Fluorescent assay based on phenyl-modified g-C₃N₄ nanosheets for determination of thiram

Phenyl-modified graphitic carbon nitride nanosheets (Ph-g-C₃N₄ NSs) were synthesized by a thermal copolymerization and ultrasonic exfoliation method. The Ph-g-C₃N₄ NSs are used as a fluorescent assay for determination of thiram. The results of X-ray photoelectron spectroscopy, ¹³C solid-state nuclear magnetic resonance and Fourier transform infrared spectra confirm that phenyl group is integrated into the heptazine network of g-C₃N₄. Compared to the g-C₃N₄ NSs, the Ph-g-C₃N₄ NSs show bigger stokes shift about 185 nm and higher fluorescence intensity. The fluorescence of Ph-g-C₃N₄ NSs is quenched by Cu²⁺ via the photo-induced electron transfer mechanism, which then recovers in the presence of thiram. The fluorescence restoring of Ph-g-C₃N₄ NSs is correlated with the concentration of thiram. Under the optimized conditions, the fluorescent intensity of g-C₃N₄ NSs at excitation/emission wavelengths of 310/455 nm give a linear range of 33.0-670 nM with detection limit of 9.90 nM. While fluorescent assay based on the Ph-g-C₃N₄ NSs show the linear range of 6.70-1300 nM at excitation/emission wavelengths of 310/495 nm with detection limit of 2.01 nM. Graphical abstract Schematic representation of fluorescent "on-off-on" assay based on phenyl-modified graphitic carbon nitride nanosheets (Ph-g-C₃N₄ NSs) for determination of thiram.