Zinc oxide (ZnO) is a wide bandgap semiconductor of great scientific and technological interest due to its high exciton binding energy and outstanding structural and optical properties, making it an ideal material for applications in optoelectronics, sensors, and photocatalysis. This study presents the rapid synthesis of highly crystalline ZnO nanostructures using two alternative routes: (1) direct thermal decomposition of zinc acetate and (2) a physical-green route assisted by Mangifera indica extract. Both routes were subjected to identical calcination thermal conditions (400 °C for 2 h), allowing for an objective comparison of their effects on structural, vibrational, morphological, and optical characteristics. X-ray diffraction analyses confirmed the formation of a pure hexagonal wurtzite phase in both samples, highlighting a higher crystallinity index (91.6%) and a larger crystallite size (35 nm) in the sample synthesized using the physical-green route. Raman and FTIR spectra supported these findings, revealing greater structural order. Electron microscopy showed significant morphological differences, and UV-Vis analysis showed a red shift in the absorption peak, associated with a decrease in the optical bandgap (from 3.34 eV to 2.97 eV). These results demonstrate that the physical-green route promotes significant improvements in the structural and functional properties of ZnO, without requiring changes in processing temperature or the use of additional chemicals.

The degradation of agricultural soils and the low efficiency of conventional fertilizers pose significant challenges to sustainable agricultural production. In this context, nanobiofertilizers have emerged as a promising alternative for increasing nutrient availability and improving early plant development. This study evaluated the effect of a zinc oxide nanobiofertilizer (NBF-ZnO) synthesized via a green route using Mangifera indica leaf extract on the germination and early growth of maize (Zea mays L.) seedlings. The synthesized nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-Vis spectroscopy to confirm their structural and optical properties. Subsequently, germination and early growth trials were conducted under four treatments: control, mango extract, conventional fertilizer (Triple 15), and NBF-ZnO, using soil affected by mining activities in the department of Cesar (Colombia). The results showed that the NBF-ZnO treatment achieved the highest germination (93%) and seedling growth (92.5%), outperforming the conventional fertilizer and the other treatments. Statistical analysis using the chi-square test confirmed significant differences between treatments (α = 0.05). These findings suggest that ZnO nanobiofertilizers obtained through green synthesis could represent a promising strategy for enhancing early maize development and contributing to the sustainable management of soils affected by mining activity.