An acylhydrazone-linked covalent organic framework for removal of Cu(II) from aqueous solution and its applications in catalysis

Abstract

An acylhydrazone-linked covalent organic framework (TH-MT–COF–OH) was synthesized using 2,5-dihydroxyterephthalic hydrazide and 2,4,6-tris(4-methoxybenzaldehyde)-1,3,5-triazine as building blocks. The obtained TH-MT–COF–OH exhibited excellent adsorption capacity for Cu(II) from aqueous solution, with maximum removal efficiency of 99.2 % at pH = 7. The theoretical maximum adsorption capacity (Qm) reached 137.17 mg/g based on Langmuir model. Moreover, the adsorption kinetics simulated results consistent with the pseudo-second-order model, suggesting the adsorption mechanism of Cu(II) by TH-MT–COF–OH was mainly governed by chemisorption. Interestingly, after adsorbing Cu(II), the spent adsorbent Cu@TH-MT–COF–OH could be used as a reusable catalyst for organic synthesis, such as Ullmann-type cross-coupling reactions. These results further demonstrated the strong interaction between copper ions and adsorbents leading to the stable adsorption against the erosion of organics. What's more, the pristine TH-MT–COF–OH also presented high catalytic activity in Knoevenagel condensation reactions. In addition, the TH-MT–COF–OH and Cu@TH-MT–COF–OH were recyclable and could be reused.