Optimized Sieving Effect for Ethanol/Water Separation by Ultramicroporous MOFs

Abstract High‐purity ethanol is a promising renewable energy resource, however separating ethanol from trace amount of water is extremely challenging. Herein, two ultramicroporous MOFs (UTSA‐280 and Co‐squarate) were used as adsorbents. A prominent water adsorption and a negligible ethanol adsorption identify perfect sieving effect on both MOFs. Co‐squarate exhibits a surprising water adsorption capacity at low pressure that surpassing the reported MOFs. Single crystal X‐ray diffraction and theoretical calculations reveal that such prominent performance of Co‐squarate derives from the optimized sieving effect through pore structure adjustment. Co‐squarate with larger rhombohedral channel is suitable for zigzag water location, resulting in reinforced guest‐guest and guest‐framework interactions. Ultrapure ethanol (99.9 %) can be obtained directly by ethanol/water mixed vapor breaking through the columns packed with Co‐squarate, contributing to a potential for fuel‐grade ethanol purification.