Surface-enhanced Raman Spectroscopic Studies On Water At Transition Metal Electrode/aqueous Interfaces

The orientation and configuration of interracial water play a vital role in various surface processes and deeply influence the structure and function of different interfaces. Therefore,it has been a key fundamental issue in surface science,biology,chemistry and geology etc.for a long time.In order to completely understand the structure and behavior of water at the solid/aqueous,various in situ and ex situ techniques had been developed. However,until now the information obtained for the interfacial water is very limited because the interference from the bulk water(55 mol/L) is too severe to extract the very signal of interracial water.Normal Raman technique has a too low detection sensitivity to obtain information of the solid/aqueous interface due to the low Raman cross section of water.Surface-enhanced Raman Spectroscopy(SERS) with its ultrahigh detecting sensitivity to surface species has unique advantages over other surface techniques. However,up to now SERS of water can only be observed on silver,gold and copper with great difficulty,and the development is much slower than expected,Therefore,to obtain SERS signals of water from transition metal(ⅤⅢB group) surfaces with a wider application is a very challenging project with important scientific significance,which is the core of present thesis.We have tried but we are unable to directly obtain SERS signal of water from Pt group metal surfaces with only weak SERS-activity.Therefore,we utilized a "borrow" strategy,i.e.,by coating a very thin transition-metal layer(Pt or Pd) over the high SERS-activity Au nanoparticles,in virtue of the long range effect of electromagnetic enhancement of Au core,to obtain the SERS signal from Pt and Pd surfaces.The main results of this thesis include:(1) The detection sensitivity for detecting surface species was improved by optimizing experimental and instrumental conditions,especially the collecting efficiency of the instrument,including adopting suitable instrumental parameters,designing and utilizing a vertical setup of cell and thin-layer solution method.This also allows the in situ SERS investigation in the severe hydrogen evolution region. (2) Pinhole-free Gold core thin platinum or palladium shell nanoparticles with high SERS activity were synthesized and used as substrate to successfully obtain the SERS signal of inteffacial water.A brief discussion on the on electromagnetic enhancement was made on the basis of the result modeled by 3D-FDTD calculation.(3) For a completely understanding the process of water adsorbed on various metal surfaces and the SERS mechanism,the influence of solution pH value,the concentration of the electrolyte and the type of cations of supporting electrolyte on the structure of interfacial water was investigated.Significant difference in the SERS of water has been observed on Pt,Pd and Au surfaces.To account for the difference,a quantum chemical study was carried out and three preliminary models for water adsorbed on the three metal surfaces was proposed.