Investigating The Plasmon Catalyzed Conversion Of Para-nitrothiophenol On Metal Surface By SERS

Para-nitrothiophenol(PNTP) can be catalyzed by plasmon to p, p’-dimercaptoazobenzene(DMAB), and reduced by potential to form para-aminothiophenol(PATP). Since two reactions can not be separated easily, it is necessary to accelerate or inhibit one reaction in order to analyze the reaction mechanism. Surface Enhanced Raman Spectroscopy is a powerful tool to investigate surface reaction. In this dissertation, the plasmon catalyzed conversion and electrochemical reduction of PNTP were explored by SERS to control the reaction. The main results were listed below:1. Explored the plasmon-induced surface catalytic reaction of PNTP transfering to DMAB on Au nanoparticle monolayer film. The influence from several issues, involving the surfactant, coadsorption species, the solvents and the water, were systemically investigated to probe the acceleration and inhibition on the plasmon catalysis reaction. The concentration and molecular weight of surfactant PVP exhibited significant influence in the reactive activity for the plasmon catalyzed dimerization of PNTP to DMAB. A suitable molecular weight of 10000 and concentration of 10 mg·m L-1 were beneficial for improving the conversion efficiency of PNTP to DMAB. The higher molar ratio of coadsorbed molecules and the aprotic solvents resulted in the inhibition of the conversion reaction. The plasmon catalysis in the ionic liquids suggested that the water was essential for the dimerization of PNTP, in which it was used to accelerate the reaction rate and severed as the hydrogen source.2. Investigated the electrochemical reduction of PNTP. By SERS we confirmed the final reductive product was PATP. The conditions of electrochemical reduction were locked by SERS dection in different substrates and electrolyte solutions. The occurrance of electrochemical reduction of PNTP need a nanometer roughness polycrystal surface and the existence of water. What’s more, reduction hydrogen atmosphere was very important for the electrochemical reduction. The results indicated that acidic solution or Si-H surface was better for PNTP conversion to PATP, while in neutral or alkaline solution, PNTP preferred to first generate DMAB, then transformed to PATP.3. Improved the procedure for the synthesis of Au@Pt nanoparticles. Stable and uniform Au@Pt nanoparticles were obtained. The uniform and compact core-shell Au@Pt nanoparticle monolayer film could be formed at water/air interface. Since the monolayer film had good uniformity, stability and reproducibility, it could be served as the ideal SERS substrate and used to catalyze methanol and reduce PNTP.