Concentration differences of intercalated cations may be responsible for the observed water flux trend. The number of moles of intercalated cations in the X-M-GO cannot be precisely controlled. However, in the X-S-GO, it is more probable to do so. Therefore, water filtration experiments were conducted on X-S-GO with controlled intercalated cations (0.2 µmol) using K + , Na + , Ca 2+ , Mg 2+ and Fe 3+ . As shown in Figure , we find a similar trend as in Figure that water flux decreased with increasing hydrated diameter of cations. As mentioned above, the number of intercalated cations may also vary for X-S-GO. However, we could not find a matching trend of mass loading and hydrated diameter in any of the experiments. Figure shows that the water flux decreases with increasing hydration diameter despite arbitrary mass loadings of different cations (Table ). This suggests that the mass loading is not the primary explanation for the observed trend in water flux. The water flux for membranes prepared using both preparation methods decrease with increasing interlayer space. This is surprising as a decreased interlayer space should offer less room for the water molecules to travel. As reported in our previous study and by others, this is true for untreated GO where smaller interlayer space resulted in a decline in water flux .