Unveiling Advances in Membrane Materials for CO ₂ Separation and Direct Air Capture (DAC): From Membrane Design to Applications

The increase in carbon dioxide (CO 2 ) concentration in the atmosphere has resulted in adverse and irreversible effects in terms of climate change and global warming. To limit the temperature rise to less than 2 °C by the end of this century, it is urgent to reduce the CO 2 concentration in the atmosphere. Direct air capture (DAC) is considered a carbon-negative emission technology which could efficiently remove CO 2 from air. Membrane gas separation is a promising technology for CO 2 capture, owing to its higher energy efficiency, greater scale-up ability, and smaller carbon footprints compared with conventional sorption processes. The application of membranes in the DAC process (m-DAC) is still in its infancy, owing to the low CO 2 concentration (400 ppm) in air. However, simulations and laboratory studies have demonstrated the feasibility of m-DAC. With the development of high-performance membrane materials and the design of multistage membrane processes, the implementation of m-DAC will be a promising strategy for the efficient reduction of CO 2 concentration in air. This review presents current studies on the m-DAC process and recently developed membranes for CO 2 /N 2 separation which could be potentially used in that process, as well as highlighting research gaps that currently represent obstacles to the wider use of membranes for m-DAC. In conclusion, challenges and future prospects are presented, along with a roadmap for the future development of m-DAC, to provide a deeper insight into m-DAC processes.