Functionalized porous aromatic frameworks for CO<sub>2</sub>/N<sub>2</sub> high adsorption capacity and separation: A molecular simulation study

Abstract

Carbon capture and storage (CCS) has received widespread concerns as a promising strategy to allow the continued use of fossil fuels whilst alleviating excessive emissions of CO2 into the atmosphere. On the basis of this strategy, a large number of adsorbent materials with high CO2 adsorption capacity and selectivity have emerged. Porous aromatic frameworks (PAFs) were recently synthesized with the higher surface area and porosity to date; one such PAFs_303 has diamond-like structure building blocks and exhibits exceptional thermal and hydrothermal stabilities. Herein, we computationally designed PAFs_303 by introducing polar organic groups, and then investigated their single-component adsorption and competitive behavior of binary CO2/N2 mixture by using grand-canonical Monte Carlo (GCMC) simulations. Among these functional PAFs, we find at low pressure the introduction of functional groups can improve the adsorption capacity of CO2/N2, especially for 303_DHF; and at high pressure PAFs_303 shows the best adsorption capacity of CO2/N2 due to the difference of pore structure characteristics. Temperature had a negative effect on the single-component adsorption of CO2/N2. Meanwhile, the selectivities of CO2 over N2 are enhanced because of functionalization effect, which demonstrate the following sequence according to selectivity: 303_DHF>303_NH2>303_OH>PAF_303. Evaluation of adsorption capacity and analyses of the isosteric heat and radial distribution functions confirm that functionalization can evidently enhance the interaction between CO2/N2 and frameworks. Overall, this work highlights the effects of edge-functionalization on the adsorption and separation of CO2/N2 in NPCs, and provided an effective strategy for designing and screening adsorbent materials for carbon capture and separation.