As-Prepared Single-Crystalline Hematite Rhombohedra and Subsequent Conversion into Monodisperse Aggregates of Magnetic Nanocomposites of Iron and Magnetite
TL;DR: Monodisperse nanocrystalline rhombohedral composites of Fe and Fe3O4 magnetic materials have been obtained employing a reduction reaction, in a flowing gas mixture of H2 and N2, of single-crystalline, submicron-sized α-Fe2O3 rhombohedra precursors as mentioned in this paper.
Abstract: Monodisperse nanocrystalline rhombohedral composites of Fe and Fe3O4 magnetic materials have been obtained employing a reduction reaction, in a flowing gas mixture of H2 and N2, of single-crystalline, submicron-sized α-Fe2O3 rhombohedral precursors This synthesis is significant in that we were able to create a nanocomposite with hard and soft magnetic phases juxtaposed within one discrete, anisotropic structure In turn, the precursor hematite rhombohedra of reproducible shape were successfully prepared using a facile, environmentally friendly, large-scale molten-salt reaction Rhombohedra represent a high-surface-area, anisotropic formulation of an industrially important material (iron oxide), which is an active component of gas sensors, photocatalysts, and other types of catalytic materials Moreover, the predictive formation of these materials has been investigated through a systematic variation of experimental parameters Extensive structural characterization of as-prepared samples has been performed
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TL;DR: The recent progress in SMS of inorganic materials, including oxide ceramic powders, semiconductors and carbon nanostructures, is reviewed here and special emphasis is placed on materials with nanostructure generated by SMS, and the possible modulation of materials structures at the nanoscale in the salt melt.
Abstract: Materials synthesis in the liquid phase, or wet-chemical synthesis, utilizes a solution medium in which the target materials are generated from a series of chemical and physical transformations. Although this route is central in organic chemistry, for materials synthesis the low operational temperature range of the solvent (usually below 200 °C, in extreme 350 °C) is a serious restriction. Here, salt melt synthesis (SMS) which employs a molten inorganic salt as the medium emerges as an important complementary route to conventional liquid phase synthesis. Depending on the nature of the salt, the operational temperature ranges from near 100 °C to over 1000 °C, thus allowing the access to a broad range of inorganic crystalline materials and carbons. The recent progress in SMS of inorganic materials, including oxide ceramic powders, semiconductors and carbon nanostructures, is reviewed here. We will introduce in general the range of accessible materials by SMS from oxides to non-oxides, and discuss in detail based on selected examples the mechanisms of structural evolution and the influence of synthetic conditions for certain materials. In the later sections we also present the recent developments in SMS for the synthesis of organic solids: covalent frameworks and polymeric semiconductors. Throughout this review, special emphasis is placed on materials with nanostructures generated by SMS, and the possible modulation of materials structures at the nanoscale in the salt melt. The review is finalized with the summary of the current achievements and problems, and suggestions for potential future directions in SMS.
474 citations
TL;DR: Advances in the use of the molten-salt synthetic methods, hydrothermal protocols, and template-directed techniques are described as environmentally sound, socially responsible, and cost-effective methodologies that allow us to generate nanomaterials without the need to sacrifice sample quality, purity, and crystallinity.
Abstract: Environmentally friendly synthetic methodologies have gradually been implemented as viable techniques in the synthesis of a range of nanostructures. In this work, we focus on the application of green-chemistry principles to the synthesis of complex metal oxide and fluoride nanostructures. In particular, we describe advances in the use of the molten-salt synthetic methods, hydrothermal protocols, and template-directed techniques as environmentally sound, socially responsible, and cost-effective methodologies that allow us to generate nanomaterials without the need to sacrifice sample quality, purity, and crystallinity, while allowing control over size, shape, and morphology.
305 citations
TL;DR: In this article, α-Fe2O3 hierarchically nanostructured hollow spheres assembled by nanosheets were prepared by thermal decomposition of a precursor which was obtained using FeCl3·6H2O, NaOH, and sodium dodecylbenzenesulfonate in the solvent ethylene glycol by a facile microwave-assisted solvothermal method.
