Synthesis Of Magnetic TiO₂ Nanocomposites And Its Application In Remediation Of Water Pollution

Due to industrial development, more and more pollutants have beenreleased into the environment. Among them, the co-contamination with heavy metal ionsand toxic organic pollutants is particularly serious. The co-contamination is a serious threat to human health and environment and can’ t be simultaneously removed by traditional methods. Because of the superiorities of TiO₂ on photocatalysis and magnetic nanoparticles on solid-liquid separation, a series of magnetic TiO₂ nanocomposites were prepared and applied to treat wastewater containing heavy organics and metal. In this study, three magnetic TiO₂ nanocomposites including Fe（III）-TiO₂, magnetic Fe₃O₄@TiO₂ nanocomposites and magnetic FexOy-TiO₂ nanocomposites were successfully synthesized. The application in wastewater treatment was investigated.Chapter 2 of the paper investigatedthe preparation and application of Fe（III）-TiO₂. Firstly, Fe（III）-TiO₂ was prepared via self-assembly surfactant-based sol-gel method. Then, the photocatalytic activities of thesamples were evaluated by the photodegradation of BPA under visible light irradiation. The effect of the relative concentration of Fe（III）, the calcination temperaturevalue, the calcination time and the present of H₂O₂ on the photocatalytic activity was also studied and the optimal value was found out. The results show that the dopant of Fe（III） could enhance the photocatalytic efficiency of TiO₂ and the optimal amount was 0.001 mol. The optimal calcination temperature was 450°C and the optimal calcination time was 3h. With the present of H₂O₂, the photocatalytic efficiency of Fe（III）-TiO₂ was significantly enhanced. The results suggested that Fe（III）-TiO₂ had potential superiority in removal of BPA from wastewater.Chapter 3 of the paper was mainly centered in magnetic Fe₃O₄@TiO₂ nanocomposites. In this chapter, a novelmagnetic Fe₃O₄@TiO₂ nanocompositeswas fabricated through self-assembly surfactant-based sol-gel method. Then, the photocatalytic activities of thesamples were evaluated by the photodegradation of BPA under visible light irradiation. The results show that magnetic Fe₃O₄@TiO₂ nanocomposites exhibited more preferential photocatalytic activity than TiO₂ nanocomposites and Fe₃O₄ nanocomposites. The increased photocatalytic activity of Fe₃O₄@TiO₂ nanocomposites might be attributed to the expanded absorption range and the effective separation of electron–hole pairs. The effect of the relative concentration of Fe₃O₄ nanocomposites and the initial p H value on the photocatalytic activity was also studied and the optimal value was found out. The results show that the optimal amount of Fe₃O₄ nanocomposites was 0.001 mol. At the same time, the photocatalytic efficiency of Fe₃O₄@TiO₂ nanocomposites was significantly enhance with the PH descends. Moreover, Fe₃O₄@TiO₂ nanocomposites could be easily separated from aqoeous solution and recycled by using magnetic field. When Fe₃O₄@TiO₂ nanocomposites was used for the eighth time, the photodegradation efficiency of BPA still reached 38.3%. These superior properties demonstrate that Fe₃O₄@TiO₂ nanocomposites is attractive for practical applications in treatment of water contamination by BPA.Chapter 4 of the paper discussed the application of magnetic Fe_xO_y-TiO₂（FT） nanocomposites in removal of BPA and Cr（VI）. The magnetic FexOy-TiO₂（FT） nanocomposites have been synthesized via self-assembly surfactant-based sol-gel method. The as-prepared samples were characterized by powder X-ray diffraction（XRD）, field emission scanning electron microscopy（FESEM）, X-ray photoelectron spectroscopy（XPS）, UV-vis diffuse reflectance spectra（UV-vis DRS） and Brunauer-Emmett-Teller（BET） area. The photocatalytic activities of the samples were evaluated by the simultaneous photodegradation of BPA and photoreductionof Cr（VI） under visible light irradiation. The results show that the photocatalytic efficiency of FT for BPA is 93.1% while the pure TiO₂ is 75.6%, and the photocatalytic efficiency of FT for Cr（VI） is84.3% while the pure TiO₂ is 64.8%. The increased photocatalytic activity of FT might be attributed to the expanded absorption range, the effective separation of electron–hole pairs and the larger specific surface area. Especially, the rate constants for removal of BPA was enhanced 3.37 times with the presence of Cr（VI） and the rate constants for removal of Cr（VI） was enhanced 9.29 times with the presence of BPA, demonstrating an obvious synergism between BPA degradation and Cr（VI）reduction. The effect of the relative concentration of BPA and Cr（VI） and the initial pH value on the photocatalytic activity was also studied and the optimal value was found out. When FT was used for the eighth time, the removal efficiency of BPA and Cr（VI） still reached 68.9% and 57.9%.