Silver nanoparticles embedded sulfur doped graphitic carbon nitride quantum dots: A fluorescent nanosensor for detection of mercury ions in aqueous media

Abstract

Graphitic carbon nitride (gCN) quantum dots, in recent years, have captivated enormous attention in the field of sensing due to their unique optical and electronic properties. We have reported a facile synthesis of silver nanoparticles (AgNPs) embedded sulfur-doped gCN quantum dots (Ag-S-gCN QDs) using thiourea, trisodium citrate, and silver nitrate precursors. The as-prepared quantum dots with an average particle size of 3.7 nm emitted strong blue fluorescence with a relative quantum yield of 36.5%. They exhibited significant stability against photobleaching and high ionic strength. The Ag-S-gCN QDs, under optimal conditions, were employed for fast sensing of Hg2+ ions in 3 min at pH 5. The limit of detection (LOD) and limit of quantification (LOQ) were measured to be 0.13 μM and 0.43 μM, respectively, with a linear range of 0.1–0.6 μM. The average lifetime of Ag-S-gCN QDs was calculated as 7.79 ns from a time-resolved decay experiment. A static quenching mechanism was proposed from the average lifetime calculation accompanied by a redox reaction via electron transfer from metallic Ag to Hg2+ ions. A substantial amount (>85%) of Hg2+ ions in the real water samples were recovered within a relative standard deviation (RSD) of ≤ 5%. The proposed nanosensor was anticipated to open up a new avenue for convenient, efficient, sensitive, and selective sensing of potentially hazardous Hg2+ ions.