The ATR-FTIR spectra (Figure 5a) confirmed the successful embedding of the MOF nanoparticles into the TFN membranes. The presence of the characteristic bands of C=O (amide I) and N–H (amide II) at 1645 and 1550 cm⁻¹, respectively, in the ATR-FTIR spectra of the membranes confirmed the successful formation of a polyamide layer on the HPAN substrate. The increase in sharpness of the 1435 and 1260 cm^-1 peaks confirmed the successful UiO-66(Zr)-NH₂or UiO-66(Zr/Ti)-NH₂ loading, respectively, during the IP reaction (Figure 5b). Furthermore, the additional peaks at 1255 and ~800 cm⁻¹, which were ascribed to the C–O bonds³⁹ and Zr–O clusters⁴⁰, respectively, further confirmed the formation of bonds between the UiO-66-NH₂ nanoparticles and polyamide layer on the surface of the HPAN substrate during the IP reaction. The fabricated TFC, TFN-(Zr)-2, and TFN-(Zr/Ti)-2 membranes were further analyzed using XPS, and the results confirmed the presence of UiO-66(Zr)-NH₂ or UiO-66(Zr/Ti)-NH₂nanoparticles in the fabricated TFN membranes (Supporting Information, Figure S11). In addition, the zeta potentials of the TFN-(Zr)-1, TFN-(Zr)-2, TFN-(Zr/Ti)-1, and TFN-(Zr/Ti)-2 membranes at various pH values revealed that the surfaces of the TFN membranes were negatively charged at neutral pH, which is a requirement for the electrochemical cation permselective separation of both the Na⁺/Mg²⁺ and Li⁺/Mg²⁺ systems (Supporting Information, Figure S12).