Mg/S@g-C₃N₄ nanosheets: A promising fluorescence sensor for selective Cu²⁺ detection in water

This work describes the development of a novel fluorescence sensor based on magnesium/S@g-C₃N₄ nanosheets for selective detection of copper (Cu²⁺) ions in water. Mg/S@g-C₃N₄ nanosheets were prepared by the polycondensation technique and investigated by X-ray diffraction (XRD), ATR-FTIR spectroscopy, scanning electron microscopy (SEM), surface area (BET), and UV-Vis optical absorption measurements. XRD and ATR-FTIR analysis showed the characteristic peaks for S@g-C₃N₄. The broad full width at half maximum (0.056 radians) implies a smaller crystallite size, representing smaller Mg/S@g-C₃N₄ sheets. SEM micrograph showed non-exfoliated nanosheets with flake-like structures. The EDS mapping confirmed the presence of magnesium, carbon, nitrogen, and sulfur throughout the nanosheets. The Mg/S@g-C₃N₄ nanosheets possess a high surface area of 40 m²/g and mesopores within the nanosheets, with a size of 1.57 nm. The band gap of the Mg/S@g-C₃N₄ nanosheet was estimated to be 3.0 eV. The sensor exhibits a strong quenching response towards Cu²⁺ ions, with a decrease in fluorescence intensity as the concentration of Cu²⁺ increased from 1 μM to 20 μM. The Stern-Volmer quenching constant (K_SV) showed a relatively high value of 185053 M^-1. The estimated value of LOD by the Mg/S@g-C₃N₄ sensor for Cu²⁺ was 16.2 nM. The sensor offered high sensitivity and selectivity for Cu²⁺ detection over other heavy metals.