Construction of Multiple-Component Covalent Organic Frameworks by an In-Situ Approach for Boosting Palladium Recovery from Strong Acid

Multiple-component covalent organic frameworks (COFs) show outstanding advantages in both structure and function over the common two-component COFs. Herein, we show a simple but general synthesis of multiple-component COFs through an in-situ approach. In the simplest C4 + C2 binary condensation system, we observed substitute-induced in-situ formed linkers and consequently a conversion from a two-component sql COF to a three-component sql-defect COF. However, in another C4 + C3 binary condensation system, we observed both topology- and substitute-induced in-situ formed linkers and finally a conversion from a three-component 3,4-connected COF to a two-component hcb-defect COF. Such a difference in the topology between three- and two-component COFs is very different from the established three-component COFs that show the same topology as observed in the comparable two-component COF. These new finds, as evidenced by both experimental and theoretical results, mainly originated from the steric hindrance effect. Moreover, we also disclosed a structure–function relationship among palladium recovery, substitute effect, and pore size of COFs, and one multiple-component COF was found to show benchmark performance in palladium recovery from strong acid (3 M). The results shed light on a fundamental design for a multiple-component COF and its advanced application.