Study of Ion Permeation through the Graphene Oxide/Polyether Sulfone Membranes

The ion diffusion process through the graphene oxide (GO)/polyether sulfone(PES) membrane was probed by using electrochemical techniques. It was found that the GO/PES membrane exhibited lower rejection when feeding a solution with higher ion concentration. The calculated diffusion coefficient indicated that the Donnan repulsive interaction from the GO platelets might play a key role in the rejection of GO/PES membrane. Computational calculation confirms that interlayer spacing shrinks less than 5 % when increasing the solution concentration. These results suggest that, compared with interlayer spacing, the Donnan repulsive interaction is more important for ion permeation during concentration-gradient-driven diffusion. To investigate the detail of ion diffusion, electrochemical impedance spectroscopy (EIS) was utilized to probe the GO/PES membrane at the initial immersing process. The EIS results showed an additional inductive loop at low frequency in the Nyquist plot at the initial diffusion stage, which would be more visible for the GO/PES membrane immersing at lower ion concentration. This inductive loop could be attributed to the uneven distribution of ions in GO/PES membrane, which is related to the cation-adsorption capacity of GO.