Study On The Adsorption Properties Of Organic Carboxylic Acid And Nitrogen-containing Ligand MOFs Materials For Gas And Dye

Metal-Organic Frameworks（MOFs）are a new type of porous materials that have developed most rapidly in recent decades.They They are typically crystalline porous materials formed by self-assembly of metal ions/clusters and organic ligands.Due to its unique structure,adjustable pore size and easily functionalized surface,it has shown potential application prospects in gas separation and storage,chemical sensing,dye degradation and drug carriers.Both inorganic and organic parts of MOFs can provide a good platform for luminescence,and the charge transfer of metal-ligands also provides more possibilities for multifunctional luminescence.At the same time,MOFs have a highly regular pore structure,and the pore size is adjustable,so that MOFs can absorb some gas molecules to achieve the purpose of gas storage and separation.In this work,seven kinds of MOFs were designed and synthesized based on organic carboxylic acid ligands and nitrogen-containing heterocyclic ligands,and a series of characterizations were carried out,including single crystal X-ray diffraction,element analysis and infrared spectrum analysis.Based on this,the dye adsorption,fluorescence sensing and gas adsorption and separation properties were also explored.The specific contents are as follows:1.We selected the dicarboxylic acid ligand 2-hydroxyterephthalic acid（hta）,1,4-naphthalene dicarboxylic acid（1,4-ndc）,2,5-dihydroxyterephthalic acid（dhta）as the main ligand,and the nitrogen-containing ligand triethylenediamine（dabco）as the auxiliary ligand,and reacted with the transition metal ions Cd（II）and Zn（II）to construct three metal-organic frameworks[Zn₄（hta）₇（eg）₂]_n（1）,[Zn（1,4-ndc）₄（dabco）]_n（2）and[Cd（hta）₂（dabco）₂（DMF）]_n（3）.In order to study the potential application of MOF 1 and MOF 2 in gas capture and separation,the adsorption isotherms of CO₂ and C₂H₂ at l atm,273 K and298 K were obtained.It is found that MOF 1 and 2 have high C₂H₂adsorption capacity,and can adsorb 105.1 cm³/g and 161.6 cm³/g of C₂H₂at 273 K.The enthalpies（Qst）of adsorption of C₂H₂ and CO₂ by MOF 1and MOF are calculated to be 48.1 k J/mol,30.7 k J/mol and 44.8 k J/mol,28.1 k J/mol,respectively,indicating that there is a stronger interaction between crystal and C₂H₂molecule.Finally,we further confirmed that MOF 2 has certain separation ability for C₂H₂/CO₂through dynamic penetration experiment.2.We selected the azole ligands 3-amino-1,2,4-triazole（3-at）,3,5-diamino-1,2,4-triazole（3,5-dat）,5-amino-tetrazole（5-atz）as the main ligands,terephthalic acid（tpa）as the coligands,and reacted with the transition metal ion Zn（II）,to successfully obtain the metal-organic frameworks of[Zn（3-at）₃（tpa）]_n（4）,[Zn（3-at）₃（tpa）]_n（5）,[Zn（3,5-dat）₃（tpa）]_n（6）and[Zn（5-atz）₃（tpa）]_n（7）.The solid-state photoluminescence properties of MOF 5 and 6 are studied.The results show that MOF 5 and 6 have potential application value in this field.With the addition of NB,MOF 5 and MOF 6 showed obvious fluorescence quenching,and the quenching rates were 99.3%and 99.5%,the detection limits are 1.13×10^-5 M and 1.81×10^-5 M respectively.In addition,the dye adsorption properties of MOFs 5 and 6 were also investigated.Four organic dye molecules with different sizes were selected as adsorption objects.According to the naked eye observation and UV-Vis spectrum measurement results,MOF 5 and 6 showed significant selective separation of Congo red（CR）dyes.According to the calculation,the adsorption rates of MOF 5 and 6 for CR are 75.6%and74.9%,the adsorption quantity are 10.7 mg/g and 8.33 mg/g,respectively.