| Summary: | 碩士 === 東海大學 === 化學系 === 99 === Core-shell structure bimetallic nanoparticles have received much attention, particularly, by combining Au and Ag into a core-shell configuration to provide a new handle for controlling electronic, optical and catalytic properties. In this research, we have studied the amino acid tyrosine as a reducing agent to yield stable Au-Ag core-shell nanoparticles (NPs) under alkaline conditions by using small-angle X-ray scattering (SAXS), including the particle shape and size.However, tyrosine has three pKa , the proton will be dissociated with different pH values.When the pH value is greater than 10.07, the reducing capability of tyrosine is shown to arise due to ionization of the phenolic group of tyrosine, which by electron transfer to silver ions, then synthesis of Au-Ag core-shell nanoparticles.The results suggest that the spherical Au NPs of the mean size is about 4 nm, synthesized in NaBH4 reduction procedure. On the other hand, the spherical Au-Ag core-shell NPs of the mean size is 8.5 nm, synthesized via using Au NPs as seed and tyrosine molecules bound to the surface of Au nanoparticles through amine groups may be used to reduce silver ions under alkaline conditions and heat to form a gold -silver core-shell bimetallic structure. Another way, we also confirmed that the synthesized nanoparticles is gold-silver core-shell nanoparticles by anomalous small angle X-ray scattering(ASAXS).Finally, the conditions in experiment to change the pH and the concentration of silver ions to achieve the synthesis of core-shell nanoparticles for control shell thickness is indispensable factor.
Through rapid mixing system, change the pH values of solution can be controlled the reduction properties of tyrosine in the UV-vis measurements. Adding different amount of silver ions 1.0 × 10−4 M(C 1 ) and 2.0 × 10−4 M(C 2 ) in reaction for comparison, the result of SAXS shows C1 shell thickness is 1.7 nm and C2 shell thickness of 2.7 nm.That mean the more amount of silver ions make the thicker shell nanoparticles.
Finally, change molar concentration ratio between the seed and the silver ion, we can precise control the thickness 1.2 ~ 3.0 nm of silver shell to achieve controltheir optical properties of surface plasma absorption in the range of 414 ~ 518 nm.
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