Reticular Chemistry within Crystalline Porous Gas Adsorbents and Membranes.

Abstract

ConspectusAdsorptive and membrane separations are recognized as highly energy-efficient technologies, critically dependent on the properties of adsorbent and membrane materials. Crystalline porous materials (CPMs), such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs), metal-organic cages (MOCs), and hydrogen-bonded organic frameworks (HOFs), have emerged as exceptional candidates for high-performance adsorbents and membranes due to their intrinsic structural tunability. Their orderly pore structure, high porosity, and large surface facilitate gas storage and separation processes. Furthermore, modifying the inner surface, controlling the pore size, and regulating the framework flexibility can significantly enhance CPMs' adsorption capacity and separation selectivity. Therefore, the precise structure regulation of CPMs is the key to optimizing gas separation and purification.Reticular chemistry is the use of strong chemical bonds to connect discrete molecular structures (molecules or molecular clusters) to create extended structures, such as CPMs. It allows precise atomic-level control and offers a method for regulating the structures of CPMs, enabling tailored pore environments that enhance selectivity for target separations. This approach is crucial to designing effective gas separation materials. For example, by functionalizing organic ligands, regulating metal ions, and modifying secondary building units, the pore size, porosity, and functionality of CPMs can be finely controlled while keeping the framework topology unchanged, thereby optimizing the gas separation performance.In this Account, we present an overview of our group's research efforts on optimizing gas separation by fine-tuning CPM adsorbents and membranes. Using reticular chemistry, we have developed strategies such as multiple cooperative regulation, adaptive pore control, pore environment engineering, preprocessed monomer interfacial polymerization, and precursor solution processing to create highly selective CPM adsorbents and membranes. Additionally, we elucidate the underlying mechanism of multiple hydrogen bonding and dipole-dipole interactions between CPMs and hydrocarbon molecules. By precise structural regulation, we further optimize the gas separation performance and broaden CPMs' applications. Finally, we discuss the challenges and future directions for CPM adsorbents and membranes, including material design, synthesis, stability, performance, and the structure-activity relationship. We also propose a membrane-adsorptive separation coupling technology as a potential solution for achieving high-purity gas separation. By utilizing CPM-based adsorbents and membranes, we aim to establish an energy-intensive and environmentally friendly pathway for the separation of low-carbon hydrocarbons, hydrogen, and natural gas, providing a sustainable alternative to conventional high-energy gas separation processes.