Templated growth of superparamagnetic iron oxide nanoparticles by temperature programming in the presence of poly(vinyl alcohol)

Magnetite (Fe₃O₄) nanostructures with different morphologies including uniform nanoparticles, magnetic beads and nanorods were synthesized via a co-precipitation method. The synthesis process was performed at various temperatures in the presence of polyvinyl alcohol (PVA) at different concentrations. It is shown that small amounts of PVA act as a template in hot water (70 °C), leading to the oriented growth of Fe₃O₄ nanorods, which was confirmed by selected area electron diffraction. Individually coated magnetite nanoparticles and magnetic beads were formed at a relatively lower temperature of 30 °C in the folded polymer molecules due to the thermo-physical properties of PVA. When a moderate temperature (i.e. 50 °C) was used, nanorods and nanobeads co-existed. At higher concentrations of PVA (polymer/iron mass ratio of 5), however, the formation of magnetic beads was favored. The nanorods were shown to be unstable upon exposure to electron beams. Freezing/thawing process was applied post synthesis as temperature programming to fabricate stable nanorods with rigid walls.     

High rate flame synthesis of highly crystalline iron oxide nanorods

Single-step flame synthesis of iron oxide nanorods is performed using iron probes inserted into an opposed-flow methane oxy-flame. The high temperature reacting environment of the flame tends to convert elemental iron into a high density layer of iron oxide nanorods. The diameters of the iron oxide nanorods vary from 10 to 100?nm with a typical length of a few microns. The structural characterization performed shows that nanorods possess a highly ordered crystalline structure with parameters corresponding to cubic magnetite (Fe(3)O(4)) with the [100] direction oriented along the nanorod axis. Structural variations of straight nanorods such as bends, and T-branched and Y-branched shapes are frequently observed within the nanomaterials formed, opening pathways for synthesis of multidimensional, interconnected networks.     

Novel environmentally friendly synthesis of superparamagnetic magnetite nanoparticles using mechanochemical effect

A novel method for synthesizing superparamagnetic magnetite nanoparticles in water system via coprecipitation under an environmentally friendly condition has been developed. In this method, an almost neutral suspension containing ferrous hydroxide and goethite is used as the starting suspension and subjected to a ball-milling treatment. The product was characterized by transmission electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, dynamic light scattering, superconducting quantum interference device magnetometry, and Mössbauer spectroscopy. The mechanochemical effect generated by the ball-milling treatment promoted the reaction between ferrous hydroxide and goethite even at room temperature, resulting in the formation of homogeneous magnetite nanoparticles. Simultaneously, it also contributed to crystallize the formed magnetite nanoparticles while inhibiting the particle growth. This resulted in the formation of ultrafine magnetite nanoparticles of about 10 nm having a single crystal structure. This method could provide ferromagnetic magnetite nanoparticles with superparamagnetism under the moderate condition without neither heating nor any additives such as surfactant and organic solvent.     

Effect of ferrous/ferric ions molar ratio on reaction mechanism for hydrothermal synthesis of magnetite nanoparticles

Magnetite nanoparticles were prepared by hydrothermal synthesis under various initial ferrous/ferric molar ratios without adding any oxidizing and reducing agents in order to clarify effects of the molar ratio on the reaction mechanism for the formation of magnetite nanoparticles. The magnetite nanoparticles prepared were characterized by a scanning electron microscope, powder X-ray diffractometer, and superconducting quantum interference device (SQUID). At the molar ratio corresponding to the stoichiometric ratio in the synthesis reaction of magnetite from ferrous hydroxide and goethite, the nucleation of magnetite crystals progressed rapidly in an initial stage of the hydrothermal synthesis, resulting in formation of the magnetite nanoparticles having a smaller size and a lower crystallinity. On the other hand, at higher molar ratios, the particle size and crystallinity increased with increasing molar ratio because using surplus ferrous hydroxide the crystallites of magnetite nanoparticles grew up slowly under hydrothermal conditions according to the Schikorr reaction. The magnetite nanoparticles prepared under various molar ratios had good magnetic properties regardless of the molar ratio.     

One-pot simple synthesis and characterisation of Mn2+-doped GaN nanorods by RAPET method

In this work, we display one-step reactions under autogenic pressure at elevated temperature (RAPET) method-based synthesis of Mn-doped GaN nanorods by varying the atomic ratio of Mn:Ga as 0, 0.02, 0.04, 0.06 and 0.08, respectively. The synthesised nanorods are characterised by X-ray diffraction, high-resolution transmission electron microscopy (HRTEM) and Raman spectral methods. It is observed that there is a decrease in the lattice constant with an increase in the concentration of Mn (from 0.02 to 0.08 wt%). Moreover, the smaller covalent radius of Mn is the key for the doping process. The Mn-doped GaN nanocrystals show rod-like morphology with a length of 40–50 nm and width of 8–12 nm. This size factor mainly depends on the doping of Mn [from transmission electron microscopy (TEM) analysis] into GaN components. Well-defined lattice fringes are elucidated for the growth of crystalline hexagonal GaN (wurtzite type) nanocrystals.     

