| Summary: | 碩士 === 國立聯合大學 === 環境與安全衛生工程學系碩士班 === 106 === Solar photocatalysis using partial shell-core Ag/P3HT@TiO2 as catalysts for the degradation of carbofuran pesticide wastewater was investigated in this study. The nano-photocatalyst of Ag/P3HT@TiO2 composite was prepared by a novel partial shell-core method and photoreduction method. The physical and chemical properties of Ag/P3HT@TiO2 nano-particles were characterized by Flame Atomic Absorption Spectrometry (AAS), the results showed that a 95% of the noble metal (Ag0) could be deposited on the surface of TiO2 in 5 minutes. The results of Scanning Electron Microscope (SEM) and X-ray Energy Dispersive Spectrometer (EDS) showed the prepared Ag/P3HT@TiO2 was indeed a partial shell-core type, and TiO2 was not completely covered by the addition of Ag and P3HT. The spectrum of UV/VIS Diffuse Reflectance Spectroscopy (UV/VIS DRS) showed that Ag/P3HT@TiO2 composites were much more responsive to visible light than TiO2. Accordingly, the drawback that TiO2 can only absorb part of sunlight (basically, λ<387 nm) can be improved, leading to solar energy can be effectively utilized. Moreover, the results of X-ray diffraction (XRD) indicated the crystal pattern of TiO2 still presented mainly anatase form in Ag/P3HT@TiO2 composites, and the grain size range is approximately 11-20 nm. The results of X-ray Fluorescence (XRF) analysis of Ag/P3HT@TiO2 also confirmed that the Ag element did exist in the photocatalysts.
The results showed that a 83.11% of the abs@λmax reduction efficiency and a 99.66% of carbofuran degradation efficiency could be achieved with a 0.5 g/L of Ag(0.1%)/P3HT(0.5%)@TiO2, a light irradiation of 500 W/m2, and a reaction time of 30 min for a 20 mg/L initial concentration of carbofuran pesticide wastewater. As the dosage of photocatalyst was reduced from 0.5 g/L to 0.25 g/L, the reaction rate of carbofuran wastewater also reduced 50%. However, the dosage of photocatalyst was increased to 0.75 g/L, the reaction rate of carbofuran wastewater increased slightly. The optimal dosage of photocatalyst used in this study was then supposed around 0.5 g/L.
In addition, the abs@λmax reduction rate of carbofuran pesticide wastewater could increase 3.31 times and the degradation rate of carbofuran in wastewater could increase 2.64 times as light irradiation increased from 250 to 750 W/m2. This may be due to accelerate the generation of electrons and holes in photocatalyst, leading to accelerate the formation rate of hydroxyl radicals, and then promote the oxidation of carbofuran. Moreover, the effect of the variation of wastewater temperature showed that increasing wastewater temperature was beneficial to improve the photocatalytic efficiency, especially in the water temperature of 15-25 0C.
With the assistance of Fresnel lens in the solar photocatalytic degradation of carbofuran wastewater, it was found that the degradation rate of carbofuran wastewater could increase 1.91 times. The molecule of carbofuran was more efficiently decomposed into low-molecular-weight organic acids which were further mineralized into carbon dioxide and water, resulting in a much lower microtoxicity of treated water.
Based on the results obtained in this study, using the Ag and P3HT (Poly 3-hexylthiophene) to modify the TiO2 can significantly improve the photocatalytic activity of TiO2. Solar photocatalysis using partial shell-core type Ag/P3HT@TiO2 as catalysts, particularly by the aid of Fresnel lens, could be a promising technology for the treatment of refractory organic wastewater such as pesticide wastewater.
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