Abstract: Based on the polyelectrolyte-mediated electrostatic adsorption (layer by layer method), Au@TiO2 core shell nanoparticles were prepared through the modification of the different layers of TALH on Au nanoparticles followed with a calcination. By using thiophenol as probe, the surface enhanced Raman scattering (SERS) effect was observed from Au nanoparticles attached with the TiO2 precursor. The SERS effect was dependent on the shell thickness. After coated with three layers of TALH, SERS effect from the Au nanoparticles core disappeared. The photocatalytic processes of methylene blue (MB) was investigated on Au@TiO2 by in situ SERS under UV illumination. The observation of C-N-C skeleton deformation vibrational mode at 450 cm-1 and 504 cm-1 indicated that MB adsorbed on the Au@TiO2 surface in a dimmer or polymer formation at the initial stage. With the increase of the UV illumination time, the band at 481cm-1 assigned to the monomer of MB was enhanced and the bands at 1180 cm-1 and 1073 cm-1 assigned to the C-H relevant vibrational modes disappeared. It indicated that the photocatalytic degradation of MB on Au@TiO2 underwent the transformation of dimmer or polymer to the monomer initially, followed with the degradation of methyl group. The in situ SERS technique combined with UV illumination might be developed as one of powerful tools for monitoring the photocatalytic reactions.

Key words: Au@TiO2 core shell nanoparticles, Surface enhanced Raman spectroscopy, Layer-by-layer technique, Photocatalysis, Mechanism