Synthesis And Properties Investigation Of Azobenzene-based Photo-responsive Covalent Organic Framework Materials Linked By Imine Bonds

Covalent organic frameworks（COFs）are new type of porous material with low density,good porous structure,high chemical and thermal stability.Therefore,COFs have potential application in gas storage,gas separation,catalysis,and biomedicine.At present,the construction of functionalized COFs has become a hot research topic in this field.Among them,photo-responsive COFs have attracted much research attention due to the advantages of clean and safe light source,accurate control of the wavelength,intensity,position and time of the light,and convenient use.However,the reported photo-responsive COFs have the following shortcomings such as insufficient structure stability,weak photoisomerization properties,and difficulty in design the building blocks.In this paper,photo-responsive COFs with good stability and good photo-response are constructed using imine as linkage and photo-responsive azobenzene derivative as building blocks,their performance was characterized,and the potential application in CO₂ and dye adsorption was investigated.The thesis is divided into five parts.The main content includes:The first chapter introduces porous materials,the preparation,classification and application of COFs,and the research on stimulus-responsive COFs.The research status of photo-responsive COFs is introduced in detail.In the second chapter,an ultraviolet/visible responsive COF（COF-Azo-1）is designed and synthesized by solvothermal synthesis using visible light-responsive azobenzene 4,4’-dialdehyde azobenzene and 1,3,5-tris（4-aminophenyl）triazine as building blocks.The influence of experimental conditions including solvent,reaction time,reaction temperature,catalyst type and concentration on the properties of COFs is discussed,and optimized reaction conditions are obtained,and COF-Azo-1 is prepared under the optimized conditions.COF-Azo-1 is characterized using FT-IR to confirm the formation of imine bond,PXRD to characterize its crystallinity,TGA to analyze its thermal stability,SEM to characterize its micro morphology,BET to determine its specific surface area and pore size distribution.The isomerization performance of COF-Azo-1 under irradiation at 365 and 440 nm is investigated.COF-Azo-1 has excellent photo-reversibility.In the third chapter,a visible light-responsive COF（COF-Azo-2）is synthesized using 4,4’-diaminoazobenzene and 2,4,6-tris（4-formylphenoxy）triazine as building blocks.The effect of experimental conditions including solvent,reaction time and reaction temperature on the synthesis of COFs materials is investigated,and appropriate reaction conditions are obtained.The structure and performance of COF-Azo-2materials are characterized.The photo-responsive behavior of COF-Azo-2 under irradiation at 405 and 550 nm is investigated,an obvious change in specific surface area of 15%is observed.COF-Azo-2 also has excellent photo-reversibility.Its light-controlled adsorption performance for dyes is studied,COF-Azo-2 has a strong specific adsorption capacity for rhodamine B with a maximum adsorption capacity of68.4 mg/g.The adsorption ratios of COF-Azo-2 to rhodamine B and methyl orange and methylene blue are 8.2:1 and 20:1,respectively.In the fourth chapter,a series of tri-component（DAB/TAPT/TFPT）doped visible light-responsive COF material COF-Azo-3-X is synthesized using4,4’-diaminoazobenzene（DAB）,2,4,6-tris（4-formylphenoxy）triazine（TFPT）and1,3,5-tris（4-aminophenyl）triazine（TAPT）as building blocks.The influence of DAB/TAPT molar ratio is studied,and X=0.5 is more suitable.A photo-responsive COF-Azo-3-0.5 with certain crystallinity is successfully synthesized.The isomerization behavior of COF-Azo-3-0.5 upon irradiation at 405 and 550 nm is studied.Finally,its photo-controllable adsorption of dyes is investigated,the results show that COF-Azo-3-0.5 has a strong specific adsorption capacity for rhodamine B with a maximum adsorption capacity of 239.6 mg/g.The ratio of maximum adsorption capacity of COF-Azo-3-0.5 is 5:1 and 35:1 for rhodamine B/methyl orange and rhodamine B/methylene blue,respectively.Chapter 5 summarizes the main research work and experimental results of this paper,and prospects the future research directions of photo-responsive COFs.