Synthesis Of Schiff-base Covalent Organic Frameworks In Green Solvents And Study On Adsorption Of Organic Dyes

As a type of porous materials that own crystalline structures,covalent organic frameworks?COFs?are built from building blocks linked by covalent bonds,whose molecular structures can be modulated by using the principle of topology.The reversible formation of covalent bonds is the key to the construction of COFs,which allows for error correction to generate highly ordered frameworks.COFs have great application prospects in dye adsorption,catalysis,proton conduction,gas storage and separation as a result of low density,high surface area,uniform pores,high thermal stability and easy functionality.Solvothermal method is commonly used to synthesize COFs,which is usually carried out in closed systems using a mixture of volatile and toxic organic solvents.In order to reduce environmental pollution,it is necessary to study the green synthesis of COFs.This paper was focused on the synthesis of COFs in green solvents as well as their properties and appplications.The main research contents include the following two parts:1.Four kinds of two-dimensional?2D?COFs were successfully synthesized by using an ionic liquid 1-butylsulfonic-3-methylimidazolium hydrogensulfate?[BSMIm]HSO₄?as the green reaction medium with the condensation of1,3,5-triformylresorcinol?TFP?and amine monomers through Schiff-base reactions in an open system,including a new COF?TFP-AHAn-COF?synthesized for the first time.Based on the open channels of 2D COFs,the ionic liquid can be removed completely,and COFs exhibited crystallinity and porous properties similar to those prepared by solvothermal synthesis.Not only the ionic liquid acted as both solvent and catalyst,it was also recycled for further use without activity loss,showing broad prospects for the synthesis of COFs as green solvents.2.Using a deep eutectic solvent?DES?tetrabutylammonium bromide and glyoxaline?Bu₄NBr/Im?as the green reaction medium,a carboxyl-functionalized COF?TFP-PaCOOH-COF?was prepared by the reaction of TFP and2,5-diaminobenzoic?PaCOOH?as monomers through Schiff-base reaction.The synthetic process was carried out in an open system because of the low vapor pressure of the Bu₄NBr/Im DES.TFP-PaCOOH-COF had good crystallinity,porosity,and high thermal stability.In addition,TFP-PaCOOH-COF exhibited poor adsorption capacity for anion dye?Eosin B?,while it showed excellent adsorption capacity for two cationic dyes?Safranine T and Methylene blue?.