4. Conclusion
Our results confirmed the formation of very uniform UiO-66(Zr/Ti)-NH2 thin films on the surface of a HPAN substrate. The TFN membranes contained multidimensional subnanometer-sized ion transport channels, which were highly suitable for the simultaneous increase in cation permeation and ion-charge selectivity. Consequently, the TFN-(Zr/Ti)-2 membrane presented high monovalent ion fluxes (\(J_{\text{Na}^{+}}\ \)= 7.15 × 10−8 mol cm−2 s−1and\(\ J_{\text{Li}^{+}}\) = 5.43 × 10−8 mol cm−2 s−1). Furthermore, the mono- over divalent cation separation performance of the TFN-(Zr/Ti)-2 membrane (\(P_{\text{Na}^{+}{/\text{Mg}}^{2+}}\) = 13.44 and\(P_{\text{Li}^{+}{/\text{Mg}}^{2+}}\) = 11.38) surpassed that of the TFC membrane. The high separation performance and outstanding stability during ED testing of the TFN membranes confirmed the benefits of the addition of UiO-66(Zr/Ti)-NH2 nanoparticles to these membranes. In addition, the prepared TFN membranes presented high LCDs, which is a highly desirable characteristic for energy-efficient ion separation without unnecessary water splitting. Thus, the proposed strategy for the fabrication of UiO-66(Zr/Ti)-NH2-containing membranes and excellent permselective performance of the fabricated membranes could expand the large-scale use of MOFs for membrane applications.