Tetraphenyladamantane-Based Microporous Polyimide and Its Nitro-Functionalization for Highly Efficient CO₂ Capture

Abstract

A new microporous polyimide network (PI-ADNT) is synthesized from 1,3,5,7-tetrakis(4-aminophenyl)adamantane and naphthalene-1,4,5,8-tetracarboxylic dianhydride. Subsequently, PI-ADNT is nitrated in fuming nitric acid with different nitration time to produce three nitro-decorated porous polyimides (PI-NO 2 s). Their chemical structures and nitration degrees are characterized by FTIR, solid-state 13 C CP/MAS NMR spectra and element analysis. The interesting evolution of porous morphology and porosity of PI-NO 2 s with nitration time is investigated in detail. The results show that PI-ADNT has the BET surface area of 774 m 2 g –1 with microporous size centering at 0.75 nm. After nitration-modifications, PI-NO 2 s display decreased surface area but remarkably increased CO 2 uptake up to 4.03 mmol g –1, which is superior to most of porous polymers reported in the literature. Moreover, the CO 2 adsorption selectivites over CH 4 and N 2 in PI-NO 2 s are also significantly improved in comparison with PI-ADNT. The CO 2 adsorption/separation properties of PI-ADNT and its nitrated products are studied and explained in terms of the variations of porous structure and chemical composition as well as the interaction parameters between CO 2 molecule and polymer skeleton such as Henry’s constant, first virial coefficient, and enthalpy of adsorption.