Fabrication of a Reversible Fluorescence Sensor Based on Nitrogen‐Sulfur Co‐Doped Multiwalled Carbon Nanotubes for Detection of Mercury Ions: Experimental and DFT Insights

An eco‐friendly approach involving hydrothermal treatment followed by thermal annealing was adopted for the preparation of nitrogen‐sulfur co‐doped multi‐walled carbon nanotubes (NS‐CNT@600) using melamine and thiourea as precursors. The prepared NS‐CNT@600 were characterized using X‐Ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR), X‐Ray Diffraction (XRD), High‐Resolution Transmission Electron Microscopy (HR‐TEM), Ultraviolet and Visible Spectroscopy (UV‐Vis). They were applied for the fluorescent detection of Hg 2+ ions in water. A fluorescence quenching sensor for sensitive and precise detection of Hg 2+ ions was developed by making use of the sensitivity of NS‐CNT@600 to fluorescence quenching behavior caused by interaction with Hg 2+ ions. Additionally, the selectivity of NS‐CNT@600 towards Hg 2+ ions was thoroughly investigated in the presence of other interfering metal ions. There was a linear relationship between fluorescence intensity and Hg 2+ concentration from 10 to 50 nM with a limit of detection (LOD) of 6.3 nM. The proposed method was also tested on real water samples with positive results. Physicochemical features and interaction mechanism of analyte‐material transduction were exclusively studied by combining fluorescence spectrophotometry and density functional theory (DFT) calculation techniques. The strategy provides an easy way to develop low‐cost, selective and sensitive probes for rapid fluorescent sensing of Hg 2+ ions in aqueous solutions.