One-step synthesis of hematite (α-Fe2O3) nano-particles by direct thermal-decomposition of maghemite

In this research work, α-Fe₂O₃ nano-particles were prepared by direct thermal-decomposition of γ-Fe₂O₃. Precursor powders (γ-Fe₂O₃) were synthesized by wet chemical method at room temperature and then, the precursors were subsequently calcined in air for 1 h at 500 °C. Samples were characterized by thermal gravimetric analysis (TGA), X-ray diffraction (XRD), energy dispersive spectra (EDS), infrared spectrum (IR) and transmission electron microscopy (TEM), respectively. The XRD, EDS, and IR results indicated that the synthesized α-Fe₂O₃ particles were pure. The TEM image showed that the α-Fe₂O₃ nano-particles were spherical and 18 ± 2 nm in size. Magnetic properties have been detected by a vibrating sample magnetometer (VSM) at room temperature. The γ-Fe₂O₃ and α-Fe₂O₃ nano-particles exhibited a super-paramagnetic and weak ferromagnetic behavior at room temperature, respectively. Using the present method, hematite nano-particles can be produced without expensive organic solvent and complicated equipment.     

Synthesis of maghemite (γ-Fe2O3) nanoparticles by thermal-decomposition of magnetite (Fe3O4) nanoparticles

In this research work, we prepared γ-Fe₂O₃ nanoparticles by thermal-decomposition of Fe₃O₄. The Fe₃O₄ nanoparticles were synthesized via co-precipitation method at room temperature. This simple, soft and cheap method is suitable for preparation of iron oxide nanoparticles (γ-Fe₂O₃; Fe₃O₄). The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), vibrating sample magnetometer and differential scanning calorimeter (DSC). The XRD and FT-IR results indicated the formation of γ-Fe₂O₃ and Fe₃O₄ nanoparticles. The TEM images showed that the γ-Fe₂O₃ and Fe₃O₄ were spherical, and their size was 18 and 22 nm respectively. Magnetic properties have been measured by VSM at room temperature. Hysteresis loops showed that the γ-Fe₂O₃ and Fe₃O₄ nanoparticles were super-paramagnetic.     

Synthesis of monodisperse shuttle-like α-Fe2O3 nanorods via the EDA-assisted method

Monodisperse hematite shuttle-like nanorods were synthesized successfully by the ethylenediamine (EDA)-assisted method. The structure and morphology were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectrometer (EDS). XRD studies indicated that the as-prepared product was well-crystallized orthorhombic phase of α-Fe₂O₃. TEM and SEM images showed that the α-Fe₂O₃ nano-particles were of rod shape with an average length of 400 nm and diameter of about 80 nm in the middle part.     

Preparation and characterization of single-phase α-Fe2O3 nano-powders by Pechini sol-gel method

In this work, single-phase α-Fe₂O₃ nano-particles were first synthesized via Pechini sol-gel method using citric acid and polyethylene glycol-6000 as chelating agents. The structural coordination of as-prepared polymeric intermediates was investigated by FTIR analysis. Thermal behavior of the polymeric intermediates was studied by TG-DTG-DSC thermograms. The structure of the powders calcined at different temperatures was characterized by XRD and FESEM. The single-phase α-Fe₂O₃ nano-powders with uniform size were prepared when the polymeric intermediate calcined at 600 °C, and the lowest particle size was found to be 30 nm.     

Preparation and characterization of α-Fe2O3 nanorod-thin film by metal-organic chemical vapor deposition

Alpha iron oxide (α-Fe₂O₃) films were grown on catalyst-free silicon substrate using a vertical type metal-organic chemical vapor deposition process. X-ray powder diffraction and field-emission transmission electron microscopy measurements showed that these α-Fe₂O₃ films consisted of bundles of one dimensional (1D) nanorods and the nanorods in these α-Fe₂O₃ films were single crystalline with a well-ordered rhombohedral structure. The nanorods showed a preferred growth orientation in the [104] direction. Magnetic force microscopy image suggests that spin domains were formed in the α-Fe₂O₃ nanorods. Photo-catalytic property of these nanorod films was confirmed through the photo-degradation of Rhodamine B by UV irradiation. These α-Fe₂O₃ film/nanorod materials could be used as building blocks for nanodevice applications.     

