Design,Synthesis,and Properties Study Of Porous Organic Frameworks With Immobilized Functional Units

Since the 1990s,various crystalline molecule-based porous organic materials have emerged,including metal organic frameworks(MOFs),porous organic cages(POCs),covalent organic frameworks(COFs),and hydrogen-bonded organic frameworks(HOFs).These materials have the advantages of ordered network structures,strong function designability,and high porosity.Thus far,these materials have shown excellent material properties in the fields of gas adsorption,pollutant enrichment,small molecule separation,catalysis,and energy storage,having the good practical application prospects.Nevertheless,the targeted design and synthesis of function-driven materials is still one of research difficulties and core scientific issues for various materials.In this thesis,a series of crystalline porous organic materials(COFs and HOFs)are assembled through dynamic imine covalent bonds and directional hydrogen bonds,using the molecular engineering principle to implant building blocks containing redox properties,potential coordination groups,and chromophore units into porous organic frameworks.The employment of cross characterization techniques such as X-ray diffraction,gas adsorption,and theoretical simulation with the help of infrared and nuclear magnetic resonance enables the determination of the structures of these frameworks,and their applications in energy storage and conversion have been explored.Crystal engineering and theoretical simulation,as well as in situ and ectopic spectroscopy,the structure activity relationship between the chemical structure,electronic structure,and dynamic changes of materials and their properties is collaboratively and crossly explored.The research content is summarized as follows:(1)In situ growth of covalent organic framework nanosheets on graphene as the cathode for long-life high-capacity lithium-ion batteries2,7-Diaminopyrene-4,5,9,10-tetraketone(PTO-NH2)and 3,8,9,14,15-hexa(4formylphenyl)diquinoxaline[2,3-a:2’,3’-c]phenazine(HATN-CHO)with high redox sites have been synthesized and polymerized into a novel COF(USTB-6)with hxl topology through dynamic imine chemical reaction.Structural characterization reveals a biporous covalent organic framework for this COF with good crystallinity.In order to improve the electrical conductivity of the material,monolayer graphene with high electrical conductivity has been introduced into the reaction system,generating COF nanosheets with a thickness of about 8.3 nm on the graphene carbon substrate through in-situ polymerization,graphene loaded USTB-6 nanocomposites(USTB-6@G)can be obtained.As the cathode of a lithium ion battery,the specific capacity is as high as 285 mA h g-1 at a current density of 0.2 C.In addition,this material also exhibits a good rate performance,maintaining a specific capacity of 188 mA h g-1 at a high current density of 10 C.More importantly,the USTB-6 nanocomposite cathode can still maintain a reversible capacity of 170 mA h g-1 after 6000 charge-discharge cycles at a current density of 5 C.The comprehensive performance of the material is significantly superior to most COFs materials.Mechanism studies based on ectopic XPS,electrochemical testing,and theoretical simulation indicate that the outstanding characteristics of USTB-6@G electrode materials are attributed to the high density of redox active sites,the thin nanosheet structure of COF,and the strong π-πinteraction with graphene.(2)Post-modification of a two-dimensional covalent organic framework with single cobalt sites and lithium sulfur batteries performance studyA new two-dimensional imine-linked COF(USTB-27)has been prepared by polymerization of chelating group-containing building blocks,namely[2,2’bipyridine]-5,5’-diamine(BPY-NH2)with 3,8,9,14,15-hexa(4-formylphenyl)diquinoxaline[2,3-a:2’,3’-c]phenazine(HATN-CHO).Subsequently,a single cobalt ion-anchored USTB-27-Co has been generated using a post-synthetic modification strategy.Various structural characterization techniques reveal that this new COF with good crystallinity has a biporous covalent-bonded organic network,and has been successfully modified with single cobalt sites to form USTB-27-Co.The electrochemical performance of S@USTB-27-Co as a cathode material for lithium sulfur batteries was explored in a half-cell.The S@USTB-27-Co electrode delivers a high specific capacity of 1063,945,836,765,696,and 644 mA h g-1 at current densities of 0.1,0.2,0.5,1.0,2.0,and 5.0 C,respectively.Especially at a high current of 5.0 C,S@USTB-27-Co electrode retains 61%of the initial capacities in comparison with 0.1 C,indicating good rate performance.This performance is significantly superior to that for S@USTB-27(The capacity retention at 5.0 C is only 19%of the initial capacities in comparison with 0.1 C).S@USTB-27-Co cathode provided the outstanding cycling stability and retained 56%of the initial capacity after 100 cycles at 02 C.Remarkably,even after 500 cycles at a current density of 1.0 C,S@USTB-27-Co cathode still retained specific capacity of 543 mA h g-1.Theoretical studies have shown that post-modified cobalt sites can effectively reduce the activation energy during the conversion of polysulfides,therefore serving as an effective catalyst in lithium sulfur battery system.(3)Photocatalytic hydrogen evolution performance study on covalent organic frameworks with imines units as proton acceptorsThree isomeric two-dimensional hcb topological COFs,namely 1,2,and 3,have been constructed by imine polymerization using benzo[1,2-b:3,4-b:5,6b]trithiophene-2,5,8-trialdehyde(BTT)and three triamine building units with C3 symmetry,(tri(4-aminophenyl)amine,1,3,5-tris(4-aminophenyl)benzene,and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine),respectively.They have been characterized by UV-vis diffuse reflectance spectroscopy and electrochemical test,disclosing their different optical absorption properties and electronic structures.After optimization of conditions,these imine COFs and Pt co-catalyst have been used to achieve photocatalytic hydrogen production with the help of ascorbic acid(Aa)as sacrificial reagent.Among three systems,3 has the fastest hydrogen production rate,reaching 20.2 mmol g-1 h-1.Experimental testing in combination with theoretical analysis of the structure-activity relationship study show that the electronic structures of the COFs materials have been greatly affected by the protonation of their imine groups in comparison with that for unprotonated samples.In the present case,the improved charge separation efficiency and transport capacity enable the high photocatalytic hydrogen production performance for 3.(4)Lithium ion batteries performance study on hydrogen-bonded organic frameworks with redox active sitesA stable hydrogen bonded organic framework CPHATN-1 has been prepared by slowly evaporation of 2,3,8,9,14,15-hexa(4-carboxyphenyl)diquinoxaline[2,3a:2’,3’-c]phenazine(CPHATN)molecules with redox active units in a mixed solution of 1,2,4-trichlorobenzene and N-methylpyrrolidone at 100℃.The degassed and activated HOF(CPHATN-1a)doped with carbon black has been used as a cathode material for lithium ion batteries.The assembled lithium ion half battery has a specific capacity of 128 mA h g-1 at a current density of 0.1 C.After 500 cycles at a current density of 1.0 C,it maintains a specific capacity of 102 mA h g-1,providing a relatively good cycling stability.Under the same conditions,the performance of CPHATN-1a is comparable to that of some COF-based electrode materials.The energy conversion mechanism has been systematically analysed through electrochemical testing and XPS spectroscopy.This work expands the application of HOFs in the energy field,and also preliminarily explores new directions for the design and synthesis of functional electrode materials in the future.