Abstract: α-Fe2O3 hierarchically nanostructured hollow spheres assembled by nanosheets were prepared by thermal decomposition of a precursor which was obtained using FeCl3·6H2O, NaOH, and sodium dodecylbenzenesulfonate in the solvent ethylene glycol by a facile microwave-assisted solvothermal method. The growth process of the precursor was investigated. The products were characterized by X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. Because of the unique hierarchically nanostructured hollow structures composed of nanosheets, the photocatalytic property and potential application in water treatment of the α-Fe2O3 samples were also investigated.
260 citations
TL;DR: In this article, the authors report a preferable and enhanced adsorption phenomena of the dyes containing hydroxyl (−OH) groups on iron oxide nanoparticles, which can be separated by an external magnetic field and have an average size of 20−40 nm with a surface area of ∼70 m2 g−1.
Abstract: The iron oxide nanoparticles, having an average size of 20−40 nm with a surface area of ∼70 m2 g−1, have been synthesized and used for selective adsorption of various dyes (selectively containing hydroxyl groups) from aqueous solution. The nanoparticles are ferromagnetic in nature at both room and low temperature and can be separated by an external magnetic field. Herein, we report a preferable and enhanced adsorption phenomena of the dyes containing hydroxyl (−OH) groups on iron oxide nanoparticles. The group of erichrome black-T, bromophenol blue, bromocresol green, and fluorescein was adsorbed more on the iron oxide surface as compared to methyl red, methylene blue, and methyl orange, which does not have any hydroxyl (−OH) groups. The association−OH of the dye in preferential adsorption phenomena has also been supported with FT-IR analysis. The adsorption process was studied by varying different regulating parameters like solution pH, initial dye, and iron oxide concentration and analyzed in terms of k...
238 citations
TL;DR: In this article, a hollow sea urchin-like α-Fe 2 O 3 nanostructures were successfully synthesized by a hydrothermal approach using FeCl 3 and Na 2 SO 4 as raw materials, and subsequent annealing in air at 600 °C for 2Âh.
Abstract: Hollow sea urchin-like α-Fe 2 O 3 nanostructures were successfully synthesized by a hydrothermal approach using FeCl 3 and Na 2 SO 4 as raw materials, and subsequent annealing in air at 600 °C for 2 h. The hollow sea urchin-like α-Fe 2 O 3 nanostructures with the diameters of 2–4.5 μm consist of well-aligned α-Fe 2 O 3 nanorods with an average length of about 1 μm growing radially from the centers of the nanostructures, have a hollow interior with a diameter of about 2 μm. α-Fe 2 O 3 nanocubes with a diameter of 700–900 nm were directly obtained by a hydrothermal reaction of FeCl 3 at 140 °C for 12 h. The response S r ( S r = R a / R g ) of the hollow sea urchin-like α-Fe 2 O 3 nanostructures reached 2.4, 7.5, 5.9, 14.0 and 7.5 to 56 ppm ammonia, 32 ppm formaldehyde, 18 ppm triethylamine, 34 ppm acetone, and 42 ppm ethanol, respectively, which was excess twice that of the α-Fe 2 O 3 nanocubes and the nanoparticle aggregations. Our results demonstrated that the hollow sea urchin-like α-Fe 2 O 3 nanostructures were very promising for gas sensors for the detection of flammable and/or toxic gases with good-sensing characteristics.
159 citations
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TL;DR: In this article, the authors focus on the properties of quantum dots and their ability to join the dots into complex assemblies creates many opportunities for scientific discovery, such as the ability of joining the dots to complex assemblies.
Abstract: Current research into semiconductor clusters is focused on the properties of quantum dots-fragments of semiconductor consisting of hundreds to many thousands of atoms-with the bulk bonding geometry and with surface states eliminated by enclosure in a material that has a larger band gap. Quantum dots exhibit strongly size-dependent optical and electrical properties. The ability to join the dots into complex assemblies creates many opportunities for scientific discovery.
