Search

A series of highly uniform one-dimensional Ni nanochains, with diameters ranging from 20 to 200 nm, have been synthesized by a facile, template-free, wet chemical method at diverse temperature and magnetic field. Our results indicate that the crystallite size, diameter and length of the prepared nanochains depend critically on the reaction temperature. The characteristic thermodynamic cohesive energies, ΔEDand ΔEL, are obtained for the formation of the Ni nanochains. In addition, the chain length also depends on the applied field because of the Zeeman energy of the magnetic Ni nanoparticles. For the morphology control, an external field is required in order to obtain axially aligned rather than dendritic nanochains. The size-dependent magnetic properties are studied systematically. The saturation magnetization is shown to reduce inversely with the chain diameter, attributable to a core−shell structure. The thickness of the shell which encloses the ferromagnetic Ni core is determined to be about 2.3−3.4 nm.

A series of pure Ni thin chains with particle diameters ranging from 15 to 80 nm were successfully synthesized by a wet chemical method. Magnetization measurements for the Ni chains reveal that the saturation magnetization increases and the coercivity decreases with increasing particle diameter. The magnetization reversal mechanism of both the samples with a diameter of 30 and 50 nm can be described by the model of “chain of spheres”. Using the fanning mode, the calculated coercivities and the remnant ratios agree well with the experimental results. Surprisingly, the coercivity is greatly enhanced, reaching as high as 790 Oe at T= 5 K for the Ni chains with a diameter of ∼15 nm, which are composed of single-crystal particles. Meanwhile, in the degradation of pentachlorophenol (PCP) solutions with Fe0nanoparticles as reducing agents, Ni nanochains with a diameter of ∼80 nm were added, and the results indicate that the sample could serve as a good catalyst in dechlorination systems.

One-dimensional (1D) chainlike arrays of hollow magnetic Fe3O4spheres have been prepared by simply aging magnetically preassembled Fe nanoparticles in aqueous solution at room temperature. The diameter of the 1D nanomaterials is about 100−200 nm, and the length is up to 1−3 μm, observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The structure and magnetic properties of the Fe3O4hollow chains were characterized by X-ray powder diffraction (XRD) and via a superconducting quantum interference device (SQUID) magnetometer. Mechanism investigations on the time dependent process reveal these hollow nanostructures were formed based on the nanoscale Kirkendall effect. Besides the aqueous microenvironment, the partial pressure of oxygen is of great importance in the formation of 1D chainlike Fe3O4hollow nanostructures.

Nickel nanochains assembled with submicrometer-sized hollow spheres were synthesized through a mild polyol reduction method by using PVP as the soft template. The resulting fiberlike superstructures were characterized by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. A self-assembly mechanism of PVP-assisted bubble templating is responsible for the formation of hierarchical superstructures. It was found that PVP concentration plays a key role in determining both the morphology and the further self-assembly process of nickel hollow fibers. This first synthesis of such hierarchical structures implies a simple and inexpensive way to prepare transition metal superstructures on a large scale. Magnetic measurements by SQUID were also carried out to explore their magnetic properties; the micromagnetic simulation result by OOMMF code showed good agreement with the characters of our samples.

Manganese oxides are important materials in many applications. We describe, for the first time, the facile one-pot synthesis of highly crystallined -MnO2nanodisks assembled from nanoparticles through a novel wet chemical route. Morphology evolutions, magnetic properties, and phase transitions are also studied by transmission electron microscopy, scanning electron microscopy and thermal gravimetric analysis. A mechanism for the formation of the -MnO2nanodisks as well as their inner structure is proposed based on controlled experiments. The key to the successful preparation of this novel MnO2nanostructure has been a synergic control of a surfactant, polyvinylpyrrolidone, and a solvent, dimethyl sulfoxide, capable of stabilizing the microreactors and promoting the assembly of manganese nanoparticles.