Cationic agents regulated graphene oxide membranes for precise molecular sieving

Graphene Oxide (GO) membrane fabricated by stacking sheets has an interlayer distance of ∼1 nm, which provides a good platform for hierarchical and precise separation of small organics upon proper modification, but it is still challenging. In this work, cationic agents were used to regulate the interlayer distances of GO membranes by electrostatic interaction for precise separation of small organics with 100 Da differences. The modified GO membranes were prepared by vacuum filtration of suspensions containing GO nanosheets and cationic agents, including K + (39 Da), dimethyl diallyl ammonium chloride (DDA, 162 Da), or methylene blue (MB, 320 Da). The insertion of K + , DDA, and MB increased the interlayer distances of GO membranes from 9.0 to 9.7, 10.2, and 10.6 Å, respectively, and a water permeability of 15.6, 17.8, and 26.4 L m −2  h −1 ·bar −1 for the relevant membranes. These three membranes could sufficiently reject molecules with larger size than their interlayer distances with rejection ratio >91%, while those with smaller size could easily go through. This property allows them to effectively remove antibiotics from maricultural seawater. This study provides a simple way for designing GO-based nanofiltration membrane with higher stability and precise rejection ability in molecular level.