Heterocyclic covalent organic framework membranes for water purification.

The escalating global freshwater crisis demands next-generation, high-performance water purification technologies. Heterocyclic covalent organic framework membranes (HC-COFMs) have emerged as a transformative platform. By strategically integrating nitrogen-, oxygen-, and sulfur-containing heteroatoms into crystalline framework architectures, HC-COFMs achieve unparalleled control over pore chemistry, surface functionality, and molecular transport channels. This comprehensive review systematically explores the structure-property-performance relationships governing HC-COFMs in water-energy-environment applications. We critically examine rational molecular design strategies centered on heterocyclic monomers and robust linkages, alongside state-of-the-art fabrication techniques, including interfacial polymerization, in situ growth, covalent organic nanosheet (CON) stacking, and matrix blending. Furthermore, we highlight the multifunctional utility of HC-COFMs across five key application domains: molecular separation, ion sieving, membrane catalysis, solar-driven water purification, and emerging applications including critical metal recovery and remediation of emerging organic microcontaminants. All these functionalities are underpinned by the exceptional anti-fouling properties and chemical stability intrinsic to heterocyclic COF architectures. Finally, we outline current bottlenecks and future research directions, offering a strategic roadmap to guide the rational design of next-generation HC-COFMs for sustainable, cross-disciplinary water-energy-environment applications.