Advancing Ionic Liquid-Based Membrane Fabrication: Spray-Coating as a Pathway for Mixed-Matrix Membranes

This work investigates two fabrication strategies, solvent casting and spray-coating, for producing advanced IL-based mixed-matrix membranes (MMMs) incorporating functionalized silica IL (SiIL) microparticles, [Si][C₃C₁im]Cl. Membranes with 20 wt% of poly(diallyldimethylammonium) bis(trifluoromethylsulfonyl)imide, poly[pyr₁₁][NTf₂], PIL and 80 wt% of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, ([C₂mim][NTf₂]), IL with varying filler loadings were evaluated for CO₂ separation performance, including gas permeance, permeability, diffusivity, solubility, and CO₂/N₂ selectivity. Spray-coating enabled the formation of ultrathin, selective layers, resulting in CO₂ permeances up to 27 GPU, approximately twice than without silica and up to ten times higher than solvent-cast samples, while maintaining selectivity values, between 29 and 40. In contrast, solvent-cast membranes exhibited lower CO₂ permeances (2-3 GPU) but benefited from uniform filler dispersion, achieving a 63% increase in CO₂ permeability at optimal SiIL loadings. Mixed-gas experiments (15% CO₂ and 85% N₂) demonstrated that spray-coated membranes retained most of their performance under competitive conditions, with CO₂ permeance losses of only 5%-9%, whereas solvent-cast membranes showed more stable selectivity but lower overall flux. These results highlight that membrane fabrication methodology, rather than filler content alone, critically determines the membrane architecture and thus gas transport behavior. Overall, spray-coating emerges as a highly effective approach to designing scalable, high-performance MMMs for industrial CO₂ separation applications.