Novel rose-type magnetic (Fe3O4, γ-Fe2O3 and α-Fe2O3) nanoplates synthesized by simple hydrothermal decomposition

Rose-type magnetic nanoplates (RTMNPs) were synthesized by a simple hydrothermal decomposition method where FeCl₂·4H₂O was solely used as a precursor. The synthesized nanoplates were characterized using XRD, FE-SEM, UV-vis absorption (reflectance) spectra and magnetic hysteresis loops. The resulting nanoplates were in the ranges of size 350-500 nm and width 60-70 nm with high crystallinity, purity (shown by XRD) and reproducibility. These iron oxide nanoplates have a great potential in magnetic nanodevices and biomagnetic applications.     

Fabrication and magnetic property of α-Fe2O3 nanoparticles/TiO2 nanowires hybrid structure

α-Fe₂O₃ nanoparticles/TiO₂ nanowires hybrid structure is fabricated by two-step hydrothermal treatment. TiO₂ nanowires are prepared by heating of titanate nanowires, which are obtained by hydrothermal treatment of TiO₂ powder and further repeated HCl treatment. α-Fe₂O₃ nanoparticles are deposited on the surface of TiO₂ nanowires by hydrothermal treatment in Fe(NO₃)₃ solution. The HRTEM images confirm the junctions between α-Fe₂O₃ nanoparticles and TiO₂ nanowires. The formation of hybrid structures has significant influence on the magnetic properties of α-Fe₂O₃. The Morin transition temperature of α-Fe₂O₃ nanoparticles/TiO₂ nanowires hybrid structure is 190 K, which is determined by the sharp peak in the differential ZFC curve. Whereas there is no observable Morin transition for the corresponding isolated α-Fe₂O₃ nanoparticles with similar average particles size of ca. 20 nm.     

Structural and magnetization studies on nanoparticles of Nd doped α-Fe2O3

It has been observed that, compared to bulk form, the nanocrystalline α-Fe₂O₃ is finding application in various areas. Magnetic properties of α-Fe₂O₃ are found to be influenced by the size of particles and are also sensitive to synthesis method employed for sample preparation. In the present work we have prepared a series of Nd doped α-Fe_2−xO₃ samples (x = 0.0–0.5) by combustion method, without using any fuel. The analysis of room temperature neutron diffraction patterns shows that all the compounds of the series form in the hematite (α-Fe₂O₃) structure, space group R−3c. Magnetization measurements show that there is a broad distribution of particle size in the samples. We find that the increase in the Nd content results in the dilution of magnetism of α-Fe₂O₃. From results we believe that inclusion of Nd in α-Fe₂O₃ drastically modifies the magnetic properties.     

Green synthesis of hematite (α-Fe2O3) submicron particles

Iron oxide microparticles have been synthesized through a green technique using hydrogen peroxide under sunlight irradiation. The X-ray powder diffraction measurement shows that these particles are hematite (α-Fe₂O₃). The microstructure and particle size were investigated using scanning electron microscopy. The magnetic characterization shows the presence of Morin transition at about 258 K, which is very close to the normal value (263 K) of bulk hematite. These hematite particles show typical antiferromagnetic behavior at low temperature and weak ferromagnetic behavior at room temperature.     

Synthesis and structure characterization of Ru nanoparticles stabilized by PVP or γ-Al2O3

Uniform and stable Ru nanoparticles were synthesized by reduction of RuCl₃ in ethylene glycol (EG) in the presence of poly(N-vinyl-2-pyrrolidone) by using microwave-assisted solvothermal method. The obtained materials were characterized by UV-vis, FT-IR, XPS, XRD and TEM techniques, and used as precursors of heterogeneous metal colloid catalysts. Characterization by TEM showed that as-prepared PVP-stabilized Ru nanoparticles have small average diameters (below 2 nm) and narrow size distributions (1-3 nm). Diffraction data confirmed that a crystallite size is around 2.0 nm. A colloidal Ru/γ-Al₂O₃ catalyst was obtained by two different methods: immobilization of the PVP-stabilized Ru colloid on the support or by in situ deposition of Ru colloid, e.g., reduction of RuCl₃ with EG in the presence of the γ-alumina. It was found that both synthesis methods produced the Ru/γ-Al₂O₃ catalysts with narrow size distributions of metallic nanoparticles, that are distributed uniformly over the support. However, only in situ preparation of the colloidal Ru/γ-Al₂O₃ catalyst results in chlorine free system with high activity for hydrogen chemisorption. The H₂ uptake on the Ru(PVP)/γ-Al₂O₃ catalyst was very low because the ruthenium surface was strongly occluded with a thin layer of polymer molecules.     

