Characterization of reaction pathways and mechanisms, and the verification of surface intermediate species provide valuable insights to the nature of photocatalytic reaction at the molecular level and enable rational design of photocatalytic systems towards improved activity, selectivity and efficiency. SERS, which utilizes optically excited coherent oscillations of conduction electrons on a rough metal surface to create drastic enhancement in the Raman signals of absorbed molecules, is a unique spectroscopic detection technique that offers both surface-sensitive and chemical-bond specific information, ideal for the direct sensing of surface intermediates of chemical reactions. In addition, the ability of SERS to access low frequency vibration modes from 1100 cm-1 down to ~100 cm-1 allows direct detection of surface intermediate formation on metal and metal oxide catalysts, such as M=O, M-O-H and M-O-M, making it highly promising for in-situ spectroscopic study of heterogeneous catalysis reactions. We designed large area Ag nanocrystal monolayer as novel SERS platforms for real time spectroscopic monitoring of surface intermediates during heterogeneous catalytic reactions to advance the fundamental understanding of reaction mechanisms. Such platform would offer direct access to the vibrational fingerprints of surface intermediate species of nanocrystalline catalysts deposited on the film during photocatalytic reactions. As a model reaction system to demonstrate the feasibility of our design, a photocatalyst monolayer of TiO2 nanoplates decorated with co-catalyst Pt nanoclusters was overlaid onto the Ag hybrid SERS platform. Water oxidation reaction was performed under UV irradiation and surface intermediates on TiO2 surface, including surface peroxo, hydroperoxo and hydroxo, were successfully identified on these SERS platforms.

Surface enhanced Raman spectroscopy for real-time observation of intermediates for photocatalytic reactions

249th National Meeting (2015)

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