Preparation And Photocatalytic Performance Of MOF-based Z-type Photocatalysts

Metal Organic Frameworks(MOFs),also known as porous coordination polymers,represent a class of porous crystalline materials composed of Organic connectors and Metal ions/clusters.MOFs have the advantages of high specific surface area,adjustable pore size,good stability,and their easy modification,easy doping and easy recombination characteristics are also superior to some traditional semiconductors,which make MOFs useful in photocatalytic applications.However,in the photocatalytic process of pure phase MOFs,the rapid recombination of photogenerated electron-hole pairs is prone to reduce the photocatalytic efficiency.Therefore,many scientific researchers have tried their best to enhance the photocatalytic activity of MOFs from the aspects of light absorption range,electron and hole pair separation and migration efficiency.Based on the above research background,two Z-scheme photocatalysts based on MOFs have been designed and constructed,and a series of studies have been carried out on them:(1)The AgCl/Ag-doped-ZIF-8 composite photocatalyst was successfully synthesized by simple etching and doping.First,the ZIF-8 materials with regular morphology have been synthesized,and then the synthesized ZIF-8 was reacted with Ag NO₃ solution to achieve part of Ag⁺doping into the imidazole ring,thereby preparing Ag-doped-ZIF-8,which broadened the light response range of MOFs and reduced the band gap energy.Considering the difference in band gap energy,combined it with AgCl to form an AgCl/Ag-doped-ZIF-8 Z-scheme photocatalytic to further improve the photocatalytic ability.The photocatalytic activity of AgCl/Ag-doped-ZIF-8 photocatalyst was evaluated by degrading Rh B under visible light irradiation.The photooxidation and photoreduction rate was 12 times higher than that of bare ZIF-8,and it has good stability and repeated use.In addition,free radical capture experiments determined that the active groups in the photocatalytic degradation process were h⁺,·O₂^-and·OH.(2)Flower-like Bi₂WO₆ microspheres were prepared by hydrothermal method,and then ZIF-67 nanoparticles were loaded on the surface and gaps of Bi₂WO₆microspheres,and the Bi₂WO₆/ZIF-67 composite photocatalyst was successfully prepared.A series of characterization methods such as XRD,XPS,FT-IR,SEM,UV-vis were used to characterize the structure and morphology of the catalyst,and the degradation activity of the composite photocatalyst for tetracycline hydrochloride under visible light irradiation was investigated.When added to 100 m L of TC solution,the degradation rate of Bi₂WO₆/ZIF-67 was 4.53 times and 5.87 times that of Bi₂WO₆and ZIF-67,respectively,which realized the improvement of the photocatalytic efficiency of composite materials.Free radical capture experiments proved that h⁺,·O₂^-and·OH were the main active species in the photocatalytic degradation process.Through the analysis of the transfer process of photo-generated electrons and holes in the photocatalytic reaction process,the photocatalytic reaction process of Bi₂WO₆/ZIF-67 catalyst conforms to the Z-scheme photocatalytic.