Effect of particle size distribution on the magnetic properties γ-Fe2O3 nanoparticles

The magnetic response of nanocomposites formed by non-interacting well dispersed γ-Fe₂O₃ nanoparticles in a polymer matrix is presented. Various low loading fraction of particles in polymer leads to an observation of similar values of blocking temperatures and coercive fields. ac response confirms that particles are non-interacting and follow Neel–Brown model. Effect of particle size distribution on hysteresis behavior and saturation magnetization as a function of temperature is discussed. Since particles have a size distribution, the experimental results of magnetic response are compared with simulations based on Stoner–Wohlfarth model of single size particles. We have devised a measurement method in which a constant magnetic field was applied while the thermal energy is varied by sequentially heating and cooling the sample below the blocking temperature. Nanoparticle–polymer composites show reversible magnetization behavior for sequential heating/cooling cycles. However, simulation based on single size particle system shows irreversible magnetization behavior during the heating and cooling cycles. These observations are qualitatively explained in terms of different behavior of magnetization as a function of temperature for smaller superparamagnetic particles and larger blocked particles below overall blocking temperature of the composite.     

Preparation,magnetization, and microstructure of ionic ferrofluids based on γ-Fe2O3/Ni2O3 composite nanoparticles

Ionic ferrofluids based on γ-Fe₂O₃/Ni₂O₃ composite nanoparticles are a polydispersed system prepared by the Massart method. The magnetization and optical relaxation behaviors of these ferrofluids show that, in addition to the ring-free micelle aggregates, there are also chainlike aggregates in the ferrofluids. The chainlike aggregation is attributed to so-called “depletion force” in the polydispersed ferrofluids because magnetic interaction between the ferrofluid particles is so weak that these particles cannot form the aggregates just by the magnetic interaction. For the γ-Fe₂O₃/Ni₂O₃ ionic ferrofluids, the “depletion force” stimulates the larger ferrofluid particles, forming short chains in the absence of a magnetic field and their macroscopic properties, e.g., magnetization and optical relaxation, all result from the short chains. Ferrofluids having chainlike aggregates alone could have excellent magneto-optical effects.     

棒状γ-Fe2O3纳米粒子的制备及表征

在聚乙二醇(PEG-400)存在的条件下,在溶液中FeCl3与NaOH反应所得的沉淀物经抽滤后,在空气中60℃干燥6h后再在不同温度下热处理.所得的各样品用XRD、Mossbauer谱、TEM及FTIR等手段进行了表征.结果表明,沉淀经60℃干燥6h后得到结晶较差的γ-Fe2O3粉体(含少量结晶较好的α-FeOOH).经300℃热处理1h后得长径比约为5的棒形γ-Fe2O3纳米粒子.     

纳米γ-Fe2O3粒子的制备及其性能研究

以乙二醇作为前驱体,采用溶胶——凝胶法制备出了纳米γ-Fe2O3粒子,讨论了灼烧温度等对粒子大小、形貌、磁性等的影响,并采用红外光谱、X射线衍射光谱、透射电子显微镜、比表面分析仪及振动样品磁强计等对粒子的性能进行表征.结果表明:当烧结温度为450℃时,实验所得到的粒子的粒径最小,为5nm左右,磁性最强,比饱和磁化强度为65 emu.g-1,且分散较均匀.     

Synthesis,characterization and electrochemical properties of three-dimensionally ordered macroporous α-Fe2O3

Three-dimensionally ordered macroporous (3DOM) α-Fe₂O₃ electrode materials with large pore sizes and interconnected macroporous frameworks were successfully synthesized by a simply modified colloidal crystal templating strategy. The obtained samples were characterized by means of thermogravimetry, powder X-ray diffraction, nitrogen physisorption, scanning and transmission electron microscopy. The electrochemical properties of the 3DOM α-Fe₂O₃ were evaluated with cyclic voltammetry and discharge–charge experiments in an organic electrolyte containing a lithium salt. The results showed that the 3DOM α-Fe₂O₃ possessed a potential to be used as an anode material for lithium ion batteries with high initial discharge and charge capacities of 1883 and 1139 mAh g⁻¹, respectively. After 60th cycle, the reversible capacity could still be as high as 681 mAh g⁻¹ with a stable Coulombic efficiency of around 95%.     

