Study on colorimetric sensing performance of covalent organic framework for highly selective and sensitive detection of Fe2+ and Fe3+ ions

A covalent organic framework (TPDQ-COF) composed of 1,3,5-Triformylphloroglucinol (TFP) and 2,6-Diaminoanthraquinone (DAAQ) was prepared and characterized. TPDQ-COF has a regular pore structure and high thermal and chemical stability. UV-vis absorption spectra of TPDQ-COF suspension in DMF had a highly selective absorption enhancement response to Fe2+/Fe3+ ions accompanied by obvious color changes from colorless to yellow. The UV absorption intensity at 283 nm of the TPDQ-COF suspension showed good linear relationships with the concentrations of Fe2+ and Fe3+, with the detection limits of 6.91 × 10−7 M for Fe2+ and 7.14 × 10−7 M for Fe3+. The reversible absorption changes of TPDQ-COF upon the addition of EDTA indicated that the selective absorption response of TPDQ-COF was caused by the selective coordination of Fe2+ and Fe3+ ions to N and O atoms on TPDQ-COF, as well as the ligand to metal charge transfer (LMCT) effect within the TPDQ-COF framework. The x-ray photoelectron spectroscopy (XPS) and further verified the coordination effect between N and O atoms on TPDQ-COF and iron ions. The good recovery of TPDQ-COF in the Fe2+ and Fe3+ tests confirmed its sensing ability for iron ions in practical water samples. This work explored covalent organic frameworks as the colorimetric sensor to recognize and detect specific metal ions in practical water samples.