(503g) A Straightforward Technique to Control the Oxidation of Amorphous Cobalt Nanoparticles During Synthesis Using DMSO

Magnetic nanoparticles have attracted a great deal of interest lately because of their unique magnetic properties and have a wide range of potential applications. For example, nano-scale magnetic particles have enhanced magnetic susceptibility and saturation compared to their bulk-scale counterparts.  Cobalt nanoparticles can exhibit a superparamagnetic behavior, which makes these particles particularly useful as contrast agents in Magnetic Resonance Imaging (MRI). However, many of the techniques commonly used to produce well-defined cobalt nanoparticles involve the use of harsh reagents and synthesis conditions, and may require days to produce a single sample of nanoparticles.  Furthermore, it is often difficult to produce cobalt nanoparticles because they have a tendency to become overly oxidized, and can subsequently agglomerate and precipitate from the solution.

We have developed a single-step method to synthesize and stabilize cobalt nanoparticles using an FDA-approved, functional solvent, dimethyl sulfoxide (DMSO).  Moreover, this research demonstrates that DMSO can be a multi-functional component in nanoparticle synthesis by serving concomitantly as a solvent and as a stabilizing agent that effectively suppresses nanoparticle growth and prevents excessive oxidation of the nanoparticle surface. The size and morphology of the particles were determined using TEM imaging analysis.  In addition, we have performed a variety of different characterization techniques to investigate the interaction of the cobalt nanoparticles with the DMSO stabilizing molecules, including FT-IR, XPS, and XRD. Using these techniques, we found that both the sulfur and oxygen functional groups on the DMSO molecules interact with the nanoparticle surfaces via a resonance hybrid structure that stabilizes the nanoparticles.  We have also found that these cobalt nanoparticles are amorphous when synthesized at room temperature.  Ongoing studies in our lab are focused on subjecting the cobalt nanoparticles to a variety of different temperatures post-synthesis in order to determine the minimum temperature needed to induce oxidation and crystallinity within the particles. In addition, the magnetic behavior of these amorphous cobalt nanoparticles compared to the magnetic behavior of crystalline cobalt and cobalt oxide nanoparticles will be discussed.