Waste candle soot derived nitrogen doped carbon dots based fluorescent sensor probe: An efficient and inexpensive route to determine Hg(II) and Fe(III) from water

In this study, an easy and facile route is followed to synthesize carbon dots (CDs) from candle soot (CS) for efficient and selective detection of mercury (Hg (II)) and iron (Fe (III)) toxic metals ions. These CDs were obtained via oxidation process are furthermore doped with nitrogen (N) to make them more competent towards the target applications. N-doped CDs (N-CDs) are synthesized by ethylene diamine (N source) and sodium lauryl sulphate (favorable for synthesis of smaller N-CDs). The average size of synthesized N-CDs is found in between 2.0 nm to 5.0 nm and they efficaciously have emitted blue FL under UV lamp exposure (∼290-365 nm). Zeta potential shows the net surface charge of N-CDs is negative (−10.4 mV) and plays an important role for the sensitivity of sensor and its binding efficiency towards metal ions. Functional groups (amine, hydroxyl, carbonyl, nitryl and alkenes) present on N-CDs are favorable for quenching and binding probability. Optimum pH was found 4–5 for getting better FL intensity of N-CDs. This FL is disappeared during quenching of certain concentrations of Hg(II) and Fe(III) ions due to the selective quenching of N-CDs with these metal ions. The linear range and optical detection limit of Hg (II) ions are 20–50 μM and 50 nM respectively, while for Fe (III) ions these values are 20–50 μM and 10.0 nM respectively. The fabricated N-CDs are inexpensive colorimetriC–Optical detector, selective and sensitive towards the detection of Hg (II) and Fe (III) ions contaminations and could be used as FL sensor probe for the detection of toxic metals sensing applications.