Green Synthesis and Characterization of ZnO and FeO Nanoparticles Using Mangifera indica and Carica papaya Leaf Extracts for ZnO and ZnO/FeO Nanocomposite-Based DSSC Fabrication

This paper describes the green synthesis and characterization of zinc oxide (ZnO) and iron oxide (FeO) nanoparticles with aqueous leaf extracts of Mangifera indica and Carica papaya acting as reducing and stabilizing agents. The synthesis involved reacting 0.4 M zinc nitrate and iron (III) nitrate solutions with plant extracts under controlled pH (?7) and ambient temperature conditions, followed by filtering, drying, and annealing at 400°C. The procedure was easy and environmentally benign. Plant biomolecules such as flavonoids, phenolics, and alkaloids performed critical roles in nanoparticle production and stabilization. Structural, optical, morphological, and functional investigations were performed with X-ray diffraction (XRD), UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX). The XRD data indicated the development of wurtzite ZnO and cubic spinel Fe?O? phases, with crystallite sizes ranging from 15-30 nm. The FTIR spectra indicated classic Zn-O and Fe-O stretching vibrations, as well as organic functional groups, supporting the role of phytochemicals in nanoparticle capping. UV-visible investigation revealed substantial absorption in the UV area with band gap energies ranging from 3.18 to 3.50 eV, indicating semiconductivity and photocatalytic potential. SEM scans showed primarily spherical ZnO and irregular porous FeO morphologies, whereas EDX confirmed elemental purity. Dye-sensitized solar cells (DSSCs) made with synthetic nanoparticles have power conversion efficiencies (PCEs) ranging from 0.26 to 0.46%, with ZnO/FeO nanocomposites outperforming others. Overall, the study reveals an effective and sustainable method for producing multifunctional metal oxide nanoparticles appropriate for energy, catalytic, and environmental applications.