Covalent organic framework membranes for wastewater treatment: structural design, interfacial modulation, and environmental applications

The contamination of water resources by persistent organic pollutants, such as polycyclic aromatic hydrocarbons and chlorinated solvents, and inorganic contaminants, including heavy metals like lead and mercury, poses substantial risks to human health and aquatic ecosystems. Conventional wastewater treatment technologies, including biological degradation, coagulation–flocculation, activated carbon adsorption, and advanced oxidation processes, often exhibit limited efficiency in removing low-concentration or recalcitrant pollutants under variable environmental conditions. Membrane-based separation technologies offer a promising alternative due to their energy efficiency, design flexibility, and selective removal capabilities. Among these, Covalent Organic Frameworks (COFs) have emerged as a next-generation membrane material owing to their crystalline porous structures, high surface areas, and tunable chemical functionalities. COF membranes often exhibit rejection efficiencies exceeding 99 % for dyes, pharmaceuticals, and heavy metals while maintaining high water fluxes. Moreover, the integration of photocatalytic moieties, ionic functionalities, or nanomaterial composites further enhances their selectivity, permeability, and anti-fouling performance. This review provides a comprehensive overview of the current progress in COF-based membranes for wastewater treatment, focusing on structure–property relationships, fabrication strategies, and factors affecting separation performance. Challenges and future directions for the development of scalable and durable COF membranes for industrial applications are also discussed.