Preparation And Properties Of Bi₂O₃/Diatomite Composite Photocatalyst

Bi₂O₃ has a narrow band gap,which can absorb and utilize the visible light in the solar spectrum,and it can oxidize and decompose organic wastewater in industry,which is of great significance in ecological protection.Although Bi₂O₃ nanocrystals have high photocatalytic activity,Bi₂O₃ powder is easily suspended in a solution,so separation and recovery from a liquid phase system are difficult,which restricts the application range.In this paper,the diatomite mineral material with porous structure was supported Bi₂O₃ by hydrothermal method,and Bi₂O₃/diatomite composite photocatalysts with visible light response and easy recycling were prepared.In this paper,the diatomite was used as carrier to carry out air calcination,reduction roasting and hydrogen peroxide treatment at different water bath temperatures to control the content and state of organic carbon on the surface of the diatomites.The surface organic matter content,zero potential and surface functional groups of the pretreated carriers were analyzed by means of DSC,mass titration,XRD and FT-IR.The experimental results show that the organic carbon on the surface of the diatomaceous earth calcined in the air atmosphere has been completely removed,the zero potential value is large,and the adsorption capacity is relatively small.Most of the organic matter on the surface of carbonized diatomite is converted into amorphous carbon,the zero potential value is large,and the adsorption capacity is small.Hydrogen peroxide treatment can oxidize and decompose organic matter.As the temperature of the water bath increases,the organic matter content gradually decreases,the point of zero charge is gradually increased,and the adsorption capacity is gradually reduced.When the water bath temperature reaches 80^oC,the surface organic matter is basically removed.Hydrogen peroxide treatment of diatomaceous earth at different water bath temperatures not only regulates the content,state and surface charge of the organic matter on the surface of the diatomaceous earth,but also activates the diatomaceous earth.In the synthesis of Bi₂O₃ precursor,Bi₂O₃ nanosheets were prepared by hydrothermal method,and Bi₂O₃/diatomite composite catalyst was prepared under the optimal conditions.The effects of hydrothermal conditions,pH value and loading mass ratio on the structure and properties of composite samples were investigated.The experimental results show that the carrier soil not only inhibits the phase transition of Bi₂O₃,but also broadens the pH range of Bi₂O₃ catalyst.The surface organic carbon of diatomite affects the growth morphology of Bi₂O₃ nanosheets.The surface organic matter of diatomite is treated by hydrogen peroxide,which is beneficial to the Bi₂O₃ nanosheets grow vertically on the surface of diatomaceous earth,and densely interlaced to form a three dimensional structure.The point of zero charge on the surface of diatomites affects the adsorption capacity of the composite sample.The smaller the zero charge,the stronger the surface acidity and the greater the adsorption capacity.the hydrothermal temperature is 180°C,the hydrothermal time is 10 hours,the hydrothermal pH value is 8.0⁸.5,and the loading mass ratio of Bi₂O₃/diatomite is 2:1,which is the best preparation condition for composite samples.Under the optimal conditions,the degradation rate of rhodamine B can reach to 80%with Bi₂O₃/50^oC-HD composite photocatalyst after visible light for 8 hours,and the levofloxacin was completely degraded after 4 hours of visible light irradiation.And the degradation rate of rhodamine B was over 100%after exposure to ultraviolet light for 1 hours.Photocatalytic mechanism studies show that Bi₂O₃/50^oC-HD composite photocatalyst exhibits excellent photoelectrochemical performance response,and its excellent photocatalytic activity may be due to the strong adsorption capacity of the Bi₂O₃/50^oC-HD composite sample,as well as the three-dimensional structure of Bi₂O₃nanosheets can effectively separate electron and holes.