| Summary: | 碩士 === 國立中央大學 === 化學工程與材料工程學系 === 102 === The purpose of this study was focused on preparing a photocatalyst with high photoactivity under UV light illumination and could be utilized on corrosion protection. This study used organic dye such as methylene blue to carry out photocatalytic reaction. Moreover, we coated as-prepared liquid photocatalyst onto stainless steel so as to analyze the anticorrosion effect about protecting interior metal substrate. Due to using WO3 to modify TiO2, the photoinduced electrons could be transferred from the conduction band of TiO2 to the conduction band of WO3 and stored on the storage system- WO3. Thus, it could be applied to dark condition and still had great effect of anticorrosion. If applied to the photocatalysis of degrading methylene blue, it could be take the advantage of lower band gap and lower conduction band of WO3 to inhibit the recombination of electron-hole pairs and enhance the separation rate of electron-hole pairs to increase the photoactivity. The literature used sol-gel method to synthesize W-modified TiO2 in liquid phase and then utilize dip-coating to coat as-prepared sol onto substrate. Because of liquid photocatalyst could be reused again and again, the cost of preparing photocatalyst could be decreased significantly. Moreover, the structure of different photocatalyst on different preparing conditions could be analyzed by XRD, SEM, TEM, HRTEM and XPS. The cycle potential range of cyclic voltammetry to analyze anticorrosion effect was set from -0.8 V to 0.6 V. The electrolyte used 5 wt% NaCl(aq). The photocatalytic reaction was carried out with methylene blue destruction by 20 W UVC light illumination and the concentration of every sample could be analyzed with UV-visible spectrophotometer. From the figures of XRD, the as-prepared TiO2 nanoparticles were all in anatase phase. Then, there were no peaks corresponding to WO3 due to the low amount of WO3. From SEM images, the as-prepared thin film of photocatalyst was very uniform and the thickness of thin film was around 348.84 nm. As shown in the SAED from TEM and the lattice space from HRTEM, both could be verified that the TiO2 nanoparticles were all anatase. Seen by the figures of TEM and HRTEM, the major and minor axis of pure TiO2 and W-modified TiO2 nanoparticles were 30-77 nm, 15-31 nm, 33-53 nm and 7-12 nm, respectively. It could be indicated that doping WO3 into TiO2 could decrease the minor axis obviously. From the data of XPS next, the chemical states of Ti and W were Ti3+, Ti4+, W5+ and W6+. Ti3+ and W5+ could gather holes; however, Ti4+ and W6+ could trap photoinduced electrons. The amount of these chemical states affected the recombination of electron-hole pairs. In the analysis of photoactivity, placing coated stainless steel substrates with photocatalyst thin film into 5 wt% sulfuric solution could be tested the anticorrosion effect. The results demonstrated that HT (1) exhibited great effect of corrosion protection. If using the same coated substrates to do cyclic voltammetry analysis, the results also indicated the same result, that is, the sample with the weight ratio of TiO2:WO3 = 100 : 1 could have lowest current density and the amount of charge. It could be showed the best effect of anticorrosion. The other photocatalysis with destruction organic dye illustrated NT (4) and HT (4) performed the best photoactivity on degrading methylene blue solution. Among the two different W precursors, NT, which was used Na2WO4 as precursor, exhibited the best photoacivity no matter in anticorrosion or in degradation. This study revealed W-modified TiO2 could be influenced by the amount of adding W and different W precursors.
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