Hierarchical pore architectures from 2D covalent organic nanosheets for efficient water/alcohol separation

By mimicking the respiratory system in organisms, hybrid membranes with hierarchical pore structures were constructed by covalent organic nanosheets (CONs) and poly(ether sulfone) (PES). Two kinds of amide modified CONs, TpPa-1 and TpBD, with different pore sizes were facilely synthesized by the Schiff base reactions of 1,3,5-triformylphloroglucinol (Tp) with p-phenylenediamine (Pa-1) and benzidine (BD), and separately incorporated into the PES. The hierarchical pore structures within the hybrid membranes including micropores (0.278-0.289 nm), mesopores (2-50 nm) and macropores (1-10 mu m) were generated by the addition of CONs. The microporous structures in top dense layer with high separation accuracy arose from CONs and PES chains. The mesoporous structures and the macroporous structures in porous sublayer with ultralow resistance arose from sponge-like pores and finger-like pores of PES, respectively. A smooth transition of micro-, meso-and macroporous structures rendered the membranes desired level of separation efficiency as well as high stability. Remarkably, the hybrid membrane consisting of TpPa-1 CONs (8 wt%) showed a high water/ethanol separation factor of 1150, while the membrane consisting of TpBD CONs (8 wt%) exhibited a high water/n-butanol separation factor of 2735. The permeation fluxes for both separation systems were higher than 2.5 kgm(-2) h(-1). The links between hierarchical architectures and performance in membranes could facilitate the rational design of novel membrane architectures with advanced properties.