Pristine and Carboxyl-Functionalized Tetraphenylethylene-Based Ladder Networks for Gas Separation and Volatile Organic Vapor Adsorption

Abstract

A novel tetraphenylethylene-based ladder network (MP1) made by polycondensation reaction from 4,4′,4″,4‴-(ethene-1,1,2,2-tetrayl)tetrakis(benzene-1,2-diol) and 2,3,5,6-tetrafluoroterephthalonitrile and its COOH-functionalized analogue (MP2) were synthesized for the first time. Their structures were confirmed by solid-state nuclear magnetic resonance (13C cross-polarization magic angle spinning), Fourier transform infrared spectroscopy, and elementary analysis. MP1 exhibited a high Brunauer–Emmett–Teller surface area (1020 m2 g–1), whereas the COOH-functionalized MP2 showed a much smaller surface area (150 m2 g–1) but displayed a more uniform pore size distribution. Because of the high density of nitrile groups in the network polymers of intrinsic microporosity (PIMs) and strong interaction with quadrupole CO2 molecules, MP1 exhibited a high CO2 adsorption capacity of 4.2 mmol g–1 at 273 K, combined with an isosteric heat of adsorption (Qst) of 29.6 kJ mol–1. The COOH-functionalized MP2 showed higher Qst of 34.2 kJ mol–1 coupled with a modest CO2 adsorption capacity of 2.2 mmol g–1. Both network PIMs displayed high theoretical ideal adsorbed solution theory CO2/N2 selectivities (51 and 94 at 273 K vs 34 and 84 at 298 K for MP1 and MP2, respectively). The high selectivities of MP1 and MP2 were confirmed by experimental column breakthrough experiments with CO2/N2 selectivity values of 23 and 45, respectively. Besides the promising CO2 capture and CO2/N2 selectivity properties, MP1 also demonstrated high sorption capacity for toxic volatile organic vapors. At 298 K and a relative pressure of 0.95, benzene and toluene sorption uptakes reached 765 and 1041 mg g–1, respectively. Moreover, MP1 also demonstrated some potential for adsorptive separation of xylene isomers with adsorptive selectivity of 1.75 for m-xylene/o-xylene.