Naphthalene-Based Microporous Polyimides: Adsorption Behavior of CO2 and Toxic Organic Vapors and Their Separation from Other Gases

Naphthalene was selected as a building block to prepare three polyimide networks with different topological structures via one-pot polycondensation from naphthalene-1,4,5,8-tetracarboxylic dianhydride with tetrakis(4-aminophenyl)methane, tris(4aminophenyl)amine, and 1,3,5-tris(4-aminophenyl)benzene. The resultant polymers have moderately large BET surface areas with narrow pore size distribution at around 6 A. Interestingly, it is found that they can uptake 90.5 wt % benzene vapor (298 K, 0.8 bar), and the separation factors of benzene over nitrogen, water, and cyclohexane are as high as 759.3, 40.3, and 13.8, respectively. The high adsorption capacity and selectivity of benzene vapor are attributed to the incorporation of large amount of naphthalene groups in the network since naphthalene is highly hydrophobic in nature and has strong pi-electron-delocalization effect. On the other hand, the CO2 uptakes in polymers reach 12.3 wt % (273 K, 1 bar), and the adsorption curves are reversible. Moreover, the separation factors of CO2/N-2 and CO2/CH4 are 88.6 and 12.9, respectively, superior to many other microporous organic polymers. The above experimental results were analyzed and explained with respect to the kinetic diameters, polarity, critical temperature of the vapors and gases, and the stereoconfiguration of net nodes, porous characteristics, and hydrophobic/hydrophilic nature of the pore walls of the microporous polyimides.