The separation of salts from seawater using polymeric membranes: Approaches with inorganic additives

The demand for fresh water is rapidly increasing due to factors such as population growth, agriculture, industrialization, urbanization, rising living standards, and climate change. This situation exerts significant pressure on existing water resources, increasing the risk of water scarcity. Desalination technologies offer an effective solution to this problem by converting seawater and brackish groundwater into drinking water. Among desalination methods, thin-film composite reverse osmosis (RO) technology stands out. This technology allows only water molecules to pass through and can treat seawater and brackish water with high efficiency under high pressure. Reverse osmosis membranes offer advantages such as high salt rejection capacity, durability, low operating cost, and energy efficiency. Polymeric membranes used in water filtration are notable for their chemical resistance, flexibility, and ability to operate over a wide pH range. In this study, a commercial NF-270 polysulfone membrane was used as the support layer. A polyamide (PA) layer was synthesized on the NF-270 using the interfacial polymerization method with m-phenylenediamine (MPD) and trimesoyl chloride (TMC) monomers. ZSM-5 was prepared and incorporated into the polymeric membranes at different loadings (0.68%, 0.90%, 1.13%, 1.56%) to produce composite membranes, which were then characterized. Structural analyses were performed using X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR); thermal behavior was examined with thermogravimetric analysis (TGA), and particle sizes were determined by dynamic light scattering (DLS). The surface hydrophilicity of the ZSM-5 membranes was evaluated through contact angle measurements. The water flux and salt rejection performance of the membranes were tested using an RO system. Pure water permeability tests were carried out at 10 and 20 bar, followed by tests with 2000 ppm NaCl and 2000 ppm Na₂SO₄ solutions under the same conditions. The composite membrane with the highest salt rejection capacity, high thermal stability, and pressure resistance was identified. As a result, it was concluded that ZSM-5-incorporated membranes can be effectively used in RO systems.