Internally functionalized MnO₂ nanotubes in modification of thin-film nanocomposite membranes for water and wastewater treatment

Membrane technologies such as nanofiltration membrane are utilized for treatment of water resources. In this study, MnO₂ nanotubes were prepared through hydrothermal process, and then, the inner surface of nanotubes was functionalized through a novel procedure with different polymers (polydopamine and polystyrene) to alter their inner diameter. Then, the neat and modified nanotubes were used in the synthesis of thin-film nanocomposite (TFN) membranes and their performances in terms of permeation and rejection of monovalent (Na⁺) and divalent (Cu²⁺) ions were studied. In case of polystyrene inner coated MnO₂, the flux increased by 48% compared to TFC membrane that may be related to better dispersion of the nanotubes in PA layer and promoting the permeation through the nanotubes. The nanotubes worked as the channels for water movement through the structure of the membrane and the inner coating makes more restriction for the ions and improves the rejection. Furthermore, the addition of the nanoparticles can reduce the concentration of MPD in the reaction zone and thinner polyamide layer can be expected. In case of polydopamine inner surface-coated MnO₂, the flux improved 84% compared to TFN membrane containing unmodified MnO₂ that is linked to the affinity between polydopamine and water molecules which facilitates the penetration of water through the nanotubes.