Graphene Quantum Dots with Amine-Modification: A Smart Fluorescent Probe for Effective Detection of Heavy Metal Ions in Wastewater

In this work, we have developed an optical fluorometric sensor for detection of lead (II) ion (Pb²⁺) and copper (II) ion (Cu²⁺) in wastewater using fluorescent amine-modified graphene quantum dots (a-GQDs). A simple preparation process, i.e., hydrothermal method is used for the preparation of a-GQDs. The prepared a-GQDs emits green luminescence and have an average particle size around 1.26 ± 0.16 nm with uniform distribution. The a-GQDs utilized for detection of various biologically essential metal ions like Pb²⁺ and Cu²⁺ ions in aqueous solution using fluorescence-based spectroscopic technique. Here, UV–visible absorption spectra of a-GQDs with and without Pb²⁺ and Cu²⁺ ions, shows no variation in the absorbance of a-GQDs. Further, lifetime analysis of a-GQDs shows that lifetime of a-GQDs changed from 2.02 ns to 1.37 ns in presence of Pb²⁺ and 2.02 ns to 1.62 ns in presence of Cu²⁺ ions, confirms the dynamic quenching mechanism. The a-GQDs have detected Pb²⁺ and Cu²⁺ ions in the linearity range of 2–200 µM and 2–300 µM with limit of detection (LOD) of 1.60 µM and 1.66 µM, respectively. Therefore, this work demonstrates the sustainability of a-GQDs as a favorable fluorescence (FL) probe that may be used to detect heavy metal ions in wastewater and aqueous solution.