One pot solid-state synthesis of highly fluorescent N and S co-doped carbon dots and its use as fluorescent probe for Ag+ detection in aqueous solution

Abstract Highly fluorescent N and S co-doped carbon dots (CDs) were synthesized in one pot using caffeine as a raw material via a facile, green and cost-effective solid-state method. It is found that when caffeine and a mixture of caffeine and urea were heated, the CDs were not produced. However, when a mixture of caffeine and ammonium persulfate was heated, the CDs were fabricated successfully and exhibited the blue fluorescence with a quantum yield of 38%. In addition, the formation of CDs was enhanced with excellent optical properties when urea was added to the mixture of caffeine and ammonium persulfate. Without further chemical modification, the CDs emitted bright blue fluorescence with a high quantum yield as high as 69% due to the enhancement effect of N and S co-dopants on the surface of the CDs. Owing to the strong blue fluorescence, the CDs fabricated in this study could be used effectively as a fluorescence probe for Ag +  ions that exhibited high sensitivity and selectivity.