Metal-Organic Frameworks Confined Within Covalent-Organic Frameworks: Advances & Perspectives.

The concept of MOF-in-COF (metal-organic frameworks confined within covalent-organic frameworks) refers to a class of hybrid materials in which MOF structures are confined in a pearl-like chain of unit cells within the 1D channels of 2D COFs. This review summarizes the emergence and recent advances in the development of MOF-in-COF materials, focusing on topics such as the synthesis strategies aimed at achieving specific pore structures and functionalities, particularly in gas separation and ion conduction applications. The tailored pore structure of MOF-in-COF materials imparts two distinctive features: a pore size smaller than that of the basal COF and a modulated internal surface environment within the pores. These unique characteristics enable the synergy of precise molecular sieving and efficient ion transport. Consequently, MOF-in-COFs have been explored as selective gas separation membranes and ion-sieving materials. This perspective article provides an outlook on the future development and potential applications of MOF-in-COF structures, based on their reported properties and current applications.