Emulsion-templated porous alginate shells enable enhanced CO₂ uptake and faster uptake–release in ionic-liquid microcapsules

Ionic liquids (ILs) are attractive CO₂ capture media but their deployment is constrained by high viscosity, slow gas–liquid mass transfer and solvent-handling issues. Here, we show that these limitations can be substantially relaxed by architecting the IL phase inside sodium alginate microcapsules using an all-aqueous Ca 2+ crosslinking and freeze-drying route. A simple dripping process produces SA–IL capsules with compact shells, whereas introducing a controlled emulsification step generates ESA–IL capsules with hierarchically porous shells and percolated transport channels, without resorting to microfluidic hardware or sacrificial templates. Structural and thermal analyses confirm that [BMIM][BF₄] is physically confined in amorphous alginate networks and that emulsification/freeze-drying reshapes the shell into a mechanically robust, multi-scale porous framework.Under high-pressure CO₂, ESA–IL reaches a capacity of 60.99 cm 3 (STP) g −1 at 298 K and 50 bar on a dried-capsule mass basis, exceeding the dense-shell SA–IL and the neat [BMIM][BF₄] tested under the same protocol. For solvent-level comparison, the corresponding IL-normalized capacities (per gram of [BMIM][BF₄]) are reported in parallel. This improvement is consistent with the process-generated porous shell increasing accessibility and thereby promoting more effective utilization of the confined IL.Isosteric heats derived from 298/323 K isotherms fall in the range of 12–18 kJ mol −1 for both microcapsule types, indicating physisorptive interactions; ESA–IL shows modestly higher values at intermediate and high loadings, consistent with strengthened IL/alginate microenvironments rather than a change in adsorption mechanism. ESA–IL also displays pronounced CO₂/N₂ discrimination, with CO₂ uptakes exceeding N₂ by more than an order of magnitude at elevated pressures, and retains over 98% of its initial capacity after 20 pressure-swing cycles at 298 K. These results indicate that a low-cost emulsification–crosslinking–drying route can produce hierarchically structured IL microcapsules with enhanced CO₂ uptake in the encapsulated format, rapid uptake–release kinetics, and favourable CO₂/N₂ separation-related characteristics, while maintaining good regenerability—thereby offering a practical and scalable platform for CO₂ capture from N₂-rich flue gases.