Nickel Colloid Nanoparticles: Synthesis, Characterization, and Magnetic Properties

Abstract

Nickel nanoparticles stabilized in aqueous emulsion of copolymers were prepared in a few minutes using polyol assisted-microwave (MW) process. This approach based on the reduction of metal salt (NiCl2·6H2O) in the presence of low concentration of hydrazine hydrate (N2H4·H2O) using a commercial copolymer (latex) as both, reducing and stabilizing agents. The reaction parameters such as the precursor concentration, copolymer and MW power affect significantly the reaction rate and the shape/size (2.5 nm to 7 nm) of Ni nanoparticles. Ni NPs were stored at room temperature for approximately 6 months without any visible change, which indicate the important role of latex copolymer as a good stabilizer for Ni NPs, The structural and optical properties have been studied separately using UV–Visible spectroscopy, Transmission Electron Microscopy (TEM) and Energy-Dispersive X-ray Spectroscopy (EDXs). TEM images using high magnifications identified the Ni NPs as spherical shapes. The FTIR spectra indicate that Ni nanoparticles attached to the copolymers (latex) at the surface by the stretching vibration of O–H bond, which gives crucial information on the interface structure Ni NPs/Latex marked by a reduced coupling between spins at NPs surfaces. Magnetic properties were demonstrated using SQUID (Quantum Design Squid/VSM). The shift observed in hysteresis loop (M–H) measured at 2 K due to the spin–spin reduced coupling at the nanoparticles surfaces, which gives spin-glass like behavior in the system. In other hand, the zero-field-cooled (ZFC) and the field-cooled (FC) measurements under magnetic field of 100 Oe exhibited the blocking temperature TB that strongly depends on Ni particle sizes.