Construction of S,O-Doped g-C3N4 Encapsulated in Eu-MOF with Dual-Emission for Ratiometric Fluorescence Detection of Hg²⁺

Mercury ions (Hg ²⁺ ) are categorized as environmental pollutants, which distributed in water, soil, and food systems due to environmental contamination. Hence, designing a sensitive assay for the convenient determination of Hg ²⁺ is of great importance. Herein, S and O-doped graphite phase nitrogenized carbon quantum dots (S,O-C ₃ N ₄ QDs) was encapsulated within a europium -based metal-organic framework (Eu-MOF) to construct a novel ratiometric fluorescent nanoprobe for the quantitative detection of Hg ²⁺ . The native emission of S,O-C ₃ N ₄ QDs at 445 nm is used as a response signal, while Eu-MOF with fluorescence offers a reference signal at 619 nm. Hg ²⁺ exhibits high affinity for the surface functional groups of S/O-C ₃ N ₄ QDs, forming non-fluorescent chelation complexes that induce static quenching. This results in significant attenuation of the fluorescence intensity at 445 nm, while the emission at 619 nm remains invariant. A ratiometric fluorescence sensing platform was established based on the intensity ratio (F ₄₄₅ /F ₆₁₉ ) for the selective detection of Hg ²⁺ . The linear range of S,O-C ₃ N ₄ QDs/Eu-MOF of Hg ²⁺ was 0.25–35 µM and with a detection limit of 4.3 nM. The satisfying results demonstrate the effectiveness of the developed S,O-C ₃ N ₄ QDs/Eu-MOF-based fluorescence probe for Hg ²⁺ detection, highlighting its promising potential for environmental monitoring applications.