Scalable Jet-Based Fabrication of PEI-Hydrogel Particles for CO₂ Capture

The capture, regeneration, and conversion of CO₂ from ambient air and flue gas streams are critical aspects of mitigating global warming. Solid sorbents for CO₂ absorption are very promising as they have high mass transfer areas without energy input and reduce emissions and minimize corrosion as compared to liquid sorbents. However, precisely tunable solid CO₂ sorbents are difficult to produce. Here, we demonstrate the high-throughput production of hydrogel-based CO₂-absorbing particles via liquid jetting. By wrapping a liquid jet consisting of an aqueous solution of cross-linkable branched polyethylenimine (PEI) with a layer of suspension containing hydrophobic silica nanoparticles, monodisperse droplets with a silica nanoparticle coating layer was formed in the air. A stable Pickering emulsion containing PEI droplets was obtained after these ejected droplets were collected in a heated oil bath. The droplets turn into mm-sized particles after thermal curing in the bath. The diameter, PEI content, and silica content of the particles were systematically varied, and their CO₂ absorption was measured as a function of time. Steam regeneration of the particles enabled cyclic testing, revealing a CO₂ absorption capacity of 6.5 ± 0.5 mol kg⁻¹ solid PEI in pure CO₂ environments and 0.7 ± 0.3 mol kg⁻¹ solid PEI for direct air capture. Several thousands of particles were produced per second at a rate of around 0.5 kg per hour, with a single nozzle. This process can be further scaled by parallelization. The complete toolbox for the design, fabrication, testing, and regeneration of functional hydrogel particles provides a powerful route toward novel solid sorbents for regenerative CO₂ capture.