Dual-function fluorescent hydrazone-linked covalent organic frameworks for acid vapor sensing and iron(iii) ion sensing

Abstract

Covalent organic frameworks (COFs) exhibit good chemical stability, large specific surface areas and abundant pores, and they can provide good transport channels and sufficient binding sites. Therefore, COFs are promising candidates in the field of fluorescence sensing. In this study, we used a typical bicarbazole as the main building blocks and a hydrazone as the linkage to generate a 2D COF named CZ-DHZ-COF, which emits bright cyan color in the solid state. Notably, on the one hand, the as-synthesized CZ-DHZ-COF powder showed rapid fluorescence response to acid vapor with weakened and red-shifted fluorescence; on the other hand, the suspension liquid of CZ-DHZ-COF exhibited specific recognition to Fe(III) ions with remarkable fluorescence quenching. To make it closer to actual application, we prepared its aerogel sample with chitosan as the aerogel base material to obtain CZ-DHZ-COF&Chitosan aerogel (CZCA). The CZCA not only exhibits better detection ability with a faster response speed to acid vapor than that of the as-synthesized CZ-DHZ-COF powder, but also exhibits clear recognition to Fe(III) ions. These results indicated that the CZ-DHZ-COF would be a good candidate in fluorescence sensing to detect acid vapor and Fe(III) ions. Meanwhile, the strategy to prepare composite materials with aerogels is of great significance to acid vapor sensing and will provide a new way to break the limitation of detection condition for COF-type fluorescence sensors.