Herein, a novel fluorescent ionic covalent organic framework (BTTA-BDNP) based on a linked carbazole unit was constructed for the synchronous monitoring and capture of TcO4-/ReO4-. BTTA-BDNP has a fast fluorescence response time with a low detection limit (66.7 nM) for ReO4- (a non-radioactive substitute for TcO4-). Meanwhile, the high charge density and hydrophobic skeleton of BTTA-BDNP enable it to exhibit rapid and selective trapping of ReO4- in complex environments.