One-Step Green Synthesis of Water-Soluble Fluorescent Carbon Dots and Its Application in the Detection of Cu²

Renewable biowaste-derived carbon dots have garnered immense interest owing to their exceptional optical, fluorescence, chemical, and environmentally friendly attributes, which have been exploited for the detection of metals, non-metals, and organics in the environment. In the present study, water-soluble fluorescent carbon dots (CDs) were synthesized via facile green microwave pyrolysis of pine-cone biomass as precursors, without any chemical additives. The synthesized fluorescent pine-cone carbon dots (PC-CDs) were spherical in shape with a bimodal particle-size distribution (average diameters of 15.2 nm and 42.1 nm) and a broad absorption band of between 280 and 350 nm, attributed to a π-π* and n-π* transition. The synthesized PC-CDs exhibited the highest fluorescent (FL) intensity at an excitation wavelength of 360 nm, with maximum emission of 430 nm. The synthesized PC-CDs were an excellent fluorescent probe for the selective detection of Cu²⁺ in aqueous solution, amidst the presence of other metal ions. The FL intensity of PC-CDs was exceptionally quenched in the presence of Cu²⁺ ions, with a low detection limit of 0.005 μg/mL; this was largely ascribed to Cu²⁺ ion binding interactions with the enriched surface functional groups on the PC-CDs. As-synthesized PC-CDs are an excellent, cost effective, and sensitive probe for detecting and monitoring Cu²⁺ metal ions in wastewater.