(705a) Tunable Assembly of Metallic and Magnetic Nanoparticle Clusters in DMSO Solvent Systems

A variety of different techniques have been developed in the last several years to synthesize various metal and magnetic nanoparticles of controlled size, but these popular methods are often time-intensive and require the use of harsh and expensive solvents and reagents.  One step to further simplify and improve nanoparticle synthesis would involve development of a method that uses a single molecule “functional solvent” for both solvation and nanoparticle stabilization. This study explores the production of cobalt and gold nanoparticles using simple and sustainable synthesis techniques which employ the use of a dimethyl sulfoxide (DMSO) functional solvent.  Previous work in our lab has demonstrated the successful use of DMSO as a functional solvent to produce monodisperse samples of palladium nanoparticles.  It was found that both the sulfur and oxygen functional groups on the DMSO molecules interact with the nanoparticle surfaces via a resonance hybrid structure which very effectively stabilize the nanoparticles.  Similarly, this synthesis technique has been extended to produce other nanoparticle systems in our lab.  For example, DMSO has recently been found to successfully function as both the solvent and the stabilizing agent to produce cobalt nanoparticles of precise size that can be tunably assembled into nano-scale clusters of controlled sizes by variations in synthesis temperature, thereby affording unique opportunities to affect the clusters’ physicochemical properties, such as magnetism.   Moreover, the solubility and dispersibility of these cobalt nanoparticle clusters can then be further manipulated by introducing polar co-solvents (e.g. water, ethanol) to the nanocluster dispersions after synthesis to redisperse nanoparticles and clusters of different sizes.  It has been found that the redispersibility of these cobalt nanoparticle clusters into individual single-crystalline nanoparticles is simply the result of the preferential solvation that may occur between the DMSO molecules already present in the solution and the newly introduced co-solvent.  Subsequently, it has been found that coupling DMSO with other molecules, such as fatty acids, produces nanoparticle dispersions that are stable for a longer duration than those produced without a fatty acid stabilizing agent.  The use of UV-vis spectroscopy to understand the reduction of both the bulk-scale cobalt and gold metals to the nano-scale and analyze any unreduced metallic intermediates that may persist during nanoparticle formation will be discussed. Furthermore, the size of these cobalt and gold nano-scale particles were investigated using TEM, and the interaction between the nanoparticle surface and the DMSO solvent/fatty acid stabilizing agent was studied using FT-IR.