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 CO2 from the atmosphere. The captured CO2 is considered to be a carbon source for chemical reduction to other value-added chemicals. However, the chemical reduction of CO2 is disrupted by any O2 in the captured gas. Therefore, membranes with high CO2/O2 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 O2 within the membrane to achieve high CO2/O2 selectivities. We found that the CO2/O2 selectivity increased with both the MNP content and the externally applied magnetic field strength, signifying the magnetic interaction of paramagnetic O2 with MNP, while the permeation of CO2 remained unaffected. The experimental results were supported by our mathematical model. Overall, the magnetic PolyActive-MMMs containing 40 wt % MNPs achieved the highest CO2/O2 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 O2 from other gases.