Design,Synthesis And Properties Of Ionic Metal-Organic Frameworks Based On Polycarboxylic Acid Ligands

In recent years,the acceleration of urbanization and the rapid growth of population have increased the demand for clean water.However,water can dissolve many substances,which makes water vulnerable to pollution.Fresh water,sea water and other water resources are being eroded by man-made garbage and waste,which further aggravates the pressure of human water use.Therefore,we need to find a material or technology to quickly identify,detect and deal with pollutants in order to alleviate the increasingly serious problem of water pollution.Metal organic framework（MOF）is a periodic network formed by connecting metal ions with organic ligands.It has the advantages of large specific surface area,adjustable structure and good stability.Ionic MOF（i MOF）can adsorb dye molecules through size effect,ion interaction and adsorption site interaction between host and guest due to its charged skeleton;Secondly,i MOF has unique fluorescence characteristics,which can selectively recognize metal ions or small organic molecules by testing the change of fluorescence intensity;In addition,some i MOF have visible light response and good stability.Their electron transfer ability and adsorption ability can be further improved through appropriate functional group modification,which can be used as high-efficiency photocatalysts.Through the design and synthesis of i MOF,we can add new members to the MOF family and enrich its application research in many fields.Secondly,the use of i MOF for adsorption,fluorescence sensing and photocatalytic performance research can provide new methods and technical support for on-site analysis,monitoring and treatment of sewage,and provide reference for the industrial development of new technology.Studying the action mechanism of i MOF can accumulate experience for future generations and promote the process of scientific development.Based on this,this paper intends to synthesize a variety of i MOF for dye adsorption/separation,fluorescence recognition,sensing and photocatalytic properties.The details are as follows:In this thesis,1 anionic MOF,6 cationic MOF and 3 neutral MOF were designed and synthesized,and their applications in the adsorption of organic dyes,metal ion recognition and photocatalysis were studied.The specific research contents are as follows:1.A new anionic in MOF,namely[（CH₃）₂NH₂]₂[In₂（H₃L）₂（OX）]·3DMF·2H₂O（JOU-23）（H₃L=triphenyl-3,4’,5-tricarboxylic acid;OX=oxalic acid）,was synthesized by solvothermal method.Single crystal X-ray diffraction results show that JOU-23 is a three-dimensional anion skeleton with double interpenetrating network structure.Due to the negatively charged and porous network structure of JOU-23,it can be an effective adsorption and separation of cationic organic dyes.Further studies show that the charge and size of dye molecules will affect the adsorption and separation of dyes.In addition,JOU-23 dispersed in dimethylformamide（DMF）showed strong fluorescent emission at about 364 nm.Therefore,it has been developed as a fluorescent probe material for the detection of Fe³⁺ions and nitroaromatic compounds.2.Two neutral In-MOFs based on TCA ligands were synthesized by solvothermal method,namely JOU-24 and JOU-25 respectively（TCA=4,4’,4’’-triphenylamine tricarboxylic acid）.Single crystal X-ray diffraction results show that JOU-24 has an infinitely extended In-O-In straight chain and forms a two-dimensional layer connected by TCA ligands.JOU-25 has two unique homochiral In-O-In helical chains,which are connected by TCA ligands to form a 3D porous framework.Due to their strong fluorescence emission and uncoordinated carboxyl groups exposed in the channel,JOU-24 was developed as a fluorescent probe for the detection of Co²⁺and nitroaromatic compounds in water,while JOU-25 was developed for the detection of Cu²⁺,Fe³⁺and nitroaromatic compounds in water.This work provides a new clue for the construction of chiral MOF and a reference for the development of new MOF based fluorescent probe materials.3.A neutral MOF based on Zn（II）,namely[Zn₂（TBAPy）（H₂O）（DMF）]·4DMF·2H₂O（JOU-34）（TBAPy=1,3,6,8-tetra（p-benzoic acid）pyrene,was synthesized by solvothermal method;DMF=n,n’-dimethylformamide）.Single crystal X-ray diffraction results show that JOU-34 is a three-dimensional microporous skeleton with a new topology.Due to the introduction of pyrene group,JOU-34 shows strong fluorescence emission at about 470 nm.In addition,JOU-34 showed good fluorescence recognition performance for nitroaromatic compounds,especially nitrobenzene.4.Four cationic Fe-MOFs containing electron donating methylthio units were successfully synthesized by solvothermal method,namely MTBDC-TPT-Fe,MTBDC-TPY-Fe,MTBDC-TPB-Fe and MTBDC-Fe（MTBDC=2,5-Bis（methylmercapto）benzene-1,4-dicarboxylic acid,TPT=2,4,6-tris（pyridin-4-yl）-1,3,5-triazine,TPY=2,4,6-tris（4-pyridyl）pyridine,TPB=1,3,5-tris（4-pyridyl）benzene）.Fe-MOFs modified by methylthio have narrower band gap,higher adsorption capacity and faster charge transfer efficiency.Due to these advantages,the prepared Fe-MOFs can be used as a high-efficiency photocatalyst for the reduction of Cr（VI）.It is found that the high acid concentration in the photocatalytic system may contribute to the protonation of pyridine groups in Fe-MOFs,which can not only improve their adsorption capacity for Cr₂O₇^2-,but also promote the separation and transfer of carriers.In addition,MTBDC-TPT-Fe shows the best photocatalytic performance,which is mainly due to its larger specific surface area,more adsorption sites and faster electron transfer ability.Finally,the main active components of photocatalytic removal of Cr（VI）were analyzed,and the photocatalytic mechanism was discussed.In this work,a new strategy is proposed to synthesize an efficient Fe-MOFs catalyst for the removal of Cr（VI）in water.5.A series of cationic MOFs were successfully synthesized by post modified ion exchange method,namely In3-TCA,Fe2In-TCA and Fe3-TCA respectively.The unique structure of these In/Fe-MOF gives them a wide absorption spectrum and high carrier separation/migration efficiency.Based on the above advantages,Fe2In-TCA was a high-efficiency photocatalyst for the degradation of ofloxacin.Under the optimum conditions,98%of ofloxacin could be degraded within 30 minutes.On this basis,the structure-activity relationship of In/Fe-MOF was discussed in detail,and the possible photocatalytic mechanism was proposed.This work provides a reference for the design and synthesis of multifunctional photocatalysts.