Study On Photocatalytic Properties Of WO₃-based And Bi₂WO₆-based Nanomaterials

With the development of modern industrial production,a large amount of industrial waste water containing organic matter and heavy metal ions was discharged and increased dramatically.One of heavy metal ions,chromium in compound is common trivalent valence and hexavalent valence.Trivalent chromium is beneficial to humans in some ways,and hexavalent chromium is inhaled toxins and is easily absorbed by the body.It can penetrate the body through the digestive tract,respiratory tract,skin and mucous membranes.Exposed short-term to high-dose hexavalent chromium,the human body will have adverse effects on the body,including ulcers,nasal irritation and nasal septum perforation.So it is urgent to govern pollution from hexavalent chromium.In this paper,hexavalent chromium is photoreduced to trivalent chromium which is beneficial to human body.The photocatalyst used in this paper is some materials based on tungsten trioxide and bismuth tungstate.The main contents are as follows:1.Flower-like WO₃ was prepared by hydrothermal method.WO₃/Ag and WO₃/TiO₂ composites based on flower-like WO₃ were prepared by hydrothermal method.The products were characterized by SEM,XRD and DRS.The photoreduction efficiency of Cr?VI?on the two composites was compared.The results showed that the reduction efficiency on WO₃/Ag was higher than on WO₃/TiO₂.2.In view of low reduction efficiency of Cr?VI?on WO₃ and its composites,it is needed to find other catalyst.So Bi₂WO₆ responding to visible light was paid much attention.Three Bi₂WO₆ materials with different morphology were prepared by hydrothermal method.The products were characterized by SEM,XRD,DRS and BET.The photocatalytic activity for Cr?VI?reduction on these three samples was compared,and the results showed that the reduction efficiency of sample S3 with much large surface area was highest.3.The 3D flower-like Bi₂WO₆ with the highest photocatalytic activity studied on the above experiment was selected as substrate to prepare Bi₂WO₆/CdS and Bi₂WO₆/Ag composites.The products were characterized by SEM,XRD and DRS.By varying the amount of CdS,three Bi₂WO₆/CdS heterostructured photocatalysts was prepared.In this study,Bi₂WO₆/CdS heterostructured photocatalyst refers to the sample prepared with 0.3 mmol cadmium nitrate because this sample exhibits the highest photocatalytic activity for Cr?VI?reduction among these three samples.The photocatalytic performance of Bi₂WO₆/CdS and Bi₂WO₆/Ag composites was compared and it is found that these two composites showed higher activity than pure Bi₂WO₆.It is worth noting that type II heterostructured Bi₂WO₆/CdS composite formed by two semiconductors exhibits prominently enhancement for Cr?VI?photoreduction.The photocatalytic mechanism of heterostructured Bi₂WO₆/CdS composite was proposed.