Graphene oxide nanofiltration membrane for efficient dyes separation by hexagonal boron nitride nanosheets intercalation and polyethyleneimine surface modification

In the field of nanofiltration membrane development for water treatment, laminar graphene oxide (GO)-based membranes hold considerable promise. However, improving their permeability and stability has been a research challenge. This study developed a facile and effective method to intercalate hexagonal boron nitride (h-BN) nanosheets between GO laminates and to modify polyethyleneimine (PEI) on the membrane surface to fabricate highly stable novel GO nanofiltration membranes. The composite membranes, which were predominately based on a separation mechanism involving the steric hindrance effect, displayed excellent separation performance for various dyes. Moreover, they exhibited ultrafast water permeability under low-pressure conditions (1 bar), with a pure water flux of 57.84 L m-2 h-1 bar-1, which was 722% of that of the original GO membrane. To explain the high permeability of the composite membrane, we propose a “hydrophilic–hydrophobic” ideal transport path hypothesis: water molecules first aggregate on the hydrophilic surface of PEI and then rapidly flow into the hydrophobic nanochannels constructed by h-BN. In addition, the composite membrane has excellent stability and durability, as evidenced by its ability to maintain the integrity of its membrane structure after one month of shaking in water or even in strong acid and alkali solutions, in addition to its consistent Congo red dye rejection rate (> 96%) in five cycling experiments.