Synthesis And Adsorption Properties Of Bridged Carboxylic Acid/Polypyridine Coordination Polymers

Due to the special structure and properties of coordination polymers,such materials have important influences in the fields of gas adsorption and separation,and liquid phase adsorption.Therefore,the self-assembly of coordination polymers has become a hot field of coordination chemistry research.The main factors affecting the self-assembly of coordination polymers are the coordination types of metal ions,the structural characteristics of organic ligands,the ratio of metal and organic ligands,the reaction temperature and p H value.Among these factors,the selection of organic ligands plays a key role.In this paper,seven new coordination polymers were prepared by hydrothermal method or mixed solvent method with bridged carboxylic acid compounds:azobenzene-4-4’-dicarboxylic acid,6-（4-carboxybenene）nicotinic acid,and nitrogen-containing heterocyclic compounds:5,5’-dicyano-2,2’bipyridine,4-（3,5-dicarboxylphenyl）-2,2’:6’,2’-tripyridine as ligands.Their structures and adsorption properties were studied.The details are as follows:（1）We used azobenzene-4-4’-dicarboxylic acid（L₁）and 6-（4-carboxybenzene）nicotinic acid（L₂）as ligand to react with metal Zr⁴⁺,respectively,and obtain new coordination polymers A₁and A₂similar to Ui O-67.The new coordination polymers A₁and A₂were characterized,the results showed that the coordination polymers A₁and A₂are microporous materials with good thermal stability and high specific surface area.Through the study of the gas adsorption properties of A₁and A₂,it is found that they have better selective adsorption for N₂/O₂,CO₂/CH₄,N₂/CO₂,especially for N₂/O₂,which is the most potential application material for the adsorption and separation of N₂/O₂.Through the study on the adsorption properties of dyes,it is found that they have good adsorption properties for MO,MB and RB dyes.The adsorption kinetics fitting results show that the adsorption process of MO,MB and RB by A₁and A₂is in accordance with the quasi second-order kinetic equation.（2）We used 5,5’-dicyano-2,2’-bipyridine（Y₁）and azobenzene-4-4’-dicarboxylic acid（Y₂）as ligands and 2-methylimidazole as auxiliary agent to react with metal Cr³⁺,and obtained three new coordination polymers B₁,B₂and B₃.Their structures were characterized,the results showed that the coordination polymers B₁,B₂are micro-mesoporous material with high specific surface area,and coordination polymer B₃is a mesoporous material.The research on the gas adsorption performance of B₁found that it has a higher selective adsorption for N₂/O₂,which indicates that it is a valuable candidate for adsorption and separation of N₂/O₂.The adsorption properties of B₁,B₂and B₃for MO,MB and RB were studied.The results showed that they had the best adsorption capacity for MB.The fitting results of adsorption kinetics show that the adsorption process of MO,MB and RB by B₁,B₂and B₃is in accordance with the quasi second-order kinetic equation.（3）Two novel complexes:C₁and C₂,were obtained under mixed solution-thermal conditions using 4-（3,5-dicarboxylphenyl）-2,2’:6’,2’-terpyridine（S₁）and transition metal salts as starting materials.Their structures were characterized by X-ray powder diffraction,scanning electron microscopy,thermogravimetry,infrared spectroscopy,and X-ray photoelectron spectroscopy.