A novel covalent organic framework containing triazine–trithiophene for dual-mode fluorescent and colorimetric detection of Fe2+ and Fe3+ in water, kale and bovine liver samples

Abstract

A novel covalent organic framework (BTTC-TTA COF) containing triazine–trithiophene was successfully synthesized through a Schiff-base reaction using 5-[3,5-bis(5-formylthiophen-2-yl)phenyl]thiophene-2-carbaldehyde and 4,4′,4′′-(1,3,5-triazine-2,4,6-triyl)trianiline as building blocks. The resulting BTTC-TTA COF features a spherical morphology with a porous crystalline structure, demonstrating exceptional thermal and chemical stability. When dispersed in DMF, the BTTC-TTA COF exhibits remarkable dual-mode sensing capabilities, functioning as a highly sensitive and selective “on–off” fluorescent and colorimetric sensor for Fe²⁺ and Fe³⁺ ions. Notably, the material shows superior specificity toward iron ions over other competing metal ions. Under a 365 nm UV lamp, the fluorescence color of the BTTC-TTA COF suspension darkened after the addition of Fe²⁺/Fe³⁺. Observed by the naked eye, the hue transitions from colorless to pale yellow with Fe²⁺, and to flesh pink with Fe³⁺. The fluorescence intensity at 492 nm and absorbance at 350 nm display a linear relationship with the concentration of Fe²⁺ and Fe³⁺ over a broad range, with low detection limits at the micromolar level. XPS and FTIR spectra reveal that the BTTC-TTA COF forms a complex with Fe²⁺/Fe³⁺ via N and S atoms within its framework. The absorption competition quenching (ACQ) mechanism results in fluorescence quenching. The BTTC-TTA COF demonstrates high recovery in detecting Fe²⁺ and Fe³⁺ in practical water, kale and bovine liver extract samples, making it an effective chemical sensor for identifying and quantifying Fe²⁺ and Fe³⁺ in practical water and biological samples.