Preparation of carbon-dot-based red-fluorescent polyamide 6 nanocomposites via in situ polymerization for anti-counterfeiting/encryption and Fe3+ detection

Carbon-dot-based red-fluorescent materials (CRFMs) have attracted significant attention due to advantages such as excellent interference resistance. However, the development of solid-state CRFMs has been hindered by aggregation-caused quenching (ACQ). In situ polymerization can significantly improve the migration resistance and dispersion of fluorescent nanofillers within polymers, thereby suppressing ACQ. Herein, novel solid-state CRFMs were successfully synthesized via in situ polymerization. Quasi-spherical o -phenylenediamine-based carbon dots (O-pd-CDs) with an average particle size of 2.39 nm were hydrothermally synthesized, demonstrating deep-red fluorescence (633 nm) in formic acid, with an average fluorescence lifetime (τ ave ) of 2.41 ns and an absolute fluorescence quantum yield (QY) of 17.51%. O-pd-CDs feature nitrogen-doped highly conjugated graphitic carbon nuclei and amorphous surface layers enriched with amino and hydroxyl groups, while exhibiting exceptional thermal stability within the range of 150−272 °C. Subsequently, amide-bonded O-pd-CDs-based polyamide 6 nanocomposites (PA6@O-pd-CDs-x, where x represents the mass percentage of O-pd-CDs relative to caprolactam without the % sign) were successfully synthesized via in situ polymerization, which effectively suppressed ACQ. PA6@O-pd-CDs-x-based fluorescent nanofibrous membranes (PA6@O-pd-CDs-x-FNFM) with bright red fluorescence (596−601 nm) were fabricated via electrospinning, exhibiting excellent ultraviolet resistance, with a τ ave of 1.91−2.86 ns and an absolute fluorescence QY of 1.01−1.34%. Moreover, PA6@O-pd-CDs-x-FNFM exhibit excellent performance in anti-counterfeiting and information encryption. Based on red fluorescence quenching, PA6@O-pd-CDs-1.5-FNFM exhibits a wide detection range (0−0.5 mM) and a low limit of detection (2.05 μM) for Fe 3+ in water, with excellent anti-interference capability. The fluorescence quenching observed when PA6@O-pd-CDs-1.5-FNFM contacts Fe 3+ is mainly attributed to static quenching and redox reactions.