2D Open Framework Materials: Chemistry, Materials, and Applications

2D open framework materials (2D OFMs), including metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), have emerged as a versatile class of materials that combine atomic precision, intrinsic porosity, and tunable chemical functionality. By bridging the structural features of inorganic layered materials with the chemical diversity of organic polymers, 2D OFMs provide unique opportunities in molecular separations, semiconductors, and related technologies. Their in-plane periodicity and layered architectures enable precise control over pore environment, stacking mode, and electronic coupling, thereby unlocking structure-property relationships not accessible in conventional porous materials. This review highlights recent advances in the topological design of 2D OFMs, incorporating functional skeletons and programmable pore architectures, as well as emerging characterization techniques capable of resolving structural details or providing high-resolution imaging at the atomic scale. Particular attention is given to the roles of porosity and the framework skeleton in enabling adsorptive and membrane-based separations, as well as to semiconductors with electronic properties that underpin energy storage and conversion applications. By providing a comprehensive overview of current progress and future directions, this review underscores the technological promise of 2D OFMs. The advances summarized here establish a foundation for further innovation and practical deployment across diverse scientific and engineering domains.