Adsorption of 4-mercaptopyridine onto laser-ablated gold, silver and copper oxide films: A comparative surface-enhanced Raman scattering investigation

Laser ablations of gold, silver and copper metals in aqueous solution were performed. UV/Vis spectra indicate that Au, Ag and CuO nanoparticles were produced by this method. In order to obtain a strong surface-enhanced Raman scattering (SERS) effect, gold, silver and copper oxide films were fabricated by depositing laser-ablated colloids on aluminum foil. This procedure formed a rough surface with a large number of aggregated particles based on scanning electron microscope. SERS spectra of 4-mercaptopyridine (4Mpy) adsorbed on these three substrates have been comparatively investigated. Considerable differences were found in the SERS spectra of 4Mpy molecules onto various substrates, revealing the adsorption behaviors of 4Mpy varied with the substrates. From the analysis of the SERS data, it was evidenced that 4Mpy was chemisorbed through its S atom to Au and Ag surfaces at a perpendicular orientation, whereas it bonded to CuO surface via the S atom and N atom assuming a tilted orientation. Owing to the discrepancy of surface pH, the adsorbed 4Mpy molecule changed its tautomeric form from the anionic thiol structure when on Au and Ag to cationic thiolate one when on CuO.