Trace CO(2) capture by an ultramicroporous physisorbent with low water affinity

CO(2) accumulation in confined spaces represents an increasing environmental and health problem. Trace CO(2) capture remains an unmet challenge because human health risks can occur at 1000 parts per million (ppm), a level that challenges current generations of chemisorbents (high energy footprint and slow kinetics) and physisorbents (poor selectivity for CO(2), especially versus water vapor, and/or poor hydrolytic stability). Here, dynamic breakthrough gas experiments conducted upon the ultramicroporous material SIFSIX-18-Ni-β reveal trace (1000 to 10,000 ppm) CO(2) removal from humid air. We attribute the performance of SIFSIX-18-Ni-β to two factors that are usually mutually exclusive: a new type of strong CO(2) binding site and hydrophobicity similar to ZIF-8. SIFSIX-18-Ni-β also offers fast sorption kinetics to enable selective capture of CO(2) over both N(2) (S(CN)) and H(2)O (S(CW)), making it prototypal for a previously unknown class of physisorbents that exhibit effective trace CO(2) capture under both dry and humid conditions.