Functional Porous Aromatic Frameworks With Well-defined Nitro Group

Climate change is threatening the life of human beings.Facing this challenge,varieties of porous materials for gas separation and storage have been developed.Porous aromatic frameworks are famous for their high surface area,gas adsorption capacity and thermal stability.We intend to introduce nitro groups to PAFs with the hope of constructing nitro-functionalized PAFs with clear structure to improve PAFs' CO2 capture capacity.Micro/mesoporous NO2-PAF-1 was synthesized via Cu-mediated Ullmann coupling and the BET surface was 649 m2/g.NO2-PAF-1 possessed CO2 capacity at 50.0 cm3/g and CO2 heat of adsorption at 38.4 k J/mo l,indicat ing the improvement of CO2 capacity through the introduction of nitro groups.Later,microporous NO2-PAF-2 and unfunctionalized EOF-6 were synthesized via Pd catalyzed Suzuki coupling,and NO2-PAF-2 possessed BET surface area at 571.The CO2 capacity of NO2-PAF-2 was at 48.5 cm3/g and CO2 heat of adsorption was at 34.0 k J/mo l,which were both higher than EOF-6.Further invest igat ion indicated that the strong interactio n between nitro-funct ionalized surface and CO2 can be attributed to the polarit y of nitro groups.Data also displayed the increment of hydrogen adsorption of nitro-introduction.Finally,meso/macroporous NO2-PAF-3 was prepared by Cu-mediated Ullmann coupling through which ether bonds were introduced to the framework,and its BET surface area(233 m2/g),CO2 capacity(30.0 cm3/g)and pore volume(0.58 cm3/g)were all higher than unfunctionalized material,further proved the activation of Ullmann reaction and enhancement of CO2 adsorption by the introduction of nitro groups.Comparing the performance of synthesized materials,we found that the introduction of nitro groups does activate Ullmann reaction and improve CO2 adsorption.Microporous materials were preferred for high temperature CO2 adsorption,whereas soft segment provides high pore volume.This work discovered some influence of reactions and functional groups to properties and adsorption of porous materials,which makes it possible to achieve varied functional porous materials by choosing pore size and functional groups.