Study On The Preparation And Photocatalytic Activity Of MIL-53(Fe,Cr) And Its Composites

Photocatalytic technology uses light energy to degrade organic pollutants into water and carbon dioxide,which is a green and environmentally friendly method.The research and development of photocatalysts play an important role in the application of this technology.Increasing the active sites of photocatalysts under certain specific surface area is the key to improve their catalytic performance.Metal-organic frameworks?MOFs?are novel materials with a spatial three-dimensional network structure,which have large specific surface area,high porosity,and rich metal active sites and so on..They are widely concerned in the fields of catalysis.With the metal oxygen cluster structure of the secondary structural unit,MOFs material can show the properties of semi-conductor.So it has potential application value in the field of photocatalysis.Bimetallic MOFs have more metal active sites than mono-metallic MOFs,so their catalytic performance is improved.In this paper,terephthalic acid was used as the organic ligand,iron and chromium were used as the metal source,and the bimetallic organic framework structure material MIL-53?Fe,Cr?was synthesized by solvothermal method.Exploring the optimal preparation conditions of photocatalysts by changing a variety of single factor variables,The optimum preparation conditions are as follows:the solvothermal synthesis time for 15h,central metal ion ratio Fe³⁺:Cr³⁺=0.80:0.20?molar ratio?,post-treatment calcination temperature is 150?,and calcination time is 2h.The photocatalytic activity was determined by the removal rate of methylene blue solution under ultraviolet light.The results show that the highest removal rate of methylene blue by MIL-53?Fe,Cr?is 95.12%within 3h under ultraviolet light.The synthesized materials were characterized by XRD,SEM,EDS,FT-IR and XPS techniques.XRD and SEM show that the crystallization of MIL-53?Fe,Cr?under the optimal conditions was better.EDS indicates the presence of two metal ions in MIL-53?Fe,Cr?,FT-IR indicates that the central metal ion of the bimetallic MOFs material reacts with the organic ligand,forming the metal complexes.XPS analyzes the valence states and existence forms of major elements in MIL-53?Fe,Cr?.The univariate method shows how the catalyst activity is influenced by pH value of simulated pollutant methylene blue solution,catalyst dosage and treatment of methylene blue solution with different concentrations.The experimental results show that the synthesized photocatalyst MIL-53?Fe,Cr?has a wide range of pH?pH=4¹1?.The optimum dosage of the catalyst was 1.00 g/L.The capture experiments of the active substances show that photogenic electrons and·OH are the main active substances in the photocatalytic process.In order to further improve the photocatalytic performance and recycling rate of MOFs under visible light,In this paper,MIL-53?Fe?and MIL-53?Fe,Cr?photocatalysts were synthesized and then combined.The materials were characterized by XRD,SEM,EDS,FT-IR and XPS techniques.By combining two kinds of MOFs materials MIL-53?Fe?and MIL-53?Fe,Cr?with nanomaterials N,F-TiO2 and magnetic particles Fe3O4@SiO2,the photocatalytic activity under visible light and the recovery efficiency of the catalyst were improved at the same time.Finally,two kinds of composite photocatalysts N,F-TiO₂@Fe₃O₄@SiO₂@MIL-53?Fe?and N,F-TiO₂@Fe₃O₄@SiO₂@MIL-53?Fe,Cr?with visible light response and magnetic properties were obtained.The removal rates of 10.00mg/L methylene blue by the two composite photocatalysts within 3h of visible light are73.1%and 74.1%,respectively.Active material capture experiments show that the composite photocatalyst produced more·OH due to the addition of N,F-TiO2.The catalyst reuse experiments show that the reusing effect of the composite photocatalyst is significantly better than that of the uncomposited MOFs.