Indoor CO₂ removal : decentralized carbon capture by air conditioning

Growing evidence indicates that an elevated CO₂ concentration as low as 1000 ppm could lead to direct human health risks, while the CO₂ concentration in a lot of indoor environments may exceed that figure by several times. Employing the latest developed moisture swing sorbent, we here built a CO₂ purification module to be incorporated with existing air conditioning units to keep the indoor CO₂ concentration at healthy levels. The sorbent binds CO₂ spontaneously from ambient air when dry and then releases CO₂ in the presence of moisture, thanks to the moisture-driven reversible hydrolysis reaction of carbonate ions at a nano interface. Thus, the indoor dry air circulation and the outdoor air flow (for cooling the condenser) of the air-conditioning system provide a perfect carbon capture platform for the moisture swing sorbent to work. Tests in an acrylic box (mimicking an indoor environment) showed that the CO₂ purification module can keep the indoor CO₂ level to be close to or even lower than outdoor levels with an initial CO₂ concentration of 1000 or 2000 ppm. An enlarged test was further conducted in an air-conditioned office to demonstrate the effectiveness of the purification module. Finally, we discussed the potential of this kind of decentralized carbon capture facility enabled by retrofitted air conditioners to contribute to negative emissions and mitigation of the global warming and climate change crisis. © 2023 Elsevier Ltd