Synthesis of rGO–Ag nanoparticles for high-performance SERS and the adsorption geometry of 2-mercaptobenzimidazole on Ag surface

The sliver nanoparticles (AgNPs) with diameters of 30∼50 nm were self-assembled onto the surfaces of reduced graphene oxide (rGO) sheets simply by mixing AgNO3 aqueous solution and GO dispersion via a synchronous reduction process. Structure and morphology of the rGO–AgNPs hybrids were well characterized. More significantly, the surface-enhanced Raman scattering (SERS) spectrum of 2-mercaptobenzimidazole (MBI) adsorbed on the solid rGO–AgNPs surface shown that the rGO–AgNPs system gives a very strong SERS intensity at in-plane vibrational modes in comparison to the out-of-plane vibrational modes. This large enhancement effect is most likely a result of charge-transfer (CT) mechanism. Based on the surface selection rules and the information provided by the highly enhanced in-plane vibrational modes, it can be found that MBI molecule was adsorbed on AgNPs surface as a thiol form via the sulphur and nitrogen atoms with a slightly tilted geometric conformation.