Specific detection of Hg²⁺ based on a ZnO/C dual-quantum-dot system

Mercury is a highly toxic non-essential metallic element that circulates through the food chain, causing various environmental problems affecting plants, animals, and humans. Therefore, developing an effective sensor for detecting mercury ions in water samples is particularly important. In this study, zinc oxide quantum dots (ZnO QDs) and carbon quantum dots (C QDs) were prepared via sol-gel and hydrothermal methods, respectively. Leveraging their mutual interactions, a ZnO/C dual-quantum-dot fluorescent sensor was successfully constructed. The fluorescence intensity of ZnO/C QDs + Hg²⁺ is twice that of ZnO QDs + Hg²⁺ and 1.4 times that of ZnO QDs alone. The presence of C QDs enhances the fluorescence intensity of the ZnO/C dual-quantum-dot system at 540 nm, improving the sensitivity for detecting Hg²⁺. Based on the specificity of mercury ions (Hg²⁺) toward the fluorescence of these composite quantum dots, a quantitative fluorescence detection method for Hg²⁺ was established and applied to practical wastewater testing. Experimental results demonstrate excellent linearity between fluorescence intensity at 540 nm and Hg²⁺ concentration within the range of 1-25 µmol L^-1, with the linear equation y = 0.02313x + 0.06644 (R² = 0.9973) and LOD = 0.3470 µmol L^-1. Spiked recovery experiments with real water samples yielded recovery rates between 99.59% and 100.38%, with relative standard deviations (RSDs) below 5%. This demonstrates the method's high accuracy and reliability for practical applications, indicating broad prospects for environmental monitoring.