| In this dissertation,thioacetamide and L-cysteine were used as sulfur source,several kinds of semiconductor metal sulfide nanomaterials with special morphologies including PbS nanocubes,PbS nanorods,PbS nanorice,urchin-like nano-sizedγ-MnS,flower-like nano-sized CuS,and rose-like nano-sized MoS2 were successfully prepared a environmental-friendly,economic,simple,and high-efficient liquid-phase method.A series of characterization techniques have been used to characterize the phase and morphology of the PbS nanocubes,PbS nanorods,PbS nanorice,urchin-like nano-sizedγ-MnS,flower-like nano-sized CuS,and rose-like nano-sized MoS2.Tentative explanations for the growth mechanisms of the semiconductor metal sulfide nanomaterials were proposed.The optical properties（optical absorption,photoluminescence）and photocatalytic properties of related materials have been studied.1.Uniform PbS nanocubes,nanorods and nanorice were successfully prepared in high yield using lead acetate trihydrate（Pb（CH3COO）2·3H2O）as lead source and thioacetamide（TAA）as sulfur source at low temperature in aqueous solution by controlling the molar ratio of Pb（CH3COO）2·3H2O/TAA and reaction temperature with the assistance of surfactant cetyltrimethylammonium bromide（CTAB）.The morphology,structure,and optical properties of the products were characterized by means of X-ray powder diffraction（XRD）,energy-dispersive X-ray spectrometry（EDX）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,raman spectroscopy,Fourier transform infrared spectroscopy（FTIR）,UV-Vis-NIR absorption spectroscopy,and photoluminescence（PL）spectroscopy.It was found that the as-prepared PbS nanocubes and nanorods are single crystal structure with good crystallinity,regular morphology and uniform particle size distribution.The mean edge length of the PbS nanocubes is 60 nm,and the nanorods have an average diameter of 36nm and an average length of 110 nm.The as-prepared PbS nanorice have polycrystalline structure which have an equatorial diameter of 4555 nm and a length of 90150 nm.Three different growth mechanisms were proposed to illustrate the formation process of PbS nanocubes,nanorods,and nanorice respectively according to the time-dependent experiments.It is worth noting that the morphology evolution of PbS nanocubes could be summarized as‘‘particle-rod-cube mechanism,’’which might be model systems for understanding the growth process of other kinds of nanomaterials with face-centered cubic structure and directing their synthesis.The absorption and emission peaks of PbS nanocubes and nanorods exhibit remarkably blue-shift when compared to the bulk PbS.Dark-field light scattering measurement showed that the PbS nanocubes and nanorods scatter orange light,indicating that the as-prepared PbS nanocubes and nanorods may have potential applications in molecular imaging and in vivo cancer diagnosis and therapy.2.Uniform urchin-like nano-sizedγ-MnS was successfully prepared using MnSO4·H2O as manganese source and L-cysteine as sulfur source via a facile hydrothermal method without using any surfactant or template.The phase,composition,morphology,and structure of the product were characterized by XRD,EDX,XPS,FESEM and TEM,UV-Vis,and BET techniques.The as-prepared urchin-like nano-sizedγ-MnS with a diameter of 45.5μm is formed by the assembly of numerous nanorods.A possible growth mechanism was proposed to illustrate the formation process of urchin-like nano-sizedγ-MnS according to the time-dependent experiments.The roles of solvents,sulfur sources,manganese sources and the molar ratio of reactants in the forming of urchin-like nano-sizedγ-MnS were investigated.The results show that solvents,sulfur sources,manganese sources and the molar ratio of reactants play crucial roles on the morphology and size of the product.The urchin-like nano-sizedγ-MnS exhibits a large specific surface area of 34.55 m2/g.The absorption peak of the as-prepared urchin-like nano-sizedγ-MnS has been observed at 264 nm.Based on the UV-Vis absorption spectrum,the band gap energy of direct gap semiconductor of urchin-like nano-sizedγ-MnS is calculated to be 3.95 eV,which implied that urchin-like nano-sizedγ-MnS is suitable for UV light photocatalyst.Compared with bulk MnS,which has a band gap of 3.7 eV,the as-prepared urchin-like nano-sizedγ-MnS exhibits a blue-shift,which could be attributed to the strong quantum size effect.The photocatalytic properties of urchin-like nano-sizedγ-MnS were studied through the UV light photocatalytic degradation of methylene blue（MB）.The results show that MB discolours dramatically up to 92%after 80 min UV light irradiation,indicating the higher UV light photocatalytic properties of the as-prepared urchin-like nano-sizedγ-MnS,which can be mainly ascribed to