Covalent organic frameworks combined with graphene oxide to fabricate membranes for H2/CO2 separation

Covalent organic frameworks (COFs) are getting more attention by virtue of their intriguing architectures and properties. However, the obstacle for fabricating sequential COF-based membranes for gas separation has become a challenge. In this research, a series of TpPa COFs are successfully synthesized by a facile approach of mechanical grinding. To alleviate the dilemma of membrane formation, we introduce graphene oxide (GO) that owns two-dimensional flexibility to sufficiently assist the COFs to form lamellar membranes. By directly mixing the solutions of GO and COFs, robust and continue COFs/GO composite membranes are prepared without defects via the vacuum filtration. The thickness and the H2/CO2 selectivity of the membranes can be regulated by increasing the amount of GO. The optimal membrane obtained with a GO/COFs ratio of 33.33% (TpPa-1-30/GO-10) exhibits the H2/CO2 selectivity of 25.57 with H2 permeance of 1.067 × 10−6 mol·m−2·s−1·Pa−1. This work provides a simple, universal and applicable approach to prepare COF-based composite membranes for separation.