Studies On The Preparation Of Gold-silver Bimetallic Nanoparticles And Their SERS Effects

Precious metal nanoparticles with controllable shape have attracted much attention due to their potential applications in localized surface plasmon resonances(LSPR),catalysis,sensing and other fields,especially gold and silver nanocrystals.Their amazing enhanced performance for molecular Raman scattering makes them widely used in surface-enhanced Raman spectroscopy(SERS).Compared with the traditional single-component substrate used in SERS,the development of multi-component metal composite nanostructure possessing synergistic effect as a new SERS substrate is expected to further expand the important applications of SERS technology in advanced and cutting-edge fields such as catalysis,specific molecular recognition and medical diagnosis,etc.For this reason,more and more researchers began to focus on the study of SERS substrate of multi-component metal composite nanostructures.It was found that the multi-functional bimetallic nanomaterials with SERS activities could be constructed by micro-adjusting the surface structure of silver nanostructures through surface replacement reaction,surface etching,surface deposition and other methods.Focusing on the Au-Ag bimetallic nanoparticles and using the Ag decahedral nanoparticles(AgDeNPs)as the precursors,this thesis prepared Au-Ag bimetallic nanoparticles with higher SERS activities by modifying the silver nanoparticles with the gold clusters on their surfaces through substitution reaction.This thesis carried out related research work in the following three aspects:(1)Controlled synthesis of Au-Ag bimetallic decahedral nanoparticles(Au-AgDeNPs)Ag De NP_S with uniform morphology and size were prepared by a two-step strategy with sodium borohydride as the reducing agent,sodium citrate as the reducing agent and stabilizer.The as-prepared silver decahedral structures were stabilized by adjusting the p H value of the colloid Then,micro areas on the surface of Ag De NP_S were etched by chloroauric acid(HAu Cl₄)through the galvanic replacement reaction.The as-prepared Au-Ag NPs were characterized by UV-vis extinction spectroscopy(UV-vis),high-resolution transmission electron microscopy(HR-TEM)and energy dispersive X-ray spectroscopy(EDS).(2)Studies on SERS activities of Au-Ag bimetallic decahedron nanoparticlesUsing 4-mercaptobenzoic acid(4-MBA)as the probe molecule,the SERS activities of Au-AgDeNPs were studied;the influence of synthetic conditions(concentration of gold ion,concentration of chloride ion,etc.)on the SERS activities were preliminarily studied as well.The results showed that the prepared Au-AgDeNPs displayed high SERS activities,and the SERS enhancement factor was estimated as6.5×10⁵,and the detection limit of 4-MBA could reach as low as 10^-9M.Under certain concentration range of HAu Cl₄ and chloride ions,the as-prepared Au-AgDeNPs provided higher SERS activities than those of their precursors.(3)Studies on SERS activities of Au-Ag bimetallic nanoparticles with different morphologiesIn order to explore the generalizability of the above method,silver nanoparticles in shape of quasi sphere(Ag Sp NPs)and flat triangle(Ag Pr NPs)were selected as the precursors,and their corresponding Au-Ag bimetallic nanoparticles were prepared by using the abovementioned method.The self-assembled films of the as-obtained bimetallic nanoparticles were employed as the SERS substrates,and their SERS activities were studied by the presence of 4-MBA as the probing molecule.The results showed that the abovementioned method can be a universal method to promote the SERS activities of silver substrates.