Harnessing Collective Magnetic Forces for Enhanced Modulation of Oxygen Diffusion in CO₂/O₂ Separation toward Direct Air Capture

Membrane-based direct air capture (m-DAC) has recently been introduced as a simple, scalable, and environmentally friendly method to capture CO 2 from the atmosphere. The captured CO 2 is considered to be a carbon source for chemical reduction to other value-added chemicals. However, the chemical reduction of CO 2 is disrupted by any O 2 in the captured gas. Therefore, membranes with high CO 2 /O 2 selectivity are essential for the m-DAC process. In this work, we design magnetic mixed matrix membranes (MMMs) with magnetic nanoparticle (MNP) fillers in polymer matrices, which exhibit room-temperature trapping of gaseous O 2 within the membrane to achieve high CO 2 /O 2 selectivities. We found that the CO 2 /O 2 selectivity increased with both the MNP content and the externally applied magnetic field strength, signifying the magnetic interaction of paramagnetic O 2 with MNP, while the permeation of CO 2 remained unaffected. The experimental results were supported by our mathematical model. Overall, the magnetic PolyActive-MMMs containing 40 wt % MNPs achieved the highest CO 2 /O 2 selectivity of 35 under a magnetic field of 800 mT, corresponding to a selectivity enhancement of 60% over pure PolyActive membranes. Our findings demonstrate the potential of using magnetic fields to control gas transport for applications that require the separation of O 2 from other gases.