Surface-enhanced Raman spectroscopic investigation on surface plasmon resonance and electrochemical catalysis on surface coupling reaction of pyridine at Au/TiO2junction electrodes

Surface plasmon resonance (SPR) is proved to induce catalysis and generate surface-enhanced Raman scattering (SERS) effect. However, it remained a significant challenge in developing the efficient approach to in situ monitor the surface reaction and extending the SPR catalysis as a general approach in surface organic synthesis, especially for the C-C coupling. Herein, SPR from the Au nanoparticles played the bifunctional roles to induce the surface catalysis reaction and enhance the surface Raman signal. The SPR and electrochemical potential became two necessary external fields for the surface coupling reaction to produce 2,2 '-bipyridine, which was explored by SERS. The adsorbed pyridine molecules underwent a dimerization to producecis-configuration 2,2 '-bipyridine at the -0.7 V by appropriate laser irradiation. It demonstrated that the surface dimerization efficiency was critically dependent on the laser, potential, the solution properties, and so on. It was improved significantly at the relative negative potential and by 638 nm laser. The solvent with oxygen facilitated the surface dimerization reaction. Pd nanoparticles played the assistant role to capture the hydrogen released from the pyridine to accelerate the breaking of C-H bond and C-C coupling reaction. The surface reaction mechanisms involved the electrons transfer from Au to TiO(2)and injected electron delivery to alpha-H of pyridine for activation and the formation of carbon free radicals and coupling together to produce 2,2 '-bipyridine. This strategy is expected to further provide an alternative approach to the C-C coupling reaction and to extend the SPR and electrochemical catalysis to a practical application in surface modification as well as organic synthesis, and SERS is anticipated to be a promising in situ technique for the surface chemical reaction.