Iron-based microstructured or nanostructured materials, including Fe, γ-Fe2O3, and Fe3O4, are highly desirable for magnetic applications because of their high magnetization and a wide range of magnetic anisotropy. An important application of these materials is use as an electromagnetic wave absorber to absorb radar waves in the centimeter wave (2−18 GHz). Dendrite-like microstructures were achieved with the phase transformation from dendritic α-Fe2O3 to Fe3O4, Fe by partial and full reduction, and γ-Fe2O3 by a reduction−oxidation process, while still preserving the dendritic morphology. The investigation of the magnetic properties and microwave absorbability reveals that the three hierarchical microstructures are typical ferromagnets and exhibit excellent microwave absorbability. In addition, this also confirms that the microwave absorption properties are ascribed to the dielectric loss for Fe and the combination of dielectric loss and magnetic loss for Fe3O4 and γ-Fe2O3.

Hierarchical Dendrite-Like Magnetic Materials of Fe3O4, γ-Fe2O3, and Fe with High Performance of Microwave Absorption

http://fulltext.calis.edu.cn/rsc/Green%20Chemistry/b804703k.pdf

Green synthesis of silver and palladium nanoparticles at room temperature using coffee and tea extract

Metal nanocrystals with highly branched morphologies are an exciting new class of nanomaterials owing to their unique structures, physicochemical properties, and great potential as catalysts, sensing materials, and building blocks for nanoscale devices. Various strategies have recently been developed for the solution-phase synthesis of metal nanocrystals with branched morphologies, such as multipods and nanodendrites. In this Minireview, the procedures and mechanisms underlying the formation of branched metal nanocrystals are presented in parallel with recent advances in synthetic approaches based on kinetically controlled overgrowth, aggregation-based growth, heterogeneous seeded growth, selective etching, and template-directed methods, as well as their properties for catalytic or electrocatalytic applications.

Metal nanocrystals with highly branched morphologies.

This Review is focused on the recent progresses in the synthetic approaches to the precise control of structure, size, shape, composition and multi-functionality of metal and metal alloy nanoparticles. Many of these strategies have been developed based on colloidal methods, and to limited extent, the galvanic and other methods. The shape, size and composition often govern the chemical and catalytic properties that are important for electrochemical energy applications. The structure–property relationship and the design in controllable structures and morphologies for specific reactions such as oxygen reduction reaction (ORR) are emphasized.

Synthesis of colloidal metal and metal alloy nanoparticles for electrochemical energy applications

Comprehensive knowledge over the shape of nanomaterials is a critical factor in designing devices with desired functions. Due to this reason, systematic efforts have been made to synthesize materials of diverse shape in the nanoscale regime. Anisotropic nanomaterials are a class of materials in which their properties are direction-dependent and more than one structural parameter is needed to describe them. Their unique and fine-tuned physical and chemical properties make them ideal candidates for devising new applications. In addition, the assembly of ordered one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) arrays of anisotropic nanoparticles brings novel properties into the resulting system, which would be entirely different from the properties of individual nanoparticles. This review presents an overview of current research in the area of anisotropic nanomaterials in general and noble metal nanoparticles in particular. We begin with an introduction to the advancements in this area followed by general aspects of the growth of anisotropic nanoparticles. Then we describe several important synthetic protocols for making anisotropic nanomaterials, followed by a summary of their assemblies, and conclude with major applications. (Published: 16 February 2011) Citation: Nano Reviews 2011, 2 : 5883 - DOI: 10.3402/nano.v2i0.5883

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Anisotropic nanomaterials: structure, growth, assembly, and functions

In this study, a well-defined dendritic silver nanostructure can be large-scale synthesized in AgNO3 (aqueous) at room temperature. The nonequilibrium and anisotropic growth at different silver ion concentrations result in controllable morphologies and morphological evolution. At high silver ion concentrations, a strong anisotropic growth contributes to a fine single crystalline silver dendrite. As the reaction proceeds, the dendritic structure transforms into a thermodynamically stable hexagonal structure. At a relatively low silver ion concentration, a particle-aggregated fractal pattern can be obtained due to relatively small anisotropy. As the reaction time increases, the transition from polycrystalline aggregates to a single crystal during silver dendritic growth can be observed. An oriented attachment mechanism can be used to explain the structural and morphological evolution of silver nanostructures. Silver nanostructures with various morphologies are expected to have significant potential applicat...

Dendritic Silver Nanostructure Growth and Evolution in Replacement Reaction

We explored a route to prepare a high enhancement factor of SERS substrate via a high density of Ag flowerlike pattern. The finite difference time domain (FDTD) calculations indicate that the Ag flowerlike pattern may demonstrate a high quality SERS property owing to the high density and abundant hot spot characteristic. Using an unusually high overpotential with electrodeposition system, the fractal flowerlike patterns and the high density nanoparticle arrays were experimental synthesized. The SERS measurement of above different Ag nanostructures verified the predications from the FDTD calculation.

Yan Yi

Papers

Dendritic Silver Nanostructure Growth and Evolution in Replacement Reaction

A route to increase the enhancement factor of surface enhanced Raman scattering (SERS) via a high density Ag flower-like pattern