Design,Synthesis And Adsorption Application Of Nitrogen-Rich Functionalized Covalent Organic Frameworks

Covalent organic frameworks(COFs)are a two-dimensional(2D)or three-dimensional(3D)network porous polymer with a long-range ordered periodic structure which can be precisely assembled by cross-linking covalent bonds between structural units.Due to the advantages of low framework density,high specific surface area,and abundant pores,this material has good applications in the fields of adsorption and separation,catalysis,semiconductor,sensing,and energy storage.Compared with other porous materials,COFs have regular pores,modifiable framework,high specific surface area and good stability.Especially thanks to the modifiable characteristics of COF framework,we can introduce various functional groups to COF framework,then COFs can effectively adsorb small guest molecules rely on the host-guest interaction.Studies have shown that connecting nitrogen-containing functional groups to the COF framework can provide abundant active sites for COFs to adsorb specific small guest molecules.In addition,due to the two-dimensional COFs with oriented vertical one-dimensional pores and an ordered periodic network structure,small guest molecules can diffuse smoothly in the pores without clogging.Therefore,2D COFs have great advantages in dye adsorption and removal of harmful molecules.This thesis mainly includes the following aspects:Part ?:First,we briefly introduced the development history of the covalent organic frameworks;Secondly,we focused on the methods of functionalized COFs and their applications.Finally,the research significance and purpose of this thesis were put forward.Part ?:First,4,4'-diaminobenzanilide(DABA)and 1,3,5-Benzenetricarboxaldehyde(BT)were selected as linkers,and a new type of amide functionalized two-dimensional COF(JUC-578)was prepared by solvothermal method.Then,powder X-ray diffraction(PXRD),infrared spectroscopy(FT-IR),thermo gravimetric analysiss(TGA),solid state ¹³C(CP/MAS)NMR spectroscopy,scanning electron microscopy(SEM)and other methods were used to characterize the material,such as the crystallinity,morphology,crystal structure and other aspects.More importantly,we used the nitrogen-rich characteristics of JUC-578 to apply it to the adsorption of dyes in aqueous solutions,and used UV-visible absorption spectroscopy to detect the process of adsorption.We found that JUC-578 can selectively adsorb different dyes,and explained its adsorption mechanism then.Finally,we further explored its cycle performance.Part ?:Committed to the research of nitrogen-rich COF,we used two organic monomers,N,N,N',N'-tetrakis(4-aminophenyl)-1,4-phenylenediamine(TAPD)and2,2'-Bipyridine-5,5'-dialdehyde(2,2'-BPy DCA),to obtain a bipyridine-functionalized nitrogen-rich two-dimensional COF(TAPD-2,2'-BPy DCA COF)by solvothermal method.The material was characterized by PXRD,SEM,N₂ adsorption,FT-IR and other methods.Then,we used the bipyridyl group in the framework as a functional ligand to enhance the binding force between the COF framework and the elemental iodine molecule,thereby enabling it to exhibit ultra-high iodine capture performance and good cycling.Part ?:The content of this article is summarized,and the future development prospects of COFs are prospected.