Zinc nitride quantum dots as an efficient probe for simultaneous fluorescence detection of Cu²⁺ and Mn²⁺ ions in water samples

The exceptional ascending heights of graphene (carbon) and boron nitride nanostructures have invited scientists to explore metal nitride nanomaterials. Herein, Zn₃N₂ quantum dots (QDs) were prepared via a simple hydrothermal route from the reaction between zinc nitrate hexahydrate and ammonia solution that possess efficient strength towards sensing applications of metal ions (Cu²⁺ and Mn²⁺). The as-prepared Zn₃N₂ QDs show bright fluorescence, displaying an emission peak at 408 nm upon excitation at 320 nm, with a quantum yield (QY) of 29.56%. It was noticed that the fluorescence intensity of Zn₃N₂ QDs linearly decreases with the independent addition of Cu²⁺ and Mn²⁺ ions, displaying good linearity in the ranges 2.5–50 µM and 0.05–5 µM with detection limits of 21.77 nM and of 63.82 nM for Cu²⁺ and Mn²⁺ ions, respectively. The probe was successfully tested for quantifying Cu²⁺ and Mn²⁺ in real samples including river, canal, and tap water, providing good recoveries with a relative standard deviation  < 2%. Furthermore, the masking proposition can successfully eliminate the interference if the two metal ions exist together. It was found that thiourea is efficiently able to mask Cu²⁺ and selectively quenches Mn²⁺, and l-cysteine is able to halt the quenching potential of Mn²⁺ and is selectively able to sense Cu²⁺. The Zn₃N₂ QDs provide a simple way for the simultaneous detection of both Cu²⁺ and Mn²⁺ ions in environmental samples at low sample preparations requirements.