The Aikens Research Group

Chemical and Physical Properties of Noble Metal Nanoparticles

Gold and silver nanoparticles are useful for many applications. Gold nanorods have very tunable absorption properties and are finding application in cancer therapy. Other gold nanoparticles are useful as biolabels. Many nanoparticles have a sharp peak in their absorption spectrum called a surface plasmon resonance (SPR) band. This band depends sensitively on the size, shape, and composition of these nanoparticles, and thus properties of the nanoparticles can be tuned by adjusting these parameters. In addition, the SPR band is useful in techniques such as surface-enhanced Raman scattering (SERS) and LSPR sensing which can detect compounds at low concentration. Not all nanoparticles have a SPR band, and the smaller nanoclusters exhibit complex optical absorption properties that are characteristic of their size. Recently, both plasmonic and non-plasmonic nanoparticles have been used to enhance photocatalytic activity, so understanding these systems can lead to advances in renewable energy and fuels.

The Aikens group studies both monolayer-protected nanoclusters (such as thiolate-protected gold and silver nanoparticles) as well as bare nanoparticles using theoretical methods. We investigate physical properties of these nanoparticles such as optical and chiroptical absorption, paramagnetism, and luminescence. We also examine their chemical reactivity, including growth mechanisms (to understand how to control nanoparticle size and function), catalysis (to create new, valuable molecules), and ligand exchange (to improve functionality and biocompatibility). Furthermore, we study the electron dynamics in these systems to elucidate how excitation by sunlight can lead to novel reactivity.

This work has been funded by the Air Force Office of Scientific Research, the Department of Energy, and the National Science Foundation.

Catalysis and Reactivity on Nanostructured Metal Oxide Surfaces and Clusters

Bioinspired Water Splitting Catalysts

Development of renewable and clean sources of energy is one of the most pressing needs of the 21st century. Hydrogen production via water splitting has the potential to provide a clean alternative to fossil fuels. The best catalyst currently known for the water splitting reaction is the oxygen-evolving complex of Photosystem II, which contains a manganese-calcium oxide core. The Aikens group is examining aspects of this system that make it a good water splitting catalyst in order to aid in the development of synthetic catalysts with similar efficiencies.

This work is funded by the National Science Foundation (CAREER).

Biorenewable Materials

In order to develop a sustainable world, our current dependence on fossil fuels must be diminished. Because many of the polymers we use are derived from fossil fuels, replacement of petroleum-based monomers with biorenewable monomers is one possible way to decrease our reliance on nonrenewable resources. Polymers derived from biomass could potentially replace some petroleum-derived polymers, but fundamental research is required before this is viable. Starting materials derived from biomass typically possess a greater number of carboxylic acid and hydroxyl functional groups than petroleum-derived products. In consequence, these functional groups interact differently with catalyst surfaces than do hydrocarbons. Understanding the interactions of functional groups with catalyst surfaces is the first step to controlling the transformation of biomolecules into value-added chemicals. The Aikens group is currently interested in understanding how lactic acid binds to metal oxide surfaces. (This work is funded by the American Chemical Society Petroleum Research Fund.) The Aikens group collaborates with other researchers in the Center for Biobased Polymers by Design (CBPD) at Kansas State University.