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Three powder samples of Ni nanochains formed of polycrystalline Ni nanoparticles with an estimated diameter of about 30 nm have been synthesized by a wet chemical method using different organic surfactants. These samples, having magnetically/structurally core-shell structures, all with a ferromagnetic Ni core, are Ni@Ni(3)C nanochains, Ni@Ni(SG) nanochains with a spin glass (SG) surface layer, and Ni@Ni(NM) nanochains with a nonmagnetic (NM) surface layer. The average thickness of the shell for these three samples is determined as about 2 nm. Magnetic properties tailored by the different surface magnetism are studied. In particular, suppression in the saturation magnetization, usually observed with magnetic nanoparticles, is revealed to arise from the surface magnetic states with the present samples.

The finite size effect on the antiferromagnetic transition temperature, TN, has been investigated with Co3O4 nanoparticles of 75, 35, and 16 nm in diameter. Along with the results from the previous experiments on the Co3O4 nanoparticles with average diameter of 8 and 4.3 nm, the variation of TN with the particle diameter, d, appears to follow the finite size scaling relation. The shift exponent is determined as λ=1.1±0.2 and the correlation length ξ0=2.8±0.3 nm. The value of the shift exponent is consistent with the description by the mean field theory. [ABSTRACT FROM AUTHOR]

Elaborate design of highly active catalysts from earth-abundant elements is important for the development of water-splitting devices. We have synthesized {2̅ 1 1} high index-faceted Ni12P5 nanoplates and Ni12P5 spherical nanoparticles (SNPs) by the one-step solvothermal method. The Ni12P5 nanoplates show enhanced hydrogen evolution reaction activity with a lower overpotential of −128 mV and a smaller Tafel slope of 60.6 mV dec−1 compared to Ni12P5 SNPs. Stability tests reveal exceptional durability of the catalyst. This study offers an attractive catalytic material for large-scale hydrogen production technology. [ABSTRACT FROM AUTHOR]

Abstract: Co-based (Co and Co3O4) nanoparticles were self-integrated into SiO2 nanotubes with a methodology based on the use of a Co salt as a template structure for the formation of SiO2 nanotubes. Within the confinement of tubular matrix of SiO2, the nanofibres of cobalt precursor, i.e., [Co(NH3)6](HCO3)(CO3)·2H2O, were treated in a H2 atmosphere with different parameters. With a sufficient reduction on the cobalt precursor, sphere-like Co-based nanoparticles are obtained, being well aligned in the interior space of the SiO2 nanotubes. With an insufficient reduction, platelet-like Co-based nanoparticles are formed, being arranged in a random manner inside the SiO2 nanotubes. The sufficiently reduced Co–SiO2 nanocomposite exhibits an open hysteresis loop in the low field region (<3kOe) and a paramagnetic response in high field (>3kOe) at 300K. An observed wide separation between the zero-field-cooling (ZFC) and field-cooling (FC) curves over the whole temperature region has demonstrated a characteristic feature of ferromagnetism with a magnetically anisotropic barrier diverting the easy axis from the axis of the applied field. The predominant factor leading to this anisotropic potential barrier is attributed to the shape anisotropy native to the one-dimensional arrangement of Co-based nanoparticles within the tubular matrix, i.e. SiO2 nanotubes. [Copyright &y& Elsevier]

Abstract: A novel Co complex [Co(NH3)6Cl3] nanorods with diameters of 150–200nm and 2–2.5μm in length were synthesized successfully through a simple solution chemical route. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and superconducting quantum interference device (SQUID) system. We propose a possible reaction process for the formation of Co(NH3)6Cl3. A control experiment shows that PVP plays a soft-template to uniform the morphology and size of the products. [Copyright &y& Elsevier]