Carbon nanodots synthesized from used tobacco molasses as promising selective probes for Fe (III) ion sensing

Carbon nanodots (CNDs) as an emerging and new class of nanomaterials have been widely used as sensing probes for metal cations based on fluorescence quenching. Several precursors have been utilized as starting materials for the synthesis of CNDs, either natural, artificial, or waste materials. Herein, we present a new precursor and cost-effective method to synthesize CNDs aligning with circular economy and green chemistry principles. Two classes of CNDs were obtained, starting from used (smoked) tobacco molasses, through two processes. First, extraction was directly carried out on molasses residue to isolate one class of CNDs, i.e. D-CNDs; then the residual solid was treated by chemical oxidation, yielding a different population of CNDs, named O-CNDs. Synthesized CNDs exhibited different properties in terms of size, functional groups, and optical properties. These features lead to different sensing abilities toward Fe3+ cation. O-CNDs showed better results in terms of sensitivity (0.0045 μM−1), limit of detection (LOD = 3.9 μM), and limit of quantification (LOQ = 13 μM) compared to D-CNDs (Sensitivity = 0.0029 μM−1, LOD = 7.2 μM, and LOQ = 24 μM). The quenching mechanism attained in both CNDs is due to a combined static-dynamic effect in which the static is the dominant component. Therefore, the synthesized O-CNDs could serve as promising and low-cost nanomaterials for selective sensing of Fe3+ cation in contaminated water.