Investigations of Sized and Confined Effects of Nano-material on Molecular Behaviors of Adsorbed Alcoholic Molecules

• Main Authors: Yun-Chih Lin, 林允智
• Other Authors: Bing-Joe Hwang
• Format: Others
• Language: en_US
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/20657616342333440663

博士 === 國立臺灣科技大學 === 化學工程系 === 97 === Understanding the complex behaviors of adsorbed alcoholic molecules on or in nano-materials is essential for improving the performance of energy conversion/storage materials. Sized and confined effects of nano-materials on behaviors of alcoholic molecules were thoroughly investigated and discussed in this thesis. The nano-sized effects of Pt catalysts in terms of the surface coverage, electrochemical response and reaction kinetics during the electro-catalytic methanol oxidation reaction (MOR) have been extensively investigated by systematic electrochemical measurements, in situ electrochemical FTIR spectroscopy (EC-FTIRS) technique and Density Functional Theory (DFT) computational approaches. In contrast to bulk Pt, a relatively higher COads coverage on the nano-sized Pt catalyst was observed at the end of forward sweep (+1.0 V/RHE) from the in situ EC-FTIR investigations. The IR observations resulted from the fact that the electro-catalytic MOR appears to be diffusion-controlled process on the bulk Pt catalyst, whereas it was kinetic-controlled process on the nano-sized Pt catalyst due to both the higher kinetic barrier of COads + OHads reaction and lower diffusion resistance. By considering the in situ EC-FTIR and DFT computational results, the surface coverage models of the electro-catalytic MOR on the bulk and the nano-sized Pt catalysts were proposed. Here, the graphitization of pyrolyzed confined sucrose in SBA-15 was investigated by solid state NMR. It showed that the confined effects facilitated the formation of oxygenated carbon, indicating the cross-linking degree of pyrolyzed sucrose increased due to confined effects. Meanwhile, a range of NMR measurements comprising of 1H spin-lattice (T1), spin-spin (T2) relaxation, 13C cross-polarization (CP), and 1H-1H two dimensional nuclear Overhauser enhancement spectroscopy (1H-1H 2D NOESY) with the magic angle spinning (MAS) technique were employed to investigate the dynamics and to observe the stacking structure of confined 1-butanol in SBA-15. The results of 1H, 13C-CP/NMR, T1 and T2 measurements confirmed that the molecular motion of confined 1-butanol molecules is extremely restricted. It also indicated that 1H-1H 2D NOESY technique is an appropriate tool to obtain the relatively average distance between protons of 1-butanol molecules when the molecules are confined in SBA-15. The result of 1H-1H 2D NOESY measurement demonstrated that the distance between inter-molecular hydrophobic sides of confined 1-butanol molecules was shorter than that between hydrophilic sides. Moreover, the distance between inter-molecular hydrophobic and hydrophilic sides of confined 1-butanol molecules is shorter than that between intra-molecular hydrophobic and hydrophilic sides. It not only indicates that the confined 1-butanol molecules in SBA-15 are stacked as a bilayered structure, but also indicates a considerable fraction of the 1-butanol molecules are stacked as a tilted bilayered structure. That is first time to observe that the confined alcoholic molecules stacked in an ordered structure in the host of SBA-15. According to the analysis of Raman spectrum, the graphitization degree of the pyrolyzed sucrose increases when the sucrose is confined in mesoporous SBA-15. The increment of the graphitization degree of the confined pyrolyzed sucrose therefore mainly resulted from the ordered stacking structure of confined sucrose molecules rather than from the decrease of cross-linking degree. The results and methods of the nano-sized and confined effects not only provide new aspects to the understanding of the phenomena of adsorbed alcoholic molecules on the novel nano-materials, but also open new possibilities of applied research in materials synthetic methodologies, steam reforming and biological applications.