COF RIO-18/Polyurethane Mixed Matrix Membranes with Enhanced CO₂ Permeability and CO₂/N₂ Selectivity

A beta-ketoenamine-linked covalent organic framework named RIO-18, also reported as TpPa COF, featuring CO₂-philic CO/N-H sites and ∼17 Å pores, was incorporated into polyurethane by the casting method at loadings of 0.1-5 wt % to prepare xRIO-18@PU mixed matrix membranes (MMMs). Pure-gas permeation of CO₂, CH₄, and N₂, along with their corresponding ideal selectivities, were evaluated at different feed pressures. Thermal and structural analyses confirm that the COF was successfully incorporated into the matrix without altering the polymer structure. Gas permeation tests revealed a substantial increase in CO₂ permeability (up to 138%) and CO₂/N₂ ideal selectivity (up to 454%) as compared with unloaded PU, with the highest permeability and selectivity gains observed at 3 bar, while CO₂/CH₄ selectivity remained comparatively stable across the pressure range studied. These improvements are consistent with preferential CO₂-COF interactions and additional transport pathways associated with well-dispersed RIO-18 particles, with COF loading strongly affecting permeation. Overall, the results identify CO₂/N₂ separation, relevant to postcombustion CO₂ capture scenarios, as the most promising application for these proof-of-concept MMMs, while mixed-gas permeation, sorption/diffusion analysis, and long-term stability remain to be addressed in future work.