Polymer-supported superbases for carbon dioxide adsorption

Abstract

With the high demand to tackle climate change, direct air capture of CO2 has emerged as a potential technology. The choice of adsorbents significantly impacts the cost and efficiency of the process. The critical factor in this application is the stability and selectivity. Superbases are structurally stable and low-toxic compounds that contain amidine or guanidine groups. They have been identified as high-potential CO2 adsorbents due to their high CO2 capacity and fast kinetics. Despite the prevalent use of liquid sorbents containing superbases, solid adsorbents have received attention as well. In this master’s thesis, solid porous polymers combine with superbases by loading superbases on the polymer support through impregnation and covalent bonding methods to achieve high CO2 capacity and selectivity. The structure of the CO2 adsorbent was analyzed by attenuated total reflectance-Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), and element analysis (EA). At the same time, the morphologies were characterized by Brunauer-Emmett-Teller/Barrett-Joyner-Halenda (BET/BJH) analyses and scanning transmission microscopy (SEM). CO2 adsorption properties were assessed using thermogravimetric analysis. Among these, hyper-crosslinked toluene (HCT)-impregnated superbase exhibited a CO2 capacity of 1.03 mmol/g and an amine efficiency of 33% under 14-vol% CO2/N2 dry conditions. After adsorption-desorption cycles, the adsorbent remains stable. A high amount of superbase impregnated with substrates can increase CO2 capacity. Conversely, superbase will aggregate on the porous polymer surface, clog pore cavities, and thus reduce the efficiency of CO2 diffusion. Therefore, in order to improve CO2 adsorption performance, emphasizing the mass ratio of substrate to superbase during impregnation and the choice of solvent is crucial. It is significant to achieve functionalization while maintaining a porous structure after impregnation.