Three in one: engineering MOF channels via coordinated water arrays for regulated separation of alkanes and alkenes

Purifying alkenes (mainly ethylene and propylene) by removing their corresponding alkanes is crucial yet challenging in the chemical industry. Selective physisorption shows promise for effective separation but demands precise pore dimensions and/or pore chemistry of adsorbents. We report an yttrium-based metal-organic framework, Y2(TCHB)(OH)2·2H2O (HIAM-317, TCHB = 3,3′,5,5′-tetrakis(4-carboxyphenyl)-2,2′,4,4′,6,6′-hexamethyl-1,1′-biphenyl), that can separate ethylene/ethane and propylene/propane via mechanisms regulated by coordinated water arrays. In the presence of coordinated water arrays, HIAM-317 sieves alkanes from alkenes. When fully activated by removing coordinated water arrays, it selectively adsorbs ethane over ethylene and propylene over propane. This separation ability has been experimentally verified, and the underlying mechanism was uncovered through theoretical calculations and modeling.