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Three novel thin-film composite (TFC) nanofiltration membranes are prepared using an ultrafiltration membrane (UFM) of organic polymer resin polyacrylonitrile followed by a mineralization process. The UFM was hydrolyzed (H-UFM) and then transferred in dopamine (DA) and tris buffer (TRIS) solutions. DA–TRIS coating is further favorable for the growth of nanoparticles (NPs), titania (TiO2), and zirconia (ZrO2) on membrane piece surface. A scanning electron microscope (SEM) was combined with an energy-dispersive spectrometer (EDS) in order to provide important insights into the arrangement and potential functions of NPs, due to their unambiguous chemical signal, for possible characterization and modification of materials at the atomic scale. Depending on whether the top layer is made of TiO2, ZrO2, or both, the membranes are called, respectively, TFC-NFTitan, TFC-NFZircon, and TFC-NFTitanZircon. The three membranes under the optimized preparation conditions (30 °C, 12 h of hydrolysis time, and operating pressure of 0.6 MPa) exhibited high rejection and permeation performance. TFC-NFTitanZircon showed the highest rejection (89–95%) for divalent cations with the salt rejection sequence of , while the permeate flux is not less than . All three membranes demonstrated long-term durability under 120-h testing. HIGHLIGHTS Thin-film composite nanofiltration membrane (NFM) for salt rejection.; Novel in situ NFM fabrication using the insights provided by a scanning electron microscope combined with an energy-dispersive spectrometer on the arrangement and potential functions of nanoparticles.; Modification of an ultrafiltration membrane to the NFM for salt removal.; Organic–inorganic NF preparation using a mineralization process.;