Amino-functionalized POSS nanocage intercalated graphene oxide membranes for efficient biogas upgrading

Graphene oxide (GO) membranes with two-dimensional (2D) interlaminar channels display fascinating properties in gas separation where the separation efficiency is governed by the size and interlayer interactions of 2D channels. Incorporating intercalators into GO interlayers is recognized as an effective strategy to create appropriate microenvironments for biogas upgrading (remove CO 2 from raw biogas, specifically CO 2 /CH 4 separation). Herein, we proposed a strategy of using a kind of nanocage, amino-functionalized polyhedral oligomeric silsesquioxane (POSS–NH 2 ), as versatile intercalator to regulate the channel structure and afford favorable microenvironments for CO 2 /CH 4 separation in GO membranes. The channel size of GO membranes was reduced from 9.1 Å to 4.7 Å by POSS-NH 2 crosslinking, which could elevate the diffusion selectivity of CO 2 /CH 4 . The amino groups on POSS-NH 2 are able to react with CO 2 reversibly, facilitating the transport of CO 2 . Through synergistically intensifying diffusion selective and facilitated transport mechanisms, the optimized membrane CO 2 /CH 4 selectivity reached 74.5, which is superior to most reported values of 2D membranes. Moreover, we selected another POSS intercalator without amino groups, in order to distinguish the contribution of physical and chemical mechanisms to selectivity. Our study may provide a novel avenue in designing versatile intercalators to construct high-performance 2D membranes.