博士 / 國立中興大學 / 環境工程學系所 / 100 / As natural resources are rapidly exhausted, renewable energy sources show promise as alternative resources. Photocatalytic hydrogen (H2) production, one of attractive green technologies, uses solar energy and water as material source. In addition, the technology produces very few pollutants during photocatalysis. Therefore, photocatalytic H2 production via photocatalysts has great potential for solving environmental and energy issues. To enhance H2 production from solar light induced water splitting, it is necessary to increase the efficiency of photocatalysis and the light adsorption range of photocatalyst.
In order to increase the efficiency of photocatalytic H2 production, the influence of the following operational parameters, namely initial sacrificial reagent concentration, reaction temperature, photocatalyst concentration, initial solution pH, and irradiation time, was the main focus. The hydrogen evolution was experimentally found to be strongly affected by the above parameters. The optimum values of initial solution pH, photocatalyst concentration, and sacrificial reagent concentration were obtained. The results showed that the utilization of the photocatalyst with the proper operational conditions could lead to considerably high efficiency of photocatalytic hydrogen production.
To reduce the recombination rate of e-/h+ pairs, oxidation /reduction-treated Pt/TiO2 photocatalysts were synthesized and the influences of redox-treated Pt/TiO2 photocatalysts on H2 production were investigated. In terms of H2 production rate, the oxidation treatment showed higher reactivity than the reduction treatment. The reduction treatment allowed the formation of metallic Pt(0), which more easily catalyzed the transition of TiO2 from the anatase to the rutile phases. Reduction-treated Pt/TiO2 photocatalysts had lower SBET values than oxidation-treated Pt/TiO2 photocatalysts due to the higher percentage of TiO2 in the rutile phase. Combining the results of X-ray photoelectron spectroscopy (XPS) and optical analyses, PtO/TiO2 showed a higher energy band gap than metallic Pt(0)/TiO2, indicating that oxidation-treated Pt/TiO2 was more capable of achieving water splitting for H2 production. According to the results of this study, the oxidation treatment of Pt/TiO2 photocatalysts could significantly enhance the reactivity of photocatalytic H2 production because of their homogenous distribution, lower phase transition, higher SBET, and higher energy band gap.
To enhance the light adsorption range and the reactive sites of photocatalyst, the effects of calcination temperature on the properties and H2 production ability of nitrogen-doped (N-doped) TiO2 photodeposited with 0.2 wt% Pt (platinum) were studied. The results showed that the calcination temperature of Pt/Ndoped TiO2 obviously affected the structure, morphology and N atomic content, resulting in different TiO2 phases, SBET values, and visible light absorption abilities.
Besides, the SBET results indicated the pore size of N-doped TiO2 photocatalyst was significantly affected by calcination temperature. When the N-doped TiO2 calcined at 400 oC, the adsorption hysteresis of the isotherm was close to the Type H4. Field-emission-transmission electron microscopy analysis (FE-TEM) showed the mesoporous structure was composed of nanoparticles. However, high clacination temperature resulted in less visible light absorption region of the N-doped TiO2. In this study, the effect of calcination atmosphere on the properties of N-doped TiO2 was discussed. The results showed that the visible light absorption region of the N-doped TiO2 was significantly improved by calcination atmosphere (N2 and NH3 atmospheres). Moreover, the pore size, crystalline phase, and chemical state were not changed under this calcination condition. Therefore, the H2 production of modified N-doped TiO2 raised effitiency three times than no modified one.
To further increase solar light induced H2 production rate, the Pt/TiO2-xNx/SrTiO3 triplejunction was designed. First, N-doped TiO2 was grown on the surface of the SrTiO3 via sol-gel process and the effect of SrTiO3 on the heterojunction was studied by various ratios of SrTiO3/N-doped TiO2. The results of X-ray diffraction (XRD) and XPS analyses showed that the N-doped TiO2 was successfully fabricated and then combined with SrTiO3. N-doped TiO2 coupled with SrTiO3 prevented particle agglomeration and thus the heterojunction materials had higher specific surface areas than the theoretical values. In addition, SrTiO3 coupled with N-doped TiO2 enhanced the visible light absorption range. The photocatalytic H2 production rates of the heterojunction were significantly increased, especially at 5%, which could be ascribed to the enhancement of e-/h+ separation, charge migration from the photocatalyst interior to the surface, and the prevention of particle agglomeration. Then, the triplejunction was prepared by coating Pt on the TiO2-xNx/SrTiO3. The solar light induced H2 production rate was much enhanced by the triplejunction. Based on the energy levels of SrTiO3, N-doped TiO2, and Pt, it was deduced that the photogenerated charges of the triplejunction migrates from the interior of the material to the surface, thus promoting the redox reaction and reducing the e-/h+ recombination rate. Therefore, the triplejuncion effectively split H2O to produce H2 under solar light irradiation.
| Identifer | oai:union.ndltd.org:TW/100NCHU5087006 |
| Date | January 2012 |
| Creators | Bing-Shun Huang, 黃柄橓 |
| Contributors | Ming-Yen Wey, 魏銘彥 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 176 |
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