Preparation Of α-Fe₂O₃/Ag Core/Shell Nanocomposites And SERS Properties

Core-shell structure composite materials not only maintain the properties of nanoparticles, but also enhance the biocompatibility, thermal, mechanical and chemical properties. Due to their special structures and properties of magnetic core-shell structure composites, they have become an increasingly active area.α-Fe₂O₃ nanoparticles with good magnetic, catalytic, gas sensitivity and other properties. The preparation methods are simple and the price is not expensive. After coating by Ag particles,α-Fe₂O₃ nanoparticles not only enhance their activity of Raman, but also increase their chemical stability, biocompatibility property and so on. At present, there has been a few aboutα-Fe₂O₃/Ag compound nanoparticles, especially for the less reported SERS. The study is quite novel and its research result may apply in the field of biomedical for target administration and detection of biological molecules.The main works of this thesis were that to prepare theα-Fe₂O₃/Ag core-shell structure composite nanoparticles and the study of their SERS activity using silane coupling agent as connecting bridge. (1) Sphericalα-Fe₂O₃ nanoparticles were prepared by hydrothermal method. It was added PEG as dispersant. The effects of the concentration of Fe³⁺, PEG on theα-Fe₂O₃ nanoparticles were analyzed. Theα-Fe₂O₃ nano-particles were modified byγ-aminopropyl triethoxysilane (APS) as a briage. And the mechanism for modification was analyzed. It is characterized by FTIR to further verify the surface ofα-Fe₂O₃ nanoparticles was coated by Fe-O-Si bond. (2) With the seeding method,α-Fe₂O₃/Ag core-shell composite nanoparticals were prepared by the reduction of [Ag(NH3)2]+ with formaldehyde as reductant. The influences of the concentrations of APS, the volume ratio of alcohol to water ratio, reaction speed and other conditions on the coated effect and performance of nanocomposites were investigated. It was characterized by XRD,SEM,TEM and EDX and so on. The mechanism of formationα-Fe₂O₃/Ag core-shell composite was investigated. (3) Pyridine (Py) as a molecule probe was studied Raman spectroscopy (SERS) properties and stability of theα-Fe₂O₃/Ag core/shell composite particles, and calculated the enhancement factors and their stability.According to large numbers of experiments, some conclusions have been drawn: (1) By hydrothermal method,α-Fe₂O₃ particles were spherical, well-dispersed and the average sizes were approximate 40nm. As an additive, PEG had effect on the preparation ofα-Fe₂O₃ nanoparticles. When the content of PEG was 0.5%,α-Fe₂O₃ particles dispersed significantly improved, but it had little effect on the particle morphology. When the concentration of Fe³⁺ was 0.5mol/L, it was better for the nucleation ofα-Fe₂O₃. It is characterized by FTIR to further verify the surface of Fe₂O₃ nanoparticles was coated by Fe-O-Si bond, which was easier to be coated by Ag particles. (2) When the content of APS was 0.75wt% and the volume ratio of alcohol to water was 5:1, the obtainedα-Fe₂O₃/Ag composites by the method were coated completely, well-dispersed and the average sizes were approximate 60nm. By contorting the molar ratio of AgNO3 andα-Fe₂O₃, the thickness of Ag cell composites were tuned. When the molar ratio of AgNO3 toα-Fe₂O₃ was 1,α-Fe₂O₃/Ag composite particles were coated fully and the surface roughness was good. When formaldehyde was 3.7%, and temperature was controlled at room temperature, the preparation effect of composites was better. (3) Compared the Raman substrates of Py signal intensity onα-Fe₂O₃ /Ag coated particles,α-Fe₂O₃ seeding particles and rough Ag film, it was known that the Raman signals was strong. By enhancing factor calculation formula, it can be got Ef = 9.8×105. By coating Ag layer,the intensities of SERS are enhanced at 1010cm-1 and 1038cm-1. And this substrate is fairly stable after being placed in air for a while.