Nanoconfined electrostatic interaction for efficient anion sieving in graphene oxide membranes.

Controllable ion transport and precise ion sieving are crucial for sustainable water treatment and resource recovery. 2D materials, including graphene oxide (GO) with tunable nanochannels, are emerging as ideal material platforms to develop ion sieving membranes. However, accurate ion sieving remains challenging due to the swollen and enlarged interlayer spacing of GO membranes in aqueous solution, resulting in the non-selective of small ions. Here, we reformed the GO nanosheets by physical reduction method and modified them with negatively charged molecule chains. The nanochannel sizes and electronegativity of the stacked 2D membranes were precisely controlled simultaneously. As a result, 2D nanochannel membrane with fast permeability, high efficiency and accurate Cl-/SO42- separation was constructed. The characterization and performance analysis further proved that the interlayer spacing and electrification of 2D nanochannels are strongly related to ion sieving. By precisely adjusting the synergy between the two, Cl-/SO42- selectivity up to 91.83 with Cl- permeation rate of 1.03 mol m-2h-1 was achieved, which is superior to state-of-the-art ion sieving membranes. Our study provides new insights into understanding ion separation mechanisms within nanochannels and enables the development for the precise construction of nanochannels to manipulate the selective transport of ions.