Harnessing lignin in membrane engineering: from green polymer to high-performance applications

Lignin, a widely used natural polymer, has garnered significant interest as a sustainable and cost-effective resource for the production of separation membranes. This review emphasizes current progress in the application of lignin as a primary polymer and additive in diverse membrane separation technologies, including exchange, pressure-driven, antifouling, gas separation, adsorption, battery separator, and pervaporation membranes. The distinctive physicochemical characteristics of lignin-its aromatic composition, diverse functional groups, and antioxidant properties-make it a promising choice for enhancing membrane performance in terms of mechanical strength, permeability, selectivity, and fouling resistance. Various methodologies for integrating lignin into membrane structures, including blending, surface modification, and in situ polymerization, are comprehensively examined. Moreover, the environmental benefits of using lignin-based membranes, including reduced carbon footprint and biodegradability, are addressed. Despite the promising developments, challenges remain in terms of lignin purification, structural variability, and scalability of membrane production. This review concludes with perspectives on future research directions, emphasizing the need for standardization, improved processing techniques, and a deeper understanding of the structure-property-performance relationships in lignin-based membranes. Lignin is a prospective renewable resource that is consistent with the principles of green chemistry and the circular economy in membrane technology.