Synthesis And Application Of Functionalized Three-dimensional Covalent Organic Frameworks With Dia Topology

Covalent organic frameworks(COFs),as a kind of crystalline porous organic polymers,are long-range ordered structures in which small molecular building units are connected by covalent bonds.They have a high degree of structural designability,unique pore structures,and atomically accurate localization of molecular structures.These characteristics make COFs stand out in various application fields,for instance,adsorption separation,energy storage,optoelectronic devices and catalysis etc.However,the current reports on COFs materials mainly focus on 2D COFs.Although,3D COFs have some unique characteristics,such as variety of pore structure,a large number of open active sites,low density and high specific surface area,compared with2D COFs,the development of 3D COFs in functionalization and application research is still relatively slow.Moreover,the current application research of 3D COFs mainly focuses on adsorption separation and catalysis.The development of new application fields is rarely reported.Therefore,developing new functionalized 3D COFs and exploring new application fields are of great significance for the development of 3D COFs.The diamond(dia)topology is the most common and one of the most widely studied topologies in 3D COFs.On the one hand,the building units that can constitute the dia topology are relatively easy to obtain,and on the other hand,the dia topology is also easy to design and synthesize,and the structure is relatively easy to determine.Therefore,the dia topology is often a common topology for functionalized 3D COFs.Based on the above problems,the functional design and synthesis of 3D dia COFs are carried out in this paper,and their potential applications are further explored.The specific research content mainly includes the following three parts.(1)Currently,the building blocks of functionalized 3D COFs are mainly limited to traditional organic building units.The development of 3D COFs with novel building blocks is crucial to enrich their structural diversity and expand their functions.Therefore,we considered whether it is possible to introduce multifunctional inorganic building units into 3D COFs skeletons.Since the building blocks of dia topology are readily available and the dia topology is easy to synthesize.In Chapter 2,We synthesized three-dimensional crystalline polyoxometalate-based covalent organic frameworks(3D POM-COFs)with dia topology by reversibly covalently bonding amine-functionalized inorganic building blocks(polyoxometalates)and organic tetrahedral building blocks.These highly crystalline 3D POM-COFs were determined by structural simulations to have a dia topology with 3 interspersed,permanent porosity by gas adsorption tests,and high stability by thermal and chemical stability tests.In addition,3D POM-COFs also exhibited selective adsorption and separation ability for CO₂.The adsorption capacities of JUC-525 and JUC-526 for CO₂ were 76.2 mg g^-1and66.0 mg g^-1,respectively,at 273 K,which were much higher than N₂,CH₄(The adsorption capacities of JUC-525 and JUC-526 for CH₄ were 5.0 mg g^-1,4.7 mg g^-1,and the adsorption capacities for N₂ were 2.9 mg g^-1 and 3.1 mg g^-1,respectively).(2)At present,reports on the use of 3D COFs in metal-ion batteries are still limited.We consider that polyoxometalate have redox properties,which is beneficial to improve the specific capacity of the battery.In addition,covalent organic frameworks provide pore environments and structural stability which is beneficial to improve the cycling stability of the battery.Therefore,in Chapter 3,we used 3D POM-COFs directly as anode materials for LIBs.The experimental results show that 3D POM-COFs have good rate capability,high capacity(736.8 m Ah g^-1 for JUC-525 and 731.8 m Ah g^-1 for JUC-526 at 2 A g^-1),and it has ultra-long cycle performance(>2600 cycles)and exhibits nearly 100%coulombic efficiency after 2600 cycles.Through the analysis of battery kinetics,it is proved that the structure of 3D POM-COFs is favorable for electron transfer and lithium ion diffusion.(3)The development of new application areas is of great significance for the development of 3D COFs.The dia topology is easy to form multiple interpenetrated,and the interpenetration between building units often reduces the porosity and specific surface area of the obtained structure,which usually limits its application,such as gas adsorption,catalysis,etc.However,multiple interpenetrated often makes the dia topology form a one-dimensional pore structure,which also brings opportunities for some applications,such as mass transport.Therefore,in Chapter 4,we designed and synthesized crown ether-functionalized 3D COFs with 1D nanochannels,JUC-590 and JUC-591,based on a bottom-up synthesis strategy to uniformly attach 12 C4 groups to the channel walls.Since ether-functionalized 3D COFs possess 1D nanoscale channels,large surface area,and high density of 12 C4 groups,these 3D functionalized COFs can be activated by Li⁺ions and be utilized as a nanofluidic platform to control ion transport.Remarkably,these materials exhibited a close-to-open switching of the nanochannels with excellent gating ratios(as high as 23.6 for JUC-590),which is among the highest values of reported metal ion-activated 1D nanochannels,and we also demonstrate that ether-functionalized 3D COFs have the ability to collect osmotic energy potential.