the high light harvesting ability realized by the unique morphology of 3D urchin-like hierarchical structure,in which the interspaces act as the channel for light transfer.The as-prepared urchin-like nano-sizedγ-MnS may have many potential applications for industry wastewater treatment.3.Uniform flower-like nano-sized CuS was generated conveniently in aqueous solution at low temperature using CuCl2·2H2O as copper source and TAA as sulfur source without using any surfactant.The product was characterized by XRD,XPS,EDX,FESEM,TEM,UV-Vis,PL,and BET techniques.The as-prepared flower-like nano-sized CuS with a diameter of 8001200 nm is formed by the assembly of numerous nanosheets.A tentative explanation for the growth mechanism of flower-like nano-sized CuS was proposed.The roles of copper source and surfactants PVP in the forming of urchin-like nano-sizedγ-MnS were investigated.The results indicate that copper source and surfactants PVP play crucial roles on the morphology and size of the product.UV-Vis absorption spectrum and PL spectrum were used to investigate the optical properties of flower-like nano-sized CuS.UV-Vis absorption spectrum shows a broad absorption band in the visible range and PL spectrum shows a strong ultraviolet emission peak.The BET surface area of the as-prepared product was calculated to be61.55 m2/g with a dominant pore diameter of 26 nm.The photocatalytic properties of flower-like nano-sized CuS were evaluated by measuring the decomposition rate of MB aqueous solution under visible light irradiation.The results show that MB discolours dramatically up to 92%after 90 min visible light irradiation,indicating the higher visible light photocatalytic properties and good cycling stability of the as-prepared flower-like nano-sized CuS.It may be due to the unique porous structure with a large surface area,which could be exposed to the MB solution sufficiently and absorb more photons to produce electron-hole pairs conveniently under the visible light irradiation.It is expected that the flower-like nano-sized CuS will offer exciting opportunities for wastewater treatment under sunlight irradiation.4.Uniform rose-like nano-sized MoS2 was succefully synthesized on a large scale through a template-free hydrothermal method by the reaction of hexaammonium heptamolybdate tetrahydrate[（NH4）6Mo7O24·4H2O]and thioacetamide（CH3CSNH2）.The product was characterized by XRD,XPS,FESEM,TEM,UV-Vis,and BET techniques.The rose-like nano-sized MoS2 has a diameter of 350450 nm and is formed by the assembly of numerous nanosheets.A reasonable growth mechanism of the rose-like nano-sized MoS2 was proposed according to the time-dependent experiments.The roles of reaction temperature,sulfur sources,and the molar ratio of reactants in the forming of rose-like nano-sized MoS2 were investigated.The results show that sulfur sources,and the molar ratio of reactants play crucial roles on the morphology and size of the products.When the reaction temperature is between 180℃and 240℃,the products are all flower-like structures with little change in morphology.It is worth mentioning that the intensity of diffraction peaks becomes sharper with the increased temperature,indicating the improvement of crystallinity.Especially,the location of（110）peak also shifted to the high angles with the increased temperature.The as-prepared rose-like nano-sized MoS2 has a large specific surface area of33.72 m2/g with a dominant pore diameter of 46 nm.The absorption peaks of the rose-like nano-sized MoS2 have been observed at 490 nm and 620 nm.Based on the UV-Vis absorption spectrum,the band gap energy of direct gap semiconductor rose-like nano-sized MoS2 is calculated to be 2.75 eV,which indicated that the as-prepared MoS2is suitable for visible light photocatalyst.Compared with bulk MoS2,which has an absorption edges at 1040 nm（1.23 eV band gap）,the as-prepared rose-like nano-sized MoS2 exhibits a large blue-shift,probably due to the strong quantum confinement effect.The photocatalytic properties of rose-like nano-sized MoS2 was studied through the visible light photocatalytic degradation of MB.The results show that MB discolours dramatically up to 94%after 120 min visible light irradiation,indicating the higher visible light photocatalytic properties and good cycling stability of the as-prepared rose-like nano-sized MoS2,which can be attributed to the special structural feature with an open and porous nanostructured surface layer that significantly facilitates the diffusion and mass transportation of MB molecules and oxygen species in photochemical reaction of MB degradation.This resulting rose-like nano-sized MoS2are very promising visible light photocatalysts for the degradation of dye pollutants and other applications. |
