1. Chemical synthesis of structure-tailored metal nanoparticles (NPs)

Metal nanoparticles in three existing states (Fig1(a)), i.e. substrate-supported ligand-free NPs (SS-NPs), substrate-supported ligand-capped NPs (SSLC-NPs) and free-standing ligand-capped  NPs (LC-NPs), are currently being investigated in our group.

The prerequisite for structural control of NPs is to vary the size (Fig.1(b)). The local structure of these NPs is being tailored more systematically at the metal-ligand and metal-metal (multimetallic) interface, illustrated in Fig.1(c)-(e). The metal-ligand interaction can be controlled by selecting capping ligands with desired functional groups Moreover, biomolecules such as oligopeptides and proteins will also play an important role in our research towards biotechnological applications. The most interesting and technologically important area in structural control of NPs is to tailor the mixing patterns of metals (Fig.1(d),(e)). Particular interest is placed in control of the mixing pattern of superparamagnetic NPs, e.g. Fe@Au and Co@Pt core-shell NPs in light of their important applications in catalysis and biotechnology.

2. Understanding the atomic/local structure and electronic properties of NPs

Understanding the atomic arrangement of NPs, particularly multicomponent NPs, has been considered as a primary challenge in nanoscience. Element-specificity is a key requirement for selecting efficient research tools to study the local structure and electronic properties of these multicomponent metal NPs. Element-specific X-ray spectroscopy methods such as X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS) and associated methods have been widely considered as ideal tools for such studies of NPs and will used as the major research tools in the our research. The availability of synchrotron facilities will greatly enhance the capabilities of these X-ray techniques due to its ultra-high brightness and the widely tunable photon energies. Our expertise in XPS, XAFS and XAFS simulations (see Fig.2), in association with the availability of the recently installed Canadian national synchrotron facility, Canadian Light Source (CLS), is particularly advantageous in systematically understanding the structure and electronic properties of the multicomponent NPs proposed in the research.

Moreover, some laboratory-based element-specific and surface-sensitive techniques will be used to promptly study the structure and electronic properties of NPs. The recently funded surface photovoltaic spectrometer (NSERC RTI) will provide valuable information about the surface properties of metal NPs with varied capping ligands. XPS from the Institute for Research in Materials (IRM) at Dalhousie University will be used to conveniently collect X-ray data prior to synchrotron XPS experiments.

3. Applications in catalysis

The synthesis and X-ray studies of NPs with tailored structures will be a solid basis for selecting highly efficient nano-catalysts. One important application of these atomic-structure-tailored nanoparticles is in catalysis (e.g. fuel-cell catalysts). We are particularly interested in the studies of Fe, Co or Ni-based core-shell nanoparticle catalysts that exhibit advantages such as tunable reactivity, low cost and easy magnetic separation (Fig.3).

4. Biomedical and biotechnological applications

Our research in this area is being conducted in collaboration with a few biochemical/biomedical scientists. The first project is being conducted in collaboration with Dr. Michael Dunbar (clinic orthopedist in Halifax Infirmary Hospital) on the orthopedic applications of Au NPs as a chemical linker and nano-template to immobilize functional proteins, which will enhance the growth of bone cells onto the implants.

In the second project, metal NPs are used as a chemical scaffold to regulate the enzymatic activity (see illustration in Fig.4). A model enzyme system, lysozyme, is currently being studied in our group.

In the third project, as illustrated in Fig.5, superparamagnetic core-shell NPs with Au as the shell will be explored for protein-separation. It should be noted that these biocompatible core-shell superparamagnetic NPs are also considered to be promising materials for many other applications such as drug delivery, MRI contrast agents and hyperthermia therapy.