J. Vimala

FACILE SYNTHETIC ROUTE FOR SYNTHESIS OF COBALT NANORODS AND DENDRITIC STRUCTURES USING A BOMB DIGESTION VESSEL

In this article, we report a simple and fast route for the synthesis of cobalt in the shape of nanorods (Co-NRs). It involves a modified polyol process in which a cobalt hydrazine complex was taken as a precursor with poly(vinylpyrrolidone) (PVP) molecules as a stabiliser in ethylene glycol (solvent) in a stainless steel bomb digestion vessel with Teflon inner lining. The solution was heated in the bomb at 200°C for three different reaction times 30, 60 and 90 min in performing the reaction. After the scheduled reaction, which resulted in a blackish colour turned-up from an initially pink-coloured sample, the samples were cooled down to room temperature. Recovered powders by repeated washing in water were studied for further characterisations. Reactions were analysed with Fourier transform–infrared spectroscopy and the XRD patterns of the samples reveal that the PVP molecules promptly control the formation of surface modified Co-NRs of a primarily face-centred cubic phase. These samples exhibit a ferromagnetic hysteresis loop showing a reasonably smaller saturation magnetisation comparing to bulk cobalt. SEM images reveal that the 30-min reaction product consists of nearly spherical nanoparticles (with an average size of 38 nm), whereas that of the 90-min reaction product displays a different shape of tiny nanorods, ∼25 nm diameter and 30–50 nm length.

Sacrificial seed mediated synthesis of copper nanopots by a modified polyol process

A novel modified polyol process has been developed for the synthesis of hollow copper nanopots. Cobalt hydrazine complex was employed for the preparation of cobalt nanoparticles (NPs), which in turn acted as sacrificial seeds for the production of Cu nanopots and nanocups. The reduction of Cu2+ to Cu0 was observed by the colour change from bluish green to dark brownish red. The reaction was followed with the help of a UV–Vis spectrometer. A surface plasmon band at 558 nm indicated the formation of Cu NPs. Chemical characterisation was carried out using inductively coupled plasma optical emission spectrometer and Leco gas analysers, CS-444 and TC-600. Crystal structure was obtained by carrying out X-ray diffraction studies and it showed a face centred cubic structure. Particle size and morphology were obtained from scanning electron microscope. On average, copper nanopots of size 72 nm could be obtained using this method.

Effect of chemical composition and Co-core size on the magnetic and magneto-transport properties of CoyAg100−y core–shell nanocrystallites

ABSTRACT This paper describes the applicability of a modified polyol process in conjunction with a transmetallation reaction in synthesis of CoyAg100−y nanocrystallites of a core–shell structure. The substitution Co → Ag is varied as 20 ≤ y ≤ 95 by tuning the microstructure with functional magnetic and giant magneto resistance properties. The existence of core–shell structures was confirmed through transmission electron microscope and the size of Co-core increased from 8 to 50 nm with decrease in Ag-content of the sample. The magnetic behaviour of the sample changed from a pseudo-superparamagnetic nature to ferromagnetic with increase in Co-core size. Normalised saturation magnetisation values increased from 89.5 to 128.6 emu/g with increase in size of Co-core; however, none of the ferromagnetic samples exhibited any magneto resistance (MR). A value of 2.0% MR was observed in case of Co20.6Ag79.4 which increased to a maximum of 3.6% MR for Co36.6Ag63.4 sample when measured at 5 K.