About our research
Our interest in nanoparticle (NP) research covers two general aspects: (1) Chemical synthesis and self-assembly of NPs; (2) Elaboration of functional NPs for applications in a) Catalysis, b) Biomedicine and c) Energy.
We utilize the so called “bottom-up” approach to synthesize monodisperse nanoparticles (NPs). By controlling chemical reaction conditions in solutions, we have atoms “stacked” in certain dimensions and directions. As a result, we are able to tune NP sizes, compositions, and shapes. We are now exploring novel “bottom-up” approaches to prepare multi-component alloy, core/shell and dumbbell-like NPs. These NPs are stabilized by a lipid-type molecule (surfactant) and are readily dispersed in a specific solvent. The stable dispersion allows self-assembly of these NPs on a solid support via solvent evaporation, as illustrated in (Figure 1). Therefore, these NPs can be tuned to have specific physical and chemical properties for important nano-technological applications.
With the dimension controls achieved from the “bottom-up” synthesis, magnetic NPs can be made ferromagnetic or superparamagnetic. Superparamagnetic NPs are especially important for biological applications as they have no net magnetization at the biologically relevant temperature and therefore no strong dipolar interactions, which facilitate their long-term stabilization. They can be magnetized under an external magnetic field, reaching ferromagnet-like magnetizations. Once properly functionalized, these NPs are bio-compatible and target-specific (Figure 2), and have been explored extensively as sensitive probes for magnetic resonance imaging, magnetic fluid hyperthermia and smart drug delivery.
With the decrease in NP size, a large fraction of atoms become exposed. More importantly, NPs in this nanoscale have large fraction of crystal facets, edge- and corner-sites that may dominate the interaction between NP surface and molecules and show much enhanced catalysis, such as electrocatalysis for CO2 reduction and O2 reduction reactions (Figure 3). Therefore, the controls of NP size, shape, composition are essential for rational tuning of NP electronic and geometric structures for catalytic applications. At present, we are developing efficient NP catalysts for applications in next generation energy devices, such as fuel cells, metal-air batteries and water-splitting cells, as well as in selective electrochemical reduction of CO2 to CO and other hydrocarbons.
Development of strong magnet for power and magnetic applications requires new materials with high energy density (kJ per cubic meter). Nanocomposites containing exchange-coupled “hard” and “soft” phases in nanoscale can show much enhanced ferromagnetism and may serve as ideal materials for building super-strong magnets. We have been pursing chemical synthesis and self-assembly of magnetic NPs into nanocomposite magnets. By independently tuning the size and composition of each component, we are able to tailor the composite nanostructures and therefore their magnetic properties. Our studies provide both a model for fundamental understanding of magnetic properties within the nanostructures and a practical route to novel devices for magnetic energy storage applications. (Figure 4). By independently tuning the size and composition of each component, we are able to tailor the composite nanostructures and therefore their magnetic properties. Our studies provide both a model for fundamental understanding of magnetic properties within the nanostructures and a practical route to novel devices for magnetic energy storage applications.