Design And Synthesis Of Covalent Organic Framework And Application Of Fluorescence Sensing And Electrocatalysis

Covalent organic frameworks（COFs）are a novel form of crystalline organic porous material made up of hydrogen,carbon,nitrogen,oxygen,and other light elements.These materials have many advantages,including high structural designability,unique pore structure,high surface area,and high stability due to the covalent bonding between organic monomers in their backbone.It has been demonstrated that this material has a promising future in luminescence,photocatalysis,electrocatalysis,gas adsorption,and separation.By pre-designing functional active sites and taking advantage of their pore architectures,we perform an in-depth investigation of COF in the fields of fluorescence sensing and electrocatalysis.The research effort presented in this thesis is divided into three parts as follows:The danger that nitroaromatic hydrocarbon explosives pose to public safety and the environment is a global concern.Consequently,the development of a detection method for the rapid and specific identification of explosives has been a topic of intense scientific study.In principle,high surface area 3D COF with aggregation-induced luminescence（AIE）structural units are more advantageous for detection studies of explosives molecules,as they not only retain the excellent fluorescence sensing performance of the original small molecules,but their regularly arranged channels also facilitate the contact between the target analytes and the active sites,thereby further enhancing the sensing sensitivity.We synthesized similar benzidine-based precursors with different substituents to react with tetra-（4-formyl-（1,1-biphenyl））ethylene with AIE properties,obtaining TPPDA-TPTPE and JUC-646,based on two-dimensional sql and three-dimensional pts topologies,respectively.Due to the excellent luminescence performance and stability of the two examples of COFs,their potential application as fluorescence sensing platforms for the detection of a variety of nitroaromatic hydrocarbons was further investigated.Surprisingly,the fluorescence emission intensity of TPPDA-TPTPE and JUC-646 solutions decreased significantly only with increasing concentrations of nitroaromatic hydrocarbon explosive molecules 2,4,6-trinitrophenol（TNP）during the detection of multiple nitroaromatic hydrocarbon molecules,indicating that both COFs displayed excellent specific recognition of TNP.Moreover,we compared the effects of 2D and 3D COFs on specific recognition and discovered that 3D JUC-646 was more sensitive to TNP than TPPDA-TPE.This indicates that the 3D channel facilitates the contact between the target analyte and the active site,thereby increasing the sensing sensitivity.Density functional theory（DFT）simulation shows that three-dimensional JUC-646was superior for the selective adsorption of TNP,This calculation also serves as a comprehensive validation of the experimental results.In the meantime,this research increases the structural diversity of 3D COFs and their potential applications in fluorescent explosives detection,and provides new inspiration and motivation for the future design and synthesis of AIE-based COFs molecules.Cobalt,a transition metal with high catalytic activity and abundant reserves,has received the most attention among the various HER catalysts.However,the catalytic activity and stability of cobalt-based HER catalysts are still unsatisfactory;therefore,it is crucial to discover a cobalt-based HER catalyst with both high catalytic activity and stability.Theoretically,the use of COFs as a carrier for cobalt-based catalysts possesses not only the benefits of the original metal catalysts,but also the framework’s ability to disperse the metal to increase the catalytic contact area,as well as the framework’s stability and modularity,which can further improve the HER catalytic activity and facilitate the study of the reaction mechanism.First,we designed and synthesized JUC-560 based on tetrasulfovalene（TTF）,and then we investigated its potential application as a HER catalyst after coordination with cobalt ions due to its stable structure,uniform and abundant pore channels,high specific surface area,and abundant amine bonding active sites that can be coordinated with metal ions.The results indicate that JUC-560-Co exhibits high HER catalytic activity and efficient catalysis at an overpotential of 389 m V with a current density of 10 m A cm^-2in a 1.0M KOH electrolyte,which is significantly lower than JUC-560’s overpotential of 529m V.By rationally designing COFs as cobalt metal ion carriers,metal ions can be uniformly dispersed in the two-dimensional lamellar structure of COFs,thereby enhancing the catalytic activity of HER,as indicated by the experimental results.This study contributes to the development of ordered porous carriers anchored with metal ions for use as efficient HER electrocatalysts.In the preceding section,we examined the potential application of COFs coordinating cobalt ions as HER catalysts.Despite the fact that cobalt ions have significantly improved the catalytic performance of HER,its performance must still be enhanced.Metal nanoparticles（MNPs）are widely utilized in numerous electrocatalytic reaction processes,as they are one of the most important catalysts.Nevertheless,the catalytic activity and stability of MNPs are inversely proportional to their size.Therefore,preventing the reunification of MNPs is a research priority.Based on the kgd topology,we designed and synthesized two types of microporous2D COFs（JUC-624 and JUC-625）in response to the aforementioned issues.This type of 2D COF has a unique ultramicroporous pore structure due to the fact that the kgd topology employs the C₆+C₃method for connecting molecular modules.We further investigated the potential application of coordinating cobalt ions and reducing them to nanoparticles（Co NPs@JUC-624 and Co NPs@JUC-625）as HER electrocatalysts.The results demonstrated that both COFs containing cobalt nanoparticles exhibited enhanced HER catalytic activity,with Co NPs@JUC-625 exhibiting the highest electrocatalytic activity.The foregoing results are based on the unique ultra-microporous pore structure of this form of 2D COF,which is created by the connecting of molecular modules of C₆+C₃in the kgd topology and can be utilized to limit the growth of MNPs,hence limiting their particle size;Again,JUC-625 with a pre-designed triazine ring structure has more nitrogen atoms and stronger metal coordination,and the microporous structure can be employed as an effective physical barrier to make it difficult for MNPs to interact each other and decrease the agglomeration of MNPs.This study can be used in the quest to create effective HER electrocatalysts based on ordered porous supports that anchor metals.In conclusion,we successfully synthesized a series of novel COFs,which not only expanded the structure of COFs but also encouraged the development of COFs in the domains of fluorescence sensing and electrocatalysis by integrating the many benefits of COFs for application research.