Preparation Of Bi₂₅FeO₄₀ With Different Morphologies And Bi₂₅FeO₄₀/g-C₃N₄ Composites And Their Catalytic Properties For Degradation Of Organic Pollutants

Recently,as a new-type environmental friendly photocatalyst,sillenite materials Bi₁₂MO₂₀?M=Ga?Ge?Ti?have received considerable attention owing to their efficient photocatalytic properties and potential practical applications.In many of sillenite materials,bismuth ferrite(Bi₂₅FeO₄₀)is widely used in the field of environmental protection because of its unique crystal structure,non toxicity,as well as photocatalytic and Fenton catalytic properties.The study found that the catalytic activities of catalytic materials in photocatalytic and photo Fenton processes depends on its morphology,exposed facet,crystal size,light response range and separation efficiency of photogenerated electrons and holes and other factors.So,this work focused on Bi₂₅FeO₄₀ catalytic materials.We used morphology control and semiconductor composite two kinds of modification methods to control the catalyst to enhance its catalytic activity for degrading pollutants.The main researches are as follows:?1?Using bismuth nitrate and ferric nitrate as raw materials,Bi₂₅FeO₄₀microtetrahedra,microcubes and microspheres were successfully synthesized via a simple one step hydrothermal method.The formation mechanisms of Bi₂₅FeO₄₀microcrystals were discussed in detail,based on the time-dependent hydrothermal synthesis of BFO microcubes,we investigated the morphology evolution at different stages.The formation of the BFO microcrystal can be regarded as an Ostwald ripening process.The experimental and characterization analysis showed that the surface active agents have a direct influence on the supersaturation of the unit cell in the crystal growth process,which have a decisive influence on the crystal morphology and the exposed facets.?2?Rhodamine B?RhB?was chosen as the model pollutant to investigate the photo-Fenton degradation performance and mechanism of Bi₂₅FeO₄₀ catalysts with different morphologies.The results show that the microcube Bi₂₅FeO₄₀ catalyst exhibited the highest photo-Fenton catalytic activity,which could be attributed to its unique atomic arrangement on{001}facets and the iron atoms on this facet are more active,therefore resulted in higher catalytic activity.The stability of the Bi₂₅FeO₄₀samples were tested by recycling degradation experiment and FTIR spectra.The results indicated that the Bi₂₅FeO₄₀ samples have a good stability.In addition,through a series of degradation condition experiments,we found that the visible light,catalyst and H₂O₂are three essential elements in the process of photo-Fenton degradation.The reaction mechanism of the degradation of Fenton was proposed by hydroxyl radical trapping experiment.It was found that the·OH are the main active group in the photo-Fenton degradation.By comparing with the degradation effect of homogeneous Fenton experiment,we determined that the degradation type of the experiment was heterogeneous Fenton degradation.?3?Bi₂₅FeO₄₀ nanocrystals catalysts were synthesized by a sol-gel method and then coupled with g-C₃N₄ to prepare visible light Bi₂₅FeO₄₀/g-C₃N₄ composites.The physical and chemical properties of the prepared Bi₂₅FeO₄₀/g-C₃N₄ samples were tested by means of XRD,XPS,SEM,FTIR and other modern analytical methods.The results indicated that the composites were successfully synthesized,meanwhile g-C₃N₄ and Bi₂₅FeO₄₀ were closely combined to form heterogeneous structure.The results of photoluminescence spectra show that Bi₂₅FeO₄₀/g-C₃N₄ composites have a high efficiency of electron separation efficiency.The results of photocatalytic degradation of RhB suggested that the Bi₂₅FeO₄₀/g-C₃N₄ composites have a better photocatalytic activity than both Bi₂₅FeO₄₀0 or g-C₃N₄.The reason for the excellent photocatalytic activity of the catalyst was investigated.On the one hand,the excellent photocatalytic properties of catalysts can be attributed to its nanometer size,on the other hand,g-C₃N₄and Bi₂₅FeO₄₀ formed a heterogeneous structure,and its energy band structure is favorable for the separation of photogenerated electrons and holes.In addition,the photocatalytic degradation mechanism of Bi₂₅FeO₄₀/g-C₃N₄ composite photocatalyst was analyzed.