Magnetic NiFe2O4 Nanoparticles Prepared via Non-Aqueous Microwave-Assisted Synthesis for Application in Electrocatalytic Water Oxidation

Phase-pure spinel-type magnetic nickel ferrite (NiFe₂O₄) nanocrystals in the size range of 4 to 11 nm were successfully synthesized by a fast and energy-saving microwave-assisted approach. Size and accessible surface areas can be tuned precisely by the reaction parameters. Our results highlight the correlation between size, degree of inversion, and magnetic characteristics of NiFe₂O₄ nanoparticles, which enables fine-tuning of these parameters for a particular application without changing the elemental composition. Moreover, the application potential of the synthesized powders for the electrocatalytic oxygen evolution reaction in alkaline media was demonstrated, showing that a low degree of inversion is beneficial for the overall performance. The most active sample reaches an overpotential of 380 mV for water oxidation at 10 mA cm⁻² and 38.8 mA cm⁻² at 1.7 V vs. RHE, combined with a low Tafel slope of 63 mV dec⁻¹.     

红外光谱技术在纳米NiFe2O4制备过程中的应用

采用溶胶-凝胶法制备NiFe2O4纳米粉末,并经不同温度热处理.测定了制备过程中各阶段的红外吸收光谱和不同温度处理样品的红外漫反射光谱.结果表明,红外吸收光谱较好地反映了溶胶-凝胶法制备NiFe2O4纳米粉末过程中结构的变化,为确定热处理温度提供了实验依据,彻底消除有机物,热处理需在400℃以上;红外漫反射谱可以较好地反映粉末的尺寸效应和形态效应,粉末粒径越小,漫反射函数(K-M)值越大;当粒径达到一定尺寸时,红外漫反射的尺寸效应消失.     

Effect of Magnetic Carrier NiFe2O4 Nanoparticles on Physicochemical and Catalytic Properties of Magnetically Separable Photocatalyst TiO2/NiFe2O4

A series of magnetically separable photocatalyst TiO₂/NiFe₂O₄(TN) with different mass ratios of NiFe₂O₄ to TiO₂ was prepared by sol-gel method. The X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), transmission electron microscopy(TEM), ultraviolet-visible spectroscopy(UV-Vis), Brunauer-Emmett-Teller(BET) surface analysis and photoluminescence spectroscopy(PL) were used to characterize the photocatalyst TN. The XRD patterns of TN indicate that adulterating a smidgen of NiFe₂O₄ into TiO₂(about 0.1%, mass ratio) can promote the phase transformation of TiO₂, however, when the doped amount of NiFe₂O₄ surpasses 1%, the introduction of NiFe₂O₄ can inhibit the growth of TiO₂ crystal grain and reduce the size of TiO₂ crystal grain. The XPS results of TN indicate that some Fe³⁺ replace Ti⁴⁺ of the TiO₂ lattice forming Fe―O―Ti bonds. The PL analysis of TN shows that the NiFe₂O₄ nanoparticles in photocatalyst TN play the role of the effective recombination centre of the photogenerated electrons and holes, leading to the decrease in photocatalytic activity.     

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.     

Nanocomposites NiFe2O4/SiO2 and CoFe2O4/SiO2-Preparation by Sol-Gel Method and Physical Properties

This paper aims to characterise the systems NiFe₂O₄/SiO₂ and CoFe₂O₄/SiO₂ prepared by the sol-gel method. After heat treatment, the various samples have been studied by means of X-ray diffraction, Mössbauer spectroscopy, magnetic measurements and transmission electron microscopy (HR TEM).X-ray diffraction and Mössbauer spectra confirmed the presence of the spinel phase. HR TEM observations revealed the nanocrystals with the size in the range of 2–25 nm. Magnetic measurements showed a superparamagnetic behaviour of the samples heated at lower temperature (800°C) and ferrimagnetic character for the samples heated at higher temperature (900, 1000°C).The final phase composition of the heated samples depends on the preparation conditions. The samples, treated up to 300°C in vacuum and then subsequently heated at 800°C or 900°C, do not contain hematite (the most stable phase at higher temperatures). On the contrary, the samples heated at 1000°C or 1250°C display certain content of hematite.     

