| Noble metal nanomaterials have many excellent physical and chemical properties that are not possessed by bulk materials,so they have broad application prospects in the fields of electronic information?chemical industry?energy?environmental protection?military industry and biomedicine,and therefore have become targets of competition for research.As a kind of noble metal,Au nanoparticles have attracted extensive attention due to their peculiar surface plasmon resonance properties.However,due to its chemical inertness,Au nanoparticles have higher catalytic activity only when their size is less than 4 nm.Because the morphology of Au nanoparticles with size smaller than 4 nm is difficult to control and the surface plasmon resonance is very weak,so its application is greatly limited.How to improve the catalytic activity of Au nanoparticles in larger size has become one of the most urgent problems in the wide application of Au nanoparticles.In this dissertation,the SERS and catalytic activity of Au nanoparticles with large size have been improved by morphology control and electronic structure control.The specific contents of this dissertation are as follows:1.Developing a wet chemical method to controlable synthesize colloidal porous Au nanoparticle and studied the surface enhancement Raman scattering(SERS)and catalytic perforamcne of prepared porous Au nanoparticles.The growth of gold on the PbS nanocrystals is accompanied with the etching of PbS by the growth solution,which produces porous gold nanoparticles.Firstly,PbS nanocrystals were prepared by hydrothermal method,and then porous Au nanoparticles were prepared by using PbS nanocrystals.Detailed studies were carried out on the study of gowth condition of growth of porous Au nanoparticles,the results show that only in fast nucleation and gworth in the etching liquid conditions to PbS nanocrystals,can form porous Au nanoparticles.Owing to the high density of strong electromagnetic "hot spots" within the porous gold nanoparticles,the nanoparticles show excellent SERS performance with an enhancement factor of(1.23 ± 0.10)×107 on single particles under off-resonant excitation.Moreover,because of the highly dense low-coordinated atoms in the porous gold nanoparticles,the catalytic activity of the nanoparticles is several times of those of previously reported larger porous gold particles and porous gold sheets.2.Using the different electrical properties of ionic surfactants,the electronic structure of Au nanoparticles was tuned successfully,so the catalytic activity of Au nanocrystals was improved.Firstly,Au nanospheres and nanorods capped with cationic surfactant CTAB were prepared through seed growth method.Secondly,cationic CTAB was exchanged into anionic surfactant polystyrene(PSS)and citrate(citrate)using surfactant exchange method.Zeta potential,infrared spectra and X-ray photoelectron spectroscopy(XPS)confirmed the surfactant that on the surface of Au nanocrystals was exchanged successfully.Transmission electron microscopy(TEM)characterization and UV-vis absorption spectra showed the exchange of surfactant did not change the morphology of Au nanocrystals.Finally,the effect of surfactant charge on the catalytic activity of Au nanocrystals was studied by the oxidation of o-phenylenediamine(OPDA)to 2,3-diaminophenazine(DAP)and electro-oxidation of methanol.The results showed the catalytic performance of Au nanocrystals capped with anionic surfactant were clearly higher than that Au nanocrystals capped with cationic surfactants.Further studies showed the anion citrate enriches the electrons of nanocrystal surfaces,while cationic CTAB depletes the electrons of the nanocrystal surfaces.The different catalytic activities of CTAB and citrate-capped nanocrystals arise from the different behaviors of electron transfer between surfactants and nanocrystal surface.3.To further improve the catalytic activity of Au nanostructures,we design a method to tune the electronic structure and morphology of Au nanostructures.In this method,the Pd@Au core-shell nanostructure was prepared by using porous Pd nanoparticles as core.The results show that the morphology of core-shell nanostructure can be tuned by adjusting the volume of HAuCl4 and Pd nanoparticles.When the addition volume of HAuCl4 is very small,the surface structure of core-shell nanoparticles tends to be rough and porous.With the increasing addition volume of HAuCl4,the surface of Pd@Au core-shell structure tends to the smooth.Due to the porosity of the Pd@Au core-shell structure and synergistic effect between Pd and Au,porous Pd@Au nanoparticle show enhanced oxygen reduction reaction(ORR)catalytic activity than the porous Pd@Au core-shell structure. |
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