Synthesis Of Imine-Type Organic Molecular Cages And Their Iodine Adsorption Properties

Porous organic molecular cages(POCs)are a new type of crystalline solids.Organic imine cages prepared by Schiff base reaction,which have the advantages of low skeleton density,double pores inside and outside the cage,adjustable pore size,multiple active sites,clear structural units,etc.,and are widely used in the fields of proton conduction,loaded nanoparticles,gas adsorption and separation,and are a kind of hot materials studied in recent years.A large number of radioactive pollutants will be generated in the process of nuclear waste and nuclear accidents,among which radioactive iodine can accumulate in the thyroid gland of the human body,affect the metabolic process,and pose a threat to the safety of life and the ecological environment.Therefore,research on the efficient adsorption of radioactive iodine is of great significance.The latest studies have shown that organic imine cages have potential applications in the field of iodine adsorption,and the introduction of electricity-rich heteroatoms(N,S,etc.)may enhance their adsorption capacity of iodine.Therefore,in order to develop higher performance iodine adsorption materials,this paper designs and synthesizes a series of organic imine cages containing heteroatoms(N,S),and compares their structural properties and iodine adsorption performance.The specific research content is as follows:1.The Schiff reaction of benzyltriamine((2,4,6-trimethylbenzene-1,3,5-trimethyl)trimethylamine)employed as the amino unit with four different aldehyde units(2,5-thiophenedicarbaldehyde(SF),2,6-pyridinedicarbaldehyde(BD),isophthalaldehyde(BEN),2,2’-bithiophene-5,5’-dicarbaldehyde(LSF))afforded corresponding imine-type molecular cages(Cage XMe,X=SF,BD,BEN,LSF).The X-ray diffraction showed that Cage SFMe was[4+6] configuration and others were [2+3] configuration.The investigation on the iodine adsorption performance of the synthesized molecular cages displayed that these four molecular cages showed similar adsorption capacity for gaseous iodine,among which Cage SFMe exhibited the highest adsorption capacity(5.45g/g).Comparably,the adsorption performance for iodine solution is poor.The experimental results on adsorption mechanism suggested that the cage became amorphous after adsorbing iodine and the adsorbed iodine existed in the form of polyiodine ions.C=N and the electron-rich N and S may be effective iodine adsorption sites.2.Basd on the report that flexible skeletons facilitates the iodine adsorption,we substituted benzyltriamine with more flexible tris(2-aminoethyl)amine,which can react with abovementioned four di-aldhyde compounds(2,5-thiophenedicarbaldehyde(SF),2,6-pyridinedicarbaldehyde(BD),isophthalaldehyde(BEN),2,2’-bithiophene-5,5’-dicarbaldehyde(LSF))to generate corresponding imine-type molecular cages(Cage NX,X=SF,BD,BEN,LSF)via Schiff base reaction.Subsequent reduction of Cage NSF and Cage NLSF with Na BH4 afforded Cage NSF(H)and Cage NLSF(H).The [2+3] configuration of these cages was confirmed by X-ray single crystal diffraction.Furthermore,the iodine adsorption performance of the synthesized molecular cages was investigated and the all cages showed high adsorption capacity for gaseous iodine,among which the adsorption capacity of Cage NSF for iodine vapor could reach up to 7.15 g/g.Efficient adsorption of iodine in solution was also achieved for these cages.The further study on the adsorption mechanism demonstrated that the adsorbed iodine existed in the form of polyiodine ions.C=N and the electron-rich N and S may be effective iodine adsorption sites.Comparing and analyzing the molecular cages with the literature,it can be found that the adsorption capacity of gaseous iodine of the ten molecular cages synthesized in this paper is at a high level.