Highly fluorescent hydroxyl groups functionalized graphitic carbon nitride for ultrasensitive and selective determination of mercury ions in water and fish samples

Heavy metal ion pollution is always a serious problem worldwide. Therefore, monitoring heavy metal ions in environmental water is a crucial and difficult step to ensure the safety of people and the environment. A mercury ion (Hg 2+ ) fluorescence probe with excellent sensitivity and selectivity is described here. The functionalized graphitic carbon nitride nanosheets (T/G-C 3 N 4 ) fluorescence probe was fabricated using melamine as a precursor by the pyrolysis technique, followed by a rapid KOH heat treatment method for 2 min. The chemical structure and morphology of the T/G-C 3 N 4 probe were characterized using multiple analytical techniques including UV–Vis, SEM, XPS, XRD, and fluorometer spectroscopy. Geometry optimization of T/G-C 3 N 4 as a modified probe was performed to assess its stability and interaction ability with Hg(II) via using the density function approach. The T/G-C 3 N 4 probe showed a linear response based on quenching over the range 0–1.25 × 10 3 nM Hg(II); the detection limit was 27 nM. The remarkable sensitivity of T/G-C 3 N 4 towards the Hg 2+ ions was explained by the intense coordination and fast chelation kinetics of Hg 2+ with the NH 2 , CN, C=N, and OH groups of T/G-C 3 N 4 nanoprobe. The T/G-C 3 N 4 probe demonstrates exceptional selectivity for Hg 2+ ions among other metal ions including (Na + , Ag + , Mg 2+ , Fe 2+ , Fe 3+ , Co 2+ , Ni 2+ , Cd 2+ , K + , Ca 2+ , Cu 2+ , Pb 2+ , Mn 2+ and Hg 2+ ) and over a broad pH range (6–10), together with remarkable long-term fluorescence stability in water (> 30 days) and minimal toxicity. T/G-C 3 N 4 was used to detect and quantify Hg 2+ ions in tuna and mackerel fish and the results compared to ICP-AES. The results obtained offer a new simple and green technique for the design of multifunctional fluorescent probe appropriate for environmental applications. Graphical Abstract