Synthesis and characterization of renewable woody nanoparticles fluorescently labeled by pyrene

• Renewable fluorescent lignin nanoparticles were prepared.
• The material showed oxygen-responsive property.
• The intensities of fluorescence emission of lignin-PBA increased at first and then decreased with the increase of APTES concentration.
• The intensities of fluorescence emission increased with the increase of PBA concentration.

With growing global environmental awareness, increased attention has been paid to the development of functional bio-based material. Renewable fluorescent lignin nanoparticles were prepared by a combination of alkoxysilane chemistry, amidation and sonication. The amino groups were introduced onto the lignin through a silanization reaction with 3-aminopropyltriethoxysilane (APTES), and then the pyrene groups were grafted onto the lignin surface by amidation between the amino groups and 1-pyrenebutyric acid (PBA). The products were characterized by FTIR, 1H NMR, SEM, UV–vis absorbance, fluorescence spectroscopy, confocal microscopy and dynamic light scattering (DLS). The results indicated that the lignin-PBA was prepared by amidation of APTES-modified lignin and PBA, demonstrating obvious signals of UV absorbance and fluorescence. A higher cumulative oxygen time resulted in higher fluorescence quenching of lignin-PBA. DLS showed that the average particles diameter of lignin-PBA was 92.5 nm after sonication. Increasing the APTES concentration brought about the grafting extent of APTES increased at the surface of lignin, while the intensities of fluorescence emission of lignin-PBA increased at first and then decreased due to the self-condensation of APTES onto the lignin surface at higher APTES concentration. The intensities of fluorescence emission increased with the increase of PBA concentration due to increasing grafting extent of PBA. The fluorescent lignin may have potential applications in nano sensors.

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