| Hexavalent chromium (Cr(Ⅵ)) is a common heavy metal pollutant, which widely exists in the wastewater of pigment production, metal plating and leather tanning, etc. How to economically and efficiently treat the Cr(Ⅵ)-containing wastewater has attracted intense interest from both academic and industrial societies because of its high acute toxicity and strong carcinogenic activity to humans. A common method of treating aqueous Cr(Ⅵ) is to convert it into Cr(Ⅲ). which is less toxic and can be removed by forming precipitation at neutral or alkaline pH. Recently, the semiconductor photocatalytic reduction of aqueous Cr(Ⅵ) has received much attention due to its low cost, high reduction efficiency without secondary pollution and direct use of natural solar energy. The most extensively studied photocatalyst. TiO2, is limited in the practical application for removing Cr(Ⅵ) due to its large band gap and absorption of only the UV light, which accounts for only4%of the total sunlight. Therefore, it is significant to develop efficient and visible-light active photocatalysts for removing the Cr(Ⅵ) in wastewater. In this work, we have succesfully synthesized visible light response SnIn4S8photocatalysts via a facile hydrothennal/solvothermal method. And the photocatalytic reduction of aqueous Cr(Ⅵ) activity was investigated under visible light (λ>400nm) irradiation. In this dissertation, some works were carried out as follows:(1) The visible light response SnIn4S8photocatalysts were prepared via a facile hydrothermal/solvothermal method. The cubic and tetragonal SnIn4S8were synthesized in aqueous-and ethanol-meditated conditions, respectively. The as-prepared two samples exhibit strong photo response in the visible light region. By comparing the as-prepared two samples for photocatalytic reduction of aqueous Cr(Ⅵ) under visible light irradiation, we found that the ethanol-meditated SnIn4S8exhibit higher photocatalytic activity for the reduction of aqueous Cr(Ⅵ) than aqueous-meditated SnIn4S8. Its kinetic constant for the reduction of Cr(Ⅵ)(0.0351min-1) was about2times compared to the aqueous-meditated SnIn4S8(0.0174min-1).(2) The SnIn4S8particles with flower-like nanostructure were synthesized via a surfactant-assisted solvothermal method. The as-prepared SnIn4S8particles had strong absorption in visible region and the band gap was estimated to be from2.27to2.35eV. The polyvinyl pyrrolidone (PVP)-assisted SnIn4S8sample is composed of some hierarchical flower-like microspheres with an average diameter of about5-10μm, and there are numerous uniform pores on the surface of the microsphere. The photocatalytic reduction of aqueous Cr(Ⅵ) by flower-like SnIn4S8was evaluated under visible light (λ>400nm) irradiation. The PVP-assisted SnIn4S8sample exhibits excellent removal efficiency of Cr(Ⅵ)(～97%) and good photocatalytic stability. The predominant photocatalytic activity is due to its large surface area, strong absorption in visible-light region and excellent charge separation characteristics.(3) The Ag/SnIn4S8photocatalyst was prepared by solvothermal method, followed by a photocatalytic reduction method. The X-ray photoelectron spectra (XPS) showed that the Ag have been successfully deposited on the surface of SnIn4S8photocatalyst and mainly exists in the Ag(0) state. By comparing the photocatalysts before and after Ag loading for photocatalytic reduction of aqueous Cr(Ⅵ) under visible light irradiation, we found that its reduction of aqueous Cr(Ⅵ) activity has been improved with Ag loading. It can be ascribed to the deposited Ag on the surface of SnIn4S8photocatalyst efficiently suppressed the recombination of the photogenerated electrons and holes. |
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