Fabrication of high-crystallinity hydrazone‐linked fluorescent covalent organic framework and its sulfonated material for the design of sensing and adsorption dual-functional platforms

Abstract

Hydrazone-linked fluorescent covalent organic frameworks (COFs) with high crystallinity exhibit remarkable stability under acid-base conditions and in various organic solvents, maintaining structural integrity for cyclic utilization in sensing and adsorption processes. Consequently, developing new high-crystallinity hydrazone-linked fluorescent COFs is of significant importance. Notably, post-modification can enhance the detection diversity, selectivity, and adsorption performance of these COFs. Herein, a new hydrazone-linked fluorescent COF (namely COF-YYL) with high crystallinity was synthesized using 2,5-bis(allyloxy)terephthalohydrazide (DHzDAll) and 4,4′,4″-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde (TTB) as precursors at room temperature. COF-YYL demonstrated superior characteristics including a high specific surface area (653.33 m2·g−1), good chemical and thermal stability, and dual-functionality in detecting methyl orange (MO) and Cu2+ with limits of detection (LODs) of 33 nM (2.1 ng·mL−1) and 1 ng·mL−1, respectively, and an MO adsorption capacity of 112.81 mg·g−1. To increase functional diversity, COF-YYL underwent post-modification via “click” chemistry between the double bonds on DHzDAll and −SH on 3-mercapto-1-propanesulfonic acid sodium salt (MPS), yielding COF-SO3Na. Compared with COF-YYL, COF-SO3Na exhibited a higher specific surface area (815.23 m2·g−1), better dispersion performance, and richer functional group properties. Leveraging these advantages, COF-SO3Na served as a dual-function platform for detecting and adsorbing four cationic dyes including brilliant green (BG), crystal violet (CV), malachite green (MG), and methylene blue (MB), with satisfactory LODs (170 ng·mL−1) and good adsorption capacities ranging from 98.94 to 162.87 mg·g−1. Further, COF-YYL and COF-SO3Na were used to analyze related analytes in tap water samples, achieving satisfactory recoveries. This study introduces a new high-crystallinity hydrazone-linked fluorescent COF, along with its sulfonated material, increasing the diversity of detection and adsorption platforms.