Environmentally friendly aqueous solution synthesis of hierarchical CaWO4 microspheres at room temperature

An environmentally friendly route for the synthesis of hierarchical CaWO4 microspheres with novel morphology at room temperature has been successfully developed. CaCl2 and Na2WO4 were used as reaction regents, and distilled water was used as an environmentally friendly solvent. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence spectroscopy. This green wet-chemical route provides a simple, one-step, low-cost approach for the large-scale synthesis of hierarchical CaWO4 microspheres with relatively uniform diameters of 3-6 microm. The hierarchical microspheres are built up with numerous nanorods with an average diameter of 50 nm, which are radially oriented to the microsphere center. SEM observations of different intermediates indicate the possible growth process, in which the hierarchical structure growth is from nuclei through kayak-like, rod-like, peanut-like, dumbbell-like, and peach-like structures to final microspheres, via "self-assembled preferential end growth" of kayak-like particles in aqueous solution. The hierarchical CaWO4 microspheres exhibit a strong, broad blue emission peak of 412 nm.     

Hydrothermal synthesis of magnetite nanoparticles via sequential formation of iron hydroxide precipitates

A novel method for preparing fine magnetite nanoparticles without using any additives and organic solvents has been developed. In this method, a sequential precipitates formation method, ferrous and ferric hydroxides are not coprecipitated but sequentially formed in an alkaline solution, and then the resulting suspension is subjected to a hydrothermal treatment. The obtained magnetite nanoparticles were characterised through scanning electron microscopy observation and X-ray diffraction analysis, and the particle size and magnetic properties were measured with a dynamic light scattering particle size analyser and a superconducting quantum interference device magnetometer, respectively. In order to prepare fine magnetite nanoparticles with a uniform size, both the formation sequence of ferrous and ferric hydroxide precipitates and the supersaturation of ferric hydroxide in the solution were essential. The ferromagnetic magnetite nanoparticles with a median size 8.5?nm were relatively easily obtained in the formation process in which a ferric sulphate solution was rapidly poured into a suspension of ferrous hydroxide particles prepared beforehand using ferric chloride and sodium hydroxide, whereas the median size of magnetite nanoparticles prepared via conventional coprecipitation route was 38.6?nm.     

Co掺杂的钛酸盐和TiO2纳米棒的磁性及光学性能

利用水热合成法,以TiO2(锐钛矿)粉末、钴盐为原料,在NaOH溶液中,180℃水热合成了Co掺杂的钛酸盐纳米棒.将Co掺杂的钛酸盐纳米棒在700℃氩气氛下烧结2 h转化为锐钛矿结构Co掺杂TiO2纳米棒.利用x射线衍射仪(XRD)、扫描电子显微镜(SEM)、紫外一可见分光光度计和超导量子干涉磁强计(SQUID)等对Co掺杂的钛酸盐和Ti0,纳米棒的微结构、形貌和性能进行了表征.研究结果表明,Co掺杂的钛酸盐和未掺杂的纯钛酸盐H2Ti3O7具有相同的层状结构,在样品中未监测到Co杂质(如钴的氧化物和氢氧化物)的峰.Co掺杂的钛酸盐纳米棒表面光滑,直径大约为90 nm～120 nm,长度约1 μm,co的掺杂对纳米棒形貌没有明显影响.Co掺杂后的钛酸盐纳米棒与未掺杂的钛酸盐纳米棒相比,其紫外-可见吸收光谱的吸收峰明显红移,带宽变窄.未掺杂的纯钛酸盐纳米棒的带宽为3.2 eV,与TiO2相同;Co掺杂的钛酸盐纳米棒的带宽为2.6 eV,明显变窄.同时,Co掺杂的钛酸盐和TjO2纳米棒在300 K均具有铁磁性,且其磁化强度大小基本一致,矫顽力也相同.     

Solvothermal synthesis and characterization of functionalized graphene sheets (FGSs)/magnetite hybrids

Novel functionalized graphene sheets (FGSs)/Fe₃O₄ hybrids were synthesized through a facile one-step solvothermal method using FeCl₃ as iron source, ethylene glycol as the reducing agent and graphene nanosheets as templates. The morphology, composition and phase structure of as-prepared hybrid materials were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). These results showed that denseness, size and crystallinity of magnetite can be altered by controlling the reaction parameters. Magnetization measurement indicated that both coercivity and saturation magnetization increased linearly with increasing magnetite concentration in hybrid materials. The measured relative complex permittivity indicated that a high resistivity existed in the FGSs/Fe₃O₄ inorganic hybrids. The magnetic loss was caused mainly by ferromagnetic natural resonance, which is in agreement with the Kittel equation. The novel inorganic hybrid materials are believed to have potential applications in the microwave absorbing performances.     

