Rational design of ultrathin, functionalized UiO-66 mixed-matrix membranes for CO2 separation: balancing CO2 uptake and interfacial compatibility

Abstract

Developing high-performance membranes for post-combustion CO₂ separation is essential in addressing the ongoing climate crisis. In this study, we fabricated a series of composite mixed-matrix membranes (MMMs) featuring ultrathin 100 nm-thick films, incorporating UiO-66 nanocrystals with three distinct functional groups (–H, –Br, –NO₂) as fillers, a poly(glycidyl methacrylate-co-poly(oxyethylene methacrylate)) (PGO) polymer matrix, and poly[1-(trimethylsilyl-1-propyne)] (PTMSP)-coated polysulfone supports. The incorporation of functionalized UiO-66 fillers significantly enhanced the CO₂ permeance and CO₂/N₂ and CO₂/CH₄ selectivities of the ultrathin-film-coated MMMs, owing to improved CO₂ solubility and diffusivity. Notably, PGO/UiO-66-NO₂ MMMs exhibited superior CO₂ separation performance compared to PGO/UiO-66 and PGO/UiO-66-Br MMMs. This enhancement is attributed to the exceptionally high CO₂ adsorption capacity of UiO-66-NO₂, along with its excellent interfacial compatibility with the PGO polymer matrix. The optimal CO₂ separation performance was achieved with the UiO-66-NO₂ MMM at 20% particle loading, yielding a CO₂ permeance of 1816 GPU and CO₂/N₂ and CO₂/CH₄ selectivities of 37 and 14, respectively. These findings highlight the excellent CO₂/N₂ and CO₂/CH₄ separation efficiency of UiO-66-based MMMs, underscoring their potential as promising candidates for CO₂ capture in post-combustion processes from fossil fuels and biogas. Moreover, this study emphasizes the critical role of optimizing polymer–metal–organic framework (MOF) combinations by considering both the CO₂ uptake capacity of the filler and the interfacial compatibility between the polymer and MOF.