Graphitic carbon nitride nanosheets as a fluorescent probe for chromium speciation.

A fluorometric method was developed for simultaneous determination of Cr(VI) and Cr(III) ions using graphitic carbon nitride nanosheets (g-C3N4 NS) as a nanosized fluorescent indicator probe. The g-C3N4 NS were prepared using high-temperature carbonization of melamine followed by ultrasonication-assisted liquid exfoliation. The g-C3N4 NS display fluorescence with excitation/emission peaks located at 320 and 450 nm. The chromium speciation is based on the quenching of g-C3N4 NS fluorescence. The total concentration of chromium is determined after oxidation of Cr(III) to Cr(VI). The Cr(III) content was then calculated by subtracting the concentration of Cr(VI) from that of total chromium. The effects of pH value, probe amount, and contact time are optimized. Under optimum conditions, calibration plots are linear in the range in the 0.01 to 100 μM chromium concentration range. The limit of detection is 3 nM for for Cr(VI). The intra- and inter-day relative standard deviations (RSD) of the assay are 3.6-7.5% and 4.1-8.5%, respectively. The indicator probe was applied to the determination of chromium species in spiked water and food samples, and recoveries were satisfactory (93.9-107.0%). Graphical abstract Graphitic carbon nitride nanosheets are synthesized by melamine carbonization and employed for Cr speciation in water and food real samples. Total Cr(VI) and Cr(VI) are assessed based on the quenching of the fluorescence of nanosheets by Cr(VI).