Graphene oxide membranes with an ultra-large interlayer distance through vertically grown covalent organic framework nanosheets

Graphene oxide (GO), an emergent 2D nanomaterial, holds great promise in fabricating membranes with high permeability and precise sieving ability endowed by the tunable interlayer distance. Currently, the available interlayer distance is usually less than 2 nm. In this study, a GO-based membrane with an interlayer distance greater than 40 nm is synthesised: a kind of 2D/2D nanoheterojunction of vertically grown covalent organic framework (COF) nanosheets on GO nanosheets (v-COF@GO) is constructed and then intercalated into adjacent GO nanosheets via a vacuum-assisted self-assembly process. By tuning the size of COF nanosheets, the interlayer distance increases from 0.81 nm of the GO membrane to 42.2 nm of the GO/v-COF@GO membrane, and accordingly, the permeate flux of the GO/v-COF@GO membrane exhibits a 157-fold increase. Meanwhile, the resulting membranes acquire superior morphological stability as indicated by the fact that the permeate flux is linearly proportional to the transmembrane pressure in the range of 0-0.5 bar and the appearance of the membrane remains almost unchanged when immersed in water for two months. This study may offer a facile, generic approach to creating an ultra-large interlayer distance for GO-based membranes and many other kinds of membranes from the assembly of two-dimensional nanomaterials.