Mixed monomer derived porous aromatic frameworks with superior membrane performance for CO₂ capture

Membrane separation has great potential for carbon dioxide capture, and materials play paramount important role in the membrane technology. In this paper, the mixed-monomer strategy is proposed for synthesis of a functional porous aromatic framework (PAF) named as PAF-45DPA. The monomer of diphenyl is employed for formation of the porous network and another monomer of diphenylamine is introduced to yield basic nitrogen sites. As a consequence, the prepared PAF-45DPA material possesses a surface area of 679 m² g^-1 with dominant pore size of ~0.58 nm which educes selective adsorption property toward carbon dioxide with IAST selectivity of 63.1 and CO₂ uptake of ~45.3 cm³ g^-1 at 298 K and 101 kPa measured from CO₂ and N₂ adsorptions. PAF-45DPA is subsequently used to fabricate hollow fiber membranes by hybridization with polysulfone (PSF) through the technique of dry jet-wet quench. Gas permeation analysis of CO₂ and N₂ reveals that the separation performance of PAF-45DPA/PSF is superior to those of PAF-45 and PDPA built from unary monomers. The PAF-45DPA/PSF membrane shows a dramatic improvement in the CO₂/N₂ separation factor (24.2) compared to PAF-45/PSF (15.4) and a significant enhancement in the CO₂ permeance (72.6 GPU) compared to PDPA (51 GPU) at 298 K and 0.12 MPa. High stability of the PAF-45DPA/PSF membrane is also demonstrated together with its low cost and scale up production possibilities, which shed a light on advanced CO₂ capture technology development for industrial gas exhausts.