NiFe_2O_4/NiO纳米复合材料的制备及电催化水氧化性能

以镍铁水滑石为单一前驱体,通过高温焙烧制备了NiFe_2O_4/NiO纳米复合材料,对该纳米复合材料在碱性介质中电催化水的氧化性能进行了研究.结果表明,相比于化学共沉淀法制备的单独NiFe_2O_4、NiO及其物理混合物NiFe_2O_4+NiO,NiFe_2O_4/NiO纳米复合材料具有更高的电催化水氧化活性和更好的循环稳定性.电流密度为10 m A/cm2时过电位仅为364 m V.     

Synthesis and Characterization of Magnetic TiO2/SiO2/NiFe2O4 Composite Photocatalysts

Magnetic TiO2/SiO2/NiFe2O4 composite photocatalytic particles with high crystalline TiO2 shell were synthesized via a mild solution route.The prepared composite particles were characterized with X-ray diffraction(XRD),transmission electron microscopy(TEM),high resolution transmission electron microscopy(HRTEM),scanning electron microscopy(SEM),ultraviolet-visible(UV-Vis) spectroscopy and vibrating sample magnetometer(VSM).The results show that the obtained TiO2/SiO2/NiFe2O4 composite particles were composed...     

A Simple Microwave Method for Synthesis of CdS Nanoparticles

In this work a surfactant-free microwave method for preparation of CdS nanoparticles is reported. The effect of different parameters i.e. time and irradiation power, sulfur source and solvent on the morphology and the samples particle size have been investigated. The synthesized nanostructures were characterized by X-ray diffraction, energy-dispersive X-ray analysis, scanning electron microscopy, Fourier transform infrared, photoluminescence and ultraviolet–visible spectroscopy.     

Defective NiFe2O4 Nanoparticles for Efficient Urea Electro‐oxidation

Urea is an important organic pollutants in sewage and needs to be removed for environmental protection. Here, we report defective NiFe₂O₄ (NFO) nanoparticles with excellent performance for urea electro‐oxidation. The results show that defects can be effectively implanted at the surface of NFO nanoparticles by a facile and versatile lithium reduction method without affecting its main crystal structure and grain size. The defective NFO‐5Li nanoparticles displayed a significantly improved urea electro‐oxidation performance compared with NFO‐Pristine nanoparticles. Particularly, the NFO‐Pristine and NFO‐5Li show a potential of 1.398 and 1.361 V at the current density of 10 mA cm^?2 and Tafel slope of 37.3 and 31.4 mV dec^?1, respectively. In addition, the NFO‐5Li nanoparticles also revealed outstanding electrocatalytic stability. The superior performance can be attributed to the designed tunable surface defect engineering. Furthermore, the defect engineering strategy as well as the defective NFO nanoparticles hold great potential for applications in other materials and areas.     

磁性纳米固体碱催化剂MgAl-OH-LDHs/NiFe2O4的合成、表征与性能研究

提出用镁铝水滑石包覆镍铁尖晶石,制备磁性纳米固体碱催化剂MgAl-OH-LDHs/NiFe₂O₄.用XRD, IR, TG-DTA, BET, XPS, VSM和TEM等技术及丙酮缩合反应表征了催化剂的结构和性能.结果表明该催化剂具有以NiFe₂O₄为磁核,以MgAl-OH-LDHs为Brönsted碱催化活性相,通过Mg-O-Fe(Ni)和/或Al-O-Fe(Ni)连接于磁核上的包覆结构,给出了该催化剂的结构模型.该催化剂用于丙酮缩合反应,273 K双丙酮醇转化率略高于MgAl-OH-LDHs,然而经外加磁场回收所得回收率大幅度提高,再次用于该反应仍保持较高的催化活性.     

