The Synthesis Of Covalent Organic Frameworks Based On Benzothiadiazole Derivatives And Their Applications In Separation And Analysis

Covalent organic frameworks（COFs）are a class of porous crystalline organic polymers which constructed by organic ligands connected by reversible covalent bonds.It has attracted more and more attentions because of their structural designability,tunable pore size,high specific surface area and crystallinity as well as good physical and chemical stability.In recent years,many COFs have been designed and widely used in the fields of adsorption and separation,chemical sensing,photocatalysis,energy storage and so on.However,the complicated synthesis methods and harsh synthesis conditions of most COFs are not conducive to their practical application.Meanwhile,owing to the aggregation-induced quenching effect caused by strongπ-πstacking between the COFs layers,the fluorescence emissions of COFs are usually weak.Therefore,it is necessary to develop a fast and simple synthesis strategy and improve the fluorescence emission of COFs for their further applications.Benzothiadiazole is a kind of chromophore with strong fluorescence emission,and its derivatives usually display wide absorption range,efficient and stable fluorescence emission.At the same time,as a well-known electron acceptor,the optical band gap of the benzothiadiazole system can be modulated easily,and the photoelectric properties such as the separation and transport of charge can be improved.To design and preparation of organic ligands with benzothiadiazole and employed them for the synthesis of COFs is expected to endow COFs with unique optoelectronic properties,which could expand their practical applications in adsorption and separation,chemical sensing and optoelectronics.In this paper,a series of COFs based on benzothiadiazole derivatives were synthesized.The relationship between structures and properties as well as the facile synthetic methods of these COFs were investigated,and the applications such as adsorption and chemical sensing of these COFs were explored.The main research contents are as follows:（1）Three COFs isomers（Tp-BTD-AA,Tp-BTD-AB,Tp-BTD-ABC）with different layer stacking models were prepared by aldimine condensation between the monomer4,4’-（benzo[c][1,2,5]thiadiazole-4,7-diyl）diphenylamine（BTD）and 1,3,5-trimethyl phloroglucinol（Tp）.The relationship between the temperature or solvent systems and the stacking models of COF isomers were investigate in detail.At the same time,the optical properties and photocatalytic activities of these COF isomers were investigated.Tp-BTD-ABC can be synthesized in large-scale at room temperature,which displayed the highest generation efficiency of type I reactive oxygen species.Thus,it could be employed as the photocatalyst for the synthesis of imine from amine under visible light.（2）.Three Tp-BTD COF isomers were employed for the adsorption and recovery of Au³⁺from electronic wastewater.These COF isomers could reduce Au³⁺to Au⁰ rapidly due to their good reducibility.In addition,the adsorption rates and capacity of these Tp-BTD COF isomers for Au³⁺were greatly improved under the irradiation of visible light,compared with those one of in dark conditions.Tp-BTD-AA exhibit a highest gold capacity of 3.0946 g/g for Au³⁺in p H 5 and under the irradiation of 460 nm light.The adsorption selectivity,anti-interference ability and recyclability of Tp-BTD-AA were investigated.This COF showed high adsorption selectivity to Au³⁺as well as good recyclability,which could be used as a potential adsorbent for the recovery of gold from electronic wastewater.（3）.Three Au-Tp-BTD COFs composites were prepared by in situ reduction of Au³⁺on Tp-BTD COF isomers without adding any reducing agent.The prepared composite materials could exhibit the activity of peroxidase mimetic enzyme in the presence of Hg²⁺,which could be used for the selective detection of Hg²⁺in water.After a series of optimization of the detection conditions,Au-Tp-BTD-AA could employ as a high sensitivity and selectivity colorimetric sensor for Hg²⁺,the liner range of Hg²⁺is 50～500n M,and the limit of detection is 2.05 n M.Moreover,Au-Tp-BTD-AA could be employed for the detection of Hg²⁺in real water sample.（4）.Three isoreticular donor-accepter（D-A）COFs linked with different covalent bonds were synthesized by solvothermal method with three benzothiadiazole derivatives:4,4’-（benzo[c][1,2,5]thiadiazole-4,7-diacyl）dibenzaldehyde,4,4’-（benzo[c][1,2,5]thiadiazole-4,7-diyl）diphenylamine and 2,2’-（benzo[c][1,2,5]thiadiazole-4,7-diylbis（4,1-phenylene））diacetonitrile condensed with pyrene-based molecules（named COF-JLU22,Py-TdCOF and Py-BSD COF,respectively）.The relationship between the different covalent bonds and the photocatalytic activity of these COFs were investigated.Among the three COFs,COF-JLU22 exhibits the best photocatalytic performance under the illumination of 465 nm light,which could be used as a light-controlled peroxide-mimicking enzyme to oxidize substrates.Thus,a colorimetric method for the detection of glutathione was developed,the linear range is 1.0～100.0μM.（5）.The effects of covalent bonds on the optical properties of these three isoreticular COFs（COF-JLU22,Py-TdCOF and Py-BSD COF）were investigated.It was found that COF-JLU22 and Py-TdCOF displayed different optical properties even though they are structural isomers.Py-TdCOF and Py-BSD COF exhibit strong fluorescence emission,and could showed the mechanochromic properties after grinding and sonication.The fluorescence intensity of Py-TdCOF was greatly improved after grinding,the wavelength also red-shifted at the same time.The grounded Py-TdCOF could maintain its fluorescence emission in aqueous solution,which could be used as a fluorescence sensor and adsorbent for 2,4-dinitrophenylhydrazine（2,4-DNPH）in water.（6）.The facile synthetic methods of COF-JLU22,Py-TdCOF and Py-BSD COF were explored.The relationship between the temperature or synthesis time and the crystallinity of these COFs were investigated.Two COFs based on C=N linkage（COF-JLU22 and Py-TdCOF）can be synthesized under mild conditions.The response of COF-JLU22 and Py-TdCOF to p H and volatile acid gases can be achieved due to the protonation of the N atom.Py-TdCOF films could be prepared with different thickness by controlling the amount of the monomer.Py-TdCOF films were grown in situ on a test paper for rapid,sensitive and reversible fluorescence and colorimetric quantitative detection of trifluoroacetic acid gas.