Luminescent quenching of carbon dots originated from o-phenylenediamine for Cr3+ detection in wasted water

The detection of heavy-metal ions is necessary owing to their wide and increasing utilization. Fluorometric detection has been suggested for the detection of heavy-metal ions because of its low cost, high detection speed, and high accuracy. This study investigates heavy-metal detection using carbon dots (CDs) derived from o-phenylenediamine. The CDs were synthesized via hydrothermal synthesis and had an average particle size of 2 nm and a hexagonal lattice structure. The existence of chemical bonds between C, N, O, and H was confirmed by analyzing the XPS and FTIR spectra of the CDs. The CDs exhibited excitation-independent emission characteristics and yellow luminescence at 566 nm under ultraviolet-blue light excitation owing to the carbon–nitrogen bonds in the CDs. When Cr³⁺ was dissolved in the CD solution, the rate of decrease in the luminescence intensity was higher than that of the other experimental samples. The limit of detection was calculated to be 0.161 μM by determining the relationship between the Cr³⁺ concentration and luminescence intensity at 566 nm. Analysis of the luminescence-decay curve and luminescence intensity showed that the decline in yellow luminescence originated from photoinduced electron transfer between the Cr³⁺ ions and CDs. These results indicate that CDs can be utilized as fluorometric sensors for Cr³⁺ detection in wastewater.