Solvothermal synthesis and magnetic properties of magnetite nanoplatelets

Nanostructured magnetite plates were synthesized by a simple solvothermal route where ethylenediamine was used as the solvent and reducing agent. The morphology and structure of the as-prepared platelets were characterized using X-ray diffraction, infrared spectroscopy and transmission electron microscopy. The results showed that the products are magnetite crystals with plate like morphology whose thickness is estimated to be 20 nm. Magnetic measurements at 300 K gave the saturation magnetization and the coercive field of nanostructured magnetite 87.4 emu/g and 178 Oe, respectively, which are higher than those of cubic nanoparticles, due to the higher shape anisotropy of magnetite nanoplatelets.     

Extracellular biosynthesis of magnetite using fungi

The development of synthetic processes for oxide nanomaterials is an issue of considerable topical interest. While a number of chemical methods are available and are extensively used, the collaborations are often energy intensive and employ toxic chemicals. On the other hand, the synthesis of inorganic materials by biological systems is characterized by processes that occur at close to ambient temperatures and pressures, and at neutral pH (examples include magnetotactic bacteria, diatoms, and S-layer bacteria). Here we show that nanoparticulate magnetite may be produced at room temperature extracellularly by challenging the fungi, Fusarium oxysporum and Verticillium sp., with mixtures of ferric and ferrous salts. Extracellular hydrolysis of the anionic iron complexes by cationic proteins secreted by the fungi results in the room-temperature synthesis of crystalline magnetite particles that exhibit a signature of a ferrimagnetic transition with a negligible amount of spontaneous magnetization at low temperature.     

Ferromagnetism in Fe-doped CdSe nanorods prepared by solvothermal route

The present work deals with the role played by structural defects and doping concentration on the observed ferromagnetic behavior in pure and Fe-doped CdSe nanorods. X-ray diffraction and Raman analyses reveal the formation of wurtzite phase hexagonal structure of the pure and Fe-doped CdSe nanorods, without any additional parasitic secondary phases. Selected area electron diffraction, transmission electron microscopy and high-resolution transmission electron microscopy results show the single crystalline nature of the synthesized nanorods, possessing diameter and length around 8–15 and 100–140 nm, respectively. Energy dispersive spectroscopy and UV–visible spectra indicate the incorporation of Fe in host nanorods. Electron spin resonance analysis shows that the Fe ions are present in +3 oxidation state in host CdSe nanorods. The magnetization versus applied field (M–H) curves has been measured with vibrating sample magnetometer at room temperature. The increase of saturation magnetization with Fe-doping concentration has been observed which can be explained by the bound magnetic polaron (F-center exchange mechanism) at defect sites in the host CdSe nanorods.     

Hydrothermal synthesis of HgTe rod-shaped nanocrystals

HgTe nanorods composed of crystalline particles with the diameter of 100-300 nm and length of up to 2-3 μm have been prepared by a hydrothermal method, and characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy (TEM) and energy-dispersive X-ray analysis (EDX). It was found that ammonia played a key role in the formation of HgTe nanorods.     

Formation of ZnS nanorods entrapped in polyacrylic acid (PAA) film

A simplistic approach for synthesis of zinc sulphide (ZnS) nanorods is reported. The synthesis of ZnS nanoparticles involved mixing of zinc acetate, sodium sulphide and acrylic acid in appropriate ratio at proper conditions, which formed the core. These nanoparticles were trapped in PAA by in-situ polymerization of acrylic acid and carefully casted into the film which resulted into entrapped nanorods in the polymer matrix. The nanoparticles as well as nanorods entrapped in PAA were characterized using high resolution scanning electron microscopy (SEM) for morphological investigations; energy dispersive X-ray analysis (EDAX) for composition and its crystalinity was checked using X-ray diffraction (XRD). The length of nanorods was in the range of 2–4 μm and thickness between 50–200 nm.     

Magnetic properties of magnetite nanoparticles synthesized by forced hydrolysis

We report the synthesis of superparamagnetic nanoparticles of iron oxide in magnetite phase with diameters of approximately 15 nm. Nanoparticles of magnetite were synthesized by forced hydrolysis method, controlling the oxidation with a nitrogen atmosphere during the synthesis. Nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectroscopy and vibrating sample magnetometry. Quantitative analysis of crystalline phases was done by performing Rietveld refinement of the XRD profiles. In order to obtain nanometers sizes of magnetite phase solely, the parameters of formation such a pH and molar concentration were analyzed and determined by an equilibrium thermodynamics model with the chemical computer code MINTEQA [Allison Geoscience Consultants, Inc., HydroGeoLogic, Inc., MINTEQA2 for Windows, Equilibrium Speciation Model. Ver 1.5(2003)].     

