Preparation Of Functionalized Metal-Organic Frameworks And Their Adsorption And Separation Of Organic Dyes In Water

Water is the source of all life on earth,which is indispensable to human beings,but the quality of water resources is increasingly threatened by pollution.The main source of water pollution is the improper discharge of domestic and industrial wastewater,which contains a large variety organic pollutants.The adsorption method overcomes the disadvantages of traditional biological treatment apparatus such as high cost,complicated procedure,lack of pertinence,and easily causing secondary pollution,which has been widely applied in the treatment of various types of pollutants due to its simplicity,safety,and environmental protection.As an adsorbent material,its water stability,pore size,specific surface area,and adsorption site are very important.New adsorbent metal-organic framework（MOF）materials have been widely developed and applied in the adsorption of various pollutants due to their advantages of large specific surface area and designability.However,currently developed MOF materials are mostly microporous and have limited stability,which lacks targeted design.In addition,the defects such as poor water stability,small pore size,and lack of adsorption sites make them impossible to the demand for efficient selective adsorption of organic pollutants in wastewater.In response to these questions,the thesis provides some strategic solutions mainly involving the design and modulation of the electronic properties of the framework,and the construction and modification of the pore and channel properties.Three types of MOFs,Bio-MOF-2Me,MIL-140C-2NMe⁺and MIL-53（Fe）@EDTA·2H were synthesized,which show the efficient and selective adsorption and separation of the ionic organic dyes from the binary dye mixtures.Micrometer crystals of zinc-based anionic Bio-MOF-2Me were constructed by using a hydrophobic methyl-containing 2,2’-dimethyl-4,4’-biphenyldicarboxylic acid（H₂DMBPDC）and adenine as organic ligands via a solvothermal reaction.Based on the energetic electrostatic interactions between the host MOF and guests,the rapid and selective adsorption of cationic organic dyes was realized,and the separation efficiency of the cationic dyes in the mixture of cationic and anionic dyes was up to 99.0%.Moreover,the corresponding mixed matrix membrane material was prepared by blending the powder material with the PVDF matrix,which solved the problem that the powder sample might cause secondary pollution when applied to actual water treatment.This research not only provides a method to improve the water stability of MOF adsorbents,but also expands the way of device preparation of adsorbents that can reduce the secondary pollution caused by the powder adsorbent.In order to expand the design and utilization of neutral materials,we selected 2,2’-bipyridine-5,5’-dicarboxylic acid（H₂BPYDC）with Lewis basic N site as the organic ligand to synthesized neutral zirconium-based MIL-140C-2N with triangular one-dimensional channels by solvothermal method.The cationic MOF material MIL-140C-2NMe⁺was constructed by cationization of the N site of MIL-140C-2N through a post-synthesis alkylation modification strategy.The adsorption force is provided by electrostatic interaction and ion exchange,thus showing high adsorption capacity for anionic pollutants.Compared with MIL-140C-2N,the adsorption efficiency of MIL-140C-2NMe⁺was increased by 42.24times,and the adsorption capacity was increased by 11.9 times.This study provides a general approach for designing neutral frameworks to transform into cationic framework materials.In order to improve the adsorption capacity of microporous materials,we used the mixture of hydrochloric acid and EDTA disodium salt to chemically etch the MIL-53（Fe）framework to construct an anionic MIL-53（Fe）@EDTA·2H with improved pore size.After the conversion of pristine MIL-53（Fe）to hierarchically porous MIL-53（Fe）@EDTA·2H,the main pore size distribution is enlarged from 7.0（?）to 13.93（?）,which is large enough to accommodate many organic dyes.The synergistic effect between the host-guest interaction and the size matching enables MIL-53（Fe）@EDTA·2H to selectively adsorb cationic dyes in mixed dye solutions,thereby realizing the separation of mixed anion-cationic organic dye systems.The modification strategy using this chelate etching is expected to expand the development of microporous MOFs in the fields of macromolecular encapsulation,organic pollutant adsorption,and drug loading.