Design And Application Of Salen Metal Covalent Organic Frameworks Materials

Porous materials have been widely used in gas separation,energy storage,catalytic reactions and other fields due to their high specific surface area and stable chemical properties.There are many types of porous materials,including molecular sieves,zeolites,Metal Organic Frameworks(MOFs),Covalent Organic Frameworks(COFs),etc.Among them,it has become one of the research hotspots of porous materials,because COFs have the advantages of high chemical stability,low density,and can meet the needs of various practical applications by introducing functional groups.Salen is a base called Schiff base obtained by combining aldehydes and amines through a condensation reaction.There are active coordination sites of metal on Salen,which is easy to combine with metal.Therefore,it is often used to synthesize Salen complexes.Salen-metal(Salen-M)is a Salen complex with a metal atom as the center.Different chemical functions can be achieved by changing the metal atom because of its unique coordination form.The research work in this paper is applied to carbon dioxide catalysis and ethylene/acetylene separation,and new Salen-M-COFs materials are designed by introducing Salen-M into COFs.The traditional material development method is trial and error,and the research and development of a new material usually takes more than ten years.For this reason,in order to speed up the development of materials,researchers began to use material simulation and design methods to conduct simulation studies on the structure and function of materials before material preparation and testing.Therefore,in order to realize the efficient development of Salen-M-COFs materials,first,the mechanism of Salen complexes with precious metals as the central atom in the reaction of carbon dioxide hydrogenation to formate was studied through theoretical simulation method.According to the theoretical calculation results,the Salen-M structure with the best catalytic performance was screened out,and then applied to the catalytic reaction of carbon dioxide hydrogenation to formic acid through experimental methods to synthesize the corresponding COF structure of Salen-M.In addition,the separation selectivity of ethylene and acetylene was explored,and finally the two Salen-M structures with the best separation effect were screened out.Based on the transition metal elements in the fourth period of the periodic table,a series of Salen-M complexes were designed.The main research results of this work are as follows1.The focus is on the performance optimization and application of COFs materials containing seven kinds of precious metals Salen-M structure,starting from the design and development of porous materials.The energy barriers of these seven Salen-M complexes catalyzed by the hydrogenation of carbon dioxide to formate were calculated based on the density functional theory(DFT)method.Among them,the lowest reaction energy barrier is only 10.09 kcal/mol,which is Salen-Pd.The simulation results show that Salen-Pd can realize the reaction of carbon dioxide hydrogenation to formate under normal temperature and pressure.Salen-Pd was introduced into the COF framework,and the corresponding Salen-Pd-COF materials were prepared,based on the theoretical prediction results.The result of structural characterization proved that the corresponding COF structure was synthesized.Using the synthesized Salen-Pd-COF material,the experiment of carbon dioxide hydrogenation to formic acid is carried out under normal temperature and pressure,and the reaction can be carried out.Continued cyclic experiments have verified that the Salen-Pd-COF catalyst has good stability.2.The adsorption energy of 14 Salen-M complexes on ethylene and acetylene gas molecules was systematically studied,using DFT method.It is found that Salen-Mn(Ⅱ)and Salen-Ni(Ⅱ)complexes may have the best separation performance of acetylene and ethylene by comparing the difference in the adsorption energy of 14 kinds of Salen metal complexes on the two gas molecules.The periodic three-dimensional structure of the two materials 3D-Salen-COF-Ni and 3D-Salen-COF-Zn was constructed.Through further research,the Salen-Ni and Salen-Zn structures were embedded in the COFs framework.The adsorption performance of two COFs materials to ethylene and acetylene was simulated using the Grand Canonical Monte Carlo(GCMC)method.By comparison,it is found that 3D-Salen-COF-Ni has better separation selectivity for ethylene and acetylene,which supports the conclusion obtained by DFT calculation.The related simulation results are contributed to develop porous materials for effectively removing a small amount of acetylene in ethylene gas.