Synthesis,Crystal Structure And Organic Dyes Adsorption Of Transition Metal-Organic Frameworks With Tripod Imidazole Carboxylic Acid

As a novel nanoporous material,metal-organic frameworks(MOFs)have received extensive attention from researchers due to the diverse structures and adjustable pore sizes.MOFs with characteristic structures are potential of many functional properties and show excellent performances inthe fields of gas storage,fluorescence sensing,heterogeneous catalysis,organic pollutant adsorption,drug transportation,and so on.In this work,we have successfully constructed two novel MOFs based on the tripod imidazole carboxylic acid ligand and transition metal ions(Zn(II),Cd(II)).The crystal structures and components of the prepared MOFs have been characterized in detail.The functionalities in organic dye adsorption and fluorescence for two MOFs have been investigated as well.The details are as follows:Firstly,based on 4,4’,4"-(1H-imidazole-2,4,5-triyl)tribenzoic ligand and Zn(II)/Cd(II)centers,two different transition metal-organic frameworks were synthesized through solvent-thermal method,namely:[Zn3(ITTC)3](Me2NH2)3·3DMF·H2O(1)and[Cd2(ITTC)3](Me2NH2)5·2DMF(2).Structural analysis reveals that two MOFs are anionic MOFs with a 2-fold interpenetrating 3D framework.In compound 1,the cross size of the open one-dimensional rectangular channels is 31.7 ? × 15.6 ?,and the framework could be regarded as a(3,3,4,5)-connection network with the Schl?afli symbol of{4.6^2}2{4^2.6^6.8^2}{6^3｝{6^5.8}.The diameter of the open one-dimensional regular hexagonal channel in compound 2 is about 34.1 A.The topological analysis points out that the network can be rationalized as a(3,4)-connected network with the point(Schlafli)symbol being of {6^3}｛6^5.8}.The TG curves illustrate that the decomposition temperatures of 1 and 2 are 395℃ and 400℃,respectively,indicating that both MOFs exhibit excellent thermal stability.Secondly,in view of the structural traits of the anionic frameworks in both MOFs,the organic dye adsorptione and fluorescent performances of two compounds were performed.The results unveil that both 1 and 2 have excellent selective adsorption capacity for the cationic organic dye methylene blue,while the concentration of the organic dye solution is 10 mg-L-1 and the adsorbent is 5 mg at 25℃.For 1,the adsorption equilibrium of the methylene blue solution is completed within four hours,with the adsorption amount Qe of 14.88 mg·g-1 and the dye removal rate of 96%.The kinetic model has been used to analyse the experimental results which are in good agreement with the pseudo-second-order kinetic model.The value of the correlation coefficient R2 is about 0.9929,indicating that the adsorption rate is mainly dominated by the active sites in the porns.For compound 2,the adsorption equilibrium of the methylene blue solution is achieved within three hours with the adsorption amount Qe of 15.56 mg·g-1 and the dye removal rate of 99%.The experimental datas are also in good agreement with the pseudo-second-order kinetic model.The value of correlation coefficient R2 is about 0.9986.All results confirm that both MOFs can be employed as promising and environmentally friendly adsorbents for the removal of cationic organic pollutants from dye wastewater.Fluorescence experiment results declare that both 1 and 2 are characteristic of luminescence owing to the emission of ligands.