Metal/covalent–organic framework based thin film nanocomposite membranes for advanced separations

Abstract

Polyamide (PA) membranes fabricated using interfacial polymerization (IP) currently dominate the membrane industry and have contributed to various liquid/gas separations. Nonetheless, the major difficulty in controlling the rapid, irreversible IP reaction frequently results in thick polyamide (PA) films with limited free-volume elements, impeding efficient molecule/ion separations. Metal/covalent organic frameworks (MOFs/COFs), with orderly aligned pores and adjustable pore characteristics, offer advantages over traditional fillers in constructing thin film nanocomposite (TFN) membranes. They provide additional selective nanochannels to improve molecule/ion transport, facilitate a better control of film thickness and surface physicochemical properties, and confer enhanced features like improved antifouling and chlorine-resistant performance. In addition, their customizable pore structures and functions render them promising for the design of TFN molecular membranes for task-specific separations. This review introduces different types of MOFs/COFs and expounds their crucial features for membrane design. Furthermore, recent advancements in ultrahigh permselective MOF/COF-based composite membranes based on molecular-level design are presented, with a focus on comprehensive understanding of their structure–property–function relations. A further analysis of TFN membranes used for gas/liquid separations as well as emerging applications is outlined. Finally, concise conclusions, current challenges, and future prospects for the development and applications of MOF/COF-based TFN membranes are discussed.