Covalent organic frameworks promoted single metal atom catalysis: Strategies and applications

With the motive of bridging the gap between homocatalysis and heterocatalysis, atomically dispersed single metal atom catalysts (SACs) on different supports have rapidly progressed in the field of catalysis. In recent years, covalent organic frameworks (COFs) have been recognized as promising 2D and 3D crystalline polymers for producing SACs, featured with distinct benefits of porous structure, tailored functionality and high metal loading. The superior efficiency of catalytic reactions in COF modified SACs mainly depends upon the single atom catalytic active sites, ultrafine atomic dispersion of metal atoms, and coordination environment provided by COFs skeleton which collectively determines the electronic properties. This review explores the strategic synthesis routes, advanced characterisation, and catalytic applications of COF-based SACs. The versatile potentials provided by COFs for fulling the prerequisites of SACs formation are discussed. A critical discussion on the strategic synthesis of COF-based SACs is proposed, by exploiting the structural merits of COFs. We summarize the strengths of advanced characterization techniques in identifying the successful construction of SACs. A sketch of the reported work is presented for catalytic energy related applications including photocatalysis, electrocatalysis and carboxylation processes. Also, a suggestive overview on the existing challenges, foresighted ideas and future perspectives for COF-based SACs are mentioned.