Ultrahigh permeability of graphene-based membranes by adjusting D-spacing with poly (ethylene imine) for the separation of dye wastewater

Graphene oxide (GO) as a unique 2D material attracts much attention. It can be employed to prepare graphene-based membranes by vacuum filtration on microporous substrates. However, the permeability of graphene-based membranes is mainly limited by its interlamellar spacing. In this work, the interlamellar spacing of graphene-based membranes is expanded by grafting poly (ethylene imine) (PEI) on GO sheets. The novel graphene-based membranes present ultrahigh permeability without sacrificing the rejection for the filtration of dye wastewater. The original GO membrane (GOM) only has a pure water permeation flux (PWP) value of 27.0 L·m−2·h−1 bar−1. However, the novel graphene-based membranes prepared with the modified GO by PEI-600 and PEI-10000 (recorded as PGOM-600 and PGOM-10000) markedly increase to 208.1 and 450.2 L·m−2·h−1·bar−1 respectively. In the separation of dye wastewater, GOM, PGOM-600 and PGOM-10000 exhibit much higher rejections for direct red and methyl blue. However, the modified graphene-based membranes (PGOM-600 and PGOM-10000) present more than 7–20 times higher permeation flux than that of original GOM without sacrificing dye rejection. Thus, this work provides graphene-based membranes with ultrahigh permeation flux for dye removal from wastewater.