Design And Synthesis Of Porous Covalent Organic Materials And Study On Their Photo Catalytic And Enzymatic Properties

Nanozymes are a class of nanomaterials with enzymatic catalytic properties,which have drawn extensive attentions due to their advantages of low cost,easy preparation,tunable catalytic activity and high stability,and have been rapidly developed in different fields such as biosensing,environmental monitoring,medical treatment,etc.However,nanozymes are still faced with shortcomings such as low catalytic activity and insufficient research on reaction mechanisms,which greatly limit their application in analytical sensing and other fields.In addition,currently most nanozymes focus on redox enzyme activity,and developing nanozymes with non-redox enzyme activity remains a challenge.Porous covalent organic materials（COMs）,represented by covalent organic frameworks（COFs）,have attracted extensive attention in recent years.Their monomers can be designed at the molecular level to adjust and optimize the energy band structure and surface properties,achieve fast electron-hole separation and wide visible light absorption,and show significant advantages and great application potential in the field of photocatalysis.However,the photocatalytic performance and nanozyme activities of most porous organic materials still need to be further improved,and their regulatory strategies need to be further enriched and expanded.Introducing biomolecules or embedding metal centers in the skeleton is considered an effective way to solve this dilemma.Based on this,this thesis focuses on the design and synthesis of porous covalent organic materials and study on its photocatalytic and enzymatic properties,mainly including the following:1.The feasibility of using single-stranded DNA（ss DNA）to the simultaneous modulation of different types of enzymatic activities of the same COF was proposed.In this work,a photosensitive covalent organic framework（Tph-BT）was synthesized using5,10,15,20-tetrakis（4-aminophenyl）-21H,23H-porphyrin（Tph）and4,7-bis（4-formylphenyl）-2,1,3-benzothiadiazole（BT）as the building blocks.Interestingly,Tph-BT exhibits excellent oxidase activity and weak peroxidase activity,while ss DNA demonstrates reversed regulation effects on the two enzyme-mimetic activities of Tph-BT.The effects of base type,base length and other factors on the activities of two enzymes were studied.The results showed that the adsorption of ss DNA on the surface of Tph-BT prevents the intersystem crossing and energy transfer process,reduced the generation of ¹O₂,and thus inhibited its oxidase activity.The electrostatic interaction between ss DNA and 3,3’,5,5’-tetramethylbenzidine（TMB）can enhance the affinity of Tph-BT for TMB to facilitate electron transfer between TMB and^·OH,and thus enhance the peroxidase activity of Tph-BT.2.Due to the reverse regulation of the two enzymatic activities of Tph-BT by ss DNA,the DNAzyme-derived nucleic acid aptamer was selected for the colorimetric analysis of uranium.After adding DNA aptamers with specific recognition for UO₂²⁺,the adsorption of DNA on the surface of Tph-BT significantly inhibited the oxidase activity of Tph-BT,while the peroxidase activity was significantly enhanced.In the presence of UO₂²⁺,the DNA aptamer interacts with it to form secondary structures and detaches from the surface of Tph-BT,thereby restoring the two enzymatic activity of Tph-BT.Based on the reversed regulation effects of DNA aptamer on the two types of enzymatic activities of Tph-BT,a sensitive and selective“off-on”and“on-off”detection platform was constructed for the colorimetric analysis of UO₂²⁺.3.A series of metal covalent organic polymers（MCOPs）based on M-OH sites were synthesized for the photocatalytic degradation of nerve agent simulants.A series of MCOPs（M=Fe,Zn,Ni,Co,Cu）containing the active site of M-OH-M bimetals were prepared by solvothermal reaction of 1,10-phenanthroline-5,6-diamine（PTD）,4,4’,4’’-（benzene-1,3,5-triyltris（ethyne-2,1-diyl））tris（2-hydroxybenzaldehyde）（BTT）and acetate of different metals.Due to MCOPs have active site similar to natural hydrolases,their outstanding photocatalytic activity is further utilized to achieve efficient hydrolysis of the nerve agent analog methyl paraoxon（DMNP）under visible light irradiation.The results showed that compared with COPs without metals,various MCOPs had a significant enhancement effect on the hydrolysis of DMNP,with Fe-COP exhibiting the best hydrolysis activity and a hydrolysis half-life of about3 minutes.