One-Step Synthesis of Core(Cr)/Shell(γ-Fe2O3) Nanoparticles

Synthetic Approaches to Colloidal Nanocrystal Heterostructures Based on Metal and Metal-Oxide Materials

Composite inorganic nanoarchitectures, based on combinations of distinct materials, represent advanced solid-state constructs, where coexistence and synergistic interactions among nonhomologous optical, magnetic, chemical, and catalytic properties lay a basis for the engineering of enhanced or even unconventional functionalities. Such systems thus hold relevance for both theoretical and applied nanotechnology-based research in diverse areas, spanning optics, electronics, energy management, (photo)catalysis, biomedicine, and environmental remediation. Wet-chemical colloidal synthetic techniques have now been refined to the point of allowing the fabrication of solution free-standing and easily processable multicomponent nanocrystals with sophisticated modular heterostructure, built upon a programmed spatial distribution of the crystal phase, composition, and anchored surface moieties. Such last-generation breeds of nanocrystals are thus composed of nanoscale domains of different materials, assembled controllably into core/shell or heteromer-type configurations through bonding epitaxial heterojunctions. This review offers a critical overview of achievements made in the design and synthetic elaboration of colloidal nanocrystal heterostructures based on diverse associations of transition metals (with emphasis on plasmonic metals) and transition-metal oxides. Synthetic strategies, all leveraging on the basic seed-mediated approach, are described and discussed with reference to the most credited mechanisms underpinning regioselective heteroepitaxial deposition. The unique properties and advanced applications allowed by such brand-new nanomaterials are also mentioned.

Fine structural features of nanoscale zero-valent iron characterized by spherical aberration corrected scanning transmission electron microscopy (Cs-STEM)

An angstrom-resolution physical model of nanoscale zero-valent iron (nZVI) is generated with a combination of spherical aberration corrected scanning transmission electron microscopy (Cs-STEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDS) and electron energy-loss spectroscopy (EELS) on the Fe L-edge. Bright-field (BF), high-angle annular dark-field (HAADF) and secondary electron (SE) imaging of nZVI acquired by a Hitachi HD-2700 STEM show near atomic resolution images and detailed morphological and structural information of nZVI. The STEM-EDS technique confirms that the fresh nZVI comprises of a metallic iron core encapsulated with a thin layer of iron oxides or oxyhydroxides. SAED patterns of the Fe core suggest the polycrystalline structure in the metallic core and amorphous nature of the oxide layer. Furthermore, Fe L-edge of EELS shows varied structural features from the innermost Fe core to the outer oxide shell. A qualitative analysis of the Fe L(2,3) edge fine structures reveals that the shell of nZVI consists of a mixed Fe(II)/Fe(III) phase close to the Fe (0) interface and a predominantly Fe(III) at the outer surface of nZVI.

Void coalescence in core/alloy nanoparticles with stainless interfaces

The oxidation properties of nanoparticles with core/alloy microstructure and stainless steel like interfaces is described. In particular, 15-nm Fe/FeCr nanoparticles with a stainless steel like interface are prepared. These particles show a unique morphological transformation that is induced by surface oxidation, oxide passivation, and vacancy coalescence. This Kirkendall diffusion results in a tailorable oxide layer thickness, Fe-core size, as well as void size and symmetry. Much like the interface of bulk stainless steel, the interfacial FeCr oxide passivates oxidation, resulting in self-limited diffusion. Because of this, a highly uniform and stable core-void-shell morphology is observed.

The Dispersion of SiC Nanopowders in Ethanol

The dispersion of SiC nanopowders in ethanol solution was studied by sedimentation test, particle size measurement and TEM analysis. The dispersion behavior of SiC nanopowders in ethanol solution was strongly dependent on the pH values, types and amounts of dispersant. PEI was found to be effective for the dispersion of SiC nanopowders in ethanol solution. With the addition of PEI, the isoelectric points of SiC nanopowders in ethanol solution were at pH 9.5, and shift to pH 12.3. The stability of SiC suspension increased with the dispersant content increasing until reached 2.5 wt% PEI. The suitable pH value for the dispersion of SiC nanopowders should lower than 10.

Magnetic alloy nanoparticles from laser ablation in cyclopentanone and their embedding into a photoresist

The generation of nonoxidized magnetic alloy nanoparticles is still a challenge using conventional chemical reduction methods. However, because these nanoparticles are currently attracting much attention, alternative methods are required. In this context, the applicability of femtosecond laser ablation, which has evolved as a powerful tool for the generation of colloidal metal nanoparticles, has been investigated using the example of Ni(48)Fe(52) and Sm(2)Co(17) ablation in cyclopentanone. Besides stability and size measurements, the focus has been placed on the analysis of the elemental composition of nanoparticles, which proved the preservation of the stoichiometry of the target in Ni-Fe nanoparticles but not in Sm-Co. It is assumed that this is due to a greater difference in the heat of evaporation of the bulk alloy components in Sm-Co than in Ni-Fe. Hence, the successful generation of magnetic alloy nanoparticles is possible for alloys composed of elements with similar heats of evaporation. This one-step approach allows the fabrication of nanomagnetic polymer composites (e.g., with application prospects in microtechnology such as microactuators).

Transmission electron microscope-induced structural evolution in amorphous Fe, Co, and Ni oxide nanoparticles

The high-energy electron beams in transmission electron microscopes (TEM) are known to cause structural changes and damage in some materials. In this paper, we describe unique and reproducible TEM-induced changes to the morphology of amorphous metal oxide (Fe, Co, and Ni) nanoparticles. The studied particles were synthesized via literature methods and fully characterized by X-ray powder diffraction and time-resolved, low-dose TEM. As a result of electron beam irradiation, we observe these particles to transform from initially solid spheres to core/void/shell structures and eventually to hollow nanoparticles. The rate of these transformations depends on the size and composition of the particles but is not unique to the Fe oxide we previously reported. These data suggest that structural analysis of nanoparticles by TEM must consider the impact of the high-energy electron beam and use low-dose imaging.

Tunable synthesis and immobilization of zero-valent iron nanoparticles for environmental applications

Zero-valent iron (ZVI) nanoparticles were synthesized and immobilized using supported polyelectrolyte multilayers as nanoreactors. The ZVI nanoparticles so produced were found to exhibit superior reactivity with respect to chemical reduction and deactivation of trichloroethylene, a compound representative of a major class of chlorinated organic contaminants. Manipulation of polyelectrolyte multilayer architectures and synthesis conditions rendered the properties and reactivities of the resulting ZVI nanoparticles readily tunable. In particular, the reactivity of ZVI nanoparticles appears to depend strongly on certain architectural features of the polyelectrolyte multilayer that are regulated by the pH of the assembly media. The results suggest significant potential for use of the polyelectrolyte multilayer approach to fabricate reactive iron nanoparticles for a broad range of environmental applications, and provide a scientific basis for material design and optimization.