Enhanced fluorescent effect of graphitic C₃N₄@ZIF-8 nanocomposite contribute to its improved sensing capabilities

A novel graphitic carbon nitride (g-C₃N₄)@ZIF-8 nanocomposite was synthesized by a facile approach and applied as a fluorescent sensor. The fluorescent quenching and enhancing effect of g-C₃N₄@ZIF-8 nanocomposite was explored for potential applications in sensing metal ions and solvents based on photoluminescence (PL) measurements. Compared with g-C₃N₄ nanosheets alone, the combined g-C₃N₄@ZIF-8 nanostructure greatly improved the sensitivity for the detection of metal ions due to the special fluorescent quenching effect. In particular, the sensitivities of the detection of Cu²⁺ and Ag⁺ improve from 29.1 to 11.2 ppm and from 40 to 16.5 ppm, respectively, which were significantly improved compared to that of g-C₃N₄ nanosheets alone. The sensitivity could increase about 100% and 250% for Cu²⁺ and Ag⁺ by the g-C₃N₄@ZIF-8. The limit of detection (LOD) for Cu²⁺ and Ag⁺ by g-C₃N₄@ZIF-8 was 11.2 ppm and 13.2 ppm, respectively. Both g-C₃N₄ nanosheets and g-C₃N₄@ZIF-8 nanocomposite can be used for distinguishing Fe²⁺ and Fe³⁺ in solutions. The LOD of Fe²⁺ by g-C₃N₄@ZIF-8 was as low as 65.4 ppm. On the other hand, the relative increased luminescence of g-C₃N₄@ZIF-8 to the g-C₃N₄ in tetrahydrofuran (THF) was selective, which was successfully applied for detecting this specific solvent. An excellent linear relationship (0-1.0 v/v of THF/water) between the THF fraction and PL intensities was obtained. These results demonstrate that the g-C₃N₄@ZIF-8 nanocomposite provide a convenient and novel approach for the enhance fluorescence detection of metal ions and distinguishing of specific solvents.