Chemical Synthesis of Magnetic Nanoparticles for Permanent Magnet Applications

Permanent magnets are a class of critical materials for information storage, energy storage, and other magneto-electronic applications. Compared with conventional bulk magnets, magnetic nanoparticles (MNPs) show unique size-dependent magnetic properties, which make it possible to control and optimize their magnetic performance for specific applications. The synthesis of MNPs has been intensively explored in recent years. Among different methods developed thus far, chemical synthesis based on solution-phase reactions has attracted much attention owing to its potential to achieve the desired size, morphology, structure, and magnetic controls. This Minireview focuses on the recent chemical syntheses of strongly ferromagnetic MNPs (H_c>10 kOe) of rare-earth metals and FePt intermetallic alloys. It further discusses the potential of enhancing the magnetic performance of MNP composites by assembly of hard and soft MNPs into exchange-coupled nanocomposites. High-performance nanocomposites are key to fabricating super-strong permanent magnets for magnetic, electronic, and energy applications.     

Synthesis of Novel NiFe2O4 Nanospheres for High Performance Pseudocapacitor Applications

Russian Journal of Electrochemistry - Synthesis of monodispersed NiFe2O4 nanospheres by a simple method was reported. Structure, morphology and characterization of the nanospheres were performed...     

Synthesis and Magnetic Properties of Pt3Co/Fe3O4 Nanocomposites

Bimagnetic Pt₃Co/Fe₃O₄ nanocomposite is synthesized in aqueous solution. The nanoparticles are characterized with TEM, FTIR, and magnetic measurements. The as‐synthesized nanocomposite exhibits ferromagnetic properties at room temperature due to the exchange coupling between Pt₃Co and Fe₃O₄. Magnetic properties of Pt₃Co/Fe₃O₄ nanoparticle can be tuned by varying of the molar ratio of iron to platinum. Pt₃Co/Fe₃O₄ nanoparticles exhibit higher saturation magnetization when the molar ratio of iron to platinum is 1.     

Synthesis of NiFe2O4 Powders Well Defined in Size and Morphologies

The uniform NeFe2O4 powders with different particle size and morphologies (octahedral, cubic and spherical) have been prepared from different precursors via hydrothermal process. The nanocrystallines derived from precursor B in the weak alkali solution (pH≥10) are superparamagnetic.     

Preparation of Magnetic Photocatalyst TiO2 Supported on NiFe2O4 and Effect of Magnetic Carrier on Photocatalytic Activity

A magnetic photocatalyst TiO₂/NiFe₂O₄ (TN) with typical ferromagnetic hysteresis was prepared by a sol‐gel method, which is easy to be separated from a slurry‐type photoreactor under the application of an external magnetic field, being one of promising photocatalysts for wastewater treatment. The analysis of XRD indicated that the highly dispersed NiFe₂O₄ nanoparticles prevented the formation of rutile phase to some extent. A transmission electron microscope (TEM) was used to characterize the structure of the photocatalyst, indicating that the NiFe₂O₄ nanoparticles highly dispersed among TiO₂ nanoparticles. The prepared photocatalyst showed high photocatalytic activity for the degradation of methyl orange in water. The degradation results revealed that the NiFe₂O₄ nanoparticles played the role of recombination centre of photogenerated electrons and holes for the TN photocatalyst, which gave rise to the decrease in photocatalytic activity. Moreover, the experiment on recycled use of TN demonstrated a good repeatability of the photocatalytic activity.     

磁性NiFe2O4基复合材料的构筑及光催化应用

随着社会经济的快速发展,能源短缺与环境污染已成为当前人类面临的两大难题。人们一直致力于开发新的清洁可再生替代能源, 其中,太阳能被认为是理想且具有发展潜力的清洁能源。光催化作为一种新型的“绿色技术”,可直接利用太阳能将环境中的有机污染物降解为无害物质,进而有效解决上述问题。然而,要实现这个过程关键在于合理地设计和构筑高性能的光催化剂。铁酸镍(NiFe₂O₄)作为一种磁性材料,兼具快速的磁响应性和良好的光化学稳定性,将其与能带匹配的半导体光催化剂复合,不仅能够获得活性高的光催化剂,而且实现了光催化剂的磁分离, 从而使其在光催化领域展现出极为广阔的应用前景。本文主要综述了近5年来国内外NiFe₂O₄基复合材料的制备和光催化应用方面的最新研究进展, 这将为新型高效磁性复合光催化材料的合成及应用提供新方法和新思路。最后,对NiFe₂O₄基复合光催化材料未来的发展前景做了展望。     

