Sers Study Of Surface Plasmon-driven Catalytic Reactions

The development of nanotechnology promotes the fundamental and application research of surface plasmons.Surface plasmons are the collective oscillation of free electrons relative to ionic metal nuclei in metal nanostructures driven by the incident light,which makes the metal nanostructures exhibit a series of novel optical properties,such as selective absorption and scattering of visible light,local field enhancement,subwavelength confinement of electromagnetic wave.Surface plasmon-driven catalytic reactions,based on the hot electrons from surface plasmons decay,have attracted attention since its discovery in 2010.Owing to the advantages of providing the molecular fingerprint information and ultrasensitive detection,surface-enhanced Raman spectroscopy(SERS)has been successfully applied to in-situ and real-time investigation of surface plasmon-driven catalytic reactions.Surface plasmon-driven catalytic reaction is a new research direction,and the reaction mechanism remains to be further revealed.This thesis mainly focuses on the in-situ studying surface plasmon-driven catalytic reactions of three molecules using SERS technique.Major research works are as follows:1.In order to explore the selectivity of surface plasmon-driven oxidation and surface plasmon-driven reduction reactions,2-amino-5-nitrobenzenethiol(2A-5-NBT),which contains both an amine group and a nitro group,has been used as the research object.The catalytic reactions of 2A-5-NBT on roughed Ag electrodes have been studied using SERS combined with DFT theory calculation.It is found that 2A-5-NBTs can be selectively synthetized to 3,3’-dimercapto-4,4’-diaminoazobenzene(DM-DAAB)by the condensation of the nitro groups.Moreover,we have studied the effect of reaction environments on the reduction reactions of 2A-5-NBT using time-dependent SERS,The experiment results demonstrate that the aqueous environments are preferable to the ambient atmospheric environments for the selective reduction reaction.The product is very stable in aqueous environments.2.To reveal the reaction mechanism of surface plasmon-driven catalytic reactions on graphene-metal composite nanostructures,the dynamics processes of Ag nano wires,monolayer graphene and graphene-Ag nanowire composites have been investigated using femtosecond laser pump-probe technique.Further,we have studied the reduction reactions of 4-nitrobenzenethiol(4NBT)to p,p’-dimercaptoazobenzene(DMAB)on three catalytic systems using SERS,respectively.The results indicate that the coupling between surface plasmon in single Ag nanowire and the exciton in monolayer graphene prolongs the lifetime of hot electrons(from femtosecond to picosecond),so the efficiency of the reduction reactions of 4NBT to DMAB approachs 100%on the graphene-Ag nanowire composites.3.In order to study the catalytic reactions of para-nitroaniline(PNA)in ambient environments,we have investigated the catalytic reactions of PNA on Ag nanoparticles,graphene-Ag nanoparticles composites and graphene-Ag nanowire composites in the air using SERS,respectively.The experimental results demonstrate that PNAs are selectively reduced to 4,4’-diaminoazobenzene(DAAB)by the nitro groups of PNA,rather than oxidized to 4,4’-dinitroazobenzene(DNAB)by the amine groups,either on Ag nanoparticles or graphene-Ag composites.4.In addition to the applications of the metal-graphene composites,the metal-semiconductor nanocomposites—Ag nanoparticles-TiO2 film composites for surface plasmon-driven catalytic reactions have also been studied.The plasmon-exciton coupling degree in Ag nanoparticles-TiO2 film composites with different Ag nanoparticles size has been investigated by UV-visible absorption spectroscopy.The results indicate the strong plasmon-exciton coupling occurs when the surface plasmon resonance(SPR)peak of Ag nanoparticles is superposed with the absorption peak of the excitons in TiO2 film.The oxidation reactions of p-aminothiophenol(PATP)on the composites with strong plasmon-exciton coupling have been studied using SERS.It is found that the efficiency of the catalytic reactions on the composites is faster than those on pure metal substrates,and the product DMAB is very stable.