Intermediate-sized molecular sieving of styrene from larger and smaller analogues

• Published in: Nature materials Vol. 18; no. 9; pp. 994 - 998
• Main Authors: Zhou, Dong-Dong, Chen, Pin, Wang, Chao, Wang, Sha-Sha, Du, Yunfei, Yan, Hui, Ye, Zi-Ming, He, Chun-Ting, Huang, Rui-Kang, Mo, Zong-Wen, Huang, Ning-Yu, Zhang, Jie-Peng
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.09.2019; Nature Publishing Group
• Subjects: 119/118; 639/301/299/1013; 639/638/298/921; Adsorption; Apertures; Benzene; Biomaterials; Chemistry and Materials Science; Computer simulation; Condensed Matter Physics; Ethylbenzene; Flexibility; Hydrocarbons; Hydrophobicity; Materials Science; Metal-organic frameworks; Nanotechnology; Optical and Electronic Materials; Organic chemistry; Regeneration; Selectivity; Styrene; Styrenes; Toluene
• ISSN: 1476-1122; 1476-4660; 1476-4660
• DOI: 10.1038/s41563-019-0427-z

Molecular sieving can lead to ultrahigh selectivity and low regeneration energy because it completely excludes all larger molecules via a size restriction mechanism. However, it allows adsorption of all molecules smaller than the pore aperture and so separations of complicated mixtures can be hindered. Here, we report an intermediate-sized molecular sieving (iSMS) effect in a metal–organic framework (MAF-41) designed with restricted flexibility, which also exhibits superhydrophobicity and ultrahigh thermal/chemical stabilities. Single-component isotherms and computational simulations show adsorption of styrene but complete exclusion of the larger analogue ethylbenzene (because it exceeds the maximal aperture size) and smaller toluene/benzene molecules that have insufficient adsorption energy to open the cavity. Mixture adsorption experiments show a high styrene selectivity of 1,250 for an ethylbenzene/styrene mixture and 3,300 for an ethylbenzene/styrene/toluene/benzene mixture (orders of magnitude higher than previous reports). This produces styrene with a purity of 99.9%+ in a single adsorption–desorption cycle. Controlling/restricting flexibility is the key for iSMS and can be a promising strategy for discovering other exceptional properties. Molecular sieving separates larger from smaller molecules, but all molecules smaller than the pore adsorb, hindering selectivity. Here, a MOF is reported with both molecular sieving and gate-opening, separating intermediate-sized molecules from larger and smaller analogues.