| Semiconductor-based photocatalysts have attracted growing interest in the field of dyeing wastewater treatment. Owing to its excellent chemical stability, photofunctional properties and nontoxic nature, TiO2 is considered to be one of the apt materials for the production of clean energy resources and environmental remediation. Nevertheless, the large band gap of 3.2 eV limits its use under UV light, which constitutes only 3% of the total solar spectrum. There have been many efforts, such as incorporation of metal ions, doping with nonmetals, or decoration with noble metal to make visible-light-active TiO2, but the modified materials usually suffer from low efficiency because of the weak interaction between TiO2 and the single modifier. In order to improve their interaction, the commercial P25-TiO2 samples were first activated in the SnCl2 solution. In this process, the Sn2+ was linked to the TiO2 surface through inorganic grafting between Sn2+ and surface hydroxyl groups. Then, Au nanoparticles was well loaded on TiO2 through the in-situ reduction of HAuCl4 by the linked Sn2+ species at ambient temperature, because the standard reduction potential of the Sn4+/Sn2+ is lower than that of AuCl4-/Au. The structure and properties of the obtained TiO2 photocatalysts modified with both noble metal nanoparticles and tin oxides were characterized by TEM, XRD, XPS, N2 physical absorption, XPS and UV-vis diffuse reflectance spectra. Photocatalytic activity toward degradation of dyes aqueous solution under visible light irradiation was also carried out to investigate the promotion of SnOx and noble metal nanoparticles. Moreover, the catalytic activity of the ternary heterostructures photocatalysts was optimized by the alteration of the dosage of noble metal precursor. Based on the intrinsic relations between structural characteristic and catalytic performance, a possible photocatalytic mechanisms for the ternary heterostructure under visible light irradiation was proposed. Finally, the effect of different water sources and the mixture of dyes on the catalytic preformance were studied. The specific content of research includes:1. The promotion of Au nanoparticles and SnOx on the photodegradation efficiency of TiO2 was investigated first. In this part, TiO2/SnOx-Au ternary heterostructures were prepared via a simple in situ reduction of AuCl4- on TiO2 surface pre-modified with Sn2+. TEM studies suggest that the highly dispersive and ultrafine Au nanoparticles（NPs） that covered with SnOx was deposited onto the surface of TiO2. The heterostructures significantly enhanced the photocatalytic activity compared with the traditional TiO2/Au sample prepared by the impregnation method and also higher than that of binary TiO2/SnOx sample.2. TiO2/SnOX-Ag ternary composites were also prepared by the aforementioned in situ reduction method. The effect of the incorporation of Ag nanoparticles, wihch occupies a lower fermi level comparied with Au nanoparticles, on the chemical environment of SnOx species was investigated deeply by the XPS studies. The size of Ag NPs could be well controlled by simply tuning the dosage of AgNO3. The results suggest that Sn species on TiO2/SnOx-Ag photocatalysts were in their oxides states（both SnO and SnO2）. The optimized catalytic activity of the ternary heterostructures was obtained when the nominal dosage of Ag was 2 %.3. The aforementioned optimized ternary heterostructures were chosed as the photocatalysts to degrade and mineralize dyes. In this part, the effect of different water sources（deionized water, tap water and Qiantang River） and the mixture of dyes（RhB and MB） on the catalytic preformance were studied. The result indicates that the ternary heterostructures photocatalysts possess good suitability. Moreover, the photocatalyst could be successfully recycled and reused for at least five times with a stable conversion of 85%. Finally, we suggeted that the enhancement of photocatalytic performance could be attributed to the surface plasmon resonance effect of noble nanoparticles and electron-sink function of SnOx, which improve the optical absorption property as well as photoinduced charge carriers separation, synergistically facilitating the photocatalysis. |
