Investigated By Electrochemical Surface-enhanced Raman Scattering Of Aromatic Thiol Self-assembled Monolayers And Application In Determination

The kind of benzene compounds with thiol end group forms chemical adsorption on the metal surface of Ag and Au under certain conditions,which can further be used as modified monomolecular layer on the surface of the electrode material.According to its high detection surfactivity,SERS provides a significant foundation on deepening of the complicated investigation in interfacial effect and molecule structure,which is also an effective method in surface adsorption and analysis testing.It has been the most practical technologies in characterizing the electrochemical process of metal/solution interface at molecular level.Main research object of this thesis are thiosalicyhc acid,2,2'-dithiodibenzoic acid and salicylic acid.In order to compare the Raman enhancement effect between Ag and Au,electrochemical oxidation-reduction method is carried out on the surface of Ag/Au for rough activation.By means of NRS,SERS,EC-SERS,UV spectrun,cyclic voltammetry and polarization curves,having discussed factors including chemical adsorption,electrochemical desorption and SAMs.In addition,reaction mechanism on the vibration spectrum characteristics of thiol end group on substrates for probe molecules have been analyzed,which is helpful to achieve a further contribution to laying theoretical foundation of the regulation.Research conclusions and achievements are listed as follows:(1)Mrhen TSA that containing sulphur adsorbed to electrode surface is able to form stable SAMs,which presenting new electrochemical properties of modified electrodes.Aromatic thiols TSA have stronger intermolecular interactions with Ag than alkyl mercaptan due to the end group of neutral molecules after taking off H,forming S-Ag bond and the stabilized SERS signals are detected to some extent.(2)It's worth noting that TSA presents irreversible electrochemical oxidation procession in KCI solution by cyclic voltammetry.With the rising of pH,the anodic potential gradually reduced.It shows that C6H4(COO-)SH can be oxidized more easily than C6H4(COOH)SH.During the electrochemical oxidation of TSA,there is one H+participating in oxidation reaction with three electrons transferring.(3)The activation of Ag for SERS effect is better than Au.It can be inferred that after the cleavage of S-S,sulfur kation or sulfur anion produced which is apt to react with Ag by chemical bonding.Aromatic disulfides interact with electrochemically surfactivity Ag to obtain SAMs,mechanism of interfacial effect on Ag surface is similar to those formed by thiols.UV spectra show that ultraviolet absorption of probes and conjugated system of aromatic ring have a similar trend compared with intensity-pH of SERS.(4)End group of TSA offers rigid structure and a beneficial way to control functionally perpendicular to metal surface.The optimized EC-SERS signals are obtained at+0.7 V and 70 s respectively,and it is found that intensity became weaker till to disappear when potential is negatively shifted.Furthermore,the alignment states of TSA assembled on the surface of Au are subjected to change on account of extermal condition's variation.Therefore,different electrochemical absorption orientation of TSA and reduction/desorption behavior at negative potential of high level can be applied to special groups chemically linkage to metal interface.(5)Potassium thiocyanate is selected as the internal standard and the relative intensity is formed by aromatic ring breathing(1036 cm-1)of SA and characteristic peak(2120 cm-1)of SCN-.The linear relationship is obtained between the relative intensity and the concentration of SA.This method can be extended to the determination of other special substances.Meanwhile,it has possessed some generalized application value.