Preparation Of Functionalized MIL-101 Metal-organic Framework And Its Adsorption Properties For Benzene Gas

As a common VOC,benzene gas has a wide range of sources and is harmful to the human body.At present,the most economical and effective method for the treatment of benzene gas is the adsorption method.Metal-organic framework MIL-101 is often used as benzene gas adsorption material due to its huge specific surface area,good porosity and controllable pore structure.In this paper,terephthalic acid and dicarboxylic acid ligand 1,4-naphthalenedicarboxylic acid or tricarboxylic acid ligand 2,4,6-tris（4-carboxyphenyl）-1,3,5-triazine（H₃TATB）was used as a dual ligand to synthesize modified MIL-101 by one-step hydrothermal method.Carboxyl-modified polydivinylbenzene（PDVB）materials were prepared by solvothermal method using monomer methacrylic acid（MA）and divinylbenzene（DVB）as raw materials,and then PDVB was introduced into MIL-101 by hydrothermal method and MIL-101/PDVB composites were prepared.Using Cu（NO₃）₂·3H₂O and synthesized PDVB as raw materials,Cu²⁺and PDVB were introduced into MIL-101 by hydrothermal method to prepare MIL-101（Cr,Cu）/PDVB composites.The structure of the samples was characterized by X-ray diffractometer（XRD）,field emission scanning electron microscope（FESEM）,nitrogen adsorption and desorption instrument,X-ray photoelectron spectroscopy（XPS）,Fourier transform infrared spectroscopy（FTIR）and other testing techniques.,the adsorption capacity of benzene gas was determined by the static desiccator method,the addition amount of 1,4-naphthalenedicarboxylic acid and H₃TATB,the proportion of monomers in the preparation of PDVB,the content of PDVB in the composite material,the amount of Cu²⁺doping,the synthesis of Effects of temperature,synthesis time,adsorption time and adsorption temperature on the benzene gas adsorption performance of modified MIL-101.The results show:（1）When preparing 1,4-naphthalenedicarboxylic acid modified MIL-101,with the increase of 1,4-naphthalenedicarboxylic acid addition,the crystallinity of the crystal weakened,the crystal morphology changed from octahedron to irregular polyhedron,and the edges and corners changed.As the number of pores occupied by 1,4-naphthalenedicarboxylic acid increased,the pore volume and specific surface area of the samples gradually decreased;when the ratio of terephthalic acid to 1,4-naphthalenedicarboxylic acid was 8:1,the synthesis temperature was170℃,the synthesis time was 24 h,the adsorption temperature was 30℃,and the adsorption time was 24 h,the specific surface area and pore volume of 1,4-naphthalenedicarboxylic acid modified MIL-101 were 2087 m²/g and 1.32 cm³/g,respectively,and the saturated adsorption capacity for benzene gas was 1662 mg/g.When H₃TATB modified MIL-101 was prepared,with the increase of H₃TATB addition,the crystallinity of the crystal decreased,the grain size decreased from 200 nm to 100 nm,the crystal morphology changed from octahedron to irregular polyhedron,and the edges and corners changed.When the ratio of terephthalic acid to H₃TATB is 12:1,the synthesis conditions and adsorption conditions are the same as those of 1,4-naphthalenedicarboxylic acid modified MIL-101,and the specific surface area and pore volume of H₃TATB modified MIL-101are respectively were 2497 m²/g and 1.41 cm³/g,and the saturated adsorption capacity for benzene gas was 2074 mg/g.（2）With the increase of PDVB content in MIL-101/PDVB composites,the XRD diffraction peak positions of the samples were consistent,and the diffraction peak intensity showed a trend of increasing first and then decreasing,indicating that the introduction of an appropriate amount of PDVB would not change the type of MIL-101 crystals,but will have a certain impact on its crystallinity.The ratio of monomer DVB to MA has a great influence on the structure of PDVB and MIL-101/PDVB composites.When the ratio of DVB to MA gradually increases,the XRD diffraction peak intensity of MIL-101/PDVB composites gradually weaken.Excessive DVB monomer will inhibit its crystallization,the edges and corners of the composites become more and more blurred,the grain size is different,and agglomeration occurs.The introduction of PDVB occupies a certain number of pores,which gradually reduces the specific surface area and pore volume of the material.When the synthesis temperature was170℃,synthesis time was 24 h,adsorption temperature was 30℃,adsorption time was 24 h,the content of PDVB in MIL-101/PDVB composites was 5%,the specific surface area and pore volume of MIL-101/PDVB composites were 2236 m²/g and 1.56 cm³/g,respectively,and the saturated adsorption capacity of benzene gas of MIL-101/PDVB composites was 1916 mg/g.（3）When the introduction amount of Cu²⁺increases,the characteristic peak intensity of MIL-101（Cr,Cu）weakens,the octahedral edges and corners of the crystal are passivated,the crystal grain size decreases to about 60 nm,and the occupied pore positions increase and the specific surface area and pore volume of MIL-101（Cr,Cu）gradually decreased.When the ratio of Cr³⁺to Cu²⁺is 7:3,the adsorption temperature is 30℃,and the adsorption time is 24 h,the specific surface area and pore volume of MIL-101（Cr,Cu）were 2254 m²/g and 1.31 cm³/g,respectively,the adsorption capacity of benzene gas was 1925 mg/g.Keeping the ratio of Cr³⁺to Cu²⁺at 7:3,PDVB and Cu²⁺were introduced into MIL-101 at the same time.As the content of PDVB in the MIL-101（Cr,Cu）/PDVB composites increased,the crystal morphology changed from octahedral to irregular polyhedron,the edges and corners of the crystal are gradually blurred,and the particle size of the crystal is reduced from 200 nm to about80 nm The pore positions occupied by Cu²⁺and PDVB increased,which decreased the pore volume and specific surface area of MIL-101（Cr,Cu）/PDVB composites.When the ratio of Cr³⁺to Cu²⁺was 7:3,the content of PDVB in the MIL-101（Cr,Cu）/PDVB composites was 5%,the synthesis temperature was 170℃,the synthesis time was 24 h,and the adsorption temperature was 30℃,the adsorption time was 24 h,the specific surface area and pore volume of the MIL-101（Cr,Cu）/PDVB composites were 1915 m²/g and 1.17 cm³/g,and the benzene gas saturation adsorption capacity of the MIL-101（Cr,Cu）/PDVB composites was 2366mg/g.