Cerium oxide nanoparticles: biogenic synthesis, characterization, and effects of foliar application on photosynthetic and antioxidant performance on Brassica juncea L.

The term "green synthesis" refers to the use of sustainable and environmentally friendly methods to produce materials, chemicals, or nanoparticles (NPs). This approach emphasizes the use of renewable resources, energy-efficient processes, and non-toxic chemicals to minimize environmental impact. In our study, we synthesized cerium oxide NPs (CeO₂ NPs) of varying crystal sizes using leaf extract from the Moringa oleifera plant and evaluated their effects on the photosynthetic and antioxidant properties of mustard (Brassica juncea L.). X-ray diffraction (XRD) analysis confirmed the successful synthesis of CeO₂ NPs, with average crystal sizes determined using the Debye-Scherrer equation as 4.5 nm, 8.5 nm, and 15.4 nm (designated as A, B, and C respectively). Fourier transform infrared spectroscopy (FTIR) analysis revealed stretching frequencies at 550 cm⁻, confirming the presence of Ce-O stretching bands and the use of natural compounds in the synthesis process. Scanning electron microscopy (SEM) analysis showed that the CeO₂ NPs were irregularly shaped and agglomerated, while transmission electron microscopy (TEM) analysis confirmed that the particles were spherical and polydisperse. Dynamic light scattering (DLS) and zeta potential analysis further confirmed the polydispersity and stability of synthesized NPs in solution. Following synthesis, the CeO₂ NPs were applied foliarly to mustard crops at concentrations of 50, 100, and 150 ppm. The results demonstrated that all concentrations of NPs enhanced growth, photosynthetic efficiency, and gaseous exchange parameters in mustard. Additionally, the NPs regulated balance between oxidation and reduction (redox) reactions in cell. It helps maintain cellular function by controlling reactive oxygen species (ROS) and antioxidants, preventing damage and ensuring normal metabolism. Notably, the 4.5 nm-sized NP (A) at a concentration of 100 ppm was the most effective in improving these parameters. CeO₂ NPs show promise as a sustainable alternative to traditional fertilizers and pesticides, contributing to more sustainable agricultural practices. This pioneering research highlights the potential of biogenically synthesized CeO₂ NPs in boosting crop performance, marking a significant advancement in agricultural nanotechnology.