Interfacial Synthesis of Two-Dimensional Network Membranes for Osmotic Energy Conversion.

Two-dimensional (2D) network-structured materials, encompassing 2D polymers and covalent organic frameworks, have captivated researchers with their highly ordered, porous architectures that promote efficient mass transport and versatile functionalities across diverse applications. However, fabricating crystalline 2D network membranes with precise functionalization and ultrathin profiles remains a persistent challenge, often limited by defect formation or scalability issues. Herein, we introduce a novel interfacial strategy employing photo-triggered [2 + 2] cycloaddition at the air/water interface to synthesize ultrathin (∼1.5 nm), crystalline 2D network membranes from styrylpyridine-armed monomers. This approach capitalizes on the reaction's topochemical specificity and irreversibility, enabling stable cyclobutane linkages under mild conditions and enriching structural diversity beyond reversible chemistries. Comprehensive characterization affirmed the membranes' ordered hexagonal lattice with ABC stacking and uniform porosity. As a proof-of-concept application in osmotic energy conversion, these membranes yielded a power density of 18.9 W m-2 under a 500-fold concentration gradient, highlighting their ion-selective nanofluidic capabilities. The method's novelty resides in its ability to unlock cyclobutane-based architectures with ring strain for novel reactivity, while offering a scalable platform for enhancements in pore size and charge density. This versatile synthesis not only addresses key fabrication hurdles but also underscores the membranes' potential in energy harvesting, ion transport, and related technologies.