Figure 6. (a) Current density–membrane potential (I–V) curves of the TFN-(Zr)-1, TFN-(Zr/Ti)-1, TFN-(Zr)-2, TFN-(Zr/Ti)-2, and CSO membranes. (b) Magnified I–V curve of the area marked with a red circle in (a). Ion permeations (J) and permselectivities of the CSO, TFC, TFN-(Zr)-1, TFN-(Zr/Ti)-1, TFN-(Zr)-2, and TFN-(Zr/Ti)-2 membranes for the (c) Na+-Mg2+ and (d) Li+-Mg2+ systems at a current density of 10 mA cm−2. Here TFC denotes thin-film composite membrane, TFN-(Zr)-1 and TFN-(Zr)-2 denote thin-film nanocomposite membranes with UiO-66(Zr)-NH2 loadings of 0.01% and 0.03% (w/v) in 50 mL of n-hexane solution, respectively, and TFN-(Zr/Ti)-1 and TFN-(Zr/Ti)-2 denote thin-film nanocomposite membranes with UiO-66(Zr/Ti)-NH2 loadings of 0.01% and 0.03% (w/v) in 50 mL of n-hexane solution, respectively.