Rapid, Mild, and Catalytic Synthesis of 2D and 3D COFs with Promising Supercapacitor Applications

An approach based on Keggin heteropoly acids (HPAs) has been presented for the mild and fast synthesis of five different structures of imine and azine-linked two-dimensional (2D) and three-dimensional (3D) covalent organic frameworks (COFs). Traditionally, these crystalline materials have been synthesized via the Schiff base polycondensation reaction between different aldehydes and amines under harsh conditions and in the presence of acetic acid. Herein, two different Keggin-type heteropolyacids (HPAs) have been exploited as catalysts which are both Bronsted and Lewis acids to speed up the synthesis of 2D and 3D COFs and improve their materials quality. The catalyst led to the preparation of the imine and azine-linked COFs with high crystallinity and porosity under mild conditions and short reaction time. According to the results, the amine building blocks with two amine functional groups formed the COFs with higher crystallinity, porosity, and yield compared to amine with three functional groups and nonplanar structures. On this basis, under mild reaction conditions, a 2D COF named TAPA-TPT was successfully prepared with high crystallinity and good porosity. The developed TAPA-TPT COF exhibits a very good performance when used in supercapacitor applications. This COF showed excellent specific capacitance of 205 F g(-1) at a current density of 0.5 A g(-1), which is a very attractive value for supercapacitors. This study provides a synthetic approach that can lead to large-scale production of COF materials for energy harvesting.