碩士 / 國立清華大學 / 化學工程學系 / 101 / Abstract
Semiconductor photocatalysts, possessing suitable band gaps, are able to absorb solar energy and generate electron/hole pairs. When the electron/hole pairs successfully migrate to the surfaces of the photocatalyst, they may reduce and oxidize water to generate hydrogen and oxygen, respectively. This is a green process but it suffers from low efficiencies. If we are able to reduce the electron-hole recombination, the photocatalytic efficiency would be improved.
A simple carbon decoration, involving only immersion in adipic acid followed by calcination in N2 atmosphere, was developed to prepare thin carbon layer decorated TiO2 nanoparticles. The thin carbon layer was in tight contact with the TiO2 domain and served as an electron trapping centre to improve charge separations necessary for enhancement in photocatalytic water splitting performance of the TiO2 nanoparticles. With an optimal carbon loading of 0.3 wt%, a four-fold improvement was achieved for hydrogen production as compared with that achieved by pristine TiO2 nanoparticles. This simple carbon decoration provides a promising low-cost alternative to traditional Pt-decoration approaches for enhancing hydrogen productions from photocatalytic water splitting.
The second part of the thesis concerns the preparation of graphene oxide quantum dots and their application in photocatalytic water splitting. Graphene, a single layer of graphite, has the characteristics of high conductivities, high surface areas, and high electron mobilities. It has been shown that graphene oxides with a size below 10 nm can absorb UV lights shorter than 300 nm and exhibit significant photoluminescent emissions, implying the semiconductor features of the graphene oxide quantum dots.
In this work, graphene oxide quantum dots were applied for photocatalytic hydrogen production for the first time. Well dispersed graphene oxide quantum dots in aqueous solution were prepared from carbon fibers under 120℃ heat treatment. According to HRTEM analyses, the size of the graphene oxide quantum dots was about 3 to 6 nm. From the AFM analyses, these graphene oxide quantum dots were with a thickness of 1 to 2 atomic layers. Without use of any sacrificial reagent, the graphene oxide quantum dots showed the ability of hydrogen production with a rate of 11μmol/hr under irradiation of a 400 W high-pressure mercury lamp. During the reaction, the oxygen-containing functional groups of the graphene oxide quantum dots were gradually reduced, leading to formation of graphene quantum dots. The activity of the graphene oxide quantum dots gradually decreased with increasing irradiation time. The hydrogen evolution ceased after 14 hours. The color of the graphene oxide quantum dot suspension turned transparent from orange during the reaction. According to the high resolution X-ray photoelectron spectroscopy, the oxygen-containing functional groups of the graphene oxide quantum dots were significantly reduced after exposing the suspension to the light source, which indicates the photo-reduction of the graphene oxide quantum dots. From the UV-visible and photoluminescence spectra, the reduced graphene quantum dots lost their semiconductor features.
| Identifer | oai:union.ndltd.org:TW/101NTHU5063023 |
| Date | January 2013 |
| Creators | Chao, Kang-Ju, 趙康如 |
| Contributors | Lu, Shih-Yuan, 呂世源 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 76 |
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