| Currently, there is an increasing interest in the application of semiconductors as photocatalysts to Cr(Ⅵ) reduction. In this thesis, SnS2/SnO2nanocomposites with different composition and structure were synthesized via solid state method or hydrothermal method. The photocatalytic properties of the as-prepared products were tested by the reduction of aqueous Cr(Ⅵ) under visible-light (λ>420nm) irradiation. The main works completed are summarized as follows:1. A simple one-step in air synthesis method, which was based on heating the mixture of Sn, S and NH4CI powders in air at320℃for different times, was proposed for composition-tunable synthesis of SnS2/SnO2nanocomposites. The composition, structure, 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), N2adsorption/desorption and UV-vis diffuse reflectance spectra (UV-vis). The photocatalytic activities of the as-synthesized SnS2/SnC>2nanocomposites were tested in the reduction of aqueous Cr(Ⅵ) under visible-light (λ>420nm) irradiation, compared with that of SnS2nanoflakes. The influencing factors of photocatalytic activity including synthesis conditions, catalyst dosage, the initial concentration of Cr(Ⅵ), etc. were also researched. Besides, the effects of the coexistence of some organic compounds (e.g., phenol, rhodamine B and methyl orange) on the photocatalytic reduction of aqueous Cr(Ⅵ) over SnS2/SnO2nanocomposite were also studied. It was observed that (i) the photocatalytic activities of SnS2/SnO2nanocomposites were determined by their compositions, SnS2/SnO2-3h with a suitable composition () exhibited the highest photocatalytic activity;(ⅱ) all the as-synthesized SnS2/SnO2 nanocomposites (e.g., SnS2/SnO2-2h, SnS2/SnO2-3h and SnS2/SnO2-4h) exhibited higher photocatalytic activities than SnS2nanoflakes;(ⅲ) while the other conditions were the same, the photocatalytic efficiency of SnS2/SnO2-3h increased with the increase of the catalyst dosage (100-500mg) and the decrease of the initial concentration of Cr(Ⅵ) aqueous solution; and (ⅳ) the coexistence of phenol and rhodamine B enhanced the photocatalytic reduction of Cr(Ⅵ), whereas the coexistence of MO retarded the photocatalytic reduction of Cr(Ⅵ) over SnS2/SnO2nanocomposite. The reasons accounting for the photocataytic results were also discussed.2. An alternative in situ chemical method, which was based on thermal oxidation of SnS2nanoparticles in air at300℃for2-4h, was proposed for the preparation of SnS2/SnO2nanocomposite. The composition, structure, the 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), N2adsorption/desorption and UV-vis diffuse reflectance spectra (UV-vis). The photocatalytic properties of SnS2/SnO2nanocomposite were tested by the reduction of aqueous Cr(Ⅵ) under visible-light (λ>420nm) irradiation, and compared with those of SnS2nanoparticles, SnO2nanoparticles and SnS2/SnO2-PM (which denotes the physically mixed SnS2/SnO2nanocomposite with the same composition as SnS2/SnO2-3h). The influencing factors of photocatalytic activity including synthesis conditions, the initial concentration and pH value of Cr(Ⅵ) aqueous solution, etc. were also researched. Besides, the effects of the coexistence of some organic compounds (e.g., phenol, rhodamine B (RhB) and methyl orange (MO)) on SnS2/SnO2-3h-mediated photocatalytic reduction of aqueous Cr(Ⅵ) were also studied. It was observed that (ⅰ) SnS2/SnO2-3h not only displayed higher visible-light-activated photocatalytic activity than SnS2, SnO2and PM-SnS2/SnO2, but also displayed good reusability in the reduction of aqueous Cr(Ⅵ);(ⅱ) while the other conditions were the same, the photocatalytic efficiency of SnS2/SnO2-3h decreased with the increase of the initial concentration and pH value of Cr(Ⅵ) aqueous solution, and (ⅲ) the coexistence of phenol and RhB enhanced the photocatalytic reduction of Cr(Ⅵ), whereas the coexistence of MO retarded the photocatalytic reduction of Cr(Ⅵ) over SnS2/SnO2-3h. The reasons accounting for the photocatalytic results were also discussed.3.A simple and cost-effective one-step hydrothermal method, which was based on the reactions of tin(Ⅳ) chloride pentahydrate and different dosages of thioacetamide in water at190℃for6h, was employed for the synthesis of composition-tunable SnS2/SnO2nanoheterojunctions (e.g., SnS2/SnO2-A, SnS2/SnO2-B and SnS2/SnO2-C).The composition, structure, the 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). The photocatalytic properties of the as-synthesized SnS2/SnO2nanoheteroj unctions were tested by the reduction of aqueous Cr(Ⅵ) under visible-light (λ>420nm) irradiation. Furthermore, the photocatalytic efficiency of SnS2/SnO2-B was compared with those of PM-SnS2/SnO2(which denotes the physically mixed SnS2/SnO2nanocomposite with the same composition as SnS2/SnO2-B) and SnS2nanoflakes at different dosages of photocatalysts. It was observed that (ⅰ) the photocatalytic activities of the as-synthesized SnS2/SnO2nanoheteroj unctions depended on their compositions, and SnS2/SnO2-B with70mol%SnS2displayed the highest photocatalytic activity;(ⅱ) SnS2/SnO2-B invariably exhibited higher photocatalytic efficiencies than PM-SnS2/SnO2and SnS2nanoflakes at different dosages of photocatalysts;(ⅲ) the washing with1mol/L HNO3can effectively regenerate the used photocatalyst;(ⅳ) SnS2/SnO2-B exhibited good photocatalytic stability in reuses, with regeneration by1mol/L HNO3-washing after each cycle photocatalytic use; and (Ⅴ) Cr(Ⅵ) was reduced to Cr(Ⅲ). The possible formation mechanism of SnS2/SnO2 nanoheteroj unctions and the reasons accounting for the photocatalytic results were also discussed. |
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