A graphitic C₃N₄ nanocomposite-based fluorescence platform for label-free analysis of trace mercury ions

In this study, a nanocomposite consisting of graphitic carbon nitride nanosheets loaded with graphitic carbon nitride quantum dots (CNQDs/CNNNs) was synthesized via a one-step pyrolysis method. This nanocomposite exhibited excellent thermal stability, photobleaching and salt resistance. Then a new fluorescence sensing platform based on CNQDs/CNNNs was constructed, which showed high sensitivity and selectivity towards trace mercury ions (Hg²⁺). By using X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectra and density functional theory, the fluorescence response mechanism was elucidated where Hg²⁺ could interact with CNQDs/CNNNs, causing a structural change in the nanocomposite, further affecting its bandgap structure, and finally leading to fluorescence quenching. The linear range for detecting Hg²⁺ was found to be 0.025-4.0 μmol L^-1, with a detection limit of 7.82 nmol L^-1. This strategy provided the advantages of a rapid response and a broad detection range, making it suitable for quantitative detection of Hg²⁺ in environmental water.