| Summary: | 碩士 === 元智大學 === 化學工程與材料科學學系 === 98 === For the utilization of hydrogen, hydrogen storage technology is quite important. Metal–organic frameworks (MOFs) are a new emerging class of crystalline porous materials, displaying very low density, significant thermal stability and very high surface area. They offer significant opportunities for hydrogen storage. Therefore, the main objectives of present study were to develop and investigate the synthesis methods, fine structural characterization, and capacity of hydrogen storage of MOFs using XRD, FE-SEM/EDS, TEM, BET, TGA, XPS, and XANES/EXAFS techniques.
MOFs were synthesized with different metal nitrates in the presence of different solvents and combined with different organic linkers, with the reaction temperatures range from 110 to 120oC. These MOFs named Co2(bdc)2dabco and Zn2(bdc)2dabco have the particle size about 10~15, and 10~12 μm, respectively identified by FE-SEM microphotos. Since as-synthesized MOFs contain many impurities, these may cause low porosity. Therefore the cleaning methods, such as optimum calcination temperatures or washing several times with different solvents at warm temperatures, were effective and approved to improve higher specific surface area and porosity. Co2(bdc)2dabco and Zn2(bdc)2dabco must be noted that properties. when they were exposed to air for long time, they absorbed water from air which easily blocked the pores and specific surface area decreases. The specific surface area of Co2(bdc)2dabco and Zn2(bdc)2dabco were 1464, and 1433 m2/g, respectively. Isothermal adsorption/desorption curves of MOFs were type I. The distribution of pore diameter curves revealed that MOFs were microporous materials. EDS data indicated that MOFs consist of C, O elements and different kinds of metals. XRD patterns represented that MOFs had well crystallinity after chemical treatment. FTIR spectra exhibited vibrational bands in the region of 1400~1700 cm-1 for the carboxylic function, 1700~1950 cm-1 for benzene-1,4-terephthalic acid and 3000~3500 cm-1 for OH- group of these MOFs. TGA curves showed that these MOFs were stable up to around 260~280oC which is less than many other organic compounds.
In order to investigate and improve the hydrogen storage capacity of MOFs, metal/activated carbons mixed with MOFs were thus prepared. The BET surface area of AC, acid-treatment AC, Pt/AC and Pd/AC were 1040, 1120, 750 and 890 m2/g, respectively. FE-TEM microphotos of Pt/AC and Pd/AC indicated that the particle size were 2~5 and 5~10 nm, respectively. The EDS data showed that Pt/AC and Pd/AC are composed of Pt and Pd nanoparticles, respectively. By using XPS and XANES spectra, it had found that both Pt and Pd species had zero valency. The EXAFS data revealed that Pt/AC and Pd/AC have a first shell of Pt-Pt and Pd-Pd bonding with bond distances of 2.78 and 2.75 Å, respectively. Coordination number of both nanoparticles were close to 8 with BCC structures.
|
|---|
