a higher photocatalytic activity than that of the sample prepared by the solid-state reaction.     

Synthesis of ultra-long single crystalline CuV2O6 nanobelts

Ultra-long single crystalline CuV₂O₆ nanobelts have been successfully synthesized via a facile homogeneous reaction between peroxovanadic acid and cupric acetate. The reaction parameters, such as reaction time, and with or without H₂O₂, have profound influences on the crystal structures and morphologies of the resulting products. The time-dependent experiments reveal that the formation of ultra-long CuV₂O₆ nanobelts is related to the disassembly of urchin-like Cu₃(OH)₂V₂O₇·2H₂O nanostructures composed of radially aligned nanobelts, and the growth of CuV₂O₆ along the direction of [010]. Without the addition of H₂O₂ aqueous solution, wide and short CuV₂O₆ nanobelts coexist with some irregular particles and microrods in the products.     

Facile synthesis of MnV2O6 nanostructures with controlled morphologies

MnV₂O₆ nanostructures including nanorods, nanobelts, and nanosheets, have been synthesized by a facile hydrothermal reaction between Mn(CH₃COO)₂·4H₂O and commercial V₂O₅. The synthesized products are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The influences of synthetic parameters, such as, reaction time, temperature and medium, on the morphologies of the resulting products have been investigated. As the reaction temperatures increase from 120 °C to 180 °C, MnV₂O₆ nanorods and nanobelts are obtained, respectively. The time-dependent experimental results at 180 °C reveal that the sizes of MnV₂O₆ nanobelts increase gradually with the reaction proceeding. Interestingly, as the reaction is carried out with the aid of H₂O₂ solution, flower-like MnV₂O₆ nanosheets are formed.