Polymer-grafted carbon dots for metal contaminants monitoring: Experimental, DFT validation, and machine learning prediction

Biomass-derived carbon dots (CF) and polymer-functionalized carbon dots (CFP) were prepared from date-palm leaf fibers for fluorescence-based metal ions sensing. CF was produced through carbonization under nitrogen, followed by nitric acid activation. CFP was prepared by in situ copolymerization of acrylamide and acrylic acid in the presence of CF. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) confirmed the formation of carbonaceous structures and the incorporation of polymer-associated nitrogen- and oxygen-containing functionalities. Under identical conditions, CF showed its strongest fluorescence response toward Mg(II), whereas CFP exhibited selective fluorescence quenching toward Cr(VI) and Fe(III). The CF fluorescence lifetime increased from 17.533 to 24.250 ns after Mg(II) addition, while the CFP lifetime decreased from 24.250 to 1.039 ns with Fe(III) and to 0.934 ns with Cr(VI). The calibration plots showed strong linearity, with correlation coefficients of 0.9986, 0.9985, and 0.9982 for CF–Mg(II), CFP–Cr(VI), and CFP–Fe(III), respectively. Density functional theory (DFT) calculations suggested preferential Mg(II) coordination at carbonyl oxygen sites and stronger interaction of CFP with Cr(VI) than with Fe(III). Machine-learning (ML) models trained using 113 experimental data points achieved test accuracies of up to 97%. These findings demonstrate the potential of date-palm leaf-derived carbon dots for selective fluorescence-based monitoring of metal-related contaminants in water.