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

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 hydrazonelinked 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 center dot 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 center dot mL-1) and 1 ng center dot mL-1, respectively, and an MO adsorption capacity of 112.81 mg center dot 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 COFSO3Na. Compared with COF-YYL, COF-SO3Na exhibited a higher specific surface area (815.23 m2 center dot 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 center dot mL- 1) and good adsorption capacities ranging from 98.94 to 162.87 mg center dot 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.