A novel synthesis method for manganese ferrite nanopowders: The effect of manganese salt as inorganic additive in electrosynthesis cell

Manganese ferrite nanoparticles were electro-crystallized in an electrochemical cell containing two iron electrodes, and an electrolyte solution of sodium sulfate, sodium butanoate, and manganese sulfate hydrate. The samples were characterized by X-ray diffraction, electron microscopy, magnetometry, and Mössbauer spectroscopy methods. The crystal structure of the samples was studied using X-ray diffraction. Based on obtained results we found that the manganese ferrite nanoparticles are formed in the electrochemical cell containing 0.001 M manganese sulfate hydrate. Also, the formation of a paramagnetic secondary phase in the sample without manganese is suppressed by adding manganese salt in the electrochemical cell. The nanoparticle size, shape, and morphology were characterized using electron microscopy. Magnetization curves show that all samples are magnetically soft and their specific magnetization ranges from 15 A m² kg⁻¹ to 75 A m² kg⁻¹, depending on the growth conditions. Room temperature Mössbauer spectra confirm the formation of nonstoichiometric spinel ferrite of magnetite or manganese ferrite, again depending on the growth conditions. Based on Mössbauer analysis, reduction in the population of octahedral sites provides direct evidence for the presence of the manganese ions substitution in the octahedral sites.     

Origin of the uniaxial magnetic anisotropy in cobalt ferrite induced by spark plasma sintering

Cobalt ferrite (CFO) is a promising candidate for magnetostrictive applications like actuators or sensors. We have recently shown that uniaxial magnetic anisotropy can be induced in CFO by reactive sintering using spark plasma sintering (SPS), which leads to an improvement of its magnetostrictive properties. However, the origin of the anisotropy and the formation mechanism remain unexplained so far. In this study, different SPS processes have been conducted to determine which parameter is responsible for the induced uniaxial anisotropy. We demonstrate that the magnetic anisotropy arises during the cooling step when done under SPS’s uniaxial compression. In addition, we also investigate the fundamental origin of the magnetic anisotropy induced during the SPS process. We show that the polycrystalline anisotropic cobalt ferrite obtained after SPS exhibits no texture. However, the SPS samples turn isotropic after being annealed in air at 400 °C/2 h, as shown by magnetic and magnetostrictive measurements. A change in ionic distribution after the annealing is also observed by Mössbauer spectroscopy. Our findings suggest that the induced magnetic anisotropy results from the ionic distribution of the Co²⁺ in the CFO’s spinel lattice, a mechanism previously observed in magnetic annealed CFO. This study advances the in-depth understanding of the relationship between SPS processing and magnetic properties of cobalt ferrite.     

应用超声消解快速检测COD方法的实验研究

提出快速检测水样化学需氧量(COD)的新方法 ,即在常温常压下利用超声消解(UASD)水样,并结合分光光度法(SP)或氧化还原电位法(ORP)检测水样COD。实验表明,UASD法消解水样的最佳时间在4 min左右;用标准邻苯二甲酸氢钾溶液绘制工作曲线,采用UASD-SP法对污水样品的COD(经稀释COD500 mg/L)进行检测,测得的COD值与国标法测定值对比,准确度在-5.4%~-2.1%,实验精密度在0.42%~2.8%。实验证明了应用超声消解快速检测COD方法的可行性。     

Enhancement of magnetic properties of Ni0.5Zn0.5Fe2O4 nanoparticles prepared by the co-precipitation method

Nano crystalline Ni–Zn ferrites of composition Ni_0.5Zn_0.5Fe₂O₄have been prepared by a chemical co-precipitation method. The powdered samples were sintered at a temperature of 800 °C and 900 °C for three hours. X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Fourier Transform Infrared (FTIR) Spectroscopy were used to study their structural and morphological changes. The enhanced magnetic properties were investigated by using a Vibrating Sample Magnetometer (VSM). The saturation magnetization was found to increase from 73.88 to 89.50 emu/g as a function of sintering temperature making this material useful for high frequency applications. Electromagnetic studies showed sustained values of permittivity up to 1 GHz. These results have been explained on the basis of various models and theories.     

Synthesis and electrochemical properties of LiAl0.05Mn1.95O4 by the ultrasonic assisted rheological phase method

Pure-phase and well-crystallized spinel LiAl_0.05Mn_1.95O₄ powders were successfully synthesized by a simple ultrasonic assisted rheological phase (UARP) method. The structure and morphology properties of this as-prepared powder compared with the pristine LiMn₂O₄ and LiAl_0.05Mn_1.95O₄ obtained from the solid-state reaction (SSR) method were investigated by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties focused on the LiAl_0.05Mn_1.95O₄ by this new method have also been investigated in detail. According to these tests results, it is obviously to see that the newly prepared sample delivers a relatively high initial discharge capacity of 111.6 mAh g⁻¹, presents excellent rate capability and reversibility, and shows good cycling stability with capacity retention of 90.6% after 70 cycles. Meanwhile, the electrochemical impedance spectroscopy (EIS) investigations were employed to study the electrochemical process of Li⁺ ions with the synthesized LiAl_0.05Mn_1.95O₄ electrode in detail.     

Augmenting the photocatalytic performance of cobalt ferrite via change in structural and optical properties with the introduction of different rare earth metal ions

In the present study, synthesis of different rare earth (RE) doped cobalt ferrite nanoparticles was done via facile sol-gel auto-combustion method using four different RE metal ions: Eu, Gd, Dy and Nd. The RE substituted cobalt ferrite nanoparticles were then characterized using FT-IR, powder XRD, HR-TEM, SAED, EDX, VSM and DRS techniques. From the characterization results, a significant variation in the structural, magnetic and optical properties of pure cobalt ferrite was observed with the introduction of different RE metal ions. This change in the properties was emerged due to the distortion of the ferrite crystal lattice due to replacement of smaller ionic radii Fe³⁺ ions with the comparatively larger ionic radii RE³⁺ metal ions. The catalytic activity of the fabricated RE doped cobalt ferrite nanoparticles was studied for the photo-Fenton degradation of cationic and anionic dyes. Under visible light irradiation, the as prepared RE doped nanoparticles exhibited great enhancement in the photo-Fenton degradation of dye molecules as compared to pure cobalt ferrite nanoparticles. The enhancement in the degradation rate was ascribed to the generation of defects in the crystal lattice, lower crystallite size and reduced band gap energy values which facilitated the facile transfer of photo-generated holes and electrons. Best catalytic results were obtained for CoNd_0.08Fe_1.92O₄ for SO dye (k?=?2.23?×?10^?1 min^?1) which were found to be around 9 times higher than the pure cobalt ferrite nanoparticles (k?=?0.23?×?10^?1 min^?1).     

Effect of oxygen flow rate on the structural and electrochemical properties of lithium nickel oxides synthesized by the sol–gel method

The structural and electrochemical properties of LiNiO₂ powders were investigated as a function of the oxygen flow rate employed in the preparation of lithium nickel oxide. It was found that oxygen played an important role in the synthesis of highly crystallized LiNiO₂(R3¯m). In the crystallization process of LiNiO₂, a deficiency of oxygen in the calcination reactor induced the formation of impurities and cubic rock-salt structure (Fm3m) in LiNiO₂ powders. For LiNiO₂ prepared at higher oxygen flow rates, the electrode delivered high discharge capacities with relatively good retention rates. But very low electrode capacity was obtained from LiNiO₂ prepared at lower oxygen flow rates.