Microporous Polyimides with Uniform Pores for Adsorption and Separation of CO2Gas and Organic Vapors

Three microporous polyimides, MPI-1, MPI-2, and MPI-3, with uniform pores were synthesized via one-pot polycondensation from tetrakis(4-aminophenyl)methane, tris(4-aminophenyl)amine and 1,3,5-tris(4-aminophenyl)benzene with pyromellitic dianhydride, respectively. The amorphous networks exhibit excellent thermal stability, large BET surface areas up to 1454 m2 g–1, and narrow pore size distribution in the range from 5 to 6 Å. Their adsorption–desorption isotherms of CO2 are reversible, and the CO2 uptakes at 273 K and 1 bar are up to 16.8 wt %. Moreover, based on the ratios of initial slopes of isotherms, the CO2/N2 and CO2/CH4 separation factors are as high as 102 and 12, respectively. The above CO2 adsorption and separation properties are attributed to the presence of abundant electron-rich heteroatoms in the polyimide networks and the unifrom ultralmicroporous structures. In addition, for MPI-1, the adsorption capacity of benzene vapor is 119.8 wt %, while the separation factors of benzene over nitrogen and water reach 342 and 28, respectively. The outstanding selective adsorptions of CO2 gas and benzene vapor endow the microporous polyimides with promising potential in CO2 capture and separation as well as air- and water-cleaning applications.