Fe_3O_4磁性纳米粒子的PEG修饰剂的合成与性能

采用共沉淀法制备了用柠檬酸包覆的Fe3O4磁性纳米粒子,为提高其生物环境适应性和生物应用,利用聚乙二醇二胺(NH2-PEG-NH2)通过碳二亚胺化学法进一步修饰,得到具有良好性能的磁性纳米粒子修饰剂,并分别用场发射扫描电子显微镜(SEM)、洛伦兹透射电子显微镜(TEM)、马尔文激光粒度仪、X-射线粉末衍射仪(XRD)、傅里叶变换红外光谱(FTIR)、综合热分析仪(TG/DTA)、振动样品磁强计(VSM)对磁性纳米粒子的表面形态、化学结构、晶体结构、热稳定性和磁性能进行了表征.在此基础上用合成的磁性纳米粒子修饰剂对盐酸阿霉素(DOX·HCl)进行了修饰,研究了修饰剂的载药和释药行为.结果表明,所制备的修饰剂近乎球形,尺寸相对均匀,粒径在15 nm左右,饱和磁化强度为68 A·m2/kg,在磁靶向药物运输中可以达到良好的磁响应性能.在水中的载药量达到83%,在p H=7.4和p H=5.0下,磁性纳米粒子载药盐酸阿霉素释放均是一个缓慢的过程,具有明显的缓释效果,此外,由于不同p H值下,DOX中的氨基质子化程度存在差异,在较低的p H值下质子化的氨基互相排斥,这更有利于DOX的释放,累计释药率在72 h后分别为65.8%(p H=7.4)与73.6%(p H=5.0).研究表明该磁性纳米粒子具有很好的载药能力及缓释效果.     

Chemical looping combustion of high-sulfur coal with NiFe2O4-combined oxygen carrier

Chemical looping combustion (CLC) of coal has gained increasing attention as a novel combustion technology for its attractive advantage in the inherent separation of CO₂. In relative to the single metal oxide-based oxygen carrier (OC), combined OC owned superiority for CLC of coal. In this research, combined NiFe₂O₄ OC was synthesized using sol–gel combustion synthesis method, and its reaction with a typical Chinese high-sulfur coal as Liuzhi (LZ) coal was performed in a thermogravimetric analyzer (TG). And then, systematic investigation was carried out to explore the evolution of sulfur species and minerals involved in coal and their interaction with the reduced NiFe₂O₄ OC through different means, including fourier transform infrared (FTIR), field scanning electron microscopy/energy-dispersive X-ray spectrometry, X-ray diffraction, and thermodynamic simulation. TG–FTIR analysis of LZ reaction with NiFe₂O₄ indicated that two reaction stages were experienced at 350–550 and 800–900 °C, respectively, far different from LZ pyrolysis, and SO₂ occurred mainly related to oxidization of H₂S with NiFe₂O₄ over 550 °C. Meanwhile, lattice oxygen transfer rates of NiFe₂O₄ involved at the two reaction stages were higher than that of directly mixed NiO with Fe₂O₃ OC and thus more beneficial for LZ coal conversion. Both experimental means and thermodynamic simulation of the solid-reduced residues of NiFe₂O₄ with LZ coal indicated that the main-reduced counterparts of NiFe₂O₄ were Ni and Fe₃O₄. In addition, though good regeneration of the reduced NiFe₂O₄ was reached, the side products Ni₃S₂ and Ni₂SiO₄ should be noted as well for its detrimental effect on the reactivity of NiFe₂O₄ OC.     

溶剂热合成法制备Mn3O4纳米粉体

溶剂热合成法制备Mn3O4纳米粉体;四氧化三锰;纳米粉体;溶剂热合成