Probing Photochemical Reactions by Raman Spectroscopy
| Autor: | Hsiang-Ling Chen, 陳緗翎 |
|---|---|
| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 This study primarily used spectral analysis techniques to investigate surface-enhanced Raman scattering (SERS) changes during photochemical reactions of Raman substrates and detection molecules. The study is divided into two parts. The first part utilizes the photosensitivity of silver oxide nanoparticles which reduces the nanoparticles to metallic silver upon their illumination with visible light. Two types of silver oxide nanoparticles with different crystal shapes were used in this experiment and methylene blue (MB) was used as a molecule detector for metallic silver, so that as the illumination time increases, the SERS effect of MB will also increase due to its interaction with metallic silver. The metallic silver formation rate constant (kobs) during the photochemical reaction was calculated using first-order kinetic equations, the kobs of octahedral silver oxide becomes smaller than that of cubic silver oxide. At lower MB concentrations, as the MB molecules mainly adsorb in a parallel fashion onto the silver oxide crystals. At higher MB concentrations, as the MB particles mainly adsorb perpendicularly onto the silver oxide crystals. The second part of this study utilizes the surface plasmon resonance (SPR) of gold nanoparticles via 532 nm laser excitation, which is close to the absorption wavelength of gold nanoparticles. The SPR of gold nanoparticles in varying concentrations is then used to catalyze the coupling reactions of 4-aminothiophenol (4-ATP) (also in varying concentrations) to form azo-bond-containing 4,4''-dimercaptoazobenzene (DMAB) molecules. As the laser illumination time increases, the SERS signal of DMAB will become increasingly distinct, which enables measurements of k, the rate constant of azo-bond formation during the reaction. During this experiment, the Lineweaver-Burk based on the the Michaelis-Menten kinetic equation were also used to obtain the maximal velocity (Vmax) and catalyst- substance affinity (Km). At higher gold nanoparticle concentrations, Vmax and Km increase with increased illumination time, and a relatively long time is required for the full generation of DMAB. At lower gold nanoparticle concentrations, however, Vmax and Km decrease with illumination time, and nano Au-4-ATP compounds are preferentially generated in the reaction instead. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|