A novel dual colorimetric fiber based on two acid–base indicators

A novel dual colorimetric fiber based on two acid–base indicators was synthesized by first aminating commercially available polyacrylonitrile fiber with tetraethylenepentamine and then covalently immobilizing ethyl orange moieties through an alkylation reaction and a diazo coupling reaction; finally, the fiber was grafted with phenolphthalein using a Mannich reaction. The functionalized fiber was characterized by elemental analysis, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier-transfer infrared spectroscopy (FTIR) and UV–vis spectroscopy, and its color-changing properties, response speed, reusability and photostability were all investigated. This fiber exhibits a remarkable color change from deep pink (pH < 1.1) to yellow (1.1 < pH < 13.0) and then to dark violet (pH > 13.0). Moreover, this fiber shows a fast response time (<1 s for 1 M HCl and 1 M NaOH), high photostability (>60 days) and excellent reusability (>300 times).

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► A novel dual colorimetric fiber based on ethyl orange and phenolphthalein was prepared.
► This colorimetric fiber shows a remarkable color change for acids and bases.
► Fast response time (<1 s for 1 M HCl or NaOH) and high photostability (>60 days).
► This fiber also shows excellent reusability (>300 times) and recycle stability.
► The color change of the modified fiber can be induced by various strong acids and bases.