| Covalent organic frameworks(COFs)are crystalline organic porous polymers linked by covalent bonds.Compared with conventional zeolites,COFs have the advantages of low backbone density,large pore window and high specific surface area;compared with metal organic frameworks(MOFs)and zeolite imidazole frameworks(ZIFs)connected by coordination bonds and hydrogen-bonded organic frameworks(HOFs),COFs frameworks have much higher acid-base stability than MOFs,ZIFs and HOFs materials.In addition,the designability and abundance of organic molecules for building COFs allows the structure of COFs materials to be not only precisely designed but also to introduce abundant functional groups.Based on these advantages,COFs have received a lot of attention in the past 15 years in terms of design,synthesis and functionalization exploration,and have been initially used in non-homogeneous catalysis,gas storage and separation,organic photovoltaics,environmental protection and many other important frontier fields.COFs materials are currently divided into two main categories by structure: twodimensional(2D)layered structures with one-dimensional pores,and threedimensional(3D)three-dimensional structures with pore penetration.Because of the π-π stacking between layers in 2D COFs,their structures tend to be more stable,and therefore 2D COFs are more frequently reported.However,3D COFs have advantages that 2D COFs do not have,such as 3D COFs have richer pore structures and interoperable pore and cage structures,which are more conducive to separation,catalysis,and object binding,etc.In addition,3D COFs tend to have higher specific surface area,lower density,and abundant active sites compared with 2D COFs,and these active sites often play an important role in actual catalysis and gas adsorption.These active sites often play an important role in actual catalysis and gas adsorption.Therefore,3D COFs effectively broaden the application scope of COFs and show better performance advantages in catalysis and gas adsorption.Therefore,the development of3 D COFs is very important and meaningful.However,the development of 3D COFs is relatively slow at present because some urgent issues need to be addressed:In Chapter 2: We designed a tetrahedral organic monomer 2,2’,7,7’-tetramethoxy-9,9’-spirobifluorene-3,3’,6,6’-tetracarbonyl(TMSFTA)with four methoxymethyl as the site resistance,and the site steric hindrance effect of this organic monomer can effectively prevent the degree of structural interpenetration in the synthesis of 3D COFs,and even obtain a non-penetrating framework.Therefore,we synthesized the first mesoporous 3D dia COFs with non-penetration by TMSFTA(JUC-550).However,due to the "dynamic effect" of 3D COFs,the structure of JUC-550 is prone to collapse.To solve this problem of structure collapse,we synthesized two other mesoporous 3D dia COFs(JUC-551 and JUC-552)with nonpenetrating mesopores by using C2 links with two or four methyl groups as the site barrier groups.Compared with JUC-550,the C2 linkage of JUC-551 has two methyl groups and its "dynamic effect" is reduced therefore its specific surface area and pore size are significantly increased.In addition,compared with JUC-550 and JUC-551,the C2 linkage of JUC-552 has four methyl groups,and its "dynamic effect" largely disappears and its specific surface area and pore size further increase.By this method,JUC-552 also achieves the highest specific surface area and the largest pore size among 3D dia COFs.Therefore,we used the steric hindrance effect to solve the two problems of the interpenetration phenomenon and the "dynamic effect" mentioned above.In addition,we replace the site steric hindrance group from methyl group to functional trifluoromethyl and carboxylic acid functional groups,which can not only partially solve the pore shrinkage caused by the "dynamic effect",but also solve the problem that 3D COFs are difficult to be functionalized.In Chapter 3: We designed a flexible steric four-node organic monomer 4,4’,4’’,4’’’-([9,9’-bicarbazole]-3,3’,6,6’-tetradecyl)tetrabenzaldehyde(BCTB-4CHO)with "dynamic single bond",which has good spatial structural plasticity.Based on this strategy,we obtained the structure JUC-620 with the conventional dia topology and a new qtz topology JUC-621,respectively.Since the building units of these COFs are two easily soluble tetranodal organic monomers and therefore its easy to obtain singlecrystal structures.We determined their exact structures by powder X-ray diffraction and transmission electron microscopy(TEM)techniques,and for the first time in COFs,we obtained the exact structures of 3D COFs using i DPC techniques.Isomerism is a widespread phenomenon in organic chemistry.These isomers have the same chemical composition and molecular formula but different spatial arrangement of atoms,and thus these isomers often have unique physical and chemical properties.Similar to the isomers of organic molecules,this group of isomeric 3D COFs exhibits significant differences in porous properties,with the qtz topology in JUC-621 exhibiting 2.3 nm mesoporous pores and a high specific surface area of 2060 m2g-1,which is much higher than that of JUC-620 with the dia topology(pore size: 1.2 nm,specific surface area:980 m2g-1).In addition mesoporous JUC-621 can effectively remove dye molecules and achieve good iodine adsorption(up to 6.7 gg-1),which is 2.3 times higher than microporous JUC-620(～2.9 g-1).This work not only reveals the first topological heterogeneity of 3D COFs and resolves their exact structures by TEM,but also provides a new way to design and synthesize and resolve new topologies of 3D COFs.In Chapter 4: We used a set of tetrahedral organic monomers TMSFTA with fixed and relatively free bond angles with 3 3,3’,5,5’-tetra(p-aminophenyl)-2,2’,4,4’,6,6’-hexamethyl-1,1’-biphenyl(BMTA)to synthesize the first zeolite-like molecular sieve topology of ZOF-1.Since the building blocks of such COFs are two readily The exact structure of ZOF-1 was determined by single-crystal three-dimensional electron diffraction(ED),which is a two-fold penetrating crb structure.Traditional zeolite molecular sieves a class of crystalline microporous oxides with well-defined pores and cages have a wide range of practical applications in the chemical industry,however,the windows and pores of zeolite molecular sieves are usually small,which greatly limits their applications in adsorption and catalysis of macromolecules.Compared with zeolite molecular sieves,ZOF-1 has a large pore size(up to 1.6 nm)and an excellent specific surface area(～2785 m2/g),which is far superior to its aluminosilicate zeolite and zeolite imidazole frameworks with the same network structure.Thus,this study opens a new way to construct pure organic framework materials similar to zeolites.In summary,we have solved the interpenetration phenomenon,"dynamic effects" and functionalization problems in 3D COFs for the first time by using "structurespecific" tetrahedral organic molecules.Using these "structure-specific tetrahedral" molecules,we not only observed the topological heterogeneity of 3D COFs for the first time,but also obtained a new COF with qtz topology,and resolved the structure of COFs for the first time by i DPC-HTEM technique.In addition,we have synthesized an organic molecular sieve(ZOF-1)material for the first time and resolved the structure of ZOF-1 by single crystal 3D electron diffraction technique,which not only solves the scarcity of 3D COFs topology but also enriches the methods to resolve the structure of3 D COFs. |