10,737 citations
TL;DR: Semiconductor nanocrystals prepared for use as fluorescent probes in biological staining and diagnostics have a narrow, tunable, symmetric emission spectrum and are photochemically stable.
Abstract: Semiconductor nanocrystals were prepared for use as fluorescent probes in biological staining and diagnostics. Compared with conventional fluorophores, the nanocrystals have a narrow, tunable, symmetric emission spectrum and are photochemically stable. The advantages of the broad, continuous excitation spectrum were demonstrated in a dual-emission, single-excitation labeling experiment on mouse fibroblasts. These nanocrystal probes are thus complementary and in some cases may be superior to existing fluorophores.
8,542 citations
TL;DR: A comprehensive review of 1D nanostructures can be found in this article, where the authors provide a comprehensive overview of current research activities that concentrate on one-dimensional (1D) nanostructure (wires, rods, belts and tubes).
Abstract: This article provides a comprehensive review of current research activities that concentrate on one-dimensional (1D) nanostructures—wires, rods, belts, and tubes—whose lateral dimensions fall anywhere in the range of 1 to 100 nm. We devote the most attention to 1D nanostructures that have been synthesized in relatively copious quantities using chemical methods. We begin this article with an overview of synthetic strategies that have been exploited to achieve 1D growth. We then elaborate on these approaches in the following four sections: i) anisotropic growth dictated by the crystallographic structure of a solid material; ii) anisotropic growth confined and directed by various templates; iii) anisotropic growth kinetically controlled by supersaturation or through the use of an appropriate capping reagent; and iv) new concepts not yet fully demonstrated, but with long-term potential in generating 1D nanostructures. Following is a discussion of techniques for generating various types of important heterostructured nanowires. By the end of this article, we highlight a range of unique properties (e.g., thermal, mechanical, electronic, optoelectronic, optical, nonlinear optical, and field emission) associated with different types of 1D nanostructures. We also briefly discuss a number of methods potentially useful for assembling 1D nanostructures into functional devices based on crossbar junctions, and complex architectures such as 2D and 3D periodic lattices. We conclude this review with personal perspectives on the directions towards which future research on this new class of nanostructured materials might be directed.
8,259 citations
TL;DR: Monodisperse samples of silver nanocubes were synthesized in large quantities by reducing silver nitrate with ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP), characterized by a slightly truncated shape bounded by {100, {110}, and {111} facets.
Abstract: Monodisperse samples of silver nanocubes were synthesized in large quantities by reducing silver nitrate with ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP). These cubes were single crystals and were characterized by a slightly truncated shape bounded by {100}, {110}, and {111} facets. The presence of PVP and its molar ratio (in terms of repeating unit) relative to silver nitrate both played important roles in determining the geometric shape and size of the product. The silver cubes could serve as sacrificial templates to generate single-crystalline nanoboxes of gold: hollow polyhedra bounded by six {100} and eight {111} facets. Controlling the size, shape, and structure of metal nanoparticles is technologically important because of the strong correlation between these parameters and optical, electrical, and catalytic properties.
5,992 citations
IBM1
TL;DR: Thermal annealing converts the internal particle structure from a chemically disordered face- centered cubic phase to the chemically ordered face-centered tetragonal phase and transforms the nanoparticle superlattices into ferromagnetic nanocrystal assemblies that can support high-density magnetization reversal transitions.
Abstract: Synthesis of monodisperse iron-platinum (FePt) nanoparticles by reduction of platinum acetylacetonate and decomposition of iron pentacarbonyl in the presence of oleic acid and oleyl amine stabilizers is reported. The FePt particle composition is readily controlled, and the size is tunable from 3- to 10-nanometer diameter with a standard deviation of less than 5%. These nanoparticles self-assemble into three-dimensional superlattices. Thermal annealing converts the internal particle structure from a chemically disordered face-centered cubic phase to the chemically ordered face-centered tetragonal phase and transforms the nanoparticle superlattices into ferromagnetic nanocrystal assemblies. These assemblies are chemically and mechanically robust and can support high-density magnetization reversal transitions.
5,568 citations