Surface-enhanced Raman Spectroscopic Studies On The Nterfacial Processes At Titanium And Oxide Electrode

Titanium （Ti） is one of the most important transition metals with a tremendousprospect of application in various fields. It has already played a significant role incosmonautics and petroleum industry. Titanium oxide （TiO₂） was used widely in surfacescience due to its advantages in the field of photo-catalysis. However, the lack of thefundamental investigation on the processes at titanium and oxide surfaces caused thebarrier in its practical application. Surface-enhanced Raman spectroscopy （SERS） is apowerful technique with ultrahigh sensitivity for probing the surface structural information,provides the information at molecular level to resolve into the mechanisms of surfacereaction by on-line monitoring the adsorption configuration, surface processes etc. Theresearches and main results are listed as follows:1. The shell-isolated nanoparticles enhanced Raman spectroscopy （SHINERS） wasemployed to obtain the high quality surface Raman spectroscopy of pyridine adsorbed ontoTi electrode. The shell-isolated nanoparticles Au@SiO2were prepared with relevantcharacterization. The observation of surface Raman spectroscopy of pyridine adsorbed onsmooth Pt and Ni electrodes indicated the generality of SHINERS. The adsorptionbehavior of pyridine on Ti electrode was investigated deeply by in situ electrochemicalSHINERS. By comparison with the traditional SERS, SHINERS exhibited the advantagesin the studies on the substrates with weak and without SERS effect2. Extending SHINERS to TiO₂electrode surfaces. By using4-cyanopyridine（4-CNPy） and thiocyanide ion （SCN-） as probe，the adsorption behaviors were investigatedat TiO₂electrode surfaces by SHINERS. By analyzing the changes in the spectral featuresand intensity of the4-CNPy and SCN-followed with the applied potential, it is reasonableto determine the adsorption orientation on TiO₂electrode surface. The results showed thatthe adsorption orientation of4-CNPy changed with the applied potential. At the opencircuit potential, the4-CNPy molecules adsorbed on TiO₂electrode by the N atom of pyridine ring in a vertical orientation. With the potential moving to more negative potential,it turned to a tilted mode. At extremely negative potentials, a flat configuration waspreferred and followed with the desorption. At the potential region positive than0V, thevertical orientation by pyridine ring’s N atom was demonstrated by the spectroscopy. Whenthe electrode was instead of TiO₂/Au nanocomposites, the adsorption behavior was unlikewith situation that4-CNPy adsorbed on the Au electrode. A combined action by4-CNPyadsorbed on TiO₂and Au was indicated by the spectrum, while4-CNPy adsorbed on theinterface of nanocomposites via N atom of pyridine ring in the positive potential. The SCN-adsorbed through N atom at the potential region from hydrogen evolution to the potentialof zero charge （pzc）. Around the pzc, a bridge-bound SCN-with both S and N terminalsbonding to the surface occurred. At more positive potential, SCN-was oxided and resultedin the broad peak.3. Exploring the surface catalytic reaction at TiO₂/Au composition electrode. TheSERS was employed to track the interfacial reaction and to provide the information atmolecular for resolving the reaction mechanisms. By using pyridine as probe, it was foundthat the coupling reaction of pyridine was occurred to produce2,2-bipyridine at relativenegative potential region by tuning the potential, electrode composition and laserirradiation. The results indicated that the C-C coupling reaction occurred only at thejunction of TiO₂and Au, the reaction mechanism was proposed preliminarily.