LIGHT-DRIVEN SYNTHESIS OF NANOMATERIALS
Nanomaterials offer unique opportunities for the conversion of sunlight into chemicals. Thanks to their sub-wavelength size, nanoscale objects interact with light in unconventional ways. Metal nanoparticles, for example, are capable of concentrating light into infinitesimal volumes, much smaller than the light’s own wavelength, enabling strongly localised temperature gradients and high electric field “hot spots”, and even catalysing “impossible” reactions.
In our research group we exploit such unconventional light-matter interactions to optically control chemical reactions which are sensitive to temperature and electric fields. For this reason we have developed a setup that allows shining tunable monochromatic radiation on a cuvette containing a solution of resonant plasmonic nanoparticles. The setup also allows simultaneous measuring of the absorption spectra of the solution to follow the evolution of the reactions occurring at the surface of the nanoparticles. Our aim is to develop a radical new approach to the synthesis of nanomaterials for solar fuel applications, using properly tuned light as the driving force for the reaction. In particular, we are currently developing photothermal syntheses of metal/metal-oxide core/shell nanoparticles and light driven self-assembly of plasmonic dimers.
Localised surface plasmon resonances (LSPRs) are collective oscillation of free electrons in metal nanoparticles, driven by an external electromagnetic field. The most studied metals in the field of plasmonics are typically coinage metals, such as gold, silver, and copper, as their plasmon resonances occur in the visible part of the spectrum. Under certain conditions, LSPRs can decay into highly non-equilibrium charge carriers, commonly referred to as hot-electrons or hot-holes. These energetic charge carriers can be harvested on metal nanoparticles used as heterogenous catalysts, to give rise to completely new catalytic properties. In the NEA group we study the fundamentals of plasmon catalysis by applying a combination of ensemble and single-particle spectroscopic techniques.
Several energy storage technologies, from lithium-ion batteries to hydrogen storage systems, are looking at the use of nanostructured materials. Nanomaterials typically display improved storage capacities, longer cycling stability and faster charging dynamics. Studying solute intercalation in nanomaterials is however challenging and so far has relied on ensemble experiments. In collaboration with the group of Jennifer Dionne at Stanford University, we study hydrogen-induced phase transitions in single metal nanoparticles, making use of an environmental transmission electron microscope.