For that, pure DI water was fed through the membranes, and the permeate of this experiment was collected and analysed by ICP-OES to determine the mass of cations that might have been washed out. The experimental details are discussed in SI section 3. As shown in Figure for all membranes, after 3-5 hours, there were no detectable cation in the permeate. The total mass of washed-out cations is below 5.5 µg (Table ), which is negligible compared with the measured mass of intercalated cations (Table ). Hence, we conclude that the cation intercalation is stable in our water flux experiments. Since the above reason could be excluded to be responsible for the observed trend in water flux, the following examination further focuses on the interaction between intercalated cations and water molecules. As shown above, the flux declines, and slip length increases with the increase of the hydrated diameter of the intercalated cation. At the same time, the interlayer space is increased with the increase in hydrated diameter as well. A higher increase in the interlayer space upon wetting the membrane is associated with increased intercalated layers of water. We speculate that the cations with higher hydration diameter have a stronger attraction towards water inside the capillaries. To investigate that, we performed ab initio molecular dynamic (AIMD) simulation with several intercalated cations and investigated the water density around the specific cation. Error! Reference source not found.A shows a simulation cell used to investigate the behaviour of nanoconfined water in the presence of cations. The simulation cell resembles a bilayer of graphene with two cations attached to the basal plane. The bilayer configuration is achieved by employing periodic boundary conditions. The space between the layers is filled with water molecules. Graphene was chosen as a model as various studies confirm that main group metal cations intercalate mainly via cation-π interaction . With that in GOMs, the main group metal cations would attach to the graphitic areas where π electrons exist. The cations may also attach to functional groups (see the simulation cell in Figure ). Hence, simulations were conducted with functionalized graphene sheets as the substrate for cation intercalation (see SI section 4). For both cases, graphitic and functionalized nanochannels, we examined the rearrangement of water molecules by projecting their distribution on the graphitic/functionalize domain plane. Starting with randomly distributed water molecules around the ions (Error! Reference source not found.B and Figure ), we let the molecules relax over 4 ps. After that period, the water molecules rearranged more densely around the cations (Error! Reference source not found.C-E and Figure ). We tried relaxing Mg atoms on graphene; however, the Mg atoms did not bind with the graphene sheet and stabilized far (> 4 Angstrom) from the graphene plane. As such, we did not include Mg atoms in our study.