Fluorescence Quenching Probe Based on Graphene Quantum Dots for Detection of Copper Ion in Water

Heavy metal contamination in water is a serious issue causing adverse effects on health, ecosystem, and environment. To monitor this contamination, fluorescence quenching probe based on the graphene quantum dots (GQDs) was used for detection of metal compounds. The effect of metal compounds on the fluorescence quenching efficiency of the GQDs was investigated. A typical sample of metal compounds was selected from copper acetate, copper chloride, copper nitrate, copper sulfate, cobalt nitrate, cobalt chloride, and zinc nitrate. It was found that the GQDs exhibited high selectivity for copper acetate. The quantity of copper acetate was obtained using Stern-Volmer plot. It was found that the plot exhibited a linear behavior for the fluorescence quenching of the GQDs by copper acetate. This analytical method could be developed for the determination of copper acetate in the concentration range of 0–2.5 mM with the Stern-Volmer quenching constant of 2445 M−1. To understand an occurring interaction between metal compounds and the GQDs in the system, redox characteristics of the GQDs mixed metal compounds were investigated. Noticeably, electrochemical potential gap (ΔE) of the GQDs mixed copper acetate with UV irradiation seems higher than that of the GQDs mixed copper acetate without UV irradiation, implying better electron transfer behavior from the GQDs to copper acetate. This result was in good agreement with the fluorescence quenching of the GQDs by copper acetate. Accordingly, the nonradiative recombination of the GQDs could be explained in terms of the fluorescence quenching. The fluorescence quenching efficiency was proportional to the amount of the copper acetate. These results can be further explored for a novel graphene quantum dots-based fluorescent probe and this method could be more widely applied in water resources.