MgAl2O4-γ-Al2O3 solid solution interaction: mathematical framework and phase separation of α-Al2O3 at high temperature

Although existence of MgAl₂O₄-γ-Al₂O₃ solid solution has been reported in the past, the detailed interactions have not been explored completely. For the first time, we report here a mathematical framework for the detailed solid solution interactions of γ-Al₂O₃ in MgAl₂O₄ (spinel). To investigate the solid solubility of γ-Al₂O₃ in MgAl₂O₄, Mg-Al spinel (MgO-nAl₂O₃; n = 1, 1.5, 3, 4.5 and an arbitrary high value 30) precursors have been heat treated at 1000°C. Presence of only non-stoichiometric MgAl₂O₄ phase up to n = 4.5 at 1000°C indicates that alumina (as γ-Al₂O₃) present beyond stoichiometry gets completely accommodated in MgAl₂O₄ in the form of solid solution. γ → α alumina phase transformation and its subsequent separation from MgAl₂O₄ has been observed in the Mg-Al spinel powders (n > 1) when the 1000°C heat treated materials are calcined at 1200°C. In the mathematical framework, unit cell of MgAl₂O₄ (Mg₈Al₁₆O₃₂) has been considered for the solid solution interactions (substitution of Mg²⁺ ions by Al³⁺ ions) with γ-Al₂O₃. It is suggested that combination of unit cells of MgAl₂O₄ takes part in the interactions when n > 5 (MgO-nAl₂O₃).     

Synthesis of Al/Fe3Al core–shell intermetallic nanoparticles by chemical liquid deposition method

In this work, an Al/Fe₃Al core–shell nanoparticle was obtained by heat treatment of a precursor in high purity of argon. The precursor, with Fe(CO)₅ and nano Al as raw materials, was synthesized simply by a chemical liquid deposition method. The evolution of the phase and morphology during the heat-treatment has been carefully studied by XRD and TEM. The results indicate that the precursor transformed to core–shell structure of Fe₃Al intermetallic nanoparticle. The formation of the Fe₃Al intermetallic nanoparticle was explored by DSC test, which reveals that the formation temperature of the nanoparticle is around 587 °C. Moreover, the TG–DSC measurements from 50 °C to 1000 °C in compressed air (20% O₂ and 80% N₂) reveal that the heat-treated powder of the precursor remains thermal stability in relatively low temperature but becomes concentrated combustion in elevated temperature.     

带状γ-Fe2O3/ZnO异质结光催化剂光催化降解四环素

针对传统ZnO光催化活性不高的问题,采用Zn(CH₃COO)₂和FeCl₃作为ZnO和Fe₂O₃的前驱体,水热条件下采用“一锅法”制备带状γ-Fe₂O₃/ZnO异质结光催化剂,采用XRD、BET比表面积测量仪、TEM、紫外-可见漫反射、电子顺磁共振(EPR)等对其晶体化学结构进行表征。在可见光光源下,探究了不同γ-Fe₂O₃负载量时γ-Fe₂O₃/ZnO异质结光催化剂对四环素的光催化降解的效果。研究表明,ZnO负载γ-Fe₂O₃后比表面积和光照吸收显著改善,禁带宽度有所减小,可见光光照120 min,n(Zn)∶n(Fe) (原子比)为20∶1的γ-Fe₂O₃/ZnO异质结光催化剂对四环素的降解率高达97.2%,多次重复使用后四环素的降解率保持在95%以上。      

Fabrication and structure characterization of MnCO3/α-Fe2O3 nanocrystal heterostructures

Novel MnCO₃/α-Fe₂O₃ nanocrystal heterostructures, with MnCO₃ nanorods 5-10 nm in diameter and 15-50 nm in length, grown onto the surfaces of the α-Fe₂O₃ nanohexahedrons sized around 30-50 nm, were fabricated via a two-step solvothermal route. The coalescent planes of the heterostructure for the MnCO₃ nanorod and the α-Fe₂O₃ nanohexahedron were determined to be (01?4) and (110), respectively. The formation of the MnCO₃ nanorods from the Mn contained amorphous flakes was tracked by transmission electron microscopy observations at various reaction stages, which suggested a rolling-broken-growth process. Evidenced by the comparative experimental result, the α-Fe₂O₃ nanohexahedrons played an important role in inducing the nucleation and growth of the hexagonal MnCO₃ nanorods on their surfaces.     

Facile synthesis and characterization of ZnFe2O4/α-Fe2O3 composite hollow nanospheres

ZnFe₂O₄/α-Fe₂O₃ composite hollow nanospheres were successfully fabricated via a facile one-pot solvothermal method, utilizing polyethylene glycol as soft template. X-ray diffraction and scanning electron microscopy analysis revealed that the prepared nanospheres with cubic spinel and rhombohedra composite structure had a uniform diameter of about 370 nm, and the hollow structure could be further confirmed by transmission electron microscopy. Energy dispersive X-ray, X-ray photoelectron spectroscopy and Fourier transform infrared techniques were also applied to characterize the elemental composition and chemical bonds in the hollow nanospheres. The ZnFe₂O₄/α-Fe₂O₃ composite hollow nanospheres show attractive light absorption property for potential applications in electronics, optics, and catalysis.