Carbonization of solvent and capping agent based enhancement in the stabilization of cobalt nanoparticles and their magnetic study

Abstract

We describe a hybrid synthetic protocol, the solvated metal atom dispersion (SMAD) method, for the synthesis and stabilization of monodisperse amorphous cobalt nanoparticles. By employing an optimized ratio of a weakly coordinating solvent and a capping agent monodisperse colloidal cobalt nanoparticles (2 AE 0.5 nm) have been prepared by the SMAD method. However, the as-prepared samples were found to be oxidatively unstable which was elucidated by their magnetic studies. Oxidative stability in our case was achieved via a pyrolysis process that led to the decomposition of the organic solvent and the capping agent resulting in the formation of carbon encapsulated cobalt nanoparticles which was confirmed by Raman spectroscopy. Controlled annealing at different temperatures led to the phase transformation of metallic cobalt from the hcp to fcc phase. The magnetic behaviour varies with the phase and the particle size; especially, the coercivity of nanoparticles exhibited strong dependence on the phase transformation of cobalt. The high saturation magnetization close to that of the bulk value was achieved in the case of the annealed samples. In addition to detailed structural and morphological characterization, the results of thermal and magnetic studies are also presented.

Fabrication of graphene supported carbon‐coating cobalt and carbon nanoshells for adsorption of toxic gases and smoke

“…Compared with GO, the I D /I G of Co 3 O 4 ‐RGO increases due to the decrease in the average size of the sp 2 graphtic domains after conjugating with Co 3 O 4 . In the Raman spectra of Co/C‐GNS, apart from the D and G bands, an additional peak at 687 cm −1 is well consistent with the typical Raman mode of metallic Co . The I D /I G of Co/C‐GNS is 1.55, which indicates the pyrolysis process promotes the formation of graphitic carbon (that is graphitic CNS).…”

Air‐Stable Carbon‐Fe Based Magnetic Nanostructures

“…Since the carbon deposited over the iron sample is amorphous, its PXRD pattern (Figure ) is featureless. It has been well demonstrated that annealing metal nanoparticles capped by long chain hydrocarbons results in formation of a carbon shell around the nanoparticles wherein, metal nanoparticles catalytically graphitize the organic ligands at moderate temperatures , . Further, annealing the sample at 300 °C for 24 h, resulted in a mixture of α‐Fe and Fe 3 C (small quantity); the PXRD pattern of this sample has been deposited in Figure S1.…”

“…It has been well demonstrated that annealing metal nanoparticles capped by long chain hydrocarbons results in formation of a carbon shell around the nanoparticles wherein, metal nanoparticles catalytically graphitize the organic ligands at moderate temperatures. [21,22] Further, annealing the sample at 300°C for 24 h, resulted in a mixture of α-Fe and Fe 3 C (small quantity); the PXRD pattern of this sample has been deposited in Figure S1. It was noted that when the duration of annealing was increased from 12 h to 24 h at 300°C, carbon formed diffuses into the Fe crystal, resulting in the formation of small grains of Fe 3 C as evidenced by the PXRD pattern ( Figure S1) and has been reported earlier in the literature.…”

One-pot synthesis of cobalt nanoparticle-embedded lamellar sheets by using inorganic complex via thermal decomposition route

“…Furthermore, elongated single domain particles present high magnetic anisotropy. The combination of high anisotropy with high saturation magnetization makes this kind of particles very attractive as precursors for hard magnetic materials [3]. Ferromagnetic cobalt nanoparticles has received considerable attention due to its extraordinary electrical, catalytic, and magnetic properties, which are of interest for basic scientific research and potential technological applications in, for example, high-density information storage, catalysts, magnetic sensors, magnetic fluids, etc.…”

“…In selective synthesis of metallic nanoparticles, capping molecules, micelles and complexing agents are usually applied to control the sizes and shapes of materials [3,13] and in many cases it prevents oxidation of the products. By controlling the growth of the particles, surfactants play an important role in synthetic procedure and result in nanoparticles with controlled size and a special morphologies.…”