Electrospun nanofiber based colorimetric probe for rapid detection of Fe2+ in water

• Colorimetric probe for the detection of Fe2+ was developed.
• Polymeric electrospun nanofibers were used as host for the signaling reagent.
• The functionalized electrospun nanofibers exhibited a selective color change in the presence of Fe2+.
• The mechanism was based on spin crossover (SCO) from high spin Fe2+ to low spin Fe2+ upon interaction with the embedded ligand.

An imidazole derivative, 2-(2′-pyridyl)imidazole (PIMH), was developed as a colorimetric probe for the qualitative analysis of Fe2+ in aqueous solution. PIMH was then used to post-functionalize poly(vinylbenzyl chloride) (PVBC) nanofibers after electrospinning so as to afford a solid state colorimetric probe. Upon treatment with Fe2+ the probe displayed a distinctive color change both in liquid and solid platforms. The linear dynamic range for the colorimetric determination of Fe2+ was 0.0988–3.5 μg mL−1. The ligand showed a high chromogenic selectivity for Fe2+ over other cations with a detection limit of 0.102 μg mL−1 in solution (lower than the WHO drinking water guideline limit of 2 mg L−1), and 2 μg mL−1 in the solid state. The concentration of Fe2+ in a certified reference material (Iron, Ferrous, 1072) was found to be 2.39 ± 0.01 mg L−1, which was comparable with the certified value of 2.44 ± 0.12 mg L−1. Application of the probe to real samples spiked with Fe2+ achieved recoveries of over 97% confirming accuracy of the method and its potential for on-site monitoring.

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