Preparation Of D-A Covalent Organic Framework Materials And Their Applications In Fluorescence Detection And Photocatalysis

Covalent organic frameworks（COFs）are a kind of new organic polymer materials with high crystallization state and high porosity,which are composed of organic building blocks with highly adjustable properties.Different from traditional polymers,COFs can accurately organize specific molecular structures into networks with structural periodicity,which provides new opportunities for the design of functional materials.In this paper,a series of donor acceptor（D-A）functional COFs materials were designed and synthesized by adjusting the pore size and replacing different functional groups,and their applications in the adsorption and detection of heavy metals,the detection of nitroaromatics,photocatalysis and so on were studied.The main research contents are as follows:Firstly,aiming at the disadvantages of complex detection process and high cost of traditional detection methods for heavy metal Hg²⁺,while most of the new fluorescence detection only depends on the change of fluorescence intensity and single detection method,a new triazine nitrogen rich D-A COF,TBN-1 with high specific surface area and excellent fluorescence performance was synthesized for the selective detection and removal of Hg²⁺in wastewater.The results show that TBN-1 shows high efficiency and sensitive detection ability of Hg²⁺.The results of adsorption kinetics showed that TBN-1 had a fast adsorption rate and great saturated adsorption capacity(1630 mg g^-1)for Hg²⁺in a wide p H range,which exceeded the highest level reported in the literature(1359 mg g^-1).TBN-1 can effectively reduce the concentration of Hg2+from 10ppm to a very low level of 0.55ppb,which is far lower than the acceptable limit of drinking water（2ppb）.Secondly,aiming at the problems of single detection method and low sensitivity of existing nitroaromatic compounds,TBN-1 was used to detect nitroaromatic compounds.The abundant electron transfer of TBN-1 ensures stronger fluorescence and quenching properties.The results show that TBN-1has good detection ability of nitroaromatics.In particular,the detection limit response of TBN-1 to picric acid is highly sensitive,only 0.15 ppm,which is much lower than that of other fluorescent probe materials for picric acid detection（0.22-22.0 ppm）.The quenching coefficient of picric acid to TBN-1is 2.89*10⁵,which is also the highest among the reported materials（0.5×10⁴-2.51×10⁵）.The simulation results of Homo and LUMO reveal the quenching mechanism of TBN-1 by nitroaromatic hydrocarbons,indicating that the electron deficiency property of nitroaromatic hydrocarbons is the main reason for the quenching of TBN-1.Thirdly,in view of the environmental pollution caused by most of the catalysts containing precious metals in a number of photocatalysis and the low catalytic efficiency of metal free COFs,COFs with electron donor acceptor structure were designed and constructed by introducing electron deficient piperazine structure and electron rich porphyrin ring.Among them,PTBC-porCOF has more suitable band gap and effective photoinduced electron hole pair separation.Under visible light irradiation,PTBC-porCOF can produce superoxide anion radical(O₂^·-),which has high selective oxidation efficiency for sulfide,with conversion of 97%and selectivity of 99%;In addition,the higher HOMO value of PTBC-porCOF can promote the reductive dehalogenation of 2-bromoacetophenone derivatives,and the conversion is99%.Finally,the effect of pore size of COFs on photocatalytic performance was investigated.Two kinds of two-dimensional D-A porphyrin based COFs with different pore sizes and similar structures,ETBA-porCOF and ETBC-porCOF,were synthesized.Simulation and photoelectric characterization showed that both COFs had good photocatalytic activity and could be used as non-metallic heterogeneous photocatalysts for oxidation reaction because of their strong ability to generate reactive oxygen species.ETBA-porCOF with small pore size has higher oxidation efficiency for small molecular phenylmethyl sulfide（the conversion reaches 95%after 3 hours of illumination）,while ETBC-porCOF with large pore size is more suitable for the oxidation of macromolecular amine conjugates（the conversion reaches99%after 6 hours of illumination）.The two COFs have good recoverability and stable catalytic performance,and can be reused for at least 5 times.This study provides a new idea for the design of 2D COFs suitable for photocatalytic reaction size,and shows the broad prospect of 2D COFs in photo driven organic synthesis.