Crosslinked graphene oxide membranes (CGOM) and their asymmetric permeation behaviors

The crosslinked graphene oxide (GO) membranes (CGOM) with reversible pressure-sensitive gating were prepared by a water-soluble polymer (polyvinyl alcohol, PVA) intercalated layered nano-barrier (GO) through layer-by-layer self-assembly technology. The PVA chain cleverly embedded between the GO nanosheets provides an adjustable water channel (membrane pore) in CGOM. The channel controllability of CGOM stems from the conformational change of the flexible PVA chain and the relative layer spacing of the GO nanosheets, which originates from the lifting-up (accompanied by a stretching of PVA chains) and pressing-back (accompanied by a compressing of PVA chains) of GO nanosheets with the change of the fluid direction, and thus the permeability and selectivity could be adjusted by simply adjusting the fluid direction and pressure. When the fluid direction changed from normal filtration mode to reverse filtration mode, the water flux of the same one CGOM was increased by 27 times, and the rejection rate of PEG-20000 was decreased from 73.4% to 2.4%. Thus, the pressure-sensitive CGOM obviously showed asymmetric permeation behavior. The results provide an insight for fabricating smart gating membranes with asymmetric permeation behavior. This membrane has great potential applications in directional fluid transport and substance separation.