Extending SERS to Dispersions for Applications in Catalysis
Summary
Dispersible SERS-active superstructures have been prepared as a tool in the study of liquid-phase catalytic reactions by Raman spectroscopy. These superstructures are composed of functionalized \ce{SiO2} nanospheres that are densely covered by Au nanoparticles (NPs) to ensure the presence of interparticle gaps of a few nanometers. Upon illumination with laser light electromagnetic hot spots are formed in these gaps, which results in an enhancement of Raman scattering. An ultrathin (1-2 nm) \ce{SiO2} shell protects these plasmonic superstructures and enables the adsorption of catalytic NPs. Raman scattering of molecules involved in reactions at the catalytic surface is enhanced by the hot spots. Since these superstructures are dispersible, liquid-phase catalytic reactions could now be studied. In the second part of this thesis, another approach to obtain SERS-active structures is discussed, in which Au NP clusters are formed using an organic linker molecule. The synthesis of these superstructures and Au NP clusters is followed by characterization with TEM, UV-Vis spectroscopy and DLS. With these techniques the formation of functionalized \ce{SiO2} spheres with a dense layer of Au NPs on the surface was demonstrated. Successful cluster formation was indicated as well. With Raman spectroscopy the SERS activity of the superstructures and Au NP clusters is confirmed.