Detection of sulphur(II) of carbon dots synthesized from residue.

The detection of anions using carbon dots (CDs) has received less attention compared to cations. Therefore, the present study aimed to develop a fluorescence sensor based on carbon dots (CDs) capable of detecting S in real water samples. The CDs were successfully prepared from the residues of a traditional Chinese herb, , which emitted green photoluminescence (PL) under ultraviolet light irradiation. The as-prepared CDs were quasi-spherical in shape and ranged in size from 10 to 30 nm. Different detailed analyses proved that the CDs had good morphology, various functional groups, high water solubility, great optical features, and excellent stability under diverse environmental conditions. The ion detection showed that only Ag had the strongest fluorescence quenching effect on the CDs, however, the addition of S could recover their fluorescence. Based on these results, an "off-on" fluorescence sensor was achieved to selectively detect the concentration of S in real water samples with a limit of detection (LOD) of 39 μM, which further expanded the application of residues from traditional Chinese herbal medicine.