Construction of new covalent organic frameworks with benzimidazole moiety as Fe3+ selective fluorescence chemosensors

Hollow structures derived from covalent organic frameworks (COFs) make them a good candida for absorption. In this study, two COFs based on benzimidazole were synthesized. Pyromellitic dihydride and perlin-tetracarboxylic anhydride reacted with 5-amino-isophthalic acid to produce initial monomers. Then, these monomers reaction with aminobenzidine in polyphosphoric acid medium converted them to benzimidazole- based COFs (COF-BI-1 and COF-BI-2). The microstructure and morphology of synthesized COF were examined by XRD, FTIR, FESEM, TEM, TGA, BET, and elemental analysis. The specific surface area of the COF-BI-1 and COF-BI-2 were 426 and 257 m2/g, respectively. The TGA thermograms showed the high thermal stability of the synthesized COFs. In the second step, benzimidazole based COFs were suspended in various solvents, and fluorescence was taken. The suitable solvent was selected, then different cations were solved in the mixture of COF and solvent, and fluorescence was taken. The results showed that by adding 10 μl Fe3+ to the mix of COF and solvent, the intensity of fluorescence was reduced. So the sensitivity of two COF-BI-1 and COF-BI-2 to Fe3+ far more than other cations. Thus, they can be used as a sensor to detect Fe3+.