Stable and Tunable Photoluminescence Emission of Functionalized Carbon Dots for Heavy Metal Ion Detection

This study investigates the tunable photoluminescence emission properties of carbon dots (CDs) derived from hemicellulose and lignin extracted from agricultural waste. Key aspects examined include production yield, fluorescence characteristics, and fluorescence quenching mechanism in the presence of heavy metal ions. Freeze-dried carbon dots from corn cobs (CC-CDs) exhibited a yield of 3.69%, which increased to 16.8% with alkali treatment (CCN-CDs). The CDs demonstrated excellent aqueous stability and emitted green fluorescence under ultraviolet light irradiation. Ultraviolet-visible spectroscopy revealed distinct absorption peaks at 200-300 nm and 300-350 nm, attributed to aromatic sp 2 core transitions and surface functional groups. Atomic force microscopy confirmed a spherical morphology with diameters of 35 nm for CCN-CDs and 51 nm for CC-CDs. Fourier-transform infrared spectral analysis identified functional groups such as phenolic hydroxyl, amines, nitrile, and carboxyl, which contribute to the tunable optical properties of the CDs. Photoluminescence spectra showed excitation-dependent emission features, with a redshift observed due to surface oxidation. The fluorescence quenching induced by ferric ions demonstrated a linear relationship between the quenching effect and concentration, with a more pronounced effect at lower concentrations of heavy metal ions, indicating the potential of these carbon dots as sensor. The quenching phenomenon was attributed to the electron transfer processes between ferric ions and CDs, providing insights into the underlying mechanisms governing their fluorescence behavior.