Synthesis of magnetite octahedrons from iron powders through a mild hydrothermal method

Magnetite (Fe₃O₄) octahedral particles were fabricated from iron powders through a simple one-step alkali-assisted hydrothermal process. The crystallinity, morphology, and structural features of the as-prepared magnetite particles were investigated using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The values of saturation magnetization (M_s) and coercivity (H) of the magnetite octahedrons characterized on a vibrating sample magnetometer (VSM) are 89.81 emu/g and 70.6 Oe, respectively. The concentration of NaOH and the reaction temperature played a key role in the formation of the magnetite octahedrons.     

Structure and superparamagnetic behaviour of magnetite nanoparticles in cellulose beads

Superparamagnetic magnetite nanoparticles were obtained starting from a mixture of iron(II) and iron(III) solutions in a preset total iron concentration from 0.04 to 0.8 mol l⁻¹ with ammonia at 25 and 70 °C. The regeneration of cellulose from viscose produces micrometrical spherical cellulose beads in which synthetic magnetite were embedded. The characterization of cellulose-magnetite beads by X-ray diffraction, Scanning and Transmission Electron Microscopy and magnetic measurement is reported. X-ray diffraction patterns indicate that the higher is the total iron concentration and temperature the higher is the crystal size of the magnetite obtained. Transmission Electron Microscopy studies of cellulose-magnetite beads revealed the distribution of magnetite nanoparticles inside pores of hundred nanometers. Magnetite as well as the cellulose-magnetite composites exhibit superparamagnetic characteristics. Field cooling and zero field cooling magnetic susceptibility measurements confirm the superparamagnetic behaviour and the blocking temperature for the magnetite with a mean size of 12.5 nm, which is 200 K.     

Preparation and photoluminescence study of mesoporous indium hydroxide nanorods

Mesoporous indium hydroxide nanorods were successfully synthesized by a mild one-step one-pot method. The obtained samples were characterized by X-ray diffraction, transmission electron microscopy with selected area electron diffraction, N₂ adsorption, ultraviolet-visible absorption and photoluminescence, respectively. Transmission electron microscopy showed that there were some pores in the samples, which were mainly composed of rod-like shapes with length of 300 nm and diameter of 90 nm. N₂ adsorption/desorption measurements confirmed that the prepared powder was mesoporous with average pore diameter of 3.1 nm. The ultraviolet-visible absorption spectroscopy analysis indicated that the band gap energy of the samples was 5.15 eV. Photoluminescence spectrum showed that there were two strong emissions under ultraviolet light irradiation. The growth mechanism of indium hydroxide nanorods and the role of cetyltrimethyl ammonium bromide were also discussed.     

Magnetic properties of biosynthesized magnetite nanoparticles

Magnetic nanoparticles, which are unique because of both structural and functional elements, have various novel applications. The popularity and practicality of nanoparticle materials create a need for a synthesis method that produces quality particles in sizable quantities. This paper describes such a method, one that uses bacterial synthesis to create nanoparticles of magnetite. The thermophilic bacterial strain Thermoanaerobacter ethanolicus TOR-39 was incubated under anaerobic conditions at 65/spl deg/C for two weeks in aqueous solution containing Fe ions from a magnetite precursor (akaganeite). Magnetite particles formed outside of bacterial cells. We verified particle size and morphology by using dynamic light scattering, X-ray diffraction, and transmission electron microscopy. Average crystallite size was 45 nm. We characterized the magnetic properties by using a superconducting quantum interference device magnetometer; a saturation magnetization of 77 emu/g was observed at 5 K. These results are comparable to those for chemically synthesized magnetite nanoparticles.     

CTAB-assisted hydrothermal synthesis of single-crystalline copper-doped ZnO nanorods and investigation of their photoluminescence properties

A simple CTAB-assisted hydrothermal synthesis of undoped and copper-doped ZnO nanorods is reported. The phase and structural analysis carried out by X-ray diffraction, shows the formation of hexagonal wurtzite structure of ZnO. Morphology of the ZnO nanorods was investigated by electron microscopy techniques which showed the formation of well dispersed regular shape ZnO nanorods of 100 ± 10 nm in diameter and 900 ± 100 nm in length. However, size of the copper doped ZnO nanorod slightly increased with increasing copper concentration. Furthermore, the selected area electron diffraction pattern and high resolution transmission electron microscopy reveal that both the undoped and copper doped ZnO nanorods were single crystalline in nature and preferentially grew up along [0001] direction. Optical property was investigated by photoluminescence spectroscopy. The effects of copper doping on the photoluminescence property of ZnO nanorods were investigated.