Crafting carbon quantum dots from acetone: dual purpose Fe³⁺ ion and pH sensing platform

We developed a low-cost single-step reflux method to synthesize acetone-based sulfonated carbon dots (acetone-CQDs) using acetone as a sole precursor. The acetone-CQDs were purified via column chromatography and characterised by IR, XRD, NMR, TEM, and XPS techniques. We hypothesized that acetone-CQDs would exhibit strong fluorescence and be effective in sensing applications. The purified acetone-CQDs displayed strong green fluorescence, a size distribution of 2 to 9 nm, and a fluorescence quantum yield of 35%. They were successfully applied as fluorescent sensors for selective and sensitive detection of Fe³⁺ ions in water. In addition, it was also demonstrated that the acetone-CQD could act as a sensitive pH sensor. The Stern–Volmer plot was drawn, from which the quenching constant was determined to be 1.02 × 10⁵ M^-1 and the quenching efficiency was 92%. The acetone-CQD was able to detect low concentrations of Fe³⁺ ions, as the LOD obtained was 4.76 µM. The fluorescence emission quenching was due to Photoinduced Electron Transfer (PET) from acetone-CQDs to the half-filled 3d orbital of Fe³⁺ ions. These findings demonstrate the potential of acetone-CQDs as effective fluorescent sensors for the sensitive and selective detection of Fe ³⁺ ions in water as well as pH sensing.