Synthesis And Catalytic Performance Of Benzothiadiazole And Nitroxide Radical Functionalized COFs

Covalent Organic Frameworks（COFs）are highly crystalline porous organic polymers composed of non-metallic elements（e.g.C,H,N,O and B）linked by strong covalent bonds.They have a wide range of applications in the fields of gas storage and separation,multiphase catalysis,sensing and detection,and energy storage.In this thesis,a series of COFs functionalised with benzothiadiazole（BTz）and nitroxide radical（2,2,6,6-tetramethylpiperidine-1-oxo-radical,TEMPO）were synthesised by grafting them onto the COFs skeleton as functionalised groups.The effects of different solvent systems on the morphology and crystallinity of the COFs were explored,and the performance of the above functionalized COFs in the photocatalytic oxidation of benzothiadiazole,α-terpinene and thermocatalytic benzyl alcohol was preliminarily investigated.The research content of this paper is mainly divided into the following two parts:（1）Synthesis and visible light catalytic performance of benzothiadiazole functionalized COFs4,7-Dibromo-2,1,3-benzothiadiazole with visible light redox activity was selected as the raw material for the synthesis of 4,4’-（benzothiadiazole-4,7-diyl）dibenzaldehyde containing an aldehyde group（the building block was the C₂ configuration）by Suzuki coupling reaction with 2,4,6-tris（4-aminophenyl）-1,3,5-triazine（TTA,C₃ configuration）by solvent Scanning electron micrographs（SEM）showed that TTA-BTz-COF consisted of highly agglomerated spherical nanoparticles.The results of the visible photocatalytic experiments showed that the oxidation of anisole to methyl phenyl sulfoxide was achieved in 39.8%under blue light irradiation（3 W,425 nm）for 5 h using methanol as solvent,anisole（0.3 mmol）and TTA-BTz-COF as catalyst（4 mg）.The 4,7-bis（4-aminophenyl）-2,1,3-benzothiadiazole building block was synthesized from 4,7-dibromo-2,1,3-benzothiadiazole by introducing the BTz group into the amino ligand using the Suzuki coupling reaction,and was synthesized with the 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde（TP）by solvothermal,sonochemical,room temperature and mechanochemical synthesis in different solvent systems(The crystallinity of the above-mentioned TP-BTz-COFs was systematically investigated in relation to the synthesis conditions,and it was found that the crystallinity of TP-BTz-COFs was mainly dependent on the crystallinity of the TP-BTz-COFs.The crystallinity of COFs was found to be mainly dependent on the synthesis method,independent of the solvent system mentioned above.Among them,the TP-BTz-COFs prepared by room temperature and ultrasonic synthesis had good crystallinity.Electron paramagnetic resonance spectroscopy（EPR）showed that TP-BTz-COFs were able to activate oxygen to generate singlet oxygen（¹O₂）and superoxide radicals(O₂^·-)under visible light irradiation,however,oxidation of anisole andα-pinene by their visible photocatalysts revealed that they were only able to selectively oxidiseα-pinene to aslidol,but catalytic conversion of anisole to the catalytic performance was poor for the conversion of methyl phenyl sulfoxide.The synthesis of highly crystalline triazine COFs is usually carried out under harsh reaction conditions,but in the study of the above-mentioned BTz-COFs,we found that TTA（C₃ configuration）and benzene-1,3,5-tricarbaldehyde（TFB,C₃ configuration）were used as monomers to rapidly synthesise TTA-TFB-COFs with high crystallinity under mild reaction conditions using ultrasonic synthesis.X-Ray Diffraction（XRD）,Brunauer-Emmett-Teller（BET）and thermogravimetric analysis（TGA）showed good crystallinity,a large specific surface area(632 m² g^-1)and good thermal stability（518°C）.Thanks to the nitrogen-rich structure of TTA-TFB-COF and its aromatic ring,TTA-TFB-COF has excellent adsorption properties on iodine monomers.15 mg of TTA-TFB-COF was added to a solution of iodine hexane at a concentration of 1 mmol L^-1,and the iodine monomers were completely removed from the solution after 4.5 h.（2）Synthesis and catalytic properties of TEMPO functionalized COFs2,5-Dibromo-N-（2,2,6,6-tetramethylpiperidine）benzamide was sele-cted as the functionalized molecule for the synthesis of amino-containing NH₂-tpdc-TEMPO（C₂ conformation）by Suzuki coupling reaction and TEMPO-functionalized TP-TEMPO-COFs with TP（C₃ conformation）by sonication synthesis in different solvent systems（solvent systems A and B）.The SEM images showed that the TP-TEMPO-COFs consisted of a large number of aggregated nanoparticles and the XRD diffraction results indicated a low crystallinity of the COF.The conversion performance of TP-TEMPO-COFs on the oxidation of benzyl alcohol to benzaldehyde was investigated at 80°C and under oxygen atmosphere using trifluorotoluene as solvent.The catalytic results showed that when tert-butyl nitrite（TBN）was added as initiator,TP-TEMPO-COF（0.3 mmol）,the conversion of benzyl alcohol to benzaldehyde was 24.17%after 24 h.Further,the BTz and TEMPO bifunctional TP-(BTz_x-TEMPO_1-x)-COFs were prepared using a mixed-ligand strategy,in which different ratios of BTz and TEMPO functionalized amino monomers were combined with TP by ultrasonication and room temperature synthesis.Photocurrent response and electrochemical cyclic voltammetry tests showed that the bifunctional combination of visible light response and electrochemical activity.The conversion of anisole by TP-(BTz_0.5-TEMPO_0.5)-COF_RT was 50.5%higher than that of TP-(BTz_0.8-TEMPO_0.2)-COF_RT（15.6%）when irradiated with a blue LED lamp（3 W,425 nm）for 5 h at room temperature as a visible light-catalyzed anisole catalyst.