Enhanced desalination and water transport performance of polyelectrolyte-modified ‘holey’ graphene oxide film

Abstract

Graphene-based membranes have great potential for seawater desalination and water treatment, although it is still a great challenge to find an effective solution for the dilemma between water flux through the membrane and removal rate of salt ions. In this study, a novel strategy of coating polyelectrolytes on holey graphene oxide was designed in order to modify the surface charge on a graphene oxide membrane, aiming to simultaneously improve water flux and desalination performance. The resultant highly-charged graphene oxide membrane presents excellent opportunity to connect sheets together by the formation of chemical bonds, subsequently effectively enhancing the stability, surface potential and hydrophilicity of the membrane in water, improving the water flux and desalination performance. The nano-pores of holey graphene oxide, formed by H2O2 etching, can improve the structure of two-dimensional nano-channels between slices and shorten the transport distance of water molecules, thus leading to a higher water flux. Moreover, coating the holey graphene oxide membrane with charged polyelectrolytes enhances excellent ion rejection by the combination of interlayer size screening and electrostatic repulsion. The cationic polyelectrolyte-coated composite membrane can achieve a water flux of 268.49 L m−2·h−1·MPa−1 and the desalination rate of 87.86% for 0.5 g L−1 NaCl, achieving an increase of 3.44 times and 37.65%, respectively, as compared with untreated graphene oxide film. The facile and scalable surface modification of this graphene oxide-based membrane produces a promising application prospect in desalination of wastewater with a high salinity.