Complex bifunctional metal nanostructures for in situ monitoring of nanoparticle-catalyzed reactions by surface-enhanced Raman spectroscopy

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In situ monitoring of heterogeneously catalyzed reactions requires interface/surface-selective techniques. Surface-enhanced Raman spectroscopy (SERS) provides molecular structural information on chemical species adsorbed onto the surface of plasmonic nanostructures such as noble metal nanoparticles. SERS and catalysis have no direct topical overlap in terms of nanoparticle functionalities since plasmonic/SERS and catalytic properties are usually disjunct. Therefore, applications of colloidal SERS in heterogeneous catalysis are currently rare, despite the wealth of chemical information accessible by vibrational spectroscopy. In order to overcome the limited use of SERS in heterogeneous catalysis, bifunctional metal nanostructures with catalysts inside the localized surface plasmon resonance field of the plasmonic metal are required. The central aim of this proposal is to design and synthesize tailor-made bifunctional metal colloids with both plasmonic/SERS and catalytic activities for in situ monitoring of nanoparticle-catalyzed reactions. Complex metal superstructures comprising a silica shell-isolated SERS-active core and catalytically active satellite particles assembled onto the core as well as bifunctional hybrid nanoparticles will be synthesized and analyzed with respect to their SERS and catalytic activities. Computational simulations will be performed in order to understand and predict the plasmonic properties of the bifunctional nanostructures. SERS monitoring of model reactions will be carried out by using microfluidic devices to study the kinetics of heterogeneous catalysis on the surface of the bifunctional nanostructures. Experimental SERS spectra will be analyzed with multivariate methods to obtain quantitative information on the involved chemical species and molecular changes during the catalytic reaction. For expanding this approach to molecules without surface-seeking groups, the bifunctional nanostructures will be coated for either capturing or enriching the involved species near the metal surface. Finally, via investigations at the single-particle level, we aim at establishing fundamental correlations between the morphology of a bifunctional nanostructure and both its catalytic and plasmonic/SERS activities.