Prism[5]arene-based Nonporous Adaptive Crystals In Adsorption And Separation

The research of advanced separation materials is of great significance for environmental friendliness and energy conservation and environmental protection.To date,various separation materials have been developed and applied,such as activated carbon,zeolite molecular sieves,metal-organic frameworks（MOFs）,covalent organic frameworks（COFs）,and porous organic polymers（POPs）.Such materials exhibit selectivity to be improved in the separation of compounds with similar structures and boiling points.In addition,the reuse of activated carbon requires high-temperature activation treatment,which consumes a lot of energy.In this paper,macrocyclic prism[5]arenes,as novel non-porous adaptive crystals（NACs）,possess an electron-rich cavity and macrocyclic crystal structure,and can adsorb specific guests through host-guest interactions,and the adsorption capacity is better than traditional separation materials,such as activated carbon and molecular sieves can be activated and reused by low-temperature vacuum heating.Therefore,they have potential application value in the field of adsorption and separation.In the first part,the prism[5]arene NP5OCH3 was prepared by one-step condensation method,its specific surface area and pore size distribution were determined by ¹H NMR spectroscopy,heat loss analysis,and nitrogen isotherm adsorption tests at 77 K.Finally,it is concluded that the prism[5]arene NP5OCH3 conforms to the characteristics of non-porous adaptive crystals,such as low specific surface area and low porosity.When the temperature is higher than 400℃,the skeleton structure of macrocycle is destroyed,and NP5OCH3 exhibits good thermal stability.In the second part,in ambient air mixed with aromatic volatile organic compounds（VOCs）,guest-induced crystalline phase transformation endowed the NP5OCH3-based NACs high capture capacities on different aromatic VOCs molecules.Except for capture capacities,the intercrystalline adsorption endowed the NP5OCH3-based NACs fluorescence enhancement for aromatic VOCs detection and high recyclability by vacuum heating with low energy consumption.Single crystal diffraction and density functional theory calculation proved the multiple non-covalent interactions（C-H···π,C-H···O）existed between the guest and macrocycle.Crystalline solid macrocycle NP5OCH3 based on the guest-induced crystalline phase transformation mechanism may provide a new idea for development of new adsorbents to capture and monitor harmful air pollutants.In the third part,prism[5]arene NP5OCH3 can capture iodine vapor at75°C with an adsorption capacity up to 1.77 g/g,which is superior to some iodine vapor adsorbents.On the other hand,the iodine element in the iodine aqueous solution can be directly captured by NP5OCH3,and the adsorption efficiency is as high as 86%.After adsorption of iodine,I₂@NP5OCH3 can be washed with hexane to remove the iodine and can be reused.In addition,the macrocycles show significant fluorescence quenching upon adsorption of iodine vapor and can be used for the detection of iodine vapor.