Abstract
The increasing use of zinc oxide nanoparticles (ZnO-NPs) in agricultural and technological applications raises concerns regarding their potential effects on plant development. In this study, ZnO materials were synthesized using flower, stem, and leaf extracts of Tithonia diversifolia and evaluated for phytotoxicity in Lactuca sativa. X-ray diffraction confirmed the hexagonal wurtzite structure, with crystallite sizes ranging from 25.6 to 34.8 nm. SEM revealed fine granular features assembled into larger agglomerates, while EDS showed differences in elemental composition and Zn/O atomic ratios, with a minor Ca signal detected only in ZnO-L. FTIR revealed Zn–O-related vibrations and differences in the vibrational characteristics of the thermally treated materials. Phytotoxicity assays showed distinct responses among the three materials. ZnO-F produced the lowest overall effect on seedling development, whereas ZnO-S caused the greatest inhibition of radicle and hypocotyl elongation. ZnO-L exhibited a biphasic response, with hypocotyl elongation above the control at 20–60 mg L⁻¹ and inhibition at higher concentrations, consistent with hormesis. Overall, the results indicate that the plant extract source influences the physicochemical characteristics and phytotoxic behavior of the resulting ZnO materials, potentially through the combined influence of multiple material properties.