Fabrication and properties of Mn0.5Zn0.5Fe2O4 nanofibers

Zn-doped α-FeOOH nanofiber was synthesized by coprecipitation method. Then the α-FeOOH was enwraped by the complex of the Mn²⁺ and citric acid. The morphology of α-FeOOH did not transform after the calcination process and Mn_0.5Zn_0.5Fe₂O₄ nanofiber was successfully prepared. The phase, morphology, particle diameter and the magnetic properties of samples were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The results indicated that Mn_0.5Zn_0.5Fe₂O₄ nanofibers with an aspect ratio over 40 and a diameter of 20 nm were prepared. Compared with the amorphous Mn_0.5Zn_0.5Fe₂O₄, the anisotropy of the Mn_0.5Zn_0.5Fe₂O₄ nanofiber increased, resulting in the higher coercivity and magnetization of the obtained sample. With an increase in the calcination temperature, the diameter and the saturation magnetization of the sample increased, while the aspect ratio and coercivity decreased. The coercivity of the sample obtained at 700 °C was maximal (up to 185.4 Oe). The saturation magnetization of the sample obtained at 900 °C was maximal (up to 65.3 emu/g). The use of citric acid method prevented the presence of Mn(OH)₂, resulting in the decrease of the calcination temperature.     

On the thermal stability of Fe2Mn0.5Zn0.5(C2O4)4

Heat of immersion and contact angle were measured for α-Si₃N₄. The electrostatic field strength, which was determined to be 0.42×10⁵ esu cm^?2, showed that the surface is much less polar than those of oxides. Slight increase of the heat of immersion in water with the increase of outgassing temperature is attributable to the rehydration of siloxane linkages which have been formed by dehydration of silanol groups on the surface. The heat of immersion in n-alkanes increased steeply with the number of carbon, n, from n=6 to 9, and became nearly constant for n>9, while in n-alkanols the heat began to rise at n=10 after the nearly constant values for n=4 to 8. The dispersion force contribution to the total surface free energy, γ^d_s, were estimated by contact angle and heat of immersion methods which have been well applied to the low energy surfaces, and found to be 25 mJ m^?2 from contact angle and 129 mJ m^?2 from the immersional heat in hexane.     

Thermal stability of the manganese-nickel mixed ferrite and iron phases in the Mn0.5Ni0.5Fe2O4/Fe composite/nanocomposite powder

The composite/nanocomposite powders of Mn_0.5Ni_0.5Fe₂O₄/Fe type were synthesized starting from nanocrystalline Mn_0.5Ni_0.5Fe₂O₄ (D = 7 nm) (obtained by ceramic method and mechanical milling) and commercial Fe powders. The composites, Mn_0.5Ni_0.5Fe₂O₄/Fe, were milled for up to 120 min and subjected to heat treatment at 600 °C and 800 °C for 2 h. The manganese-nickel ferrite/iron composite samples were subjected to differential scanning calorimetry (DSC) up to 900 °C for thermal stability investigations. The composite component phases evolution during mechanical milling and heat treatments were investigated by X-ray diffraction technique. The present phases in Mn_0.5Ni_0.5Fe₂O₄/Fe composite are stable up to 400–450 °C. In the temperature range of 450-600 °C, the interdiffusion phenomena occurs leading to the formation of Fe_1?xMn_xFe₂O₄/Ni–Fe composite type. The new formed ferrite of Fe_1?xMn_xFe₂O₄ type presents an increased lattice parameter as a result of the substitution of nickel cations into the spinel structure by iron ones. Further increases of the temperature lead to the ferrite phase partial reduction and the formation of wustite-FeO type phase. The spinel structure presents incipient recrystallization phenomena after both heat treatments (600 °C and 800 °C). The mean crystallites size of the ferrite after heat treatment at 800 °C is about 75 nm. After DSC treatment at 900 °C, the composite material consists in Fe_1?xMn_xFe₂O₄, Ni structure, FeO, and (NiO)_0.25(MnO)_0.75 phases.     

Radar Absorption Properties of Ni0.5Zn0.5Fe2O4/PANI/epoxy Nanocomposites

A nitrate? citrate gel was prepared from metallic nitrates and citric acid by sol? gel process and was further used to synthesize Ni_0.5Zn_0.5Fe₂O₄ nanocrystalline powder by auto‐combustion. Then, two novel 15 and 35% (w/w) magnetic Ni_0.5Zn_0.5Fe₂O₄ containing polyaniline nanocomposites, named as PANI‐Ni15 and PANI‐Ni35, respectively, were prepared via in‐situ polymerization of aniline in an aqueous solution containing proper amount of Ni_0.5Zn_0.5Fe₂O₄ magnetic powder. The incorporation of the nanopowders to PANI matrix was confirmed by X‐ray diffraction (XRD), IR and SEM. Synthesized PANI‐NiZn ferrite composite particles were subsequently added to an epoxy resin matrix to produce related nanocomposites. The morphological properties of these nanocomposite materials were investigated by SEM and TEM. The electromagnetic‐absorbing properties were studied by measuring the reflection loss in the frequency range of 8.0 to 12.0 GHz. Results showed the reflection loss of the PANI‐Ni35 composite is higher than pure polyaniline and PANI‐Ni15. The good reflection loss of the nanocomposites suggests their potential applicability as radar absorber.     

多核超顺磁性Ni0.5Zn0.5Fe2O4/SiO2催化载体的制备与表征

采用化学共沉淀法与溶胶-凝胶法相结合, 在制备过程中改变磁性纳米粒子和TEOS的引入方式, 成功地制备了多核超顺磁性Ni0.5Zn0.5Fe2O4/SiO2催化剂载体. 采用透射电子显微镜(TEM)、氮气吸附、X射线衍射(XRD)及物理性质综合测试系统(PPMS)对样品进行了表征, 利用永磁铁对载体的分离效果进行了验证. 研究结果表明, 改进制备方法后, 制备的载体比表面积明显增大, 这有利于催化剂在载体上的分散与固载; 样品的饱和磁化强度明显增加, 表明样品具有很好的磁响应能力, 有利于催化剂的分离, 同时, 载体的超顺磁特性也有利于液相催化体系中催化剂的分散.     

Fe2O3/Mn2O3 nanoparticles: Preparations and applications in the photocatalytic degradation of phenol and parathion in water

In this study, nanoparticles of Fe₂O₃/Mn₂O₃ mixture were obtained using the sol–gel method. The synthesis uses the combination of polyvinyl alcohol (PVA) and tartaric acid (TA). Synthesized catalysts prove superior compared to those afforded from previous reports. To be specific, desired catalysts can be received at lower calcination temperature. Furthermore, their structures display higher uniformity in term of particle sizes. Finally, they show better performance for the photocatalytic degradation of model-persistent organic compounds.     

New Synthesis and Magnetic Properties of NiFe2O4/SiO2 and Co0.5Zn0.5Fe2O4/SiO2 Nanocomposites Using Tetraglycolatosilane as Precursor

In this work the new synthesis and magnetic properties of NiFe₂O₄/SiO₂ and Co_0.5Zn_0.5Fe₂O₄/SiO₂ nanocomposites using a water‐soluble silica precursor, tetraglycolatosilane (THEOS), by the sol‐gel method were reported. Nanocomposite were obtained by the thermal decomposition of the organic part at different annealing temperatures varying from 400 to 900 °C. Studies carried out using XRD, FT‐IR, TEM, STA (TG‐DTG‐DTA) and VSM techniques. XRD patterns show that NiFe₂O₄ and Co_0.5Zn_0.5Fe₂O₄ have been formed in an amorphous silica matrix at annealing temperatures above 600 and 400 °C, respectively. It is found that when the annealing temperature is up to 900 °C NiFe₂O₄/SiO₂ and Co_0.5Zn_0.5Fe₂O₄/SiO₂ samples show almost superparamagnetic behavior with a magnetization 4.66 emu/g and ferromagnetic behavior with a magnetization 10.11 emu/g, respectively. The magnetization and coercivity values of nanocomposites using THEOS were considerably less than previous reports using TEOS. THEOS as a silica matrix network provides an ideal nucleation environment to disperse ferrite nanoparticles and thus to confine them to aggregate and coarsen. By using THEOS over the currently used TEOS and TMOS, organic solvents are not needed due to the entire solubility of THEOS in water. Synthesized nanocomposites with adjustable particle sizes and controllable magnetic properties make the applicability of ferrites even more versatile.     

Preparation and ferromagnetic properties of Ni0.5Zn0.5Fe2O4/polyaniline core–shell nanocomposites

Magnetic Ni_0.5Zn_0.5Fe₂O₄‐crosslinked polyaniline composites with a core–shell structure were prepared in the presence of Ni_0.5Zn_0.5Fe₂O₄ magnetic powder in a toluene solution containing iron chloride as a surfactant and dopant. Structural characterization by Fourier transform infrared, X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy proved that Ni_0.5Zn_0.5Fe₂O₄ in the composites was responsible for the ferromagnetic behavior of the composites. The effects of the polyaniline and temperature on the magnetic properties of the Ni_0.5Zn_0.5Fe₂O₄/polyaniline composites were studied with electron paramagnetic resonance and superconducting quantum interference device techniques. A clear evolution from ferromagnetic resonance to electron paramagnetic resonance was observed as a function of temperature, which was related to the passage through the Curie point (～420 K). The magnetic properties of the resulting composites showed ferromagnetic behavior, such as high‐saturated magnetization (saturation magnetization = 35–39 emu/g), low coercive force (coercivity = 22–28 G), and low blocking temperatures (～23 K). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2657–2664, 2006     

Preparation of magnetic nanocrystalline Mn0.5Mg0.5Fe2O4 and kinetics of thermal decomposition of precursor

The spinel Mn_0.5Mg_0.5Fe₂O₄ was obtained via calcining Mn_0.5Mg_0.5Fe₂(C₂O₄)₃·5H₂O above 400 °C in air. The precursor and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, Fourier transform FT-IR, X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer, and vibrating sample magnetometer. The results showed that Mn_0.5Mg_0.5Fe₂O₄ obtained at 600 °C had a specific saturation magnetization of 46.2 emu g^–1. The thermal decomposition of Mn_0.5Mg_0.5Fe₂(C₂O₄)₃·5H₂O below 450 °C experienced two steps which involved, at first, the dehydration of five water molecules and then decomposition of Mn_0.5Mg_0.5Fe₂(C₂O₄)₃ into spinel Mn_0.5Mg_0.5Fe₂O₄ in air. Based on Starink equation, the values of the activation energies associated with the thermal decomposition of Mn_0.5Mg_0.5Fe₂(C₂O₄)₃·5H₂O were determined.     

聚苯胺/聚丙烯酰胺/镍锌铜铁氧体复合物的制备及电磁性能

采用溶液聚合法制备了聚苯胺/聚丙烯酰胺/镍锌铜铁氧体(PANI/PAM/Zn0.4Ni0.5Cu0.1Fe2O4)三元复合物. 利用X射线衍射仪、红外光谱仪、扫描电子显微镜和振动样品磁强计分别表征了样品的结构、形貌和磁性能, 用阻抗/材料分析仪测定了复合物在1 MHz～1 GHz的频率范围内的磁损耗和介电损耗, 并研究了聚苯胺和引发剂的相对含量对复合物的磁损耗和介电损耗的影响. 结果表明复合物中磁性粒子和聚合物之间具有一定的相互作用, 复合物在1 MHz～1 GHz的频率范围内具有较大电磁损耗能力.     

Preparation and characterization of magnetic Co0.5Zn0.5Fe2O4-chitosan nanoparticles as surfactants in oilfield

Chitosan nanoparticles with magnetic properties can be potentially used as separation materials in adsorption of oil for enhanced oil recovery. Different from the traditional surfactants, the novel magnetic Co_0.5Zn_0.5Fe₂O₄-chitosan nanoparticles are of excellent biodegradation and a high level of controllability. The Co_0.5Zn_0.5Fe₂O₄-chitosan nanoparticles with core-shell structure were prepared successfully. The image of transmission electron microscope and the scanning electron microscopy showed that the cubic-shape magnetic Co_0.5Zn_0.5Fe₂O₄-particles were encapsulated by the spherical chitosan nanoparticles. The size of the Co_0.5Zn_0.5Fe₂O₄-chitosan nanoparticles was below 100 nm. The saturated magnetization of the Co_0.5Zn_0.5Fe₂O₄-chitosan nanoparticles could reach 80 emu g^?1 and showed the characteristics of superparamagnetism at the same time. The evaluation on the interfacial properties of the product demonstrated that the interfacial tension between crude oil and water could be reduce to ultra-low values (to about 10^?3 mN m^?1) when the magnetic Co_0.5Zn_0.5Fe₂O₄-chitosan nanoparticle was used in several blocks in Shengli Oilfield without other additives. Meanwhile, the magnetic Co_0.5Zn_0.5Fe₂O₄-chitosan nanoparticles possessed good salt-resisting capacity.     

Mixed phase Fe2O3/Mn3O4 magnetic nanocomposite for enhanced adsorption of methyl orange dye: Neural network modeling and response surface methodology optimization

In this research, a novel magnetic mesoporous adsorbent with mixed phase of Fe₂O₃/Mn₃O₄ nanocomposite was prepared by a facile precipitating method and characterized extensively. The prepared nanocomposite was used as adsorbent for toxic methyl orange (MO) dye removal from aqua matrix considering its high surface area (178.27 m²/g) with high saturation magnetization (23.07 emu/g). Maximum dye adsorption occurs at solution pH 2.0 and the electrostatic attraction between anionic form of MO dye molecules and the positively charged nanocomposite surface is the main driving force behind this adsorption. Response surface methodology (RSM) was used for optimizing the process variables and maximum MO removal of 97.67% is obtained at optimum experimental condition with contact time, adsorbent dose and initial MO dye concentration of 45 min, 0.87 g/l and 116 mg/l, respectively. Artificial neural network (ANN) model with optimum topology of 3–5–1 was developed for predicting the MO removal (%), which has shown higher predictive ability than RSM model. Maximum adsorption capacity of this nanocomposite was found to be 322.58 mg/g from Langmuir isotherm model. Kinetic studies reveal the applicability of second‐order kinetic model with contribution of intra‐particle diffusion in this process.     

Efficient catalytic degradation of single and binary azo dyes by a novel triple nanocomposite of Mn3O4/Ag/SiO2

The strategy of structurally integrating noble metal and metal oxides is expected to offer exceptional opportunities toward emerging functions of all. We report the creation of an efficient hetero-structured nanocatalyst consisting of Mn₃O₄ core, SiO₂ shell impregnated with noble Ag nanoparticles. The triple nanocatalyst Mn₃O₄/Ag/SiO₂ was synthesized by using a facile three-step approach to disperse Ag nanoparticles between the surfaces of functionalized Mn₃O₄ and SiO₂. The physicochemical structural characterization was performed by XRD and FTIR. The surface morphologies were observed by SEM and TEM. The EDX measurements confirmed the composition of the composite. The nanocomposite has been used as a catalyst for the degradation of Direct blue 78 in the presence of sodium borohydride (NaBH₄). It has a drastic catalytic effect as compared to Mn₃O₄/Ag and Mn₃O₄. The rate constant of Direct blue 78 reduction followed the order: Mn₃O₄/Ag/SiO₂ (0.25166 min⁻¹) > Mn₃O₄/Ag (0.07971 min⁻¹) > Mn₃O₄ (0.00947 min⁻¹). The effects of different reaction conditions of the catalytic reaction have been determined. The catalytic activity of the as- synthesized nanocomposite was examined for the binary dyes system by incorporation of an additional dye (Sunset yellow). Its influence on the degradation rate and efficiency of Direct blue 78 was investigated. The nanocatalyst exhibited excellent catalytic activity towards the complete degradation of both the Direct blue 78 and Sunset yellow. The degradation percentage for these dyes reached 99.33 and 94.68%, respectively. The recovery and reusability of the Mn₃O₄/Ag/SiO₂ nanocomposite was studied in the reduction reaction of Direct blue 78. Five consecutive recovery reaction cycles were performed. They revealed high stability and constant efficiency of the catalyst for four cycles.     

Adsorption of light green and brilliant yellow anionic dyes using amino functionalized magnetic silica (Fe3O4@SiO2@NH2) nanocomposite

Abstract

Fe₃O₄@SiO₂@NH₂ nanocomposite was prepared for highly effective adsorption of two anionic dyes one of which is triarylmethane dye (light green, LG) and the other is azo dye (brilliant yellow, BY). The characterization results demonstrated that superparamagnetic Fe₃O₄ nanoparticles were covered with silica and functionalized with amino groups successfully without losing magnetic character. The effects of adsorbent dosage, contact time, pH, temperature, and dye molecular structure on the adsorption were investigated. Acidic pH was better for both LG and BY, on the other hand, alkaline pH was favorable to some extent for LG in comparison with BY due to the contribution of stacking effect in addition to electrostatic attraction. Kinetic data demonstrated that the driving force for adsorption process could be explained by pseudo-second order mechanism in both systems. The equilibrium data were more compatible with Langmuir isotherm than those of Freundlich isotherm and the maximum adsorption capacities of Fe₃O₄@SiO₂@NH₂ calculated from Langmuir isotherm model for LG and BY at 30?°C and natural pH of the solution were 40.2 and 35.5?mg g^?1. Thermodynamic calculations related to temperature dependence demonstrated that the adsorption process was spontaneous and exothermic.     

Photocatalytic degradation of 2,4-dichlorophenoxyacetic acid using Fe3O4@TiO2/Cu2O magnetic nanocomposite stabilized on granular activated carbon from aqueous solution

Research on Chemical Intermediates - In the present study, Fe3O4@TiO2/Cu2O nanocomposites were synthetized and supported on granular activated carbon (GAC). The synthesized nanocomposite coated on...     

Mn0.6 Zn0.4 Fe2 O4 磁性亚微球的可控合成及磁性能

采用溶剂热法制备了单分散Mn0.6Zn0.4Fe2O4磁性亚微米球, 研究了反应工艺参数对磁性亚微米球结构形貌、 直径和静磁性能的影响规律. 研究发现, 随着反应时间的延长, 体系中的金属离子首先水解沉淀, 形成羟基氧化铁及Mn, Zn氢氧化物, 然后脱水转化为Mn0.6Zn0.4Fe2O4球形纳米粒子, 这些纳米粒子发生团聚, 形成结构疏松、 大小不均匀的亚微米粒子, 最后通过Ostwald熟化过程, 形成致密的单分散亚微米球. 降低反应溶液的pH值、 增加乙二醇或聚乙二醇的用量, 均会使亚微球的直径增大, 并可在150~500 nm范围内调控微球的粒径; 但组成磁性亚微球的纳米粒子的粒径逐渐减小, 产物的饱和磁化强度增大, 矫顽力和剩磁减小.     

MC2O4(M=Mn、Fe、Co、Ni、Cu、Zn)的热力学及其热分析动力学

用DSC、TGA技术分别在N₂气氛和O₂气氛下对MC₂O₄(M=Mn、Fe、Co、Ni、Cu、Zn)的脱水和分解过程作了热力学和动力学的研究. 在N₂气氛下, MC₂O₄•2H₂O(M=Mn、Fe、Co、Ni、Zn)脱水温度Tde和脱水焓ΔdeHm随原子序数Zre递增呈现明显的“二分组效应”；ΔdeHm在(96.46±7.00) kJ•mol^-1范围内波动；MC₂O₄•2H₂O (M=Mn、Fe、Ni)的分解温度Td随原子序数递增呈现良好的线性关系；且各草酸盐分解得到氧化物(CuC₂O₄生成Cu、CuO混合物)时, MC₂O₄(M=Co、Ni、Cu) 分解焓随原子序数增大也存在良好的线性关系. 各草酸盐除NiC₂O₄•2H₂O脱水过程和FeC₂O₄分解过程外, 其余各过程机理函数均为随机成核和随后成长型.     

Synthesis of Fe3O4, Fe2O3, Ag/Fe3O4 and Ag/Fe2O3 nanoparticles and their electrocatalytic properties

Two important iron oxides:Fe3O4 and Fe2O3,as well as Fe3O4 and Fe2O3 nanoparticles mingling with Ag were successfully synthesized via a hydrothermal procedure.The samples were confirmed and characterized by X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS).The morphology of the samples was observed by transmission electron microscopy(TEM).The results indicated Fe3O4,Fe2O3,Ag/Fe3O4 and Ag/Fe2O3 samples all were nanoparticles with smaller sizes.The samples were modified on a glassy carbon electrode and their elctrocatalytic properties for p-nitrophenol in a basic solution were investigated.The results revealed all the samples showed enhanced catalytic performances by comparison with a bare glassy carbon electrode.Furthermore,p-nitrophenol could be reduced at a lower peak potential or a higher peak current on a glassy carbon electrode modified with Ag/Fe3O4 or Ag/Fe2O3 composite nanoparticles.