Study On Preparation And Adsorption/Luminescence Properties Of Covalent Organic Framework-Inorganic Composite Materials

Covalent organic framework（COF）,as an emerging porous crystalline material,has attracted the attention of many researchers in recent years.Due to its excellent physical and chemical stability,designable topological structure and uniform pore size distribution,it has broad application prospects in environmental protection,analysis and other related fields.On the one hand,due to the richness of its composition structure,the monomer can be designed in advance according to actual function needs,or the synthesized frame can be post-modified;on the other hand,due to its excellent pore size distribution and large specific surface area,COF can be used as an excellent platform for in-situ loading or integrally coating of other nanomaterials to jointly enhance the overall performance of composite materials.In this thesis,composite materials with target function were prepared by multiple methods like post-modification of COF,loading and coating inorganic nanoparticles or perovskite nanocrystals,which are used for the removal of heavy metal ions in water samples,efficient uranium extract from seawater or enhance the electrochemiluminescence of materials,etc.The main research contents are as follows:1.A simple and universal loading strategy was adopted to confine small-sized indium sulfide nanoparticles（In₂S₃ NPs）in a suitable covalent organic framework（COF）cavity,and successfully prepared In₂S₃@COF nano porous composite materials（In₂S₃@Tp-BD）.First,2,4,6-trialdehyde phloroglucinol（Tp）and benzidine（BD）are reacted through Schiff base reaction under suitable conditions to prepare a covalent organic framework（COF-Tp BD）,then indium trisulfide（In₂S₃）nanoparticles are loaded in the original COF-Tp BD in situ to obtain a composite material with both In₂S₃ and COF characteristics.The material not only inherits the stable frame structure of COF,but also obtains a large amount of sulfur chelating sites in In₂S₃.On the one hand,due to the high affinity between S atoms and Hg²⁺,Hg²⁺can be adsorbed through the strong Hg-S interaction.On the other hand,the inherent large specific surface area and excellent pore size of COF can also greatly increase the adsorption capacity for Hg²⁺.In addition,it also shows excellent selectivity to Hg²⁺and excellent recycling performance.This study shows the theoretical possibility of using COF as a substrate to construct an efficient mercury adsorbent,and more importantly,it shows the potential for application in actual environmental remediation.2.An antibacterial sp² carbon conjugated covalent organic framework（AF Anti-COF）was prepared through a multi-step post-modification reaction for the extraction and enrichment of uranium in seawater.Compared with the absorbent without antibacterial properties（AF COF）,AF Anti-COF with extremely high stability,abundant amidoxime groups and antibacterial properties has greatly improved the uranium extraction ability from seawater.Through Knoevenagel condensation reaction,diazonium salt reaction and amidation,1,3,5-tris（p-formylphenyl）benzene（TFPB）and（benzene-1,3,5-triyl）triacetonitrile（BTAN）were selected to prepare antibacterial TFPB-BTAN（Anti-COF）.Further an amidoxime group-functionalized Anti-COF（AF Anti-COF）was obtained through an oximation reaction on the exposed cyano sites.Due to the strong stability of the C=C framework and the relatively stable post-modification reaction of each step,the synthesized adsorbent AF Anti-COF can maintain its structure for a long time under harsh conditions such as radiation,strong acid and alkali.Due to the cross-linking of kanamycin,AF Anti-COF showed a strong inhibition on bacterial growth,proving the material’s excellent anti-biofouling ability,thereby improving the recovery capacity of uranium in actual seawater.At the same time,AF Anti-COF maintains the good fluorescence characteristics of original COF.When UO₂²⁺exists,the specific recognition between AF Anti-COF and UO₂²⁺leads to fluorescence quenching,which proves that the adsorbent can also be used for highly sensitive,on-site and real-time monitoring of uranyl ions.This study provides an enhanced adsorbent for extracting uranium from seawater,which can effectively solve the problems of insufficient stability of materials in practical application and accumulation of marine organisms in seawater（biofouling）.More importantly,this study proves the great potential of post-modification of stable framework materials,and its general synthesis strategy can be extended to a broader field.3.Through sequential deposition methods,the perovskite nanocrystal composite material coated with a covalent organic framework was successfully prepared to enhance its electrochemiluminescence intensity and the environmental stability of the perovskite nanocrystal.Firstly,all-inorganic perovskite nanocrystals（Cs Pb Br₃）are prepared by thermal injection method,and then tris（4-formylphenyl）amine（TPA）and phenylenediamine（PD）are polymerized to form a COF shell on its surface to obtain a composite material Cs Pb Br₃@TPA-PD.The COF shell can not only isolate the external environment,especially the damage to the perovskite crystals by moisture,due to its hydrophobicity,but also,due to the presence of the tertiary amine structure in the COF framework,confer the composite material with enhanced self-luminous ECL intensity.After actual tests,the fluorescence and ECL intensity of the composites can be maintained for several days with only a small decrease.For the first time in this research,COF and perovskite are used in combination,which solves the instability of perovskite structure to a certain extent and the previous lack of need to add a co-reactant to emit light.At the same time,we believe that this strategy of synthesizing complexes can be applied to the construction of a wider range of ECL emitters.