Preparation Of Imine-based Covalent Organic Frameworks Materials And Their Adsorption Performance And Mechanism For Bisphenols Pollutants In Water

In recent years,Covalent Organic Frameworks（COFs）,as a class of porous polymer material,have been widely used in the fields of adsorption,catalysis,sensing and removal of pollutants due to its good thermal and chemical stability,large specific surface area,porosity,and adjustable pore size.COFs with proper pore sizes and suitable adsorption sites can be used for removing organic pollutants in water by well directional design and synthesis.This work is aimed at the adsorption study of the bisphenol pollutants in water environment.Based on the characteristics that pollutants generally contain polar functional groups and have specific molecular sizes,we designed and synthesized imine-based covalent organic frameworks with different pore sizes.The adsorption performance and mechanism of the material to the typical bisphenol S（BPS）and bisphenol A（BPA）pollutants in water were studied by adjusting the pore size and stability of the material.In this work,using solvothermal reaction,we successfully synthesized two imine-based covalent organic frameworks with different pore sizes（COF-1 and COF-2）by combining various aldehyde structures units and 1,3,5-tris（4-aminophenyl）benzene.At the same time,the structure characteristics of the COFs can be verified by various characterization methods.The adsorption behavior of bisphenol S and bisphenol A on COFs materials were investigated in detail,the adsorption experiences mainly included the adsorption influence factors,adsorption models and adsorption mechanism Experimental results show:（1）The adsorption kinetic study showed that COF-2 exhibited a faster adsorption rate than that of COF-1.For bisphenol S and bisphenol A,COF-2 can reach adsorption equilibrium within 1 h.Pseudo-second-order kinetic model could more described the adsorption process.（2）Based on the study of isothermal adsorption experiments,COF-2 has better adsorption capacity for bisphenol S and bisphenol A.The maximum adsorption capacities of COF-2 for bisphenol Sand bisphenol A obtained from Langmuir isotherm were calculated as200.00 mg·g-1 and 149.25 mg·g^-1.（3）The results of thermodynamic studies showed that the adsorption of bisphenol S and bisphenol A on COFs was a process of spontaneous and endothermic,and high temperature was not conducive to the adsorption of pollutants.（4）Both hydrogen bonding andπ-πinteractions might have been responsible for the adsorption of BPS and BPA on the COFs.To further explore the adsorption mechanism,different types of pharmaceuticals adsorption was studied.The adsorption capacity was ranked as follows:bisphenols pharmaceuticals>anti-inflammatory pharmaceuticals>sulfa pharmaceuticals.These results confirmed that COFs with larger pore sizes were more conducive for the adsorption of pollutants with smaller molecular dimensions.Moreover,COF-1 and COF-2 possessed excellent p H stability and recyclability,which can maintain excellent removal performance after 4 regeneration cycles.These results shown that the synthesized COFs have great application potential in removing organic pollutants in wastewater.