| Summary: | 碩士 === 逢甲大學 === 環境工程與科學所 === 99 === Since petrochemical energy on earth has gradually become insufficient and enhanced greenhouse effect by the giant emission of carbon dioxide has been worsen, this research focuses on the photocatalytic water splitting to produce renewable clean fuels, such as hydrogen and oxygen, using a promising photocatalytic technique. As solar light has only 4% energy spectrum in UV light range, it is rather important to develop a novel kind of visible-light-driven photocatalyst to fully utilize solar energy that will be beneficial to explore the limit of this new technology.
Two phases has been involved in this thesis. Phase I was the preparation of modified bismuth oxide photocatalyst using sonolysis-assisted method. Subsequently ruthenium was doped on Bi2O3 to enhance its photocatalytic activity and then platinum was deposited on the surface of Bi2O3 by photodeposition method to increase the efficiency of heterogeneous photocatalysis. Finally, chromium oxide was also loaded on the surface to inhibit the back reaction of water. The crystalline phase composition and surface structure of Bi2O3 photocatalysts were examined using SEM, XRD, UV-visible spectroscopy, XPS, and PL. The XRD and TEM results revealed that great crystallinity was observed with monoclinic structure and Pt ion phase with average size was about 5 nm. The PL intensity of Cr2O3/Pt/Ru: Bi2O3 and Pt/Ru: Bi2O3 has been found to decrease due to the reduction of the electron/holes recombination rate. Optical characterizations indicate that the Bi2O3 presents the photoabsorption properties from UV light region to visible light that is shorter than 470 nm. Phase II was photocatalytic reactions for water splitting using the modified photocatalysts as synthesized in phase I. The photocatalytic performance of the Bi2O3 and Bi2O3 composites were evaluated with the addition of sacrificial reagent in the reactant solution. According to the experimental results, the optimum amount of photocatalysts dosage for photocatalytic hydrogen production with Na2SO3 and H2C2O4 is around 1.0 g L−1. The optimum concentrations of Na2SO3 and H2C2O4 for hydrogen production are 0.3 M and 0.03 M, respectively. Under this optimum circumstance, the results of photocatalytic for water splitting with Na2SO3 and H2C2O4 show that Cr2O3/Pt/Ru:Bi2O3 could effectively increase the amount of hydrogen evolution, which is around 13.68 and 17.15 μmol g-1, respectively. In addition, the photocatalytic hydrogen evolution using Cr2O3/Pt/Ru: Bi2O3 photocatalyst with Na2SO3 solution was adjusted to pH 2 and it had the better photocatalytic reaction than the other pH solution. The plausible formation mechanisms of modified bismuth oxide and reaction mechanisms of photocatalytic water splitting mechanisms have been proposed.
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