Silver Nanoparticle Synthesis Using Improved Photochemical Methods With Accurate Regulations Of Plasmonic Resonant Wavelengths

Noble metal nano-materials(especially Ag, Au) have attracted wide attention due to their unique properties in optical, electrical, magnetic and catalytic fields. Especially in the optical fields, the local surface plasmonic resonance(LSPR) of metallic nanoparticles has been widely used in optical imaging, bio-sensing and surface enhanced spectra. One of the key characteristics of LSPR is the resonant wavelength, which varies at different shapes and sizes of metallic nanoparticles. For example, Ag nanoparticles(Ag NPs) with various shapes and sizes have been synthesized based on diversified technologies. However, it is very difficult to realize the accurate regulation of the resonant wavelength based on the existing technique.The objective of this dissertation is to solve above questions. We propose an improved method of the conventional photochemical technology towards the Ag NPs synthesis to accurately regulate the resonant wavelength of LSPR. There are two steps in the process:(1) Irradiating the precursor solutions, consisting of trisodium citrate, Irgacure 2959, silver nitrate(Ag NO3) and deionized water with a certain proportion, under the UV illumination to obtain the Ag NPs seed solution.(2) Irradiating the Ag NPs seed solution with the LEDs with specific wavelengths to form Ag NPs with anticipant shapes. The second step is carried out under a constant temperature to accurately regulate the resonant wavelength in terms of the illumination time with the LEDs, which is one of innovative point in this thesis. The main contents in the dissertation are described as follows:(1) Technological improvement of the conventional Ag NPs photochemical synthesis: We synthesized Ag NPs with various shapes, e.g., spherical, decahedral, flaky hexagonal, and flaky triangular, and then charactistized them by means of transmission electron microscope(TEM) and ultraviolet-visible spectroscopy(UV-Vis). The morphology of the Ag NPs in our experiments is much better than that reported in the previous literatures.(2) An idea on achieving decahedral Ag NPs with high accurate regulation of resonant wavelength of LSPR under a constant temperature. We synthesized decahedral Ag NPs with a 30°C, 40°C, 50°C, 60°C and 70°C reaction temperature, respectively. The results show that the resonant wavelength will linearly shift as the illumination time increases towards a long-wavelength direction for a given temperature. In addition, a higher temperature will contribute to a larger slope of the linear curve. Therefore, we can accurately regulate the resonant wavelength owing to the controllable illumination time under a specific temperature.(3) Physical insight to the working mechanism of the regulable resonance: We numerically simulated the LSPR of decahedral Ag NPs with parameters obtained from our above experiments by Finite Element Method(FEM). The numerical results reveal the redshift of the resonant wavelength resulting from the increasing particle size and the vertex angle as the illumination time increases. The related theoretical work contributed to a good physical insight to the micromechanism of the improved photochemical synthesis.