Study On The Modification Of Metal-organic Framework MIL-101 And Its Adsorption Performance On Benzene

As a common waste gas in modern industry,benzene gas has a wide range of sources and has amount of harm to human body.So far,adsorption is the most promising treatment method.Metal-organic framework（MIL-101）has huge surface area,controllable pore structure,and the organic ligands are highly adjustable.It is a highly modifiable adsorbent.New functional materials with good adsorption properties can be obtained by directional modification like introducing functional groups or metal ions.In this paper,terephthalic acid was substituted by2-aminoterephthalic acid,NH₂-MIL-101 was prepared by hydrothermal method,and then propyl group was introduced into MIL-101 through the reaction of amino group and propionic anhydride,that’s the way how to achieve post-synthesis modified MIL-101;As the raw material,Hydroxyterephthalic acid was used to introduce the propyl group into MIL-101 by one-pot method,that’s the way how to achieve pre-synthesis modified MIL-101;Cu（NO₃）₂·3H₂O and synthesized propyl terephthalic acid were used as raw materials,Cu²⁺and propyl were introduced into MIL-101 by one-pot method to achieve pre-synthesis modified MIL-101（Cr,Cu）.The obtained MIL-101 is applied to the adsorption of benzene gas.Using field emission scanning electron microscope（FESEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,nitrogen adsorption and desorption instrument,X-ray photoelectron spectroscopy（XPS）,Fourier transform infrared spectroscopy（FTIR）to characterize the structure of the sample,using the static desiccator method to determine the adsorption amount of benzene gas.To study the influence of the introduction amount of propyl group and Cu²⁺,synthesis temperature,synthesis time,adsorption temperature and adsorption time on the adsorption performance of modified MIL-101.The results showed that:（1）With the introduction of-NH₂ into MIL-101,the crystallinity of the crystals weakened,the morphology changed from regular octahedrons to irregular polyhedrons,and the particle size decreased from 200 nm to50 nm;the introduction of-NH₂ occupied part of the pores,which reduced the surface area and pore volume of MIL-101 from 3098 m²/g and 1.82 cm³/g to 1755 m²/g and 1.29 cm³/g.As the molar ratio of NH₂-MIL-101 to propionic anhydride decreased,the edges and corners of the MIL-101 crystal gradually became blurred,the crystal morphology was consistent with NH₂-MIL-101,and the specific surface area and pore volume decreased.When the molar ratio of NH₂-MIL-101 to propionic anhydride was 2:1,the reaction temperature was 45°C,the reaction time was 24 h,the adsorption temperature was 30°C,and the adsorption time was 24 h,the surface area and pore volume of the post-synthesis modified MIL-101 was 1401 m²/g and 1.20 cm³/g,respectively,and the adsorption capacity of benzene gas could reach 1574 mg/g.The introduction of propyl group caused a certain loss of the surface area and pore volume of MIL-101,but increased its adsorption capacity for benzene gas.（2）When using pre-synthesis modification,as the molar ratio of propyl terephthalic acid to terephthalic acid increased,the partical morphology gradually changed from octahedron to irregular polyhedron,the crystal edges and corners were gradually blurred,and the size decreased from 200 nm to 80 nm;as the increase in the number of pores occupied by propyl groups reduced the surface area and pore volume of pre-synthesis modified MIL-101 gradually.When the ratio of propyl terephthalic acid to terephthalic acid was 1:16,the reaction temperature was 170°C,the reaction time was 24 h,the adsorption temperature was30°C,and the adsorption time was 24 h,the surface area and pore volume of the pre-synthesis modified MIL-101 were 2750 m²/g and 1.74cm³/g,respectively,and the adsorption capacity of benzene gas could reach 2200 mg/g.Compared with the post-synthesis modified MIL-101,the best adsorption capacity of the pre-synthesis modified MIL-101 for benzene gas increased by 39%.This may due to the absence of the content of synthesizing NH₂-MIL-101,and the direct introduction of propyl groups into MI-101,which made its adsorption performance better.（3）The introduction of Cu²⁺into MIL-101 made the octahedral corners of the sample passivated,and the grain size remained the same as MIL-101,about 200 nm.As the proportion of Cu²⁺increased,the surface area and pore volume of MIL-101（Cr,Cu）gradually shrank.When the ratio of Cr³⁺to Cu²⁺was 6:4,the surface area and pore volume of MIL-101（Cr,Cu）were 2697 m²/g and 1.5 cm³/g,respectively.When the adsorption temperature was 30℃and the adsorption time was 24 h,the adsorption capacity of benzene gas could reach 2000 mg/g.Kept the introduction amount of Cu²⁺,while introducing propyl group,the crystal size was reduced from 200 nm to 80 nm.As the molar ratio of propyl terephthalic acid to terephthalic acid increased,the morphology of the crystal changed from octahedron to irregular polyhedron,and the crystal edges and corners were gradually blurred;as the pore positions occupied by propyl terephthalic acid and Cu²⁺increased,the surface area and pore volume of pre-synthesis modified MIL-101（Cr,Cu）gradually decreased.When the ratio of Cr³⁺to Cu²⁺was 6:4,the ratio of terephthalic acid to propyl terephthalic acid was 16:1,the reaction temperature was 170°C,the reaction time was 24 h,the adsorption temperature was 30°C,and the adsorption time was 24 h,the specific surface area and pore volume of the pre-synthesis modified MIL-101（Cr,Cu）were 2326 m²/g and 1.62cm³/g,respectively.The adsorption capacity of benzene gas could reach2400 mg/g.The synergistic effect of Cu²⁺and propyl makes the adsorption performance of MIL-101 better than Cu²⁺doped or modified with propyl alone.