| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 106 === This research was dedicated to investigating the potential application of titanium phosphite, denoted as M1, in the photocatalytic hydrogen evolution from sea water. The M1 was a novel material synthesized by the hydrothermal method. By means of single-crystal X-ray diffraction (SXRD) and X-ray photoelectron spectroscopy (XPS), the chemical formula of M1 was found to be Mg0.5(H2O)3[TiIIITi2IV(HPO3)6]‧x(H2O) (x ≅ 0.4), which featured composed-valence Ti3+/Ti4+. The M1 could absorb visible light mostly, which might result from Ti3+ atoms in M1’s structure, and showed photocurrent response in a 3-electrode system under simulated sunlight irradiation. Therefore, M1 was applied in sunlight-driven photocatalytic hydrogen evolution reaction. M1 showed the activity of photocatalytic hydrogen evolution in both pure water and solution of 2 mM FeCl2 (pH 2.4, adjusted by H2SO4). In addition, with the presence of 2 mM FeCl2, which was a sacrificial agent, the hydrogen evolution rate could be enhanced to 1.27 times compared with the pure water. In order to further improve the photocatalytic activity of M1, photo-deposition method was used to load different numbers of Pt nanoparticles onto M1 surface. The M1_1.0Pt gave the highest photocatalytic activity for hydrogen evolution, and its hydrogen evolution rate tripled after loaded with Pt.
The M1 was collected after photocatalytic hydrogen evolution, then was analyzed by XPS. The results showed that Ti3+ in M1 structure was oxidized to Ti4+ by photo-induced holes in pure water environment. This phenomenon was called hole-induced photocorrosion. If the sacrificial agent, 2mM FeCl2, was present in photocatalytic system, holes could be neutralized by FeCl2. Thus photocorrosion could be avoided. Therefore, the sacrificial agent FeCl2, could both enhance hydrogen evolution and prevent photocorrosion of M1. However, the consumption of sacrificial agent to conduct hydrogen evolution reaction would decrease economic profit. To solve this problem, this research tried to conduct the reaction of photocatalytic hydrogen evolution using seawater, which is an unlimited and free resource. Two sources of seawater were taken from the estuary of Tamsui River, and east coast of Taiwan. The ions in seawater could act as sacrificial agent. The experimental result showed that adding the ions of seawater into pure water could enhance photocatalytic hydrogen evolution of M1 as well as prevent M1 from photocorrosion. Furthermore, photocatalytic hydrogen evolution from natural seawater (estuary of Tamsui river, Taiwan) showed better stability than that of pure water in a long-term test.
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