Building ordered graphene membranes by intermediate layer assisted stacking method for promoted desalination

Laminar separation membranes stacked by graphene and its derivatives hold the merit of controlled mass transfer behaviors. However, precise ion separation is challenged by the disordered assembly of nanosheets on macroporous substrates with complicated surface properties. Herein, we prepare ultrathin ordered graphene membranes by an intermediate layer assisted stacking method. Nanoporous covalent organic framework (COF) nanosheets are first vacuum-filtered on macroporous substrates, followed by deposition and thermal reduction of graphene oxide nanosheets to deliver ultrathin reduced graphene oxide (rGO) layers. The COF-decorated substrates provide a hydrophilic surface with reduced pores and roughness, facilitating the formation of ultrathin rGO layers with ordered stacking patterns and reduced microporous defects. Consequently, the obtained rGO/COF composite membranes can reject ~90 % of Na2SO4, ~50 % of NaCl, and >98 % of various organic dyes, which are higher than pure rGO membranes. Meanwhile, the rGO/COF composite membranes can maintain good stability in solutions with different pH values and salt concentrations, and can be long-term operated for at least 10 days. This work is expected to deepen the understanding of the structure of laminar membranes and provides new perspectives to design ordered laminar membranes.