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Lignin-derived carbon dots made from leaf waste offer a sustainable tool for plant protection by converting agricultural residues into functional nanomaterials. High-purity lignin was extracted from Norway maple (Acer platanoides) leaves, and two classes of lignin carbon dots were synthesized by hydrothermal treatment at 200 °C (partially carbonized, pLCD-200) and 350 °C (fully carbonized, fLCD-350). Microscopy confirmed spherical nanoscale structures with mean diameters of 12.3 ± 3.8 nm for pLCD-200 and 9.3 ± 1.9 nm for fLCD-350, while zeta potential values of −13.7 and −19.9 mV indicated good colloidal stability. Spectroscopic analyses revealed distinct optical behaviors: pLCD-200 showed strong UV absorption (200–350 nm) and blue emission at 440–460 nm with excitation-dependent shifts, converting part of the absorbed UV light into photosynthetically active radiation (PAR). In contrast, fLCD-350 displayed broader UV-visible absorption and near-infrared emission around 710–730 nm with minimal excitation dependence. Under natural sunlight, pLCD-200 exhibited emission decay consistent with first-order kinetics (k ≈ 0.010 h−1; half-life ≈3 days), while fLCD-350 demonstrated persistent emission and gradual photo-brightening modeled by first-order association (kg ≈ 0.002 h−1; doubling time ≈15 days). FTIR confirmed that fLCD-350 stability arises from decarbonylation, ether bond cleavage, and condensation of aromatic domains into a carbonized core with few oxygen groups. Formulation with sodium alginate produced uniform films that retained strong leaf-surface fluorescence for at least 10 days outdoors, ensuring durable adhesion and UV shielding. Short-term photosynthesis measurements (0–48 h) and greenhouse growth assays with foliar exposure to pLCD and fLCD at 300 and 600 mg L−1 revealed no adverse effects on photosystem function or plant development. These findings demonstrate that lignin carbon dots, particularly fLCD-350, are durable, optically versatile, and plant-compatible nanomaterials functioning as long-lasting sunscreens and UV-protective foliar coatings that convert harmful UV into photosynthetically useful light. This journal is © The Royal Society of Chemistry, 2026
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Herein, CuO and ZnO nanoparticles (NPs) were biogenically synthesized using plant (Artemisia vulgaris) extracts. The biogenic NPs were subsequently evaluated in vitro for antifungal activity (200 mg/L) against Fusarium virguliforme (FV; the cause of soybean sudden death), and for crop protection (200–500 mg/L) in FV-infested soybean. ZnONPs exhibited 3.8-, 2.5-, and 4.9 -fold greater in vitro antifungal activity, compared to Zn or Cu acetate salt, the Artemisia extract, and a commercial fungicide (Medalion Fludioxon), respectively. The corresponding CuONP values were 1.2-, 1.0-, and 2.2 -fold, respectively. Scanning electron microscopy (SEM) revealed significant morpho-anatomical damage to fungal mycelia and conidia. NP-treated FV lost their hyphal turgidity and uniformity and appeared structurally compromised. ZnONP caused shriveled and broken mycelia lacking conidia, while CuONP caused collapsed mycelia with shriveled and disfigured conidia. In soybean, 200 mg/L of both NPs enhanced growth by 13%, compared to diseased controls, in both soil and foliar exposures. Leaf SEM showed fungal colonization of different infection sites, including the glandular trichome, palisade parenchyma, and vasculature. Foliar application of ZnONP resulted in the deposition of particulate ZnO on the leaf surface and stomatal interiors, likely leading to particle and ion entry via several pathways, including ion diffusion across the cuticle/stomata. SEM also suggested that ZnO/CuO NPs trigger structural reinforcement and anatomical defense responses in both leaves and roots against fungal infection. Collectively, these findings provide important insights into novel and effective mechanisms of crop protection against fungal pathogens by plant-engineered metal oxide nanoparticles, thereby contributing to the sustainability of nano-enabled agriculture.
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