| The semiconductor-mediated photocatalytic reduction method is widely regarded as a promising way in treating Cr(Ⅵ) wasterwater. The development of high performance, low cost and nontoxic photocatalysts is essential for the popularization and application of photocatalysis technique in large-scale Cr(Ⅵ) wastewater treatment. This thesis focuses on synthesis and photocatalytic performances of SnS2-based new visible light-responsive photocatalysts (SnS2nanocrystals and SnS2/TiO2nanocomposites) as well as the mechanisms involved in the synthesis and photocatalysis. The main works completed are summarized as follows:1. Hexagonal phase SnS2nanocrystals with adjustable sizes were synthesized via the hydrothermal reactions of SnCl·5H2O, thioacetamide and citric acid at130-170℃for6-24h. The phase, size, Brumauer-Emmett-Teller (BET) specific surface areas and optical properties of the as-synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), N2adsorption/desorption and UV-vis diffuse reflectance spectra (UV-vis). Besides, their photocatalytic properties were tested for the reduction of Cr(Ⅵ) in aqueous solution under visible light (λ>420nm) irradiation. The influencing factors of photocatalytic activity including synthesis conditions, catalyst dosage, the initial concentration and pH value of Cr(Ⅵ) aqueous solution, etc. were also researched. The experimental results demonstrated that:(1) the synthesis conditions of SnS2nanocrystals affect their photocatalytic activities, and the product synthesized at150℃for12h not only showed high visible light-driven photocatalytic activity in the reduction of aqueous Cr(VI), but also showed good photocatalytic stability;(2) when the dosage of photocatalyst was larger, the initial concentration and pH of Cr(Ⅵ) aqueous solution was lower, the photocatalytic efficiency is higher; and (3) Cr(Ⅵ) was reduced to Cr(Ⅲ) after photocatalytic reactions. 2. First, hexagonal phase SnS2nanoflakes were synthesized via the hydrothermal reaction of SnCl·5H2O and thioacetamide in5%acetic acid aqueous solution at150℃for24h; then composition-tunable SnS2/TiO2nanocomposites were synthesized by solvothermal treatment of SnS2nanoflakes and tetrabutyl titanate and10%acetic acid aqueous solution at180℃for12h. The structures, compositions, Brunauer-Emmett-Teller (BET) specific surface areas and optical properties of the resultant products were characterized by XRD, TEM, HRTEM, EDX, XPS, N2adsorption and UV-vis diffuse reflectance spectra. Moreover, their photocatalytic properties were tested for the reduction of Cr(Ⅵ) in aqueous solutions under visible light (λ>420nm) irradiation. The experimental results showed that:(1) SnS2/TiO2nanocomposites with different compositions were obtained;(2) photocatalytic activities of SnS2/TiO2nanocomposites depended on their compositions, and SnS2/TiO2-C containing25.5mass%TiO2displayed the highest photocatalytic activity and had a certain degree of photocatalytic stability; and (3) Cr(VI) was reduced to Cr(Ⅲ).3. Composition-tunable SnS2/TiO2nanocomposites were obtained via one-step in-situ solvothermal method from the reactions of SnCl4·5H2O, thioacetamide and different amounts of tetrabutyl titanate in the mixed solvents of ethanol and acetic acid in autoclaves at180℃for12h. The structures, compositions, Brumauer-Emmett-Teller (BET) surface area and optical properties of the resultant products were characterized by XRD, EDX, FESEM (field emission scanning electron microscopy), TEM, HRTEM, XPS, N2adsorption and UV-vis diffuse reflectance spectra, and their photocatalytic properties were tested for the reduction of Cr(Ⅵ) under visible light (λ>420nm) irradiation. Furthermore, contrast photocatalytic experiments were also conducted for different doses of the as-synthesized SnS2/TiO2nanocomposite, SnS2and physical mixture of SnS2and TiO2(PM-SnS2/TiO2). The experimental results showed that:(1) The photocatalytic activities of as-synthesized SnS2/TiO2nanocomposites depended on their compositions, and SnS2/TiO2-D with a suitable content (44.5mass%) of TiO2possessed the highest photocatalytic activity among SnS2/TiO2-A-F;(2)0.1-0.3g of SnS2/TiO2-D always exhibited much higher photocatalytic efficiencies than the same doses of SnS2and PM-SnS2/TiO2;(3) SnS2/TiO2-D had good photocatalytic stability;(4) Cr(VI) can be reduced to Cr(Ⅲ) by SnS2/TiO2-mediated photocatalysis. The heterojunction structure of the as-synthesized SnS2/TiO2nanocomposite, which can facilitate interfacial electron transfer and reduce the self-agglomeration of two components, was considered to play an important role in achieving its greatly improved photocatalytic performance. The high visible light-driven photocatalytic activity and good stability of SnS2/TiO2-D render it a promising photocatalyst in efficient utilization of solar energy for the treatment of Cr(Ⅵ) wastewater.Finally, the summary of this thesis was made. |
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