Construction of carbazole-conjugated dual-emission fluorescent covalent organic framework for distinguishing p-nitroaniline/p-nitrophenol and adsorbing nitroanilines/nitrophenols

Abstract

Nitroanilines (NAs) and nitrophenols (NPs), crucial industrial raw materials, are extensively utilized across various sectors. However, the environmental pollution and health hazards stemming from their usage are significant, necessitating urgent monitoring and removal to address environmental and safety concerns. The challenge is further compounded by the presence of NAs/NPs isomers, making the selective analysis of specific isomers crucial. In response, a new post-modified fluorescent covalent organic framework (COF) termed COF@CB, exhibiting dual-emission fluorescence, was synthesized. This synthesis involved coupling a high-crystallinity fluorescent COF (COF-TTDB) with carbazole-9-ethanol (CB) via a “Williamson” reaction. COF@CB featured exceptional dual-emission fluorescence, a high specific surface area (919.4 m²·g^-1), superior thermal stability, and abundant active sites. These attributes enabled COF@CB to function as a ratiometric fluorescence sensor capable of simultaneous detection and adsorption. The distinct number and arrangement of hydrogen bond sites in NAs/NPs isomers influenced the intramolecular charge transfer (ICT) effects on COF@CB, thereby enabling the COF@CB-ratiometric fluorescence sensor to distinguish and selectively detect p-NA/p-NP from isomers. Analysis of actual water samples further underscored the sensor's effectiveness in detecting p-NA/p-NP. Furthermore, the presence of multiple active sites on the COF@CB-ratiometric fluorescence sensor facilitated the adsorption of NAs/NPs, promoting the removal of them from actual samples.