Adsorption And Reaction Of Organic Molecules On Nanostructured Metal Electrodes

Surface-enhanced Raman spectroscopy(SERS)has an ultra-high detection sensitivity,which can be used to study the adsorption and reaction of probing molecules adsorbed on metal electrodes.It is widelly accepted that SERS has two enhancement mechanisms:electromagnetic mechanism(EM)and chemical mechanism(CM).According to the surface selection rules,EM has the same enhancement effect on the same symmetrical vibrations of the adsorbed molecules,while CM directly affects the relative Raman intensity of the same symmetric vibrational modes.Through analyses,we can obtain the informations about metal-molecule bonding,adsorption orientation and the energy level alignment at the molecule-metal interface.Meanwhile,metal nanoparticles produce strong surface plasmon resonance(SPR)under visible light irradiation,and this can be used to regulate photoelectrochemical reactions.This thesis is summarized as follows:1.Using p-methylbenzenethiol(PMBT)as a probe molecule,its normal Raman and SERS spectra were analyzed.It was first found that the normal Raman spectra of PMBT in the solid powder depend on the position of the laser irradiation,indicating that the powder has an anisotropic microcrystalline structure.At the same time,the Raman spectrum calculated by DFT is in a good agreement with the Raman spectrum observed in the nonpolar solvent CCl4,which proves the above view.Second,the excitation wavelength dependent Raman spectra of PMBT molecules on gold and silver nanostructures show that as the increase excitation wavelengths results in the relative intensity enhancement of the low wavenumber peak in the SERS spectra.This phenomenon is attributed to the presence of local low-energy excited states in the metal-PMBT interface.2.The adsorption kinetics of PMBT molecules on gold nanostructures was observed by combining electrochemical and SERS experiments.The amount of molecular adsorption on the nanostructured gold electrode was determined by electrochemical redox,underpotential deposition,and molecular electrochemical desorption on gold.The average adsorption capacity Was 1.25 nmol/cm2,which was three times larger than that on the Au(111)surface.On the basis of the above result,the studies on the adsorption kinetics of PMBT molecules show that the adsorption of PMBT molecules conforms to the two-site and second order adsorption ketenic model.3.The surface plasmon enhanced electrocatalytic reaction was explored by using electrochemical and EC-SERS detection methods.The self-assembly nanostructured gold electrodes were applied to the electrocatalytic oxidation of formic acid.The results show that gold has low formic acid oxidation activity in the dark state.However,the oxidation current of formic acid increases under light irradiation,which was blamed on the enhancement effects of SPR.Accordingly,the core-shell nanocomposite structure of Au@Pd with high catalytic activity was constructed.We investigated photocatalytic activity.It is found that the oxidation current of formic acid is greatly improved after the light in-iadiation,indicating that SPR can be used to regulate the oxidation reaction of formic acid,extended the photoelectrocatalytic field.