Monodisperse covalent organic nanosheets by in-situ oxidation method for efficient ion/molecule separation

Abstract

Two-dimensional (2D) covalent organic nanosheets (CONs) are layered crystalline porous polymers comprising periodically extended graphene-like structures, and have great application potential in membrane separation field due to the advantages of abundant optional monomers, tunable pore size and structure, facilely-tailored functionality and pre-designed properties. However, unlike graphene oxide (GO) membranes, it is hard to directly prepare 2D CON membranes by vacuum filtration because of the difficulties in preparation of ultra-thin, large-sized and well-dispersed 2D CONs. Herein, an improved buffering interlayer interface method was proposed to realize a facile one-step synthesis of GO-like CON oxides by using H2O2 as an in-situ oxidant in the buffer layer. The stereoscopic fulcrum-oxygen sites introduced into the structure of CONs lead to weaken interactions between CON layers and increased hydrophilicity, which contributes to subsequent preparation of monodisperse nanosheets. The membranes fabricated with the as-prepared monodisperse nanosheets can realize high-efficiency transport of metal ions with a precise charge-discriminated group separation ability and efficient ion rejection. The strategy of in-situ oxidation to prepare monodisperse CONs proposed in this study provides a valuable approach for the preparation of novel functionalized CONs and the achievement of fast membrane separation performance.