| Summary: | 碩士 === 元智大學 === 化學工程與材料科學學系 === 105 === Titanium dioxide has attracted considerable attention for many environmental applications because of its outstanding properties and promising applications. However, the main drawback of TiO2 is the wide bandgap (3.2 eV), which limits its light response to the UV region. In order to overcome these limitations, a novel approach to generate disordered TiO2 with extended absorption profile in visible light region and improved photocatalytic efficiency through a hydrogenation process. Therefore, the objectives of this study were to synthesize and investigate the correlation between structures and photocatalytic activity using XRD, FE-SEM, HR-TEM, Raman, FTIR, XPS, UV-Vis, PL, TGA, and XANES. Experimentally, TiO2 nanobelts composites loaded by MoS2 nanoparticles with enhanced visible-light driven photocatalytic activity were successfully synthesized via a simple two-step hydrothermal method. Preparation of highly photo-activated TNs is achievable by hydrogenation at 450 oC and 30 bar in the duration of hydrogenation (6, 12, and 24 h). In addition, the intensity diffraction peaks for TNs decrease after hydrogenation, indicating the oxygen vacancy increase in the structure and results in a slight decrease on crystal sizes.
The crystal structures of TiO2 nanobelts are 4 micrometers in length and 50 nm in width. The surface of TiO2 nanobelts modified by MoS2 nanosheets (MTNs) successfully was observed. MoS2 nanosheets with a lateral size of about 50 nm were distributed on the surface of TNs. The results suggest that the prepared MTNs heterostructure are consisted of Ti4+, S2-, and Mo4+. The characteristic Raman peaks of TNs at 142 cm-1, 197 cm-1, 398 cm-1, 515 cm-1, and 640 cm-1 were ascribed to the Eg1, Eg2, B1g1, A1g+B1g2, and Eg3 are different vibration modes of anatase, respectively. The strongest peak at 142 cm-1 was the symmetric stretching modes of O–Ti–O. Moreover, the Raman peak at both 297 cm-1 and 334 cm-1 which were ascribed to the E2g and A1g vibration modes of MoS2, respectively. Functional groups identified by FTIR on the surface of MoS2/TNs were O-H (3441cm-1), Ti-OH (1627 cm-1), and -OH (3431 cm-1). The pure TNs show a significant absorption edge at a wavelength shorter than 400 nm, which can be assigned to the intrinsic bandgap absorption. Furthermore, the calculated bandgap energy for TNs is 3.19 eV. The absorption edge of MTNs20 (20 wt% MoS2) is red-shifted, which can be attributed to the chemical bonding between TiO2 and MoS2. Similarly, the calculated bandgap energy for MTNs20 is 2.89 eV. The intensity of hydrogenated TNs increase compared relatively with unhydrogenated ones under the visible and infrared region. The absorption edges of hydrogenated TNs composited with the molybdenum disulfide composites indicated that it may produce the largest red shift. It was confirmed that the hydrogenation treatment and the load MoS2 could enhanced the photoresponse range and improve the light absorption capacity of TNs in the visible region.
The as-prepared hydrogenated MTNs20 composites show the highest photocatalytic efficiency for the photocatalytic decolorization of Rhodamine B (RhB) aqueous solution under visible light irradiation. Highly apparent photocatalytic reaction of H2 MTNs20 is about 5 times than that of pure TiO2 nanobelts. The rate constants followed the order in series are H2 MTNs20 > H2 24 h > H2 12 h > H2 6h > MTNs20 > MTNs40 > TNs > MTNs60.
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