Facile fabrication of hollow tubular covalent organic frameworks using decomposable monomer as building block

In this study, a commercial and low-toxicity hydrazide-containing building block has been used to construct azine-linked covalent organic frameworks (COFs). New style COFs were constructed between flexible formic hydrazide (FH) and 1,3,5-triformylphloroglucinal (Tp) or 1,3,5-triformylbenzene (TFB). The two resulting COFs (TpFH and TFBFH) exhibited uniform hollow tubular morphology (20-50 nm for TpFH, 50-100 nm for TFBFH). Compared to hydrazine, FH has low-toxicity and is a flexible monomer, consisting of amine and aldehyde groups. The decomposition of FH slows down the reaction rate and the as-synthesized FH-series COFs (708 m(2) g(-1) for TpFH and 888 m(2) g(-1) for TFBFH) had higher specific surface area than hydrazine-series COFs (617 m(2) g(-1) for TpAzine and 472 m(2) g(-1) for TFBAzine). A detailed time-dependent investigation was carried out to interpret the mechanism of hollow structure formation, and Ostwald ripening possibly happens during the formation of hollow COF microstructures. Considering the porous and high density N, O elements of these materials, preliminary applications of the metal ions removal from aqueous solution and gas storage were implemented.

Automated summary

In this study, a commercial and low-toxicity hydrazide-containing building block was used to construct azine-linked covalent organic frameworks, resulting in uniform hollow tubular structures. Compared to hydrazine, formic hydrazide showed lower toxicity and served as a flexible monomer, leading to the formation of COFs with higher specific surface area. Detailed investigation into the mechanism of hollow structure formation was conducted, indicating the potential for applications in metal ion removal and gas storage due to the porous nature and high density of N, O elements in these materials.