Graphene Quantum Dots for High-Sensitivity and Selective Detection of Industrial Wastewater Components

Industrial wastewater typically contains heavy metal ions and dye molecules that, once released into aquatic environments, can alter pH levels and exert harmful effects on aquatic organisms. Through bioaccumulation along the food chain, these pollutants ultimately pose serious risks to human health. In this work, graphene quantum dots (GQDs) were synthesized via a hydrothermal method using 3,4,9,10-perylene tetracarboxylic anhydride as the precursor with water, ethanol, and dimethylformamide selected as solvents of varying polarity. Systematic characterization revealed that decreasing solvent polarity led to a higher oxygen-to-carbon ratio, increased oxygen-containing functional groups, and larger average thickness, particle size, and interlayer spacing of the resulting GQDs. Optical measurements showed a progressive redshift in fluorescence emission from 480 to 590 nm, accompanied by reduced fluorescence lifetimes. Energy level analysis further indicated bandgap narrowing from 3.34 to 2.16 eV with a corresponding downward shift in energy levels. Importantly, the as-prepared GQDs demonstrated distinct sensing performances: c-GQDs exhibited high selectivity toward Cu²⁺ ions with a detection limit of 1 μM, while o-GQDs showed significant fluorescence quenching in response to methylene blue. Furthermore, o-GQDs were successfully incorporated into electrospun nanofiber membranes, which displayed reversible pH-responsive fluorescence color changes─from green to orange to yellow─as the environment shifted from acidic to alkaline conditions. These fluorescence modulations are attributed to synergistic mechanisms, including charge transfer, chelation, and surface functional group interactions. Overall, this study provides a novel strategy for tailoring GQDs with tunable optical properties, offering an effective platform for the selective and sensitive detection of industrial wastewater pollutants.