Improving the selectivity of polymer-based membranes for water treatment while maintaining their permeability can be achieved through several strategies:1. Modification of polymer chemistry: Designing and synthesizing new polymers with specific functional groups or chemical structures can enhance the selectivity of the membrane. For example, incorporating hydrophilic groups e.g., -OH, -COOH, -NH2 can improve water affinity and selectivity, while maintaining permeability.2. Blending polymers: Combining two or more polymers with complementary properties can result in a membrane with improved selectivity and permeability. For instance, blending a hydrophilic polymer with a hydrophobic one can increase water selectivity while maintaining the structural integrity and permeability of the membrane.3. Interfacial polymerization: This technique involves the reaction of two monomers at the interface of two immiscible liquids, resulting in a thin, highly selective polymeric film. By carefully controlling the reaction conditions, it is possible to tailor the properties of the resulting membrane to achieve the desired selectivity and permeability.4. Incorporation of inorganic fillers: Adding inorganic fillers, such as nanoparticles or zeolites, to the polymer matrix can enhance the selectivity of the membrane by providing additional transport pathways or adsorption sites for water molecules. This can be achieved without significantly affecting the permeability of the membrane.5. Surface modification: Modifying the surface of the membrane through techniques such as plasma treatment, grafting, or coating can alter its surface properties, such as hydrophilicity or charge, leading to improved selectivity without compromising permeability.6. Post-treatment processes: Techniques such as annealing, solvent extraction, or chemical cross-linking can be used to modify the membrane structure, leading to improved selectivity and permeability. For example, annealing can increase the crystallinity of the polymer, resulting in a more selective membrane, while solvent extraction can remove low molecular weight species, improving permeability.7. Membrane fabrication techniques: Adjusting the fabrication parameters, such as the choice of solvent, polymer concentration, or casting conditions, can influence the membrane morphology and, consequently, its selectivity and permeability.By employing one or more of these strategies, it is possible to improve the selectivity of polymer-based membranes for water treatment while maintaining their permeability. However, it is essential to carefully consider the specific application and requirements when selecting the most appropriate approach.