Self-assembly Monolayers Of 2-mercaptobenzimidazole Investigated By Surface Enhancement Raman Scttering And Electrochemical Impedance Spectroscopy

Aromatic mercapto compounds adsorb on the metal surface of the activated Ag or Au,which can further be used as a probe molecule to study surface adsorption.By the means of laser Raman spectroscopy,UV spectroscopy,SERS spectroscopy,electrochemical surface-enhancedRaman spectroscopy?EC-SERS?and electrochemical impedanceSpectroscopy?EIS?,it has discussed electrochemical desorption,self-assembled monolayers,SMAs,electric double layer capacitor and impedance in this paper.Reaction mechanism on vibration spectrum characteristics on substrates for probe molecules have been analyzed,which is helpful to achieve a furface contribution to laying theoretical foundation of the regularion.?1?2-Mercaptobenzimidazole?MBI?molecules offer stable rigid structure and end group S to control perpendicular to the Au surface.SMAs produce a strong SERS effect,and when the pH becomes large,the–NC=S vibration shows a sharp decrease because the structure of MBI molecular has changed.The optimized EC-SERS signals are obtained at+0.7 V and 80 s,and it is found that intensity became weaker till to disappear when the potential is negative shifted.Furthermore,MBI molecules assembled on surface of Au are subjected to change on account of external condition's variation.?2?The activated Ag electrode was used to investigate the self-assembled monolayers?SAMs?behavior of MBI.The SERS effect of MBI in acid solution was better than in alkaline or neutral solution.When the pH was lower than 2,MBI⁺,the main form of MBI molecule,absorbed vertically on Ag surface on with coordinate bond between S:and Ag and produced relatively higher SERS effect.When the pH was higher than 2,thiol absorbed on Ag surface with S-Ag covalent bond and N-Ag coordinate bond which resulted in competitive absorption between thiol and thione of MBI,so SERS effect decreased rapidly.As a result,thiol form of MBI lay aslant Ag surface with S-Ag covalent bond and N-Ag coordinate bond,making the weaker SERS effect than thione.?3?Ag electrode modified with SMAs of MBI molecules EIS tests show that the potential of zero charge for the two-phase system is-0.35 V.The surface of the Ag is better covered by higher concentration of MBI solution and gradually forms dense SMAs.With the increasing of concentration,the SERS effect was strengthened firstly but weakened latterly because of its steric hindrance when it happened to the high concentration.As a result,the most effective enhancement was at 1×10^-6mol·L^-1.While the concentration of the electric double layer capacitor and the the film coverage?becomes larger,MBI molecules constantly occupy laser channel on activity Ag surface which results the weaker Raman enhancement effect at high concentrations.