Executive Summary : | Heterogeneous catalysis is one of the fundamental pillars of chemistry and pharmaceutical industries. Therefore, the progress in elucidating heterogeneous catalysis with plasmonic nanostructures in real experimental condition requires an effective method, to manipulate the hot carriers on the surface and discern the reacting species at the interfaces. Surface-enhanced Raman scattering (SERS) techniques to investigate heterogeneous catalysis are rare in liquid phase. Herein, we propose a liquid-state SERS based method to visualize heterogeneous photocatalytic C-C/C-N coupling reaction using 4-bromothiophenol and benzylamine, respectively as representative molecules, on bimetallic Ag-Au, Ag-Cu, Ag-Al and Cu-Al and trimetallic Ag-Au-Cu, Ag-Cu-Al alloy substrates on a coverslip with tunable surface compositions. Plasmonic materials by virtue of intense localized surface plasmon resonances (LSPR), can enhance the applied electromagnetic field and subsequently the Raman scattering of the adsorbed organic molecule on the metal surface. This technique, known as surface-enhanced Raman scattering (SERS), even allows us to detect the Raman spectra of a single-molecule and has been demonstrated as a powerful tool to investigate the molecular evolution in heterogeneous catalysis. Simultaneously, the LSPRs also generate energetic hot-carriers, offering the possibility to drive a catalytic reaction. This combination of ultrasensitive chemically specific label-free detection and the ability to generate hot electrons and holes, endows plasmonic nanostructures the ability to visualize and manipulate the heterogeneous catalysis at single molecule level. Three different laser excitation sources, 457 nm, 532 nm and 632.8 nm, will be used for the study for the above-mentioned substrates, possessing different LSPR maxima. Although few SERS based plasmon-activated catalysis studies have been reported already, but most of these substrates lose their SERS efficiency as they agglomerate, degrade under different chemical stimuli and most importantly they are not suitable in liquid condition. But, the liquid-state measurement is very important as it can be extended to investigate a wider range of catalytic reactions to understand and propose new mechanisms, using various hole and electron scavengers. In this project, the main aim is to investigate how a photocatalytic reaction depends on the plasmonic as well as the chemical properties of the bi- and tri-metallic alloy substrates via in-situ SERS measurement. |