Ultrasmall Functionalized UiO-66 Nanoparticle/Polymer Pebax 1657 Thin-Film Nanocomposite Membranes for Optimal CO₂...

Ultrasmall 4 to 6 nm nanoparticles of the metal-organic framework (MOF) UiO-66 (University of Oslo-66) were successfully prepared and embedded into the polymer Pebax 1657 to fabricate thin-film nanocomposite (TFN) membranes for CO₂/N₂ and CO₂/CH₄ separations. Furthermore, it has been demonstrated that ligand functionalization with amino (-NH₂) and nitro (-NO₂) groups significantly enhances the gas separation performance of the membranes. For CO₂/N₂ separation, 7.5 wt % UiO-66-NH₂ nanoparticles provided a 53% improvement in CO₂ permeance over the pristine membrane (from 181 to 277 GPU). Regarding the CO₂/N₂ selectivity, the membranes prepared with 5 wt % UiO-66-NO₂ nanoparticles provided an increment of 17% over the membrane without the MOF (from 43.5 to 51.0). However, the CO₂ permeance of this membrane dropped to 155 GPU. The addition of 10 wt % ZIF-94 particles with an average particle size of ∼45 nm into the 5 wt % UiO-66-NO₂ membrane allowed to increase the CO₂ permeance to 192 GPU while maintaining the CO₂/N₂ selectivity at ca. 51 due to the synergistic interaction between the MOFs and the polymer matrix provided by the hydrophilic nature of ZIF-94. In the case of CO₂/CH₄ separation, the 7.5 wt % UiO-66-NH₂ membrane exhibited the best performance with an increase of the CO₂ permeance from 201 to 245 GPU.