In-situ Surface-enhanced Raman Spectroscopy Study For Reaction Mechanism Of Aromatic Hydrocarbon Under External Fields

Surface-enhanced Raman scattering(SERS)is highly sensitive to the surface species,which primarily originates from the giant enhanced optical field generated by surface plasmon resonance(SPR)on some metallic surfaces.Therefore,because of the low temporal resolution,there has been not any report on how to figure out the reaction pathways for an electrochemical reaction according to the EC-SERS study.In recent years,scientists found that stimulating SPR can not only accelerate the reaction process,change the reaction pathway and mechanism,and also can make some reactions taking place which cannot be realized under the condition of conventional chemical.Because this is a new research field,so a lot of advanced scientific problems need to be solved,such as some different explains about SPR induced or enhanced chemical reaction process existed in previous literatures.In this thesis,we developed a transient electrochemical surface-enhanced Raman spectroscopy(TEC-SERS)by combining transient electrochemical techniques with SERS,which was realized by synchronization of the cyclic voltammetry(CV)and chronoamperometry(CA)methods with SERS measurement,and applied to study the electrochemical reduction of PNTP.The hydrogen bonding between two PNTP molecules dimer and the dimerization of PNTP to the disulfide were investigated by Raman spectroscopy.The dimerization of ethyl phenyl sulfide to phenyl disulfide was also investigated,which widened the understanding on SPR induced chemical reactions.The main results are outlined as follows:1.We first proposed an octatomic ring structure R22(8)of PNTP in the solid state by convoluting the "fingerprint" character of Raman spectroscopy,experiment,SERS and DFT calculation.2.We applied the transient electrochemical surface-enhanced Raman spectroscopy(TEC-SERS)to the reduction of PNTP by combining transient electrochemical techniques with SERS.We did not get the spectral information of intermediates with a 5 ms temporal resolution in the CA-SERS method.We assumed the reaction was very quick which required a higher temporal resolution.Although we didn't get the information of intermediate species,but the methods and results provides informatin and direction.to study the electrochemical reduction of nitrobenzene compounds.3.We confirmed the PNTP could be selectively transformed to its disulfide derivates(NPDS)under the illumination of visible light.Our work indicates that the production of NPDS is associated with the presence of oxygen,light,and metal impurities.However,the dimerization reaction may provide a new and important guideline for the formation of thiols to disulfides.4.The dimerization of ethyl phenyl sulfide to phenyl disulfide was also investigated.We illustrated that the reactions have two different paths and reaction mechanism,by in-situ changing the substrate,laser power density,irradiation time and in different pH solutions.