Sustainable synthesis of cerium-doped carbon dots from rice husk for fluorescent detection of glyphosate in real water samples

This study reports a sustainable strategy for the synthesis of cerium-doped carbon dots (Ce-CDs) from rice husk biomass via a one-step hydrothermal process. The optimized synthesis conditions (220 °C, 3% w / v solid content, 4 h reaction time) enabled efficient biomass carbonization and high optical performance. Cerium nitrate (Ce(NO 3 ) 3 ·6H 2 O) was employed as a rare-earth dopant to enhance the photoluminescence properties of the resulting Ce-CDs. The nanomaterials were characterized by FTIR, XRD, TEM, UV–Vis spectroscopy, photoluminescence analysis, and XPS, confirming their amorphous carbon structure, spherical morphology (~2–5 nm), and the coexistence of Ce 3+ /Ce 4+ surface states. The Ce-CDs exhibited strong blue fluorescence under UV irradiation with a quantum yield of 23.77%, surpassing that of undoped rice husk CDs. The developed fluorescent probe demonstrated excellent sensitivity toward glyphosate detection through a fluorescence turn-off mechanism, mainly governed by coordination interactions between phosphonate groups and surface-exposed cerium sites, along with electrostatic effects. The fluorescence intensity displayed a linear relationship with glyphosate concentration, yielding a limit of detection (LOD) of 1.78 μmol/L (≈ 301 μg/L), enabling accurate quantitative analysis. The sensor was successfully applied to real water samples collected from Lagoa da Conceição (Florianópolis, Brazil), achieving recovery values ranging from 72.7% to 93.4% with relative standard deviations below 3.8%, demonstrating satisfactory analytical reliability in environmental matrices. These findings highlight the synergistic integration of waste biomass valorization and redox-active rare-earth doping as an effective strategy for developing green fluorescent probes for environmental monitoring of glyphosate contamination. • Rice husk biomass was valorized for the green synthesis of carbon dots. • Cerium doping enhanced fluorescence, increasing quantum yield to 23.77%. • Ce-CDs exhibited a low detection limit of 1.78 μmol/L for glyphosate. • Excellent recoveries (95.1–98.6%) were obtained in real water samples. • Ce-CDs are sustainable fluorescent